moper
Well-Known Member
Is the goal 400 horsepower? In the car or on the dyno because the differential between those two will be dramatic in that chassis. As will be the cost factor and parts choices.
Build suggestions for 340?
- Thread starter Jim64
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Had one for one summer, with a 4-speed. yanked it.
justinp61
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
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This work-up is for a manual trans streeter.
Keep your eyes on the cylinder pressures and V/P ratios
All calcs at 800ft elevation
>Here is a stock-cammed 318LA, Ica of 48*
Static compression ratio of 8:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 7.10:1 .
Your dynamic cranking pressure is 135.60 PSI.
V/P (Volume to Pressure Index) is 113
> the 340@268cam mightta looked like, Ica of 64*
Static compression ratio of 10:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 7.98:1 .
Your dynamic cranking pressure is 158.75 PSI.
V/P (Volume to Pressure Index) is 126
>same 340@268cam,blue-printed to 10.5 Scr,Ica of 64*
Static compression ratio of 10.5:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 169.18 PSI.
V/P (Volume to Pressure Index) is 134
notice the changes in VP and pressure, from just a half a point of Scr
__________________________________
from here down all are in a 340
with the 292/292/108 cam
> in a typical 1970-up stock 340; Ica of 70*
Static compression ratio of 10:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.60:1 .
Your dynamic cranking pressure is 148.68 PSI.
V/P (Volume to Pressure Index) is 111
The bottom end feels like a 318LA (see the 113VP above)
and the pressure is low, even at 10/1; lets pump it up
>blue-printed to 10.5, Ica of 70*
Static compression ratio of 10.5:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.96:1 .
Your dynamic cranking pressure is 158.21 PSI.
V/P (Volume to Pressure Index) is 118
still a low VP, and the pressure is close to the max for open-chamber iron heads; it's starting to feel like a 5.2M; Lets pump it up some more
>here it is at 165psi, Ica of 70*
Static compression ratio of 10.85:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 123
pressure maxed; feels like a 5.2M at low rpm
>cam advanced to 108*, for Ica of 66*,
and maintaining 165psi
Static compression ratio of 10.5:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 128
pressure maxed, she is feeling a lil stouter than a 5.2M..I'm not a fan of this much cam advance for this cam, in a street engine; it kills overlap, and annihilates any chance at fuel economy, because the extra degrees come straight out of the power stroke.
>Finally, let's slap some closed chamber alloy heads on it, with flat tops. Put the cam back to 102, and pump it up. This will make the combo come alive.
Static compression ratio of 11.7:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 8.68:1 .
Your dynamic cranking pressure is 177.54 PSI.
V/P (Volume to Pressure Index) is 130
compare this VP to the stocker at 126, or the blueprinted 134. Now you more or less have a stock-feeling 340 below 3000. This is more important for a manual-trans car like mine. And of course at WOT, it is ridiculously 292cam strong thru the power curve.
----------------------------------------
now in my 367
> and of course, my engine is a 367 and in at 104,
the 292/108 looked like this
Static compression ratio of 11.3:1.
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 8.60:1 .
Your dynamic cranking pressure is 175.38 PSI.
V/P (Volume to Pressure Index) is 142
Which was NOT happy with 3.55s and a 2.66 low gear. I was very disappointed with the bottom end, and with the powerpeak up at 5400, this was at; 45mph in first, 63 in second, 86 in third. The biggest problem for me was the slowest speed I could drive w/o slipping the clutch, was about 5.8mph with typical Idle-timing. She really wanted one lower gear. I sold it to a racer and yanked it out.He was a happy guy.
>I replaced that cam with a higher lift, 270/276/110 cam,
dropped the Scr back, and got this;
Static compression ratio of 10.7:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 8.80:1 .
Your dynamic cranking pressure is 180.79 PSI.
V/P (Volume to Pressure Index) is 160 Whoa!!
Notice the VP, now ~15% larger, like swapping the 3.55s out for 4.10s. And this is the combo that got me 32 mpgs point to point, on a certain roadtrip........ with a double overdrive ......1.97 final drive, and 75= 1950rpm....... With a 3.09 low, and a lil idle-retard, the slowest no-slip speed was now 3.8 mph.
Badaboom! what a ripper!! Never looked back.
I no longer care about horsepower, swapping instead to torque, and TM (Torque Multiplication). Especially at low rpms, cuz over ~90% of the time, my engine is running under say 3400rpm. I mean with a VP of 160, it don't take a lotta throttle to getchit done.
>When this 270 cam dropped lobes I installed the next bigger cam from the same manufacturer, a 276/286/110 in at 106 for an Ica of 64*,lowered the decks a tad for a lil more squish, and got this;
Static compression ratio of 10.95:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.75:1 .
Your dynamic cranking pressure is 179.44 PSI.
V/P (Volume to Pressure Index) is 154
whoops lost a lil VP, but gained a bit of useless power at high-rpm, which got me a 93mph in the Eighth, Badaboooom!, and it still spins the 295s to 60mph or more.
BTW; this Alloy-headed 367, in all three iterations, has never burned anything but 87E10, and has always run 32/34* Power-Timing, slightly delayed to all-in at 3200 to 3400. And, I run a 22* V-can, coming in as fast as possible. And when the tires are spinning, the tach runs up to just under the rev-limiter at 7200 and just stays there, until I lift. I asked my son to run it by me one time like that, but he, polite boy that he is, declined, so I only have his say-so as to how awesome it sounds, screaming thru the dual, three inch, full-length, cannons; your results may vary. lol
OP
I'm not suggesting you install a 292/292/108 cam in your open-chambered, iron-headed, 340. By the numbers above,you can see that below 3000rpm, your 340 will become lethargic due to lack of pressure and most especially VP. With a 4-speed and 3.23s, you cannot afford lethargic cuz your engine is married to the tires, with no hi-stall TC to help you. Your only option at that point is to slip the clutch to spool up the engine to where the power is. And of course, slipping the clutch only translates the excess power to heat...... or if the tires spin,then to smoke,lol.
I can pretty much guarantee you that a 292cam in a 10/1, open-chamber, iron-headed 340, with a clutch and 3.23s, is about the worst combo,that someone could throw together, in a streeter; second only to it being in a smaller engine,or with less rear gear; no laughing matter.
Keep your eyes on the cylinder pressures and V/P ratios
All calcs at 800ft elevation
>Here is a stock-cammed 318LA, Ica of 48*
Static compression ratio of 8:1.
Effective stroke is 2.89 inches.
Your dynamic compression ratio is 7.10:1 .
Your dynamic cranking pressure is 135.60 PSI.
V/P (Volume to Pressure Index) is 113
> the 340@268cam mightta looked like, Ica of 64*
Static compression ratio of 10:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 7.98:1 .
Your dynamic cranking pressure is 158.75 PSI.
V/P (Volume to Pressure Index) is 126
>same 340@268cam,blue-printed to 10.5 Scr,Ica of 64*
Static compression ratio of 10.5:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 169.18 PSI.
V/P (Volume to Pressure Index) is 134
notice the changes in VP and pressure, from just a half a point of Scr
__________________________________
from here down all are in a 340
with the 292/292/108 cam
> in a typical 1970-up stock 340; Ica of 70*
Static compression ratio of 10:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.60:1 .
Your dynamic cranking pressure is 148.68 PSI.
V/P (Volume to Pressure Index) is 111
The bottom end feels like a 318LA (see the 113VP above)
and the pressure is low, even at 10/1; lets pump it up
>blue-printed to 10.5, Ica of 70*
Static compression ratio of 10.5:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 7.96:1 .
Your dynamic cranking pressure is 158.21 PSI.
V/P (Volume to Pressure Index) is 118
still a low VP, and the pressure is close to the max for open-chamber iron heads; it's starting to feel like a 5.2M; Lets pump it up some more
>here it is at 165psi, Ica of 70*
Static compression ratio of 10.85:1.
Effective stroke is 2.43 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 123
pressure maxed; feels like a 5.2M at low rpm
>cam advanced to 108*, for Ica of 66*,
and maintaining 165psi
Static compression ratio of 10.5:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic cranking pressure is 165.15 PSI.
V/P (Volume to Pressure Index) is 128
pressure maxed, she is feeling a lil stouter than a 5.2M..I'm not a fan of this much cam advance for this cam, in a street engine; it kills overlap, and annihilates any chance at fuel economy, because the extra degrees come straight out of the power stroke.
>Finally, let's slap some closed chamber alloy heads on it, with flat tops. Put the cam back to 102, and pump it up. This will make the combo come alive.
Static compression ratio of 11.7:1.
Effective stroke is 2.38 inches.
Your dynamic compression ratio is 8.68:1 .
Your dynamic cranking pressure is 177.54 PSI.
V/P (Volume to Pressure Index) is 130
compare this VP to the stocker at 126, or the blueprinted 134. Now you more or less have a stock-feeling 340 below 3000. This is more important for a manual-trans car like mine. And of course at WOT, it is ridiculously 292cam strong thru the power curve.
----------------------------------------
now in my 367
> and of course, my engine is a 367 and in at 104,
the 292/108 looked like this
Static compression ratio of 11.3:1.
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 8.60:1 .
Your dynamic cranking pressure is 175.38 PSI.
V/P (Volume to Pressure Index) is 142
Which was NOT happy with 3.55s and a 2.66 low gear. I was very disappointed with the bottom end, and with the powerpeak up at 5400, this was at; 45mph in first, 63 in second, 86 in third. The biggest problem for me was the slowest speed I could drive w/o slipping the clutch, was about 5.8mph with typical Idle-timing. She really wanted one lower gear. I sold it to a racer and yanked it out.He was a happy guy.
>I replaced that cam with a higher lift, 270/276/110 cam,
dropped the Scr back, and got this;
Static compression ratio of 10.7:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 8.80:1 .
Your dynamic cranking pressure is 180.79 PSI.
V/P (Volume to Pressure Index) is 160 Whoa!!
Notice the VP, now ~15% larger, like swapping the 3.55s out for 4.10s. And this is the combo that got me 32 mpgs point to point, on a certain roadtrip........ with a double overdrive ......1.97 final drive, and 75= 1950rpm....... With a 3.09 low, and a lil idle-retard, the slowest no-slip speed was now 3.8 mph.
Badaboom! what a ripper!! Never looked back.
I no longer care about horsepower, swapping instead to torque, and TM (Torque Multiplication). Especially at low rpms, cuz over ~90% of the time, my engine is running under say 3400rpm. I mean with a VP of 160, it don't take a lotta throttle to getchit done.
>When this 270 cam dropped lobes I installed the next bigger cam from the same manufacturer, a 276/286/110 in at 106 for an Ica of 64*,lowered the decks a tad for a lil more squish, and got this;
Static compression ratio of 10.95:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.75:1 .
Your dynamic cranking pressure is 179.44 PSI.
V/P (Volume to Pressure Index) is 154
whoops lost a lil VP, but gained a bit of useless power at high-rpm, which got me a 93mph in the Eighth, Badaboooom!, and it still spins the 295s to 60mph or more.
BTW; this Alloy-headed 367, in all three iterations, has never burned anything but 87E10, and has always run 32/34* Power-Timing, slightly delayed to all-in at 3200 to 3400. And, I run a 22* V-can, coming in as fast as possible. And when the tires are spinning, the tach runs up to just under the rev-limiter at 7200 and just stays there, until I lift. I asked my son to run it by me one time like that, but he, polite boy that he is, declined, so I only have his say-so as to how awesome it sounds, screaming thru the dual, three inch, full-length, cannons; your results may vary. lol
OP
I'm not suggesting you install a 292/292/108 cam in your open-chambered, iron-headed, 340. By the numbers above,you can see that below 3000rpm, your 340 will become lethargic due to lack of pressure and most especially VP. With a 4-speed and 3.23s, you cannot afford lethargic cuz your engine is married to the tires, with no hi-stall TC to help you. Your only option at that point is to slip the clutch to spool up the engine to where the power is. And of course, slipping the clutch only translates the excess power to heat...... or if the tires spin,then to smoke,lol.
I can pretty much guarantee you that a 292cam in a 10/1, open-chamber, iron-headed 340, with a clutch and 3.23s, is about the worst combo,that someone could throw together, in a streeter; second only to it being in a smaller engine,or with less rear gear; no laughing matter.
Last edited:
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 25,838
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This post is all about low-rpm power with a manual trans
looking back; my iterations had VPs of 142,160, and 154.
All of these were enough to initiate a spin with 295s and carry it all the way thru first gear, with a starter-gear as small as 2.66 x3.55= 9.44
But the 142VP needed some help by way of rpm to get started, whereas the 160VP would bust them loose at under 2000rpm with the line-loc engaged, and then I could idle it right down; which was always a hit at a stoplight.
Looking back, the 142 wasn't as bad as I thought. It was just not what I was expecting nor what I wanted, and the lack of slow-running just sealed the deal. I could have lived with it using more rear gear. But living 20 minutes by hiway from the nearest urban center, and it being my DD, the fuel-economy was atrocious, even with the 3.55s I wanted to run.. I moved the cam a couple of times, but it was hardly worth it.
That said, I see no real downside to a VP of 142.... when coupled to the right application, and a clutch with a 2.66 x 3.23= 8.59 starter gear is not it. I would guess, based on my experience, that a starter-gear of 2.66 x 3.91=10.37 would be close. You can get about this, with a Commando box, 3.09 x 3.23= 9.98 . But that does nothing for second gear. You are still stuck with the same 1.92 x 3.23= 6.20 and your 340 will struggle with that, even at VP of 142 if you short shift it.
The problem for the 340 is getting to a VP of 140 or more, with open chamber,iron heads, working within the confines of pumpgas, it just cannot be done with any performance type cam.
The 268 Mopar cam is a good size for a streeter, but the 114LSA and the long slow ramps, kill pressure, and the VP with it. And therein lies the problem.
>Here is your 340, Ica of 64*,(268cam)still 800ft
Static compression ratio of 10.5:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 169.18 PSI.
V/P (Volume to Pressure Index) is 134
The VP looks fairly good at 134, but Usually, you cannot run 169psi on pumpgas. However,on this cam, the intake valves really are not yet closed, so many times you might be able to adjust the tune to get away with it. But you will have to forever run best gas.
>Lets change the Ica to 68, to more accurately reflect what the Ica might be, when rated as, say .006 tappet rise; and I get.
Static compression ratio of 10.5:1.
Effective stroke is 2.47 inches.
Your dynamic compression ratio is 8.08:1 .
Your dynamic cranking pressure is 161.41 PSI.
V/P (Volume to Pressure Index) is 123
SAME cam, SAME install, just adjusted as said above.
ok so there is the pressure you want, but the VP has dropped into the basement again, which will more accurately reflect what you will feel at low rpm.
There is no getting around this. You cannot increase the VP without also increasing the pressure. And you cannot run more pressure without having to limit your timing. If you drop the compression ratio; both numbers will fall.
>So these numbers, namely 161/123 are very nearly the best you can expect with open-chamber iron heads, and a 268 cam.
Now comes the game changer;
some FABO members say they are running up to 200psi in strokers!, on pump gas, with alloy heads. I myself have run 185 psi and more, on 87E10.
Not cheap I know, but when you consider that you can keep the 3.23s, and keep the 2.66box, and run just about any cam or pressure that you want to, the flexibility is so worth it. The better ports will be worth at least one cam size and a swap to a solid-lifter cam, will open up both ends.
Here is your 340 with alloy heads and an Ica of 66*
Static compression ratio of 11.3:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 8.83:1 .
Your dynamic cranking pressure is 181.61 PSI.
V/P (Volume to Pressure Index) is 141
adequate VP, lots of pressure; that might be a 280 cam......., see what I mean?
>Lets take some cam out, and keep the pressure close to 180 for 87E10.
One cam smaller/ Ica of 62*
Static compression ratio of 10.9:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 8.79:1 .
Your dynamic cranking pressure is 180.52 PSI.
V/P (Volume to Pressure Index) is 145
see the VP climbing
> one more smaller cam; Ica of 58*
Static compression ratio of 10.5:1.
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 8.74:1 .
Your dynamic cranking pressure is 179.17 PSI.
V/P (Volume to Pressure Index) is 149
Still more VP, and back to 10.5 Scr.. 149 is a lot of VP, and you would be sure to have a lotta fun with it.
Each cam size smaller will bring the power down about 200 rpm to work with the 3.23s. But of course the power will be some 15 hp less per cam, is my guess. You can get some of that back by tightening up the LSA. and/or increasing the lift.
A solid lifter cam more or less requires an adjustable valve gear, at additional cost.
Fun with the calculator. I have been impressed with the
Wallace Racing: Dynamic Compression Ratio Calculator
looking back; my iterations had VPs of 142,160, and 154.
All of these were enough to initiate a spin with 295s and carry it all the way thru first gear, with a starter-gear as small as 2.66 x3.55= 9.44
But the 142VP needed some help by way of rpm to get started, whereas the 160VP would bust them loose at under 2000rpm with the line-loc engaged, and then I could idle it right down; which was always a hit at a stoplight.
Looking back, the 142 wasn't as bad as I thought. It was just not what I was expecting nor what I wanted, and the lack of slow-running just sealed the deal. I could have lived with it using more rear gear. But living 20 minutes by hiway from the nearest urban center, and it being my DD, the fuel-economy was atrocious, even with the 3.55s I wanted to run.. I moved the cam a couple of times, but it was hardly worth it.
That said, I see no real downside to a VP of 142.... when coupled to the right application, and a clutch with a 2.66 x 3.23= 8.59 starter gear is not it. I would guess, based on my experience, that a starter-gear of 2.66 x 3.91=10.37 would be close. You can get about this, with a Commando box, 3.09 x 3.23= 9.98 . But that does nothing for second gear. You are still stuck with the same 1.92 x 3.23= 6.20 and your 340 will struggle with that, even at VP of 142 if you short shift it.
The problem for the 340 is getting to a VP of 140 or more, with open chamber,iron heads, working within the confines of pumpgas, it just cannot be done with any performance type cam.
The 268 Mopar cam is a good size for a streeter, but the 114LSA and the long slow ramps, kill pressure, and the VP with it. And therein lies the problem.
>Here is your 340, Ica of 64*,(268cam)still 800ft
Static compression ratio of 10.5:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 169.18 PSI.
V/P (Volume to Pressure Index) is 134
The VP looks fairly good at 134, but Usually, you cannot run 169psi on pumpgas. However,on this cam, the intake valves really are not yet closed, so many times you might be able to adjust the tune to get away with it. But you will have to forever run best gas.
>Lets change the Ica to 68, to more accurately reflect what the Ica might be, when rated as, say .006 tappet rise; and I get.
Static compression ratio of 10.5:1.
Effective stroke is 2.47 inches.
Your dynamic compression ratio is 8.08:1 .
Your dynamic cranking pressure is 161.41 PSI.
V/P (Volume to Pressure Index) is 123
SAME cam, SAME install, just adjusted as said above.
ok so there is the pressure you want, but the VP has dropped into the basement again, which will more accurately reflect what you will feel at low rpm.
There is no getting around this. You cannot increase the VP without also increasing the pressure. And you cannot run more pressure without having to limit your timing. If you drop the compression ratio; both numbers will fall.
>So these numbers, namely 161/123 are very nearly the best you can expect with open-chamber iron heads, and a 268 cam.
Now comes the game changer;
some FABO members say they are running up to 200psi in strokers!, on pump gas, with alloy heads. I myself have run 185 psi and more, on 87E10.
Not cheap I know, but when you consider that you can keep the 3.23s, and keep the 2.66box, and run just about any cam or pressure that you want to, the flexibility is so worth it. The better ports will be worth at least one cam size and a swap to a solid-lifter cam, will open up both ends.
Here is your 340 with alloy heads and an Ica of 66*
Static compression ratio of 11.3:1.
Effective stroke is 2.52 inches.
Your dynamic compression ratio is 8.83:1 .
Your dynamic cranking pressure is 181.61 PSI.
V/P (Volume to Pressure Index) is 141
adequate VP, lots of pressure; that might be a 280 cam......., see what I mean?
>Lets take some cam out, and keep the pressure close to 180 for 87E10.
One cam smaller/ Ica of 62*
Static compression ratio of 10.9:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 8.79:1 .
Your dynamic cranking pressure is 180.52 PSI.
V/P (Volume to Pressure Index) is 145
see the VP climbing
> one more smaller cam; Ica of 58*
Static compression ratio of 10.5:1.
Effective stroke is 2.70 inches.
Your dynamic compression ratio is 8.74:1 .
Your dynamic cranking pressure is 179.17 PSI.
V/P (Volume to Pressure Index) is 149
Still more VP, and back to 10.5 Scr.. 149 is a lot of VP, and you would be sure to have a lotta fun with it.
Each cam size smaller will bring the power down about 200 rpm to work with the 3.23s. But of course the power will be some 15 hp less per cam, is my guess. You can get some of that back by tightening up the LSA. and/or increasing the lift.
A solid lifter cam more or less requires an adjustable valve gear, at additional cost.
Fun with the calculator. I have been impressed with the
Wallace Racing: Dynamic Compression Ratio Calculator
Last edited:
The goal is 400 HP at the crank.
AJ,
Thanks again for all the time you're putting into this. I'm still trying to wrap my brain around all of this...
Early on, you said:
I'd settle for 380/400ftlbs at 36 mph, and all-done by 60mph/5000 rpm with 3.23s..........but that might just be me,lol.
And based on what I'm learning, maybe I would be good with that. I DO want to have some low-end power, and I'm willing to trade top-end power for it.
Can that be done with the iron head? I assume it can...now I need to figure out what cam!
-Jim
Yes, it's the cam that ends in "703". You'll be hard pressed to find a better grind for what you want.
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
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Well it's kindof tricky;
For a strong bottom end; you can do it in several ways;
1) the first is with cubes. Then
2) Torque Multiplication, or
3) a weightloss program
4) cylinder pressure, or
5) super charging.
6) budget
Given a particular engine, a particular trans, a particular rear gear, in a particular chassis;
that rules out 1,2,and sorta 3, leaving you with 4,5,and 6..
I can sense your budget constraint, so now we are down to #4) cylinder pressure
With open-chamber, iron heads; as mentioned, for pump gas, you are sorta limited to 160 psi.
And the Wallace calculator spits out the pressure when you enter the Scr and Ica.
So the First thing you have to do is figure out your Scr, exactly no guesses. And that then leaves the only variable being the Ica.
But if you have your eye on a particular Ica, then you may have to change your Scr to run it. And that usually means pistons and machining, which gets expensive in a hurry.
But the thing of it is; you can get around all this by not being married to those 3.23s. Make it a City car, and build your engine as you wish, the gears will sorta level the playing field..
Or knock 200 pounds out of the chassis; that's about equal to 20hp or one cam-size. IDK how much you can excise from an Early-A.
But honestly, your Barracuda is already much lighter than my Second Gen. I'll bet a good 400/500 pounds lighter than the 3650 my pig weighs, so you are already way ahead of me.
Furthermore, you can't put a buncha rubber in the factory wheel-tubs, so 400hp, all-in-all, IMO, for this application is way overkill; sorta like going deer-hunting with a bazooka. Just how dead do you need that deer to be.
In other words, IMO,
What was my very first comment?
Me, personally, I would not run that factory 268 cam , but in your combo it can be used to kill some pressure.
There is one more trick I use. Because VP can be directly used to compare the bottom ends of any engines, that means you can use it in other comparisons as well.
So for instance, I know my weight and VP, If I take weight over VP, and compare it to another car with a different weight and VP, I will be able to get an idea of how strong the second car will be, compared to mine, because I already know how strong mine is.
So 3650/154= 23.7
I don't have a name for this factor, so let's call it the L, for Ludicrous factor; cuz in my car, this is a ludicrously strong bottom end.
Ok so lets say your car weighs 3100 with you in it, and you want the same L-factor; then 3100/23.7=130 VP
From post 29
>same 340@268cam,blue-printed to 10.5 Scr,Ica of 64*
Static compression ratio of 10.5:1.
Effective stroke is 2.57 inches.
Your dynamic compression ratio is 8.37:1 .
Your dynamic cranking pressure is 169.18 PSI.
V/P (Volume to Pressure Index) is 134/Badaboom!
But here's the thing;
this 268/276/114 Chrysler cam makes terrible fuel mileage, mostly because of the the very short power-stroke, before the exhaust valve pops open.
And there is no good reason to run that extra 8 degrees on the exhaust duration with headers.
Nor a good reason to run a 114LSA cam in this lightweight manual trans combo!
But the problem is, that you need the 64* Ica that is on it ,to get your pressure down with a 10.5 Scr.
>But , now that we know that a VP of 130 is more than enough..... we can lower your Scr! Check this out: Ica of 60*@800ft
Static compression ratio of 9.8:1.
Effective stroke is 2.66 inches.
Your dynamic compression ratio is 8.06:1 .
Your dynamic cranking pressure is 160.88 PSI.
V/P (Volume to Pressure Index) is 132
Badaboom!
4* less Ica means we can redesign the cam to something like ;
262/268/108/48*Overlap/120compression/118 power, Ica of 60*
compared to the Chrysler cam at;
268/276/114/44 overlap/116 compression/104 power, Ica of 64*
But notice that I had to reduce the Scr to 9.8 to make it work
With a "more modern"lobe, you should be able to get the .050 up close to what the 268 was, but the tighter 108 LSA will get you a nice punchy power curve to work with the average .73 splits of the A833. I like it; It's sort-of a big-bore 318 kindof thing.
So like I said; you gotta know exactly your Scr, no guessing.
Rusty says he likes the Lunati 10200703 which is
268/276/110/52*overlap/120 comp/110 power, Ica of 60*
I like it too, except I might put it in straight up/no advance to trade away 2* of compression to get 2* of power extraction, and that would run at 10.0Scr on pumpgas,barely.
>Here it is in per the Lunati spec, Ica of 60*
Static compression ratio of 10:1
Effective stroke is 2.66 inches.
Your dynamic compression ratio is 8.22:1 .
Your dynamic epressure is 165.15 PSI. Probable iffy for 91gas
V/P (Volume to Pressure Index) is 135
and straight up / Ica of 62*
Static compression ratio of 10:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 8.09:1 .
Your dynamic pressure is 161.68 PSI. Borderline for pumpgas
V/P (Volume to Pressure Index) is 130
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Then just build my recommendation. I'm not right every time, but I'm spot on here for what you want. You won't be disappointed. Just go for it man.
Best honest advice of the thread.
You can lead a horse to water......but he'll get sidetracked every time by all the forum bullshit.
Like the BS I am going to inject into this thread and I'm not even gonna apologize first.
Does your cam recommendation go out the window when using hi-po stock manifolds a 904 and 391 gears?
OK, Sorry.
No doubt. It’s amazing that some type out glittery gold replies. Slammed with super amounts of bologna. Simple gets the job done. I’ve done what you said, first reply, add the “340 replacement HP” cam, same lift (more or less) more duration in a 110. Excellent street set up.
Like the BS I am going to inject into this thread and I'm not even gonna apologize first.
Does your cam recommendation go out the window when using hi-po stock manifolds?
OK, Sorry.
LOL. no it's a split pattern and it's conservative so it will work with either.
Not for nothing but if you wanna build power, why stick a cork in the dam thing! I bet you’ll run great with a banana up your nose as well.Like the BS I am going to inject into this thread and I'm not even gonna apologize first.
Does your cam recommendation go out the window when using hi-po stock manifolds?
OK, Sorry.
LOL. Dont need 400 ponies. Just want all I can get from a stock look.
Then stop by-jacking the thread and create a new one.
FWIW, if you just want to get the most out of your engine with exhaust manifolds, then just ignore the fact you have them....
I suggest a few more exhaust degrees of duration than normal splits
Hi-Jack over. My build is a long ways away. Just trying to glean a little info before I start my own thread. like... add a few degrees of exhaust duration.
Oh no doubt! Learn what ya can and good looking luck on the build
harrisonm
Well-Known Member
Here's the deal, IMHO. If you do a complete and thorough job on a rebuild, it won't cost all that much more to beef up the horsepower while you are at it. So doing a fairly stock rebuild is fine if that is REALLY what you want to do, but will you be kicking yourself in the butt in a few months? If you decide a year down the road that you want an extra 100 (or so) HP, you will be pulling the motor out, pulling it apart and then buying the parts you should have bought the first time. And THAT will wind up costing you more in the long run. Unless you are constrained by a tight budget, do what you really want to do the first time.
I can see 360-375 with stock unported heads and the EARLY 340 exhaust manifolds.
So thanks, Rusty, for that cam recommendation - I think it does a good job of fitting my realistic parameters!
AJ - I got the spec from Lunati about that cam, and based on that, I attempted to fill out the formula, and here's what I entered and what it calculated:
Number of Cylinders : 8
Bore in Inches : 4.08
Stroke in Inches : 3.31
Rod Length in Inches : 6.123
Static Compression Ratio : 10 :1
Inlet Valve Closes ABDC : 39°
Boost Pressure in PSI : 0
Target Altitude : 800 (Feet)
Results:
Static compression ratio of 10:1.
Effective stroke is 3.03 inches.
Your dynamic compression ratio is 9.24:1 .
Your dynamic cranking pressure is 192.80 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 9.08 :1.
V/P (Volume to Pressure Index) is 183
Either there is something off in my input, or this is an outstanding cam. Please correct me if I've entered something incorrectly...
-Jim
I thought "effective stroke" was always HALF the total stroke. That number seem strange.
I thought the same thing, but AJ has examples of 2.5, 2.6, 2.7...so I don't know where it comes from or how to calculate it. (I'm thinking it does have something to do with the timing of the intake valve closure after BDC.)
-
