Knocking 340

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My engine rebuilder had a dyno. I paid him the extra $500 to dyno it just to erase any future questions about it's horsepower. Glad I did. The other benefit is that it is now broken in, the timing is set, carb is good. Just install in car and fire it up.
As you most likely found out there is a big difference between tuning for the dyno and tuning for the street or track.
 
To get a rough figure on the HP you will need to have the calculated compression ratio and cam spec's.
Will the engine be stroked? Any head work?
They are members on here that are dam good with power calculations.
Me not so much.

Its a stock '68 forged Crank. No head work, just Stock X-Heads. 40th over KB Pistons and Im not sure of the Cam, will be a fairly mild Comp Cam. I think its the xe268h with matching lifters and springs.
 
Its a stock '68 forged Crank. No head work, just Stock X-Heads. 40th over KB Pistons and Im not sure of the Cam, will be a fairly mild Comp Cam. I think its the xe268h with matching lifters and springs.
Any engine builder worth their salt should be able to give you a guess on HP.
 
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i can tell you what i got out of my 340 with 11:4 compression mahle pistons and a smallish cam 390hp 425 tq a very mild build , nothing radical , easy going street car , I USED AN AVENGER 670 ,was enough for the car ran well ran a best of 13.1 with me , a tortoise . with a good racer and tires probably get in the 12's
GOOD LUCK

let me add had 190 cyl pressure
 
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Any engine builder worth their salt should be able to give you a guess on HP.

Im not wanting to bother him just now. I know he's busy. Just wondered if anyone had a rough guess and also wanted to update the thread. No bid deal. :)
 
i can tell you what i got out of my 340 with 11:4 compression mahle pistons and a smallish cam 390hp 425 tq a very mild build , nothing radical , easy going street car , I USED AN AVENGER 670 ,was enough for the car ran well ran a best of 13.1 with me , a tortoise . with a good racer and tires probably get in the 12's
GOOD LUCK

Damn, 11.4? Thats high! I think I'll be lucky to see the 10.5 advertised for the 340.
 
With castiron open-chamber X-heads, 11.1 is not likely on the table for a street-combo.
Not likely, but not impossible,and
not necessary either.

oops, I mean 11.4,lol.
 
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I thought it was difficult enough running 10.5 on pump fuel, can 11.4 be ran on premium?
With aluminum tight-Q heads, some guys here on FABO have claimed 200psi on pumpgas, on the street.
IMO, the Scr is just a tool we use to achieve the pressure we think we can get away with.
In 1999, I thought I could get away with 11.3Scr and the 292/292/108 cam. I was right. Because the combo only hit 185psi, and it burned 87E10 with full-timing.
So
Yes it can be done.
At least on the street.
Because on the street,
firstly you can't get any traction, and
secondly,you are usually running less carb than you should be,and
thirdly, you are only ever at WOT for 5 to 6 seconds before speeding.
By 7/8 seconds from a dead stop, you could be doing close to a hundred mph. So the street engine is not very highly stressed.
In that 292 combo, I ran 245s out back, and traction was a joke. But it sure was a lotta fun.
Not knowing where the pressure ceiling was, each combo afterwards was also adjusted to run the same-ish 180psi.... cuz I already knew that ran on 87E10, which at the time was the only gas we had. So the next cam ran at 10.7Scr, and the current cam is at 10.95 Scr. All three ran at about the same 180 psi.

BTW, in a 360/A833; on the street, 180 is all you need; it's more than enough. The bottom end is ridiculously over powered with a starter gear of 10 or 11 to 1. And second gear will take you well into speeding territory. With a 223* or so cam, you can make fuel-mileage that a 318 could only dream of. Add an overdrive to it and the numbers go crazy.
I eventually narrowed the rear end and moved the springs inboard, so that I could run 275s and then 295s and then 325s. 325s proved to be a not so good choice in the stock tubs, for cornering, so most of the time I run the 295s.
So coming to the point; the 223 cam with 275s and 3.55gears was both quicker and faster than the 292cam with 245s; also with 3.55s.
The current cam is a 230*, runs with 3.55s and 295s, and is quicker and faster than the 223, which is to be expected. But man, this 230 sucks the gas on the hiway, even with the GVod. And it gave up a lotta bottom end torque. For which I finally got a lower first gear to cover it; 3.09 vs 2.66.

That 223* was my favorite combo of all-time.
 
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With aluminum tight-Q heads, some guys are claiming 200psi on pumpgas.

I dont even know how to equate that to CR. :D

Edit: thought about it and 200psi = 13.6-1 cr?

So 10.5-1 = 152psi?

Although Ive read an early 340 is not actually 10.5-1 but closer to 9.5-1.
 
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I dont even know how to equate that to CR. :D
OK here; maybe this will help;
Cr is Compression Ratio. You take the entire volume of the cylinder with the piston at the bottom, and compare it to the entire volume when the piston is at the top.We call it Scr because it is a Static Compression Ratio number, nothing is moving . It is usually defined as;
(CV+cv)/cv where CV is the swept volume and cv is the chamber volume.
A stock 360 has a CV of 737.21 cc and a cv usually of around 105.3cc so then
(737.2 +105.3)/105.3=8.00/1 SCR or Static Compression Ratio.

But; the engine while running never has an intake valve that closes with the piston at the bottom, and compression building cannot begin until the intake valve is actually closed and not leaking.
In a performance engine, this point is often with the piston nearly halfway up the cylinder. Most performance cams will fall into the range of 60 to 70 degrees after the piston has left the bottom.
This is very bad news for the 8/1 engine, and the shorter it's stroke, the worse it is.
Lets take that 360 and say the intake valve does not close until the effective stroke is reduced to 2.58. Now the swept will be 531.2cc.. and the same chamber is 105.3 so once again;
(CV+cv)/cv = Dcr this time so
(531.2+105.3)/ 105.3=6.04 Dynamic Compression ratio . This is a decidedly un hi-performance number. With iron heads we like to target about 8/1Dcr.
So how can you get to 8/1 from 6/1 ? Principally, you have to shrink the size of the total combustion chamber; in this case a lot. 78cc is about the easiest to get so lets try that, still with the 2.58 Effective stroke.
(531.2=78)/78=7.8 Dcr, now yur getting close.
With a lil more machine work, you can get your chamber to 75.88cc and so
(531.2+75.88)/75.88=8.00/1 and there you go. Mission accomplished.

Now, from here, you have to go find a cam, with an ICA that will produce the effective stroke of 2.58, which is the only Ica that will produce the 8/1Dcr with the 75.88 total chamber size, in a 360, lol.
 
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I dont even know how to equate that to CR. :D

Edit: thought about it and 200psi = 13.6-1 cr?
So 10.5-1 = 152psi?
Although Ive read an early 340 is not actually 10.5-1 but closer to 9.5-1.
ummmmm no. PSI and cr/CR/Scr are not directly related in that way, because the intake Closing angle is governing when the pressure building begins.
You can have an 11/1 Scr engine, that will build 20 different pressures with just one cam, at different altitudes and different installs. So talking Scr is somewhat irrelevant.
The pressure is what you want to talk about. Because the same engine operating at different pressures will have different operating characteristics.
Once the operating pressure is in the zone, it is very difficult to pinpoint a "perfect" pressure.
The "zone" is somewhat ethereal, in that it's hard to pinpoint, moves around, is different for every engine and different for every combo.
#1, max pressure is only possible when the throttle is at WOT.
#2, the pressure is only maxed over a narrow operating window
#3, the maximum changes with the amount and density of the airflow.
#4, the lowest rpm that max can occur is governed mostly by the cam. as is the highest point., but
#5 the highest point of max pressure can be stretched higher by the heads, the headers and even, the exhaust.
#6, there comes an rpm band, where there is just not enough time for the atmosphere to find it's way into the chamber as it once did, and pressure begins to fade into oblivion.
#7, What streeter drives around at WOT, at 3800rpm, all the time? Nobody does that. So in all likelyhood, something like 95% of a street engines life is gonna be NOT at max pressure.So there is no "best" pressure.
But in the same engine, you can find better and worse comparative pressures, like 160 is better than 150, is better than 140 and so on, because the more pressure you have, the less throttle you will need under every operating condition, except of course at WOT,lol.
Or;
There is NOTHING you can do for a 110psi 318. It's a lazy lazy dog and will stay a dog no matter what you bolt onto it, short of a supercharger.
An Iron open-chambered 360 will not accept much more than 160 psi, before it will start to detonate itself to death, on pumpgas, at WOT, sometimes less than WOT.
So we come to a zone that is pretty safe; say 150 to 158psi, and it is desirable that more is better.
But this number changes with every cam you put into it, and every different installed Ica, and at different altitudes.
So you have to pick the cam, or at least ballpark the Ica FIRST, so you can better target the pressure.
If you goof, and the pressure is too low, all is not lost; the bottom end just gets soft, which you can mostly compensate for with stall, and rear gear. But if the pressure is too high, for pump gas, then yur screwed, and will have to make some changes, usually major ones.

In my engine, I have kept the cranking cylinder pressure very close to 180 psi with all three cams I have installed into it, by changing the total chamber volume in each case, in compensation for the changing Ica which varied from 74* to 61* to 66* . The Scr ranged from 11.3 to 10.7 to 10.95. I did this by changing gaskets and by shaving the tops of the decks. For aluminum closed-chamber tight-Q heads 180psi is a walk in the park, as witnessed by the 87E10 it burns 100% of the time, with full timing.
And 180psi is awesome; waaaaaaay better than 150 to 158,lol.
Hope this helps
 
ummmmm no. PSI and cr/CR/Scr are not directly related in that way, because the intake Closing angle is governing when the pressure building begins.
You can have an 11/1 Scr engine, that will build 20 different pressures with just one cam, at different altitudes and different installs. So talking Scr is somewhat irrelevant.
The pressure is what you want to talk about. Because the same engine operating at different pressures will have different operating characteristics.
Once the operating pressure is in the zone, it is very difficult to pinpoint a "perfect" pressure.
The "zone" is somewhat ethereal, in that it's hard to pinpoint, moves around, is different for every engine and different for every combo.
#1, max pressure is only possible when the throttle is at WOT.
#2, the pressure is only maxed over a narrow operating window
#3, the maximum changes with the amount and density of the airflow.
#4, the lowest rpm that max can occur is governed mostly by the cam. as is the highest point., but
#5 the highest point of max pressure can be stretched higher by the heads, the headers and even, the exhaust.
#6, there comes an rpm band, where there is just not enough time for the atmosphere to find it's way into the chamber as it once did, and pressure begins to fade into oblivion.
#7, What streeter drives around at WOT, at 3800rpm, all the time? Nobody does that. So in all likelyhood, something like 95% of a street engines life is gonna be NOT at max pressure.So there is no "best" pressure.
But in the same engine, you can find better and worse comparative pressures, like 160 is better than 150, is better than 140 and so on, because the more pressure you have, the less throttle you will need under every operating condition, except of course at WOT,lol.
Or;
There is NOTHING you can do for a 110psi 318. It's a lazy lazy dog and will stay a dog no matter what you bolt onto it, short of a supercharger.
An Iron open-chambered 360 will not accept much more than 160 psi, before it will start to detonate itself to death, on pumpgas, at WOT, sometimes less than WOT.
So we come to a zone that is pretty safe; say 150 to 158psi, and it is desirable that more is better.
But this number changes with every cam you put into it, and every different installed Ica, and at different altitudes.
So you have to pick the cam, or at least ballpark the Ica FIRST, so you can better target the pressure.
If you goof, and the pressure is too low, all is not lost; the bottom end just gets soft, which you can mostly compensate for with stall, and rear gear. But if the pressure is too high, for pump gas, then yur screwed, and will have to make some changes, usually major ones.

In my engine, I have kept the cranking cylinder pressure very close to 180 psi with all three cams I have installed into it, by changing the total chamber volume in each case, in compensation for the changing Ica which varied from 74* to 61* to 66* . The Scr ranged from 11.3 to 10.7 to 10.95. I did this by changing gaskets and by shaving the tops of the decks. For aluminum closed-chamber tight-Q heads 180psi is a walk in the park, as witnessed by the 87E10 it burns 100% of the time, with full timing.
And 180psi is awesome; waaaaaaay better than 150 to 158,lol.
Hope this helps


Damn, those two posts where some reading. Im gonna have to read them both again (a couple of times) to fully digest that. Thanks for taking the time to write all that out. Very interesting and written in a way I could make sense of.

Many thanks.
 
there is one more thing to keep in mind;
engines are all about getting air in. Adding the fuel to it is relatively easy, but trying to get more air into the same sized cylinders is always the hard part.
To that end it must be remembered that Air moves from a high-pressure area to a low pressure area. Engines do not suck in air. The atmosphere muscles it's way in.
The piston, falling on the intake stroke as it does,creates a low pressure in the cylinder, that the higher pressured atmosphere then tries to fill.
But the carb/intake manifold/intake valve all make it difficult, especially at idle, with the closed throttle valves. So our jobs as performance enthusiasts, is to make the airway from atmosphere to piston, as easy as possible for the atmosphere to traverse, and to try and reduce the pressure in the chamber on the intake stroke, as low as is possible, to encourage maximum air infiltration, and to try and get as many oxygen molecules stuffed into there as possible, during the "time" that the intake valve cycles from open to closed.
That "time" is principally governed by the intake duration of your camshaft. But, there are some tricks we use to try and encourage the atmosphere to come in early/stronger and pile up longer, during the allotted "time".
It's all about getting the oxygen in there.
A big cylinder to start with, is always the easiest way,lol. Once the size of the cylinder is chosen, there is only so much you can do.
It helps me, to think of the basic size of the Mopar cylinders; A 360 has ~752cc. A 340 is ~696. a 318 is about 652. A 273 has about 559cc. It's pretty easy to see that 752 cc of air would seem better than 559cc. That's a difference of 193cc or nearly 35% from small to large. That's a lot of air. Rather could be a lot of air. But it's more complicated than that.
It's complicated by the application, and by the desired useage, and the environment that the engine is gonna have to operate in, especially altitude. I mean a 5000 pound tow truck operating in the mountains would want a different engine than a 2800pound grocery getter at sealevel. Or a peppy 3400pounder at a more typical 1000 ft elevation. There is a home for every size of engine. But sometimes we try and make a too-small engine, work too hard. And sometime there really is such a thing as too big.
We can do a lot with camshafts to try and better fit the engine to the applications, but sometimes it's better to just start with the right sized engine in the first place. My yardstick for that, for a performance street application, is 10 pounds per cubic inch. So; a 340 would seem to be just right for most of us, with 1967 to 72 A-bodies, with a middle-aged driver,lol. The later fat-boy Swingers like 360s, and the earlier lightweight-As can get by with less cubes.
After the basic size is chosen, the power can be varied quite a bit from say .75 to 1.15 hp per cube, to fine-tune for the application. But for the most part, sticking to .90 to .95 is gonna make the most trouble-free engine at the most economical price, and be the most fun.
It's all about getting the air in. Trying to get 752cc of air into a cylinder of 752cc is tough enough, never mind trying to get it into a 652 cc cylinder.
_____________________
To try, IMO, is either;a rich-man's quest,a poor man's folly, or an exercise in futility. I ain't rich and my Momma didn't raise no fool; so my 3650 pound 1968 Barracuda (me in it), has....... wait for it ...... a 367 cuber.
I couldda built a 340, but then I wouldda wanted to cut out 200 pounds from the car.
I couldda built a 318, but then, my Barracuda, at 3450 now is a tad porky for a 318 at .95 hp per cube so now I would have to pump it up to say 1.13hp per cube, to match the power of the 360 at 1.0 hp per cube. But doing that, always,always, trades away low-rpm power to get the higher absolute power. So now I would have to deal with the wet-noodle bottom end; no thanks. I'm not into 3200rpm stalls and 3.91s. I actually drive my cars, some years 12,000 miles. A 318 does not fit my application. I drive a Manual-trans, and am limited to 3.55s, 3.23s preferred, so a 318 is not gonna cut it, I don't care how much power it makes; where I drive it, in the sub-3000rpm zone, a 318 just cannot process enough air for my preferences, my driving style; it's a poor match to my porky chassis.
A 340 wouldda bin a good match at 1.06hp per cube, but in my case, I wanted overkill at low rpm. So I chose a 360 at 1.0 hp per cube ....... but that quickly morphed into 1.15hp per cube when I found out just how overkill my 367 bottom-end actually was. I traded some of it away, to get the top-end rush. Yeah, it really is too-big, but it sure is fun.
I was fortunate in that, at the time I was working on this car, I was making good money.So I was able to do the things I did without compromising my lifestyle. I realize that not everyone is so blessed. So I'm here on FABO to try and help steer people into the right combo for them, the first time. But also here to share what I have learned, with the next generation. I'm 67 now, semi-retired, and running out the clock of my promised 70 years/80 if by reason of good health. " You can't take it with you" also applies to knowledge, so I share what I know to anyone who asks. If I die stoopid, having emptied my brain of knowledge, I'll be a happy happy man. I have, officially, 3 to 13 years to get it done.Time after 80, I will not be actively seeking. I get what I get.
 
there is one more thing to keep in mind;
engines are all about getting air in. Adding the fuel to it is relatively easy, but trying to get more air into the same sized cylinders is always the hard part.
To that end it must be remembered that Air moves from a high-pressure area to a low pressure area. Engines do not suck in air. The atmosphere muscles it's way in.
The piston, falling on the intake stroke as it does,creates a low pressure in the cylinder, that the higher pressured atmosphere then tries to fill.
But the carb/intake manifold/intake valve all make it difficult, especially at idle, with the closed throttle valves. So our jobs as performance enthusiasts, is to make the airway from atmosphere to piston, as easy as possible for the atmosphere to traverse, and to try and reduce the pressure in the chamber on the intake stroke, as low as is possible, to encourage maximum air infiltration, and to try and get as many oxygen molecules stuffed into there as possible, during the "time" that the intake valve cycles from open to closed.
That "time" is principally governed by the intake duration of your camshaft. But, there are some tricks we use to try and encourage the atmosphere to come in early/stronger and pile up longer, during the allotted "time".
It's all about getting the oxygen in there.
A big cylinder to start with, is always the easiest way,lol. Once the size of the cylinder is chosen, there is only so much you can do.
It helps me, to think of the basic size of the Mopar cylinders; A 360 has ~752cc. A 340 is ~696. a 318 is about 652. A 273 has about 559cc. It's pretty easy to see that 752 cc of air would seem better than 559cc. That's a difference of 193cc or nearly 35% from small to large. That's a lot of air. Rather could be a lot of air. But it's more complicated than that.
It's complicated by the application, and by the desired useage, and the environment that the engine is gonna have to operate in, especially altitude. I mean a 5000 pound tow truck operating in the mountains would want a different engine than a 2800pound grocery getter at sealevel. Or a peppy 3400pounder at a more typical 1000 ft elevation. There is a home for every size of engine. But sometimes we try and make a too-small engine, work too hard. And sometime there really is such a thing as too big.
We can do a lot with camshafts to try and better fit the engine to the applications, but sometimes it's better to just start with the right sized engine in the first place. My yardstick for that, for a performance street application, is 10 pounds per cubic inch. So; a 340 would seem to be just right for most of us, with 1967 to 72 A-bodies, with a middle-aged driver,lol. The later fat-boy Swingers like 360s, and the earlier lightweight-As can get by with less cubes.
After the basic size is chosen, the power can be varied quite a bit from say .75 to 1.15 hp per cube, to fine-tune for the application. But for the most part, sticking to .90 to .95 is gonna make the most trouble-free engine at the most economical price, and be the most fun.
It's all about getting the air in. Trying to get 752cc of air into a cylinder of 752cc is tough enough, never mind trying to get it into a 652 cc cylinder.
_____________________
To try, IMO, is either;a rich-man's quest,a poor man's folly, or an exercise in futility. I ain't rich and my Momma didn't raise no fool; so my 3650 pound 1968 Barracuda (me in it), has....... wait for it ...... a 367 cuber.
I couldda built a 340, but then I wouldda wanted to cut out 200 pounds from the car.
I couldda built a 318, but then, my Barracuda, at 3450 now is a tad porky for a 318 at .95 hp per cube so now I would have to pump it up to say 1.13hp per cube, to match the power of the 360 at 1.0 hp per cube. But doing that, always,always, trades away low-rpm power to get the higher absolute power. So now I would have to deal with the wet-noodle bottom end; no thanks. I'm not into 3200rpm stalls and 3.91s. I actually drive my cars, some years 12,000 miles. A 318 does not fit my application. I drive a Manual-trans, and am limited to 3.55s, 3.23s preferred, so a 318 is not gonna cut it, I don't care how much power it makes; where I drive it, in the sub-3000rpm zone, a 318 just cannot process enough air for my preferences, my driving style; it's a poor match to my porky chassis.
A 340 wouldda bin a good match at 1.06hp per cube, but in my case, I wanted overkill at low rpm. So I chose a 360 at 1.0 hp per cube ....... but that quickly morphed into 1.15hp per cube when I found out just how overkill my 367 bottom-end actually was. I traded some of it away, to get the top-end rush. Yeah, it really is too-big, but it sure is fun.
I was fortunate in that, at the time I was working on this car, I was making good money.So I was able to do the things I did without compromising my lifestyle. I realize that not everyone is so blessed. So I'm here on FABO to try and help steer people into the right combo for them, the first time. But also here to share what I have learned, with the next generation. I'm 67 now, semi-retired, and running out the clock of my promised 70 years/80 if by reason of good health. " You can't take it with you" also applies to knowledge, so I share what I know to anyone who asks. If I die stoopid, having emptied my brain of knowledge, I'll be a happy happy man. I have, officially, 3 to 13 years to get it done.Time after 80, I will not be actively seeking. I get what I get.
that is a pretty lame 340 in your example how much more expensive was it to get that 360 to 1.15 hp per cube ? a stock 340 will eat a stock 360 all day long of course $$ can change that .
thanks for all the info , always an interesting read .
 
Damn, those two posts where some reading. Im gonna have to read them both again (a couple of times) to fully digest that. Thanks for taking the time to write all that out. Very interesting and written in a way I could make sense of.

Many thanks.
Agreed!:D
But his post have a lot of good info that may take a read or two to ingest it all.
Always lots of info to better your learning curve.
 
Oh i forgot to say....if it was a auto transmission, it could have been loose torque converter bolts, and there is nothing wrong with that 340.
Just something that hadn't been said yet.
My 340 sounded like a DEATH KNOCK! 10 minutes, and a wrench, and knock was gone.
 
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that is a pretty lame 340 in your example how much more expensive was it to get that 360 to 1.15 hp per cube ? a stock 340 will eat a stock 360 all day long of course $$ can change that .
thanks for all the info , always an interesting read .
you know a 360 is a stroked 340 right?

But you missed the point.
 
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