Trever_20

ok, so just to confirm, .030 off the heads will be safe with the cam im running (as far as ptv clearance)? I'm trying to give the machine shop an answer asap.

what cr would .030 give me with flat tops? Low enough to run 91 octane?

RedXray

You basically have a LQ9 now with the flat tops and IIRC the LQ9 is already at 10.2:1

So with the decking and just cleaning the head surface with minimum milling you're above 10.2:1 compression. LS7 lifters have a pretty large preload window vs Morel drop in lifters so the 7.4's should still be in spec, I'd get a pushrod length tool to double check. If you have the gearing to match those big tires I don't see 91 octane an issue.

RedXray

That is a small camshaft PTV will not be an issue.
Are those flat tops fly cut?

1FastBrick

iTrader: (17)

.0025 I think would be close to 68CC

1FastBrick

iTrader: (17)

You might want to speak to a performance shop that deals with that like Texas speed or Katech. They could probably tell you from experience what you will end up with by milling X amount.

Trever_20

ok awesome. They are not flycut, basically just an lq9 piston. I got them through ws6store in their rebuild kit.

Trever_20

Do you think 91 would be ok with the .030 off the heads? Around where I live, there's nothing higher, expect one station that has 110. I guess I could always run an octane booster if I had to?

1FastBrick

iTrader: (17)

1FastBrick

iTrader: (17)

This would be on the stock side for an LQ9 depending on how far the piston was above the deck at TDC and assuming the 317 are 71CC and not 72CC. They can very some since they are a casting...

RDF1

Don't worry about the compression vs octane so much. The tune can be adjusted for that.
I've tuned some 11.5CR 5.3s and 12.0CR 6.0s on 87 octane.
running a TR6 plug and give it the timing the spark plug tells you it likes. There was quite a power difference between 87 and 93 octane with them tho.