mattster03

iTrader: (22)

I'm considering swapping my stock 241 heads on my 2002 LS1 with some low compression 317 heads for a forced induction setup. I'm aware that since the 317 heads are designed for a 4.000" bore motor, I should use gaskets designed for that bore instead of for my 3.900" bore LS1.

This makes me feel a little uneasy b/c I really want to do this right. Is there any actual performance loss or potential issues with doing this? Doesn't this make a larger "lip" at the top of the cylinder bore and the inside ring of the gasket? Would the head gasket be more prone to blowing? Thanks in advance for any input you might have!

01ssreda4

iTrader: (96)

Your LS1 is worth more then an LQ4. Just buy a longblock and sell yours. Done deal.

pwrtrip75

iTrader: (8)

Use the gasket for the head, a 6.0 gasket. otherwise a smaller bore gasket will have the fire ring inside the chamber and will burn up.

It will work, I used 317 heads on a 5.3 and worked wonders.... lots of people do.

mattster03

iTrader: (22)

I would like to stay with the aluminum block for weight reasons (I'm driving a swapped LS1/T56 RX7)

Just b/c lots of people do it, doesn't mean it's right! My question for everyone is whether or not there are any mechanical or performance problems with running a larger bore head and gasket.

sparkwirez06

iTrader: (18)

I always thought they wouldn't work, until I saw gm put the 243s( same as 317 except cc) on the 5.3. 310 hp!!

pwrtrip75

iTrader: (8)

IDK... my stock junk yard 5.3 w/ 317 heads put down 640whp boosted and ran strong for 3 years before I spun a bearing. Never had a head problem.
It worked.....obviously if you are not putting different pistons in it the 317's are a cheaper way to go... If you want to be "right" then spend "right".

You wont have a single issue putting 317s on an ls1.

mattster03

iTrader: (22)

Thanks! I guess since I don't feel like building a motor w/ low comp pistons I guess this is the best route to get my CR down despite the differing bore size...

willizm

iTrader: (10)

Without creating a whole new thread, I'm going to bump this one. What compression ratio are we looking at if we put 317 heads on a 3.900 bore ls1 with no changes to the bottom end? I'm looking at getting these heads to drop compression and keep my stock bottom end.

01ssreda4

iTrader: (96)

Stock heads are 67cc. 317s should be about 72cc. Stock compression is 10.5:1. Prolly wont drop it a lot but it will be some.

MikeLSS1

So GM sold a car from the factory that had a smaller bore cylinder with a head made for a larger bore? And they just dealt with it by doing what we're discussing with the gasket? I'm just interested... what vehicle did they do that in???
...ls4?

if you wanted to put the smaller 5.3 heads on an ls1 block would you use an ls1 3.900 bore gasket?

PREDATOR-Z

Guys, it is simple. Always go for the bigger bore when gasket size is concerned.
Head chamber bigger, go for gasket to match that, if piston cylinder bore bigger, match gasket to that.
Take a look on Utube and watch what actualy happens in a chamber upon a spark igniting the intake charge of a cylinder. an explosion

willizm

iTrader: (10)

^makes sense this way you don't have gasket exposed. What about the compression. I hear they drop a bit on a stock ls1. If you put the 317's with 72cc on then it should bring it down to around 9.1-9.2, right? This is for my turbo build so I figure this would be an easy cheap way to drop compression without doing much to my bottom end except for some arp rod bolts.

Head CC volume vs Compression Ratio:
______________________________________________

The below CR numbers are with the stock GM 5.7L displacement LS1 graphite head gaskets installed.

Installing the thicker 2003 GM MLS head gaskets will decrease your compression ratio by approx 0.1 - 0.2

72.27cc = 9.1 CR
71.71cc = 9.2 CR
71.05cc = 9.3 CR
70.59cc = 9.4 CR
70.03cc = 9.5 CR
69.74cc = 9.6 CR
68.91cc = 9.7 CR
68.35cc = 9.8 CR
67.79cc = 9.9 CR
67.23cc = 10.0 CR
66.67cc = 10.1 CR (stock LS1 head spec)
66.11cc = 10.2 CR
65.55cc = 10.3 CR
64.99cc = 10.4 CR
64.43cc = 10.5 CR (stock LS6 head spec)
63.87cc = 10.6 CR
63.31cc = 10.7 CR
62.75cc = 10.8 CR
62.19cc = 10.9 CR
61.63cc = 11.0 CR
61.07cc = 11.1 CR
60.51cc = 11.2 CR
59.95cc = 11.3 CR
59.39cc = 11.4 CR
58.83cc = 11.5 CR
58.27cc = 11.6 CR

PREDATOR-Z

What you should watch for is ringlands. Those are the weak link on boosted application in a stock bottom. Stay around 7psi with premium fuel or no more than 10psi with Meth.
Give it plenty of fuel and you'll be good for awhile.

zukboi2004

What about intercooled?
I am thinking 317's on a 5.3 with forged LS1 pistons and rods
Meaning a forged iron 5.7

I have a lm4 5.3 with 799 heads and 9:25.1 compression now

I want to know if my compression will stay the same