ricardo.benin

Hi I am building a turbo ls3, my question is what pistons and target compression would you go with? My heads are milled to 64cc chambers which is normally used for n/a which I am not doing so I need to make sure pistons and or gaskets will lower compression. The heads are second hand and cnc ported.
Thanks

ScottyBG

I'd shoot for about 10.5:1 if your going to go E85. If not I'd shoot for 10:1, if your going to run 93 octane gasoline. If you want to run lower than 93 you might want to drop to 9.5. I don't like the compression too low. Higher compression does increase the fuel requirements, but it makes it a little more responsive. Just my opinion, I'm sure you will get many others.

Detoxx03

iTrader: (14)

What he said ^^^

JoeNova

If your heads are milled down to 64cc, those are probably some pretty thin decks.

ricardo.benin

So car is going to run on 93 octane, pump gas and I will have meth injection. Do u think I hwill have problems with deck?

ScottyBG

I think your deck will be ok unless you really start pushing it. It depends on what your horsepower goals are. If your wanting to join the 1000hp club then I'd be concerned. Are they 821 castings? I think they are 68cc stock correct? I've had a set of heads shaved 10cc before on a mildly boosted street car without any trouble. I fly cut some pistons with valve reliefs, so I made the difference back by milling the heads. As always controlling detonation will be important. You won't want to run out of fuel pump, or injectors.

ricardo.benin

Thanks for reply, my heads are 823 rectangular port which I belive are 70cc stock, these were milled to 64cc. Here is specs.
- 823 rectangular port heads CNC ported and milled by Advanced Inductions, switched to hollow LS3 intake valves (milled to 64cc chanbers)
- Rocker arm trunion upgrade
- BTR Platinum Spring Kit w/Ti Retainers
- ARP head bolt kit
- Ai ChromeMoly hardened pushrods (5/16” and .080” wall thickness)

ricardo.benin

I would like to break 700hp at the tires

ricardo.benin

Car also weighs 2700 lbs

ScottyBG

700 to the tires will be cake with those heads. You will not need any more than about 12 psi of boost.

ricardo.benin

Good to know, btw since I have the dual platinum btr valve springs will stock ls7 lifters work? I am 19 so if I can get away without using aftermarket lifters that would be great but I do have some high valve seat pressures.

ScottyBG

BTR dual valve springs are not really stiff. There are crazy mechanical roller setups that are 2 to 3 times those pressures out there. Everything is fine with your stock LS7 lifters and those I believe. I've not run those exact springs and lifters, but I'd throw them in an engine and expect them to be fine if I were putting it together for myself. The thing I would be more concerned about with the valve train is having the correct length of pushrod. I'm running 0.075" shorter than stock, since my heads have been milled so much. If your heads are milled a lot you may want to run a shorter pushrod. Mine preload my lifters about 0.060" now, stock ones would preload them 0.125" Which is a lot, I think they bottom out around 0.200" Everything looks like your on the right track to me. A 2700 lb car with that much power will be a handful if you run it on the street. You will grin.

Did you deal directly Phil to get the head work done, or did you buy them from someone else? I've been please with his work, and have met him a couple times. The last couple sets of heads I've had done I took them directly to his shop (Advanced Induction in NC) and dropped them off with him, when I had business in Charlotte. He seems really sharp, I don't think he would mill them to the point of having a problem with them, under normal circumstances anyway. All of my future head work will go there.

ricardo.benin

I did buy heads second hand so I have not talked to phil, when I do get engine together I will check pushrods and get what ever I need to make sure I have the right amount of preload. How would you figure out what -cc pistons to get?

ScottyBG

There are several displacement and compression calculators online. I often use the one on the front of Thompson Motorsports home page, it can be found on the lower left side of the page.

ricardo.benin

Ok, I appreciate it

thompson

iTrader: (4)

It is good to see that people are finding the tools on the page useful.

ricardo.benin

Thanks Thompson

gnx7

iTrader: (28)

Our turbo motor is 10:1 and we only run it on e85. I would go a little lower for 93 octane/meth for safety.

Remember that in a perfect world.... every 1 bar of boost (14.7lbs) should double power. So if your LS3 makes 450rwhp n/a.... on 7-8psi you should make around 700rwhp with a properly sized turbo.

My 6.2 ran MAST LS3 heads (380cfm) and a stock LS3 intake and made 1060rwhp on 14psi. The limit of power you can make will be the clamping force of the heads and head deflection on a 4 bolt block.... you could make 1000rwhp on stock LS3 heads.... but a better and cost effective choice may be LSA heads which are rotocast and have less porosity. LSA heads don't flow as well as LS3 due to a casting swirl vane in the port which can easily be removed with mild porting.

You will have your mind blown with a turbo LSx in an RX-7 They rip.