340 Street Build

[rumblefish360]

Thought I had mentioned someone talking about dual vs single pattern selection in a paper or video. It was in a video I saw several months ago. The guy is talking about the selection based on on Exh/Int flow ratio of the heads. His breaking point was 75%. Anything above go single pattern, below go with dual pattern profile. Think it may be his personal rule of thumb. Don't know anything about the guy, just ran across his 2 part video on cam selection. He does mostly talk about Fords and Chevys but I would think the basis of air flow would apply across the board. He did say cam lift should be determined by head flow but I think that was in part 1 of the series.

Folks here may have already seen this guys videos. Here is the link to video part 2. He talks about the profiles at ~ t=16:53. At 0.500" lift the ProMaxx 171 flow chart from the manufacturer puts it at about 73.7%. 0.600" lift puts the ratio at about 76%. I was thinking of between 0.491-0.502 or in that ball park based on ProMaxx flow chart. Again, I am learning about more of the finer details matching parts of engine building, so I'm not taking everything I find on YouTube as gold. Parts ain't cheap these days but I guess "cheap" is all relative to the size of your bank account! Lol.

Links, if anyone interested.
Part 1:
Part 2:

I have seen and heard a bunch on this topic proving one over the other a few times and I think it just “depends.”

To be honest, for myself, I do t care anymore. I’m just going to play with stuff and find out what works (for me) & what doesn’t work (for me) in various combinations and settings.

 

[273]

On engine masters they did a single vs dual pattern dyno test and dual pattern won, I know that's not definitive proof, plus it's seem like over 90% of all cams and builds even pro ones are dual pattern. I'm sure there's applications where single wins but without back to back test on your engine your gonna never know, I'd put my money on dual but if there's a single pattern cam you like go for it.

 

[AJ/FormS]

Thought about a 3.09 first gear kit for the tranny but would big a larger jump to the 1.91 2nd gear or switch to a set of 3.55 gears. 3.55's show about 3050 rpm at 65mph. Not a lot of mph difference at 750 rpm (5.93 mph) 1st gear with 3.55.

Think going with a little less duration on the cam might help lower the peak torque/HP band some and lower the idle rpm capability? What do you think your DCR is in that engine about 8.5ish?[quote/]

That was taken from post #22
The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about the minimum that I wanna be at, to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right off idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.

But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear

But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design

Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.

Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which,installed at 4* advanced it is in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce;
440/318 x113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how engine size plays out

Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance. The numbers fall to;
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63, which is a typical performance cam. The numbers fall again, to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what increasing the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you think a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.

So now we get to the 340..
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
Still at 800ft,
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen with the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126/lol. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam, iron heads, and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So, in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.
But IMO, it's not gonna work at the modest 8.73 Scr
Lets try 58 degrees , and max the pressure again to 160psi.
The best the Wallace will do, is at 9.6 Scr, and I get a Dcr of 8.0/159 psi/132V/P, which IIRC is about what a 5.9 Magnum musters, so you know, ho-hum; and 5.9s do spin skinny factory tires.
Will it make 349@2200? Yes I think so.
The downside is that the 58* Ica, makes for a low power-peak , which is a kindofa waste on good heads. You might as well put small valve stock iron heads back on her.

So what's the solution?
Well, I know that my closed chamber alloy heads do NOT detonate on 87E10, at up to 195cylinder pressure, even running a constant coolant temp of 205*F, which allows me to, with an Scr variable by gasket changes from 11.0 to 11.3, run just about any Ica from a low of 54* to a high of around 72 degrees; which is a heluva thing.

Therefore, I have no trouble recommending alloy heads and high pressure.
This should make the required 349 ftlbs with ease, even at 2200; even with the 3.23s and the 2.66 box. So the money you save by NOT BUYING gears and/or an overdrive, you can stick towards alloy heads. And who knows; maybe the hi-pressure combo may run even less gear than 3.23s.
Mine, a 367, has pulled 2.76s for a short time .... allbeit with the 3.09 low, lol. That's a starter gear of 3.09 x 2.76= 8.44 which compares to your 2.66 box x 3.23s = 8.59, hunh! IDK if I ever smoked the tires with that combo. It wasn't in there for long. I was testing for something else.

BTW
If you are stuck at 8.73 Scr because of budget constraints, then there is notta chance I would spend the coin on alloy heads, because the cost to satisfaction ratio is just not there no matter what cam you put into that engine.
The smallest cam I would consider is one that can be installed at say 53* Ica, at 800 ft elevation, this works out to a
Dcr of 7.56/pressure of 148psi/and a hu-hum V/P of 138. But the cam I would choose would be a Tight LSA design of say 106*, to get some decent overlap back, to extend the operating rpm at the top, cuz that's gonna be a pretty small cam.

Here's my cam guess; 262/268/106 in at 102, will get you an Ica of 53*, and overlap of also 53*; yeah that should work at 8.7 Scr. Yes it is pretty small, but still being about 3 sizes bigger on the intake than a stock 360 2bblcam, which IIRC was 252/256/112.
A V/P of 138 is about as low as I would suffer.
altitude loss looks like (pressure and V/P)
at 800ft the numbers are ......... 148/138 V/P
By 1800 the numbers are ......... 142/133 V/P
By 2800, she be down to;.......... 137/128 V/P
by 3800, the wheezer is down to 132/123 V/P
So looking like dropping about 5 and 5 per 1000 feet.

If you are not running headers, the overlap is not helpful, so you can run a 110 cam but you will quickly lose pressure/VP again. With that same 262 cam now running a 110 Lsa and in at 106, the Ica becomes 57*; and the Wallace spits out,
142psi/119VP ....... so you know, I wouldn't do that; I'd install headers and pick up the power over the nose.

Happy Hotrodding

 

[mygasser]

i'll take options (1) 'and' (4) please

 

[1badfish67]

The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about where I wanna be to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right of idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.

But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear

But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design

Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.

Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which is installed 4* advanced and in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce
440/318x 113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how Scr plays out

Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance.the numbers fall to
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63*n which is a typical performance cam. The numbers fall again to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you ythink a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.

So now we get to the 340
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen and the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.





More coming

Lot of good information here AJ. I appreciate you going into the finer details. I took another look through a few more spark plug holes and found several nice shiny piston tops. The pistons in there look to have some amount of dome in them. They kinda look like the KB 243-030 but not 100% sure yet. KB website says 0.018" out of the hole, +6cc of dome, 10.0:1 with 64cc heads but doesn't mention with what head gasket thickness. Not sure if the listed +6cc is the net including the valve reliefs or not?

I used 10.1:1 for the 63cc heads and used the Ica of the Comp XE274H @ 63deg for the estimate.

Using those values the Wallace Calculator spits out 8.12/164.41/131. The cylinder pressure on the engine as it sits now is higher than 164. I will know more and be able to provide better actual numbers once I get it tore down, take the measurements and get actual info off the existing cam and pistons. Appreciate all your time it took to put all this down and share with us.

 

[1badfish67]

The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about where I wanna be to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right of idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.

But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear

But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design

Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.

Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which,installed at 4* advanced it is in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce;
440/318x 113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how Scr plays out

Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance. The numbers fall to;
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63, which is a typical performance cam. The numbers fall again to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you think a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.

So now we get to the 340..
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
Still at 800ft,
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen with the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126/lol. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.
But IMO, it's not gonna work at the modest 8.73 Scr
Lets try 58 degrees , and max the pressure again to 160psi.
The best the Wallace will do is at 9.6 Scr, and I get a Dcr of 8.0/159 psi/132V/P, which IIRC is about what a 5.9 Magnum musters, so you know, ho-hum; and 5.9s do spin skinny factory tires.
Will it make 349@2200? Yes I think so.
The downside is that the 58* Ica, makes for a low power-peak , which is a kindofa waste on good heads. You might as well put small valve stock iron heads back on her.

So what's the solution?
Well, I know that my closed chamber alloy heads do NOT detonate on 87E10, at up to 195cylinder pressure, even running a constant coolant temp of 205*F, which allows me to, with an Scr variable from by gasket changes from 11 to 11.3, run just about any Ica from a low of 54* to a high of around 72 degrees; which is a heluva thing.

Therefore, I have no trouble recommending alloy heads and high pressure.
This should make the required 349 ftlbs with ease, even at 2200; even with the 3.23s and the 2.66 box. So the money you save NOT BUYING gears and/or an overdrive, you can stick towards alloy heads. And who knows the hi-pressure combo may run even less gear than 3.23s.
Mine, a 367, has pulled 2.76s for a short time .... allbeit with the 3.09 low, lol. That's a starter gear of 3.09 x 2.76= 8.44 which compares to your 2.66 box x 3.23s = 8.59, hunh! IDK if I ever smoked the tires with that combo. It wasn't in there for long. I was testing for something else.

BTW
If you are stuck at 8.73 Scr because of budget constraints, then there is notta chance I would spend the coin on alloy heads, because the cost to satisfaction ratio is just not there no matter what cam you put into that engine.
The smallest cam I would consider is one that can be installed at say 53* Ica, at 800 ft elevation, this works out to a
Dcr of 7.56/pressure of 148psi/and a hu-hum V/P of 138. But the cam I would choose would be a Tight LSA design of say 106*, to get some decent overlap back, to extend the operating rpm at the top, cuz that's gonna be a pretty small cam.

Here's my cam guess; 262/268/106 in at 102, will get you an Ica of 53*, and overlap of also 53*; yeah that should work. Yes it is pretty small, but still being about 3 sizes bigger on the intake than a stock 360 2bblcam, which IIRC was 252/256/112.
A V/P of 138 is about as low as I would suffer.
altitude loss looks like (pressure and V/P)
at 800 the numbers are ........... 148/138 V/P
By 1800 the numbers are ......... 142/133 V/P
By 2800, she be down to;.......... 137/128 V/P
by 3800, the wheezer is down to 132/123 V/P
So looking like dropping about 5 and 5 per 1000 feet.

If the client is not running headers, the overlap is not helpful, so you can run a 110 cam but you will quickly lose pressure/VP again. With that same 262 cam now running a 110 Lsa and in at 106, the Ica becomes 57*; and the Wallace spits out,
142psi/119VP ....... so you know, I wouldn't do that; I'd install headers and pick up the power over the nose.

Happy Hotrodding

My internet here in the country has been like a 'pooch' lately. Tried to refresh twice before writing my last comment and the second half of your message still hadn't showed up at posting. It just now showed up. May have to give O'l Elon's internet service a try. Almost anything has got to be better than this.

 

[1badfish67]

The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about where I wanna be to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right of idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.

But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear

But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design

Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.

Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which,installed at 4* advanced it is in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce;
440/318x 113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how Scr plays out

Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance. The numbers fall to;
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63, which is a typical performance cam. The numbers fall again to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you think a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.

So now we get to the 340..
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
Still at 800ft,
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen with the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126/lol. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.
But IMO, it's not gonna work at the modest 8.73 Scr
Lets try 58 degrees , and max the pressure again to 160psi.
The best the Wallace will do is at 9.6 Scr, and I get a Dcr of 8.0/159 psi/132V/P, which IIRC is about what a 5.9 Magnum musters, so you know, ho-hum; and 5.9s do spin skinny factory tires.
Will it make 349@2200? Yes I think so.
The downside is that the 58* Ica, makes for a low power-peak , which is a kindofa waste on good heads. You might as well put small valve stock iron heads back on her.

So what's the solution?
Well, I know that my closed chamber alloy heads do NOT detonate on 87E10, at up to 195cylinder pressure, even running a constant coolant temp of 205*F, which allows me to, with an Scr variable from by gasket changes from 11 to 11.3, run just about any Ica from a low of 54* to a high of around 72 degrees; which is a heluva thing.

Therefore, I have no trouble recommending alloy heads and high pressure.
This should make the required 349 ftlbs with ease, even at 2200; even with the 3.23s and the 2.66 box. So the money you save NOT BUYING gears and/or an overdrive, you can stick towards alloy heads. And who knows the hi-pressure combo may run even less gear than 3.23s.
Mine, a 367, has pulled 2.76s for a short time .... allbeit with the 3.09 low, lol. That's a starter gear of 3.09 x 2.76= 8.44 which compares to your 2.66 box x 3.23s = 8.59, hunh! IDK if I ever smoked the tires with that combo. It wasn't in there for long. I was testing for something else.

BTW
If you are stuck at 8.73 Scr because of budget constraints, then there is notta chance I would spend the coin on alloy heads, because the cost to satisfaction ratio is just not there no matter what cam you put into that engine.
The smallest cam I would consider is one that can be installed at say 53* Ica, at 800 ft elevation, this works out to a
Dcr of 7.56/pressure of 148psi/and a hu-hum V/P of 138. But the cam I would choose would be a Tight LSA design of say 106*, to get some decent overlap back, to extend the operating rpm at the top, cuz that's gonna be a pretty small cam.

Here's my cam guess; 262/268/106 in at 102, will get you an Ica of 53*, and overlap of also 53*; yeah that should work. Yes it is pretty small, but still being about 3 sizes bigger on the intake than a stock 360 2bblcam, which IIRC was 252/256/112.
A V/P of 138 is about as low as I would suffer.
altitude loss looks like (pressure and V/P)
at 800 the numbers are ........... 148/138 V/P
By 1800 the numbers are ......... 142/133 V/P
By 2800, she be down to;.......... 137/128 V/P
by 3800, the wheezer is down to 132/123 V/P
So looking like dropping about 5 and 5 per 1000 feet.

If the client is not running headers, the overlap is not helpful, so you can run a 110 cam but you will quickly lose pressure/VP again. With that same 262 cam now running a 110 Lsa and in at 106, the Ica becomes 57*; and the Wallace spits out,
142psi/119VP ....... so you know, I wouldn't do that; I'd install headers and pick up the power over the nose.

Happy Hotrodding

Already have the new ProMaxx 171 heads, Holley 770 Street Avenger Ultra, RPM Airgap and PRW roller tip rockers still in the boxes sitting in the shop. Yes, I will be running headers. Maybe 1-5/8" tube with 3" collectors. I am at about 1000ft elevation here.

 

[273]

The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about where I wanna be to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right of idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.

But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear

But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design

Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.

Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which,installed at 4* advanced it is in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce;
440/318x 113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how Scr plays out

Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance. The numbers fall to;
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63, which is a typical performance cam. The numbers fall again to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you think a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.

So now we get to the 340..
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
Still at 800ft,
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen with the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126/lol. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.
But IMO, it's not gonna work at the modest 8.73 Scr
Lets try 58 degrees , and max the pressure again to 160psi.
The best the Wallace will do is at 9.6 Scr, and I get a Dcr of 8.0/159 psi/132V/P, which IIRC is about what a 5.9 Magnum musters, so you know, ho-hum; and 5.9s do spin skinny factory tires.
Will it make 349@2200? Yes I think so.
The downside is that the 58* Ica, makes for a low power-peak , which is a kindofa waste on good heads. You might as well put small valve stock iron heads back on her.

So what's the solution?
Well, I know that my closed chamber alloy heads do NOT detonate on 87E10, at up to 195cylinder pressure, even running a constant coolant temp of 205*F, which allows me to, with an Scr variable from by gasket changes from 11 to 11.3, run just about any Ica from a low of 54* to a high of around 72 degrees; which is a heluva thing.

Therefore, I have no trouble recommending alloy heads and high pressure.
This should make the required 349 ftlbs with ease, even at 2200; even with the 3.23s and the 2.66 box. So the money you save NOT BUYING gears and/or an overdrive, you can stick towards alloy heads. And who knows the hi-pressure combo may run even less gear than 3.23s.
Mine, a 367, has pulled 2.76s for a short time .... allbeit with the 3.09 low, lol. That's a starter gear of 3.09 x 2.76= 8.44 which compares to your 2.66 box x 3.23s = 8.59, hunh! IDK if I ever smoked the tires with that combo. It wasn't in there for long. I was testing for something else.

BTW
If you are stuck at 8.73 Scr because of budget constraints, then there is notta chance I would spend the coin on alloy heads, because the cost to satisfaction ratio is just not there no matter what cam you put into that engine.
The smallest cam I would consider is one that can be installed at say 53* Ica, at 800 ft elevation, this works out to a
Dcr of 7.56/pressure of 148psi/and a hu-hum V/P of 138. But the cam I would choose would be a Tight LSA design of say 106*, to get some decent overlap back, to extend the operating rpm at the top, cuz that's gonna be a pretty small cam.

Here's my cam guess; 262/268/106 in at 102, will get you an Ica of 53*, and overlap of also 53*; yeah that should work. Yes it is pretty small, but still being about 3 sizes bigger on the intake than a stock 360 2bblcam, which IIRC was 252/256/112.
A V/P of 138 is about as low as I would suffer.
altitude loss looks like (pressure and V/P)
at 800 the numbers are ........... 148/138 V/P
By 1800 the numbers are ......... 142/133 V/P
By 2800, she be down to;.......... 137/128 V/P
by 3800, the wheezer is down to 132/123 V/P
So looking like dropping about 5 and 5 per 1000 feet.

If the client is not running headers, the overlap is not helpful, so you can run a 110 cam but you will quickly lose pressure/VP again. With that same 262 cam now running a 110 Lsa and in at 106, the Ica becomes 57*; and the Wallace spits out,
142psi/119VP ....... so you know, I wouldn't do that; I'd install headers and pick up the power over the nose.

Happy Hotrodding

Why is the goal to roast a set of 295's at 2200 rpms?
One the OP has 235's Two if he wants burn rubber he can dump higher if he needs.

Even if 350tq is the desired low rpm goal I doubt any reasonable sized cam can't get him there, a well built 340 will make peak tq over 400 tq around 3500-4500 rpms it's not gonna disappear by 2000 rpms.

hp% of tq at 1313 rpm is 25%, 2626 rpm is 50%, 3939 rpm is 75%.
Even if a cam losses 30tq at 1313-2626 rpm range thats a 7.5-15 hp difference doubt enough to stop you from breaking your tires loose.

If the 3.23 must stay I'd would build/cam for them and or whatever gear you choose, but I don't thinks so direr you can't use a decent cam.

 

[1badfish67]

Just for grins I ran the numbers through the Wallace calculator for that old SBC 350 I had in the 73 Nova. I was bored 0.040 over with 10.5:1 TRW forged flat top pistons. Can't remember what cc head that would be with but I suspect maybe a 62 or 63cc? The heads were off of a 67 RS Z/28 Camero, 302cid engine. My buddy wanted to put a small B&M blower on the Camero and wanted to reduce the combustion chamber size/compression, so I swapped him my heads for his.

I ran the Comp Magnum 280H cam Ica (66deg ABDC) and had to use a 12.25:1 SCR to get close to the 205psi cylinder cranking pressures it had. Wallace numbers were 9.63/202.4/166. I knew I was running higher compression but no idea it may have been that high and with iron heads.

 

[1badfish67]

That was taken from post #22
The 1-2 split of the 3.09-1.92 combo, with my hi-pressure 367 works great.
The Dcr/pressure/V-P in my current combo is about 8.8/180/156
It has been to 9.3/195/169 with a smaller cam.
IMO
with a 340/3.23/2.66 street-combo, pressure is gonna be your best friend. I would gladly sacrifice power at 5500 to get over 3000 ftlbs into the axles at zero mph.
Here's how you work backwards;
From empirical testing. I know that 3000 ftlbs into the axles is about the minimum that I wanna be at, to bust a pair of 295/50-15s loose and roast them. Skinnier tires with no traction-aide, will bust loose with less. Therefore; 3000ftlbs is my target.
3000/(3.23 x 2.66) =349 ftlbs at the crank. If you want crisp take off at WOT, yur gonna have to rev up your engine until you find that amount of torque. Maybe your 340 will make it at 3000; but maybe not until 3500, it depends on the combo of parts you use and specifically on how much pressure it builds. Heaven help her if she can't get there until 4000.
FYI; My 367 makes that almost right off idle.
But say you swap out that sick 2.66 low for a 3.09; Now the numbers are 3000/(3.23 x 3.09)= 300 ftlbs. any 340 should be able to make that at under 3000 rpm at WOT.

But say you don't want have to go to WOT, all the time just to bust them loose. so say you want to be able to do that at part throttle, say at 240 ftlbs, then
3000/(3.09 x 240)= a 4.04 rear gear

But say you want to keep both the 2.66 and those 3.23s. Then
3000/(3.23 x 2.66 )= 349 ftlbs, but you want those to show up at 2200. Well your 340 is gonna need a lotta pressure to do it.
With an auto trans, you could depend on the TC to help the engine, but you don't got no TC so your engine has to do it all-motor style.
So then, how do you build a 340 to make 349 ftlbs at 2200?
IDK but I can guess;
1) it's gonna need a lotta pressure
2) Pressure is your friend
3) It all starts with, you guessed it; a high-pressure design

Ok so what is a high pressure design?
Well you can make pressure a few ways;
1) with cubic inches
2) with a High Scr design
3) with an Early closing intake
$) with forced induction.
However, you have to stay within the limits of the fuel to resist detonation.

Let's say you had a smog era 318 at a true Scr of 8.0, and the stock 240/248/112cam in it, which,installed at 4* advanced it is in at 108. The Ica becomes 48*, and so, the Wallace predicts
at 800 ft elevation; 7.1Dcr/136psi/113 V/P
Lets install that same cam into a 340 still at 8.0 Scr. The Wallace predicts 7.1/136/121 V/P, an increase of 7%, which is the exact difference in cubes from the 318, measured in percentage; therefore a 440 could be expected to produce;
440/318 x113=156V/P and that is exactly what the Wallace spits out, still at 8.0 Scr and 800ft elevation.
Now a V/P of 156 is pretty nice.
So that is how engine size plays out

Lets go back to the 318 and start playing with the Ica
First the stocker at Ica = 48* ; the Wallace predicted 7.1Dcr/136psi/113 V/P
Lets go to Ica of 58, which is just tickling performance. The numbers fall to;
6.7 Dcr/125 psi/ 97 V/P and so the bottom has fallen into the basement.
Lets add 5 more degrees to get an Ica of 63, which is a typical performance cam. The numbers fall again, to
6.47/119/89 V/P which is tickling on slanty terrible-tory. So that's what increasing the Ica does with no other changes, it kills the bottom end.
To get the V/P back up to 119, of the stocker, with that final Ica of 63*, the Scr would have to be jumped up, to 10.0 .... to have the sub 3500 rpm performance to be about the same as ... stock. And where do you think a 318 street car spends the vast majority of time? Yeah I'll bet under 3500. So don't put a big cam in a stock 8.0 Scr 318. Not ever.

So now we get to the 340..
Say this one is already at 8.73Scr, and has a stock 340 cam in it with an Ica of 64*. The Wallace kicks out;
Still at 800ft,
a Dcr of 6.99/pressure of 133psi/ and V/P of 105; which is back in the basement; under no circumstances would I build one of those. Ok but say you really wanna use that stinker of a pressure robbing cam, and yur still looking for 349 ftlbs at 2200rpm. I'm gonna say; that will never happen with the Scr still be low enough to run pumpgas, But, let's work the calculator anyhow. At 10.0 Scr the Dcr is topping out at 7.99, the pressure is topping out at 159psi, and the V/P is up to a whopping 126/lol. This is less than a stock 5.2 Magnum, so that is as much as you can expect with that cam, iron heads, and best pumpgas. Will it spin the tires? yes I think so, but a Doubt it will make 349 ftlbs at 2200, so yur gonna have to rev it up to get the numbers.
So, in that iron-headed combo, the bottom-end is still seriously soft; and keeping it a 340, and naturally aspirated, typically, you only have one other choice, which is to slam the intake closed sooner.
But IMO, it's not gonna work at the modest 8.73 Scr
Lets try 58 degrees , and max the pressure again to 160psi.
The best the Wallace will do, is at 9.6 Scr, and I get a Dcr of 8.0/159 psi/132V/P, which IIRC is about what a 5.9 Magnum musters, so you know, ho-hum; and 5.9s do spin skinny factory tires.
Will it make 349@2200? Yes I think so.
The downside is that the 58* Ica, makes for a low power-peak , which is a kindofa waste on good heads. You might as well put small valve stock iron heads back on her.

So what's the solution?
Well, I know that my closed chamber alloy heads do NOT detonate on 87E10, at up to 195cylinder pressure, even running a constant coolant temp of 205*F, which allows me to, with an Scr variable by gasket changes from 11.0 to 11.3, run just about any Ica from a low of 54* to a high of around 72 degrees; which is a heluva thing.

Therefore, I have no trouble recommending alloy heads and high pressure.
This should make the required 349 ftlbs with ease, even at 2200; even with the 3.23s and the 2.66 box. So the money you save by NOT BUYING gears and/or an overdrive, you can stick towards alloy heads. And who knows; maybe the hi-pressure combo may run even less gear than 3.23s.
Mine, a 367, has pulled 2.76s for a short time .... allbeit with the 3.09 low, lol. That's a starter gear of 3.09 x 2.76= 8.44 which compares to your 2.66 box x 3.23s = 8.59, hunh! IDK if I ever smoked the tires with that combo. It wasn't in there for long. I was testing for something else.

BTW
If you are stuck at 8.73 Scr because of budget constraints, then there is notta chance I would spend the coin on alloy heads, because the cost to satisfaction ratio is just not there no matter what cam you put into that engine.
The smallest cam I would consider is one that can be installed at say 53* Ica, at 800 ft elevation, this works out to a
Dcr of 7.56/pressure of 148psi/and a hu-hum V/P of 138. But the cam I would choose would be a Tight LSA design of say 106*, to get some decent overlap back, to extend the operating rpm at the top, cuz that's gonna be a pretty small cam.

Here's my cam guess; 262/268/106 in at 102, will get you an Ica of 53*, and overlap of also 53*; yeah that should work at 8.7 Scr. Yes it is pretty small, but still being about 3 sizes bigger on the intake than a stock 360 2bblcam, which IIRC was 252/256/112.
A V/P of 138 is about as low as I would suffer.
altitude loss looks like (pressure and V/P)
at 800ft the numbers are ......... 148/138 V/P
By 1800 the numbers are ......... 142/133 V/P
By 2800, she be down to;.......... 137/128 V/P
by 3800, the wheezer is down to 132/123 V/P
So looking like dropping about 5 and 5 per 1000 feet.

If you are not running headers, the overlap is not helpful, so you can run a 110 cam but you will quickly lose pressure/VP again. With that same 262 cam now running a 110 Lsa and in at 106, the Ica becomes 57*; and the Wallace spits out,
142psi/119VP ....... so you know, I wouldn't do that; I'd install headers and pick up the power over the nose.

Happy Hotrodding

WRT the LSA on a cam, does the narrower the LSA create more valve open overlap and overlap is the time the valves are both open? If that's right, wouldn't it tend to bleed off cylinder pressure at lower rpms? May be a dumb question but I had to ask.

 

[AJ/FormS]

no, the thing that controls when compression begins is the closing of the intake valve. The longer you delay this, at low rpm, the more time there is for the piston, which is now on the way up on the compression stroke, to push a portion of the Just inducted air/fuel charge, back up into the intake. This is what creates the low engine vacuum signal at idle, in the intake.

Maybe this will help. Here are all the durations of the Five parts of a 4-stroke engine cycle;
overlap, intake, compression, power, exhaust, and back to overlap. If you have a 268/276 cam, you already know the durations of two of those, ie 268 and 276.
But you need to know the LSA of that cam, to calculate the other three.
Let's say it's on a 114 Lsa. The overlap is calculated from averaging the intake and exhaust durations and subtracting from that, double the LSA. Ok then, the calculation looks like this
(268 +276)/2 less (2 x 114) = 44* overlap.

The compression degrees is what is leftover after you add a portion of the overlap, to 360 degrees which is half of the 4-stroke cycle. How much overlap to add depends on where you installed the cam centerline. Lets say we install it 4* advanced , therefore 114 less 4= 110. so the Formula looks like
360 plus (268/2 less 110); less 268 = compression degrees; so
360 +24 less 268= 116* of compression

the Power cycle is 360 plus whatever overlap is left, less the exhaust duration. Since we started with 44* overlap and gave 24* to the intake/compression half, we have 20* overlap left over, so
360 +20, less 276 = Power = 104*

Ok so, lets line them up in their proper order and make sure it adds up to (2 x360) plus 44 =764 which is the complete 5-stroke cycle.
268 intake, +116 comp +104 Power +276 Exh =764, so Good to go. The 44* overlap is buried in the 268 plus 276.

Ok so lets tighten up the LSA to 106* and see what happens;
First up is calculating the overlap, which was the average of intake plus exhaust, less double the LSA, and that looks like
(268 +276)/2 less (2 x106)= 60* overlap. Lets install this at split overlap giving 30* each to intake and exhaust. Therefore, to get compression,
360 +30, less 268 =122 compression. and
to get Power we add 30 to 360, and subtract the exhaust duration, like this
360+30, less 276= 114 Power, and lining them up we get
268 intake +122 comp +114 power +276 exhaust =780, and subtracting 720 for 2 full crank revolutions, we get 60* overlap, exactly as previously calculated, so we know the math is correct.
Now lets compare the 114 LSA to the 106 LSA;
268 intake +116 comp +104 Power +276 exhaust (the 114)
268 intake +122 comp +114 power +276 exhaust (the 106)
notice this trick gave us
an extra 6 degrees of compression, and
an extra 10 degrees of power extraction, for a total of 16 *
How'd that happen?
Well, it's in the overlap, which climbed from 44* to 60*, which is the same 16 degrees.
Finally, 122* of compression is usually better than 116, unless it leads to detonation. and
114 Power extraction can be better than 104, depending on what the car is being used for. At just 104* this engine is gonna be thirstier for fuel than at 114.
So, if hiway fuel economy is important, then 114 is better.
But absolute Power might be higher at 104.
However, I installed this cam at split overlap, so it could be retimed either way depending on what you need, say up to 4* retard to 6 or even 8 degrees advanced. Thus you trade compression for Power extraction, or vice-versa.
Hope that helps

 

[rumblefish360]

@AJ/FormS - Outstanding! 5 Star post. Best yet.

 

[1badfish67]

Thanks AJ. Excellent information! Appreciate the formulas and explanation(s) behind them.

 

[harrisonm]

I have a very similar setup. 340, 4 speed, headers, Comp XE268 cam and 3.55 gears. I have a rather lumpy idle with the XE268, and I love it. I would assume the XE274 would even have a more aggressive idle. That should be an awesome engine. You'll probably want a 750 carb.

 

[1badfish67]

I have a very similar setup. 340, 4 speed, headers, Comp XE268 cam and 3.55 gears. I have a rather lumpy idle with the XE268, and I love it. I would assume the XE274 would even have a more aggressive idle. That should be an awesome engine. You'll probably want a 750 carb.

For the carb I have purchased a new Holley 770 Ultra Street Avenger to sit atop Eddie Rpm Airgap intake and ProMaxx 171 heads.

Do you know if Comp Cams designs their Chrysler LA cams specifically for the .904 lifter or if they just use a lobe design for the .842 Chevy or .874 Ford and call it close enough??

Did notice that Hughes Engines claims theirs are specifically designed for the .904 lifter and they advertise some kind of No Flat Cam Guarantee, if all parts purchased as a kit on same invoice. Only 60 days though.