Switch to 243 heads or keep 317s?? Up compression worth it?
Switch to 243 heads or keep 317s?? Up compression worth it? So my setup has been running decent now for a few years and this winter I plan to pull the motor and do some under the hood work welding holes and some painting. So while the motor is out I am debating on putting some 243 heads on my setup. Quick rundown
PUMP GAS with meth
Lq4 with 408 stroker
Eagle crank, scat rods, Mahle -28cc pistons
317 heads
LS9 head gaskets
s480 turbo
So with this setup I have 8.6 compression.
This weekend Im picking up a set of 243 heads now I can either put them on my setup and try to up compression or I can put them on my wifes 01 Camaro SS with cam. What to do....??
So for my setup I calculate 9.08 CR if I just swap the heads. Now if im swapping heads Id like to get a little more out of it then just .4...
Is there a gasket that will work just as well as LS9 but maybe thinner? If I can get one that is compressed to .40 and is 4.0 bore that puts me at 9.3CR... My goal is would be gain close to 1 full point be as close to 9.5-9.6CR... Maybe knock a little bit off the heads to up CR?
Will these 243s flow just as well if not better than the 317s?
Or should I just say screw it put them on my wifes car cuz it wont be worth it?
PUMP GAS with meth
Lq4 with 408 stroker
Eagle crank, scat rods, Mahle -28cc pistons
317 heads
LS9 head gaskets
s480 turbo
So with this setup I have 8.6 compression.
This weekend Im picking up a set of 243 heads now I can either put them on my setup and try to up compression or I can put them on my wifes 01 Camaro SS with cam. What to do....??
So for my setup I calculate 9.08 CR if I just swap the heads. Now if im swapping heads Id like to get a little more out of it then just .4...
Is there a gasket that will work just as well as LS9 but maybe thinner? If I can get one that is compressed to .40 and is 4.0 bore that puts me at 9.3CR... My goal is would be gain close to 1 full point be as close to 9.5-9.6CR... Maybe knock a little bit off the heads to up CR?
Will these 243s flow just as well if not better than the 317s?
Or should I just say screw it put them on my wifes car cuz it wont be worth it?
Last edited by zapp109; Nov 15, 2016 at 08:34 PM.
How is it running now? What are your goals? Current boost level?
Most likely I'd just turn the boost up on what you have. Not worth the effort to swap IMO. With a little home port work, your 317's will flow better than the 243. Not that you need it, unported 317's have been in the 7's on a 408.
Also a full point of compression is worth squat (like 3% of your NA hp) compared to another pound of boost.... or 10. I'd run what you have.
Most likely I'd just turn the boost up on what you have. Not worth the effort to swap IMO. With a little home port work, your 317's will flow better than the 243. Not that you need it, unported 317's have been in the 7's on a 408.
Also a full point of compression is worth squat (like 3% of your NA hp) compared to another pound of boost.... or 10. I'd run what you have.
Lots of ways to go fast, but that makes no sense to me. Boost is easier on the motor than bumping compression. Also a much more effective way to make power. U built a turbo engine, makes more sense to use the turbo to do the work. 17lbs isnt much for that compressio ratio. Even if u bumped a full point of compression, 1lb of boost will net higher gains.
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It will definitely pick up power and response from the head switch but tuning window will get smaller on the low octane fuel. A 243 also has a lot more efficient chamber than a 317. At 2 atmospheres the gain from compression is 2 fold if you can run same timing. If you have to pull timing it might end up with no gain other than out of boost response.
Okay sounds like it could go either way here. I run Holley dominator to tune it, my 17 psi pull was 15 degrees of timing and intake temps have never been high. (110 by end of 9.15 run).
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Def. can go either way depending on the fuel you run. Makes the most sense to me to run an SCR that allows you to max the turbo out on the fuel you plan to run. Go too high and you’ll damage the engine, too low and you give up a little free power.
On pump gas I think you’re better off where you are. Can’t see tearing off the heads for marginal gains when the turbo isn’t tapped yet . Marks 3000lb notch mustang with a 9:1 408, untouched 317’s, LS1 intake, and ebay intercooler was trapping over 174 with a S484, 9:1, 22lbs, 116 octane… Possible to squeeze a lot more out of those 317’s is all I’m saying.
Just basic rough math but in general SCR bumps alone don’t pay out much. Say U run 400 HP at 8:1 and bump up to 9:1. 3% gain gets you 12 whole crank hp. Run 15-16lbs of boost on top of that and that 12hp turns into 24hp… yay. Take that 400 hp 8:1 motor and for every pound of boost you add, you gain about 27hp. Leaving it at 8:1 vs 9:1 on pump gas lets you get away with much more than 1 pound of additional boost. So if your turbo can keep up and you run 6 more psi you’ll gain 162hp.
On pump gas I think you’re better off where you are. Can’t see tearing off the heads for marginal gains when the turbo isn’t tapped yet . Marks 3000lb notch mustang with a 9:1 408, untouched 317’s, LS1 intake, and ebay intercooler was trapping over 174 with a S484, 9:1, 22lbs, 116 octane… Possible to squeeze a lot more out of those 317’s is all I’m saying.
Just basic rough math but in general SCR bumps alone don’t pay out much. Say U run 400 HP at 8:1 and bump up to 9:1. 3% gain gets you 12 whole crank hp. Run 15-16lbs of boost on top of that and that 12hp turns into 24hp… yay. Take that 400 hp 8:1 motor and for every pound of boost you add, you gain about 27hp. Leaving it at 8:1 vs 9:1 on pump gas lets you get away with much more than 1 pound of additional boost. So if your turbo can keep up and you run 6 more psi you’ll gain 162hp.
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Curious how you determined this? I am assuming if compression were the same between the 2, you are stating that the 243 is still more efficient? What I noticed most between my 243 and 317 heads were it looks like the valves are more unshrowded on the 243's as cast compared to the 317's.
Originally Posted by Forcefed86
Def. can go either way depending on the fuel you run. Makes the most sense to me to run an SCR that allows you to max the turbo out on the fuel you plan to run. Go too high and you’ll damage the engine, too low and you give up a little free power.
On pump gas I think you’re better off where you are. Can’t see tearing off the heads for marginal gains when the turbo isn’t tapped yet . Marks 3000lb notch mustang with a 9:1 408, untouched 317’s, LS1 intake, and ebay intercooler was trapping over 174 with a S484, 9:1, 22lbs, 116 octane… Possible to squeeze a lot more out of those 317’s is all I’m saying.
Just basic rough math but in general SCR bumps alone don’t pay out much. Say U run 400 HP at 8:1 and bump up to 9:1. 3% gain gets you 12 whole crank hp. Run 15-16lbs of boost on top of that and that 12hp turns into 24hp… yay. Take that 400 hp 8:1 motor and for every pound of boost you add, you gain about 27hp. Leaving it at 8:1 vs 9:1 on pump gas lets you get away with much more than 1 pound of additional boost. So if your turbo can keep up and you run 6 more psi you’ll gain 162hp.
On pump gas I think you’re better off where you are. Can’t see tearing off the heads for marginal gains when the turbo isn’t tapped yet . Marks 3000lb notch mustang with a 9:1 408, untouched 317’s, LS1 intake, and ebay intercooler was trapping over 174 with a S484, 9:1, 22lbs, 116 octane… Possible to squeeze a lot more out of those 317’s is all I’m saying.
Just basic rough math but in general SCR bumps alone don’t pay out much. Say U run 400 HP at 8:1 and bump up to 9:1. 3% gain gets you 12 whole crank hp. Run 15-16lbs of boost on top of that and that 12hp turns into 24hp… yay. Take that 400 hp 8:1 motor and for every pound of boost you add, you gain about 27hp. Leaving it at 8:1 vs 9:1 on pump gas lets you get away with much more than 1 pound of additional boost. So if your turbo can keep up and you run 6 more psi you’ll gain 162hp.
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Def. can go either way depending on the fuel you run. Makes the most sense to me to run an SCR that allows you to max the turbo out on the fuel you plan to run. Go too high and you’ll damage the engine, too low and you give up a little free power.
On pump gas I think you’re better off where you are. Can’t see tearing off the heads for marginal gains when the turbo isn’t tapped yet . Marks 3000lb notch mustang with a 9:1 408, untouched 317’s, LS1 intake, and ebay intercooler was trapping over 174 with a S484, 9:1, 22lbs, 116 octane… Possible to squeeze a lot more out of those 317’s is all I’m saying.
Just basic rough math but in general SCR bumps alone don’t pay out much. Say U run 400 HP at 8:1 and bump up to 9:1. 3% gain gets you 12 whole crank hp. Run 15-16lbs of boost on top of that and that 12hp turns into 24hp… yay. Take that 400 hp 8:1 motor and for every pound of boost you add, you gain about 27hp. Leaving it at 8:1 vs 9:1 on pump gas lets you get away with much more than 1 pound of additional boost. So if your turbo can keep up and you run 6 more psi you’ll gain 162hp.
On pump gas I think you’re better off where you are. Can’t see tearing off the heads for marginal gains when the turbo isn’t tapped yet . Marks 3000lb notch mustang with a 9:1 408, untouched 317’s, LS1 intake, and ebay intercooler was trapping over 174 with a S484, 9:1, 22lbs, 116 octane… Possible to squeeze a lot more out of those 317’s is all I’m saying.
Just basic rough math but in general SCR bumps alone don’t pay out much. Say U run 400 HP at 8:1 and bump up to 9:1. 3% gain gets you 12 whole crank hp. Run 15-16lbs of boost on top of that and that 12hp turns into 24hp… yay. Take that 400 hp 8:1 motor and for every pound of boost you add, you gain about 27hp. Leaving it at 8:1 vs 9:1 on pump gas lets you get away with much more than 1 pound of additional boost. So if your turbo can keep up and you run 6 more psi you’ll gain 162hp.
If you are dead set to break out of 9's it may be worth it without breaking a budget with maybe more cubes or anything along those lines but you sacrifice a bit of that cushion for error imo.