zapp109

iTrader: (13)

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?

1FastBrick

iTrader: (16)

I would swap them and run a .040 cometic gasket.

While everything is out and apart, I would pull the valves and do a light clean up in the bowl.

Forcefed86

iTrader: (4)

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.

zapp109

iTrader: (13)

It runs well. This is leaving at 5 psi ramping up to 17psi. I was just hoping not to have to run a ton of psi and go faster.

Forcefed86

iTrader: (4)

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.

stock48

iTrader: (17)

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.

zapp109

iTrader: (13)

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).

Forcefed86

iTrader: (4)

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.

roastin240

iTrader: (13)

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.

oscs

iTrader: (19)

Really wish more people would read this explanation.

Rawr256

I went with this last part really when doing my setup. Not doing anything crazy with being a DD M6 car but went from 243 to 317 heads but thought with the lower compression, not only can I turn up the boost to make up a power difference from compression but also gives me room to screw off and deal with those uh oh moments. Kind of like the time I plumbed by Eboost2 backwards for max boost and spiked to 17.5lbs on my 180k mile stock bottom end LS1.

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.