nubs4ck

I have a 347 forged shortblock for a turbo application. The motor went south and i was able to salvage rods and pistons. The pistons are oversized and i was able to acquire a used block to get machined. I have a couple of questions.

I got a pair of used 317 heads to drop the compression lower (was 9:1 with the 241 heads). I know that the 317 heads are meant for a 4" bore, but they will work on the 3.905 bore block because there is sufficient tolerance. My question is, is it worth getting the heads ported/polished for flow? Another question is, since all of the heads from patriot are the same price, would a stage 3 with 2.08 intakes and 1.60 exhaust valves still clear the 3.905 bore?

Another question is, should I go ahead and spring for a forged Compstar crank over a stock crank? My goal is between 650-750 at the wheels through a T56.

Also, 1 more question. I was considering getting thicker than stock cometic head gaskets. Is there an issue with the quench area with a .074" thick gasket? My target compression ratio is about 8.2-8.4.

Thanks in advance!

nubs4ck

No one? I also have another question. At under 750rwhp, my maximum goal, are the stock 3.905 sized sleeves the weak point? I have forged JE pistons and forged Eagle rods.

Are head studs pointless at this power level? I have already figured it would be nice to have them, but could use the money elsewhere if they are useless.

Thanks again.

killernoodle

A forged 347 should be fine at 750 hp. Apparently the stock LS1 crank has seen more than 1000 hp, so that should be fine there. Of course, if you want maximum reliability, you could always overbuild the crap out of your motor, but chances are rods and pistons are all you really need for a reliable 750hp bottom end.

Chicago TDP

iTrader: (3)

Your boost might be a little too low.
I think others might agree but I was told not to go much lower then 9:1 for the street.
You might have more lag then you like, especially with a T56 and having to shift and loose boost at every gear.

Johnv

317 heads will flow better than 243 heads, why such low compression ? 9-9.5 would be plenty low enough for your power goals, ARP head and mains studs would be a good investment at 750 rwhp
Factory crank will meet your goals easy enough.

Stick with the factory MLS gaskets.

BadgeZ28

iTrader: (28)

If you currently are at around 9 to 1 you don't want or need to go lower. The 317 heads flow better but will further drop your compression ratio into the 8's

nubs4ck

Thank you for the responses. I want to make this power on pump (93 octane) gas. The previous setup was stock LS1 heads on the forged LS1 bottom end, including the crank. According to the dyno sheet, it only made 556whp and 618tq at 14-15psi of boost, I figured that I would see much closer to 600whp. I'm running an STS setup with a t66 ball bearing turbo. Side question, is the T76 turbo the same size as the T66 as far as external dimensions? I'm talking about the flange and the outer size of the case.

I figured with the lower compression ratio I could safely run more boost. I'm pretty close to the edge of the turbos map with 14psi and 550whp, if I can increase the boost I can get several more pounds of air. The cam i have is a 227/223 with .614/.610 lift and 115LSA.

If I am making a mistake with running the 317 heads, let me know. Through my calculations (not 100% sure) I will be at about 8.51:1 compression ratio with the 317 heads. I don't have a problem using the stock gaskets, I've read that the LS9 gasket is a good one to use too.

Really, I'm just looking for advice, I want to do this right the first time. This car will mostly be a street car. From the research that I've done on turbo systems, general research not specific to LS1s, the drawbacks to a lower compression engine are less VE because more exhaust gases stay in the cylinder after the exhaust stroke as well as less power off boost. The advantages are that you can run more boost before you get detonation.

Side note:
There is a twin turbo z06 at the shop my car is at, with an 8.5:1 compression ratio and race gas he hit 900whp.

XtremeDime

iTrader: (16)

You only made 550whp on 15psi? I hope that is a mustang dyno because I made 500whp at 8 with a stock cam.

Pro Stock John

iTrader: (34)

317's can work for a budget build. There are a number of folks who have gone quick with a set of them. My last FI setup was a 3.910 LS6 block + 8:1 + AllPro heads but before that it sported a set of mildly ported 317's. Went 9.40 on the 317's and folks have gone low 8's with them.

nubs4ck

This brings me back to one of my original questions. Is it worth porting/polishing 317 heads that are going on a 347?

John, what displacement were you running, how much boost and do you know what kind of power you were putting down? Why did you choose the LS6 block? Some people are saying that they are stronger than the LS1, but then some people say they are weaker than the LS1.

TurboAv

iTrader: (6)

Better head flow always helps. Trick Flow as cast 220cc heads have a thick deck and can be had for a pretty inexpensive price.

gallo-lo

iTrader: (11)

i sent my 317 heads to get mill .0015 and 3angle valve job, and light port polish,for my 5.3 boost build.my CR should be 8.9 or 9.1 .

nubs4ck

Will CNC'd Patriot stage 3 035/317 heads fit on a stock LS1 sized bottom end without interference? Is this too much head for a 347?

Application is 99% street and an M6 with a 12 bolt.

dschmittie1

iTrader: (64)

Stick with a stage 2 head. As the valves on the 3 are much bigger and will be shrouded on the smaller bore motor.


Also I would stick to a 9.0-9.5:1 CR and just add meth. But yes your number seem VERY low for 15 psi

I saw 676rwhp on my pump 93/METH stock 241 headed 347 at 13 psi with my Procharged setup

nubs4ck

Thanks for the input! Has anyone run the Patriot stage 2 heads on their stock bore LS1?

I would like to get some feedback from some more turbo LS1 guys. Why do most people keep such high compression ratios? My reasoning behind going 8.5 or so is because you can run higher boost, higher boost means you can accomplish the same power with a smaller turbo because as the compressor map pressure increases so does the flow in lbs/min.

The pistons I have are 9:1 compression ratio based on the stock 241 66.67cc combustion chamber. By going with the 71cc combustion chamber of the 6.0 heads, I should be around 8.5-8.6. If I can reach my goals without meth, that is even better.

TuboAV, thanks for recommending those heads, but they are all smaller than stock combustion chambers, 64cc it looks like.

Again, thanks for all of your feedback.

nubs4ck

Just wanted to follow up on this. I got a set of 317 casting truck heads and I'm pretty sure I'll use them with the stock ports. I don't know if porting/polishing the exhaust runner is going to do anything when I have stock LS1 manifolds mounted to it.

I am curious about the combustion chamber though. They are pretty rough from the sand casting. Is there any advantage to using some sand paper and smoothing them out a bit by hand, or maybe with a dremel? I don't want to damage the heads, but i think a smooth combustion chamber is better than the sand cast chamber, but I'm not an expert. Would this actually hurt me instead?

If polishing up the combustion chamber is beneficial, what is the best way to go about doing it?

I would like the engine to be capable of 800rwhp through a T56/12bolt.