LSx Engine Decking?

[70TWO NOVA]

I have a 5.3 im building. Im using a set of 317 heads that i got milled .030" to get the chambers to 66cc. With the stock dish pistons (which i dont want to change) this only gets me to like 9.2:1 Compression ratio. I want to squeeze a little more compression out of it and was thinking of getting the block decked a little maybe. Is this safe of an LS motor? Is it going to cause my intake not to line up with the ports at all? Never done it and wanted to get some insight.
Thanks

[70rs]

In a recent 5.3 build done by Camaro Performers (sept 09) they used the factory 4.8 flat top pistons (which have a moly coating on the skirts too:thumbsup: )
to bump the comp ratio up a little. This engine is going in "Track Rat". With a 58cc chamber(Trrick Flow heads) they got 11.5:1 compression. Yours would be a bit less. And they are still running 91 octane gas with no detonation according to the article.
If you can't find the article PM me and I will give you a full run down on it.
:cheers:

As for your original question, I have no idea if it is safe to deck that block. But a set of factory pistons seems like a good option.

[70TWO NOVA]

i was actually looking for a set of good used 4.8l pistons but havent found any good sources yet...

[70rs]

i was actually looking for a set of good used 4.8l pistons but havent found any good sources yet...

I wonder if any of the national wrecking yards would sell you a set? Like LKQ?
They have a TON of 4.8 engines. Or a new set from Pace or one of the other dealers should be reasonable?

[70TWO NOVA]

I wonder if any of the national wrecking yards would sell you a set? Like LKQ?
They have a TON of 4.8 engines. Or a new set from Pace or one of the other dealers should be reasonable?

yeah, ill have to check into that

[WSSix]

Why not mill the heads more? Did you have them angled milled or flat milled?

You can deck the block but you need to be careful of the piston's location in the bore. I can't remember on the trucks but on the cars, the piston is already above the deck stock. So decking the block is not ideal compared to working the heads.

[Ventoso]

What are you doing for a cam, and where do you want your cranking psi to end up?

I wouldn't really get obsessive over having machine work done until you plan out where that's going, because static compression pretty much means dick all (flame suit on). The cam is where the action happens, and if you're going the custom route you have a WORLD of possibilities that are open to you in attempts to negate machine work. Evidence of this can be found in many cars landing around the 195psi mark (about the pump gas limit) on a myriad or static CR's. Conversely, the example that 70rs alluded to shows just the opposite -- I don't know the combo he's speaking of in detail, but I bet it utilizes an OTS cam and it's bleeding off a ton of psi.

Lots of variables to keep up on.

[70TWO NOVA]

Im going to be using the 2002 and later LS6 cam. I want to be somewhere around 9.5-9.8:1 static CR, and i still want to be able to run on 87 octane pump gas.

[70rs]

What are you doing for a cam, and where do you want your cranking psi to end up?

I wouldn't really get obsessive over having machine work done until you plan out where that's going, because static compression pretty much means dick all (flame suit on). The cam is where the action happens, and if you're going the custom route you have a WORLD of possibilities that are open to you in attempts to negate machine work. Evidence of this can be found in many cars landing around the 195psi mark (about the pump gas limit) on a myriad or static CR's. Conversely, the example that 70rs alluded to shows just the opposite -- I don't know the combo he's speaking of in detail, but I bet it utilizes an OTS cam and it's bleeding off a ton of psi.

Lots of variables to keep up on.


The cam they used is a Trick Flow Track Max , PN#TFS-30602002. Specs are
220/224(@0.050") and 0.575 " lift with a 112 LSA.
They also stated they were tuning for running on 91 octane. The comp ratio ended up "about"11.5:1.

the article is in the September '09 Camaro Performers magazine. Page 68.

This engine is going in Track Rat. Steve Rupp is building this '68 Camaro. He may be able to give more detailed info about the engine build.

Hope this helps a little.:cheers:

[70TWO NOVA]

yeah thats a little more cam than what im running, and more compression too. im hoping to get to 400 maybe with the combo im running

[WSSix]

I doubt you'll get to 400. Remember, the LS6 only had 400 stock and it used 10.75 compression and was 5.7 liters with the difference being 100% bore size. Your 317s are basically low compression LS6 heads. I'm afraid those heads and that cam will not allow the charge to be compressed enough for a good burn. Honestly, it's beyond my knowledge but my gut and experience tells me you need minimum 10:1 with that cam on this type engine.

My suggestion would be to approach this from a different angle. I'd ask around and say what can I do to build an 87 octane engine and state what parts you have available. I'm assuming you still have the 5.3 heads. It may turn out that the best idea is to use the 5.3 heads and a different cam. I know it adds money to the build but if you miss your mark the first time, you'll be adding time on top of costs to get it right.

Also do not forget that if you are using an automatic transmission behind the engine you have tremendous tuning abilities with the drive train to make all your ponies work for you. Manual guys don't have that luxury without getting stupid expensive with gear changes in the transmission. Use the capabilities of the torque converter and electronic control of the transmission to your advantage. I'd rather go fast than have a dyno queen

[70TWO NOVA]

I doubt you'll get to 400. Remember, the LS6 only had 400 stock and it used 10.75 compression and was 5.7 liters with the difference being 100% bore size. Your 317s are basically low compression LS6 heads. I'm afraid those heads and that cam will not allow the charge to be compressed enough for a good burn. Honestly, it's beyond my knowledge but my gut and experience tells me you need minimum 10:1 with that cam on this type engine.

My suggestion would be to approach this from a different angle. I'd ask around and say what can I do to build an 87 octane engine and state what parts you have available. I'm assuming you still have the 5.3 heads. It may turn out that the best idea is to use the 5.3 heads and a different cam. I know it adds money to the build but if you miss your mark the first time, you'll be adding time on top of costs to get it right.

Also do not forget that if you are using an automatic transmission behind the engine you have tremendous tuning abilities with the drive train to make all your ponies work for you. Manual guys don't have that luxury without getting stupid expensive with gear changes in the transmission. Use the capabilities of the torque converter and electronic control of the transmission to your advantage. I'd rather go fast than have a dyno queen

You may be right, but using the 317 heads (which ive decked to 66cc, ls6 were 64cc) and a set of flat top 4.8l pistons my SCR is about 9.8:1. I know its not quite the SCR of the LS6 (which was actually 10.5:1) but its close. That combined with the same top end (317s flow better than 243s down low) and other bolt ons that the factory ls6 didnt have like long tube headers and better flowing air intake system and a good tune should get me very close to the 400 mark. If I dont quite get there I wont be heart broken, just a goal after all