Right now I have -24cc SRP's with stock stroke, stock ported heads and Felpro 1074 gasket. That's real close to 9:1.

I'm in process of building a new engine with a 3.75 stroke, -31cc dish, same heads and gasket and minimum decked off of the surface of the block. At this point I'm making some assumptions on actuall CC of the combustion chamber and where the piston deck will end up. Should still be 9:1 +/- 0.3

-Scott.

 

If the engine will most likely never see more than 10psi, is dropping the compression that much really needed? I am just thinking along the lines of how the STS kit is advertised for a stock LT1 no mods needed. And since I would be running forged pistons and maybe better rods wouldn't it be fine?

 

Yea

 

Yes, dropping the CR to around 9 is needed or I don't need to drop it that much?

 

If you stay below 10 psi you should be between 9.0-9.5 to 1 and be fine with a good tune.

 

You don't NEED to drop the compression to run below 10psi.
I'm running 7psi just fine on my stock LT1, thinking about running 9...

If you're buying new pistons anyway, I'd get dished and shoot for about 9.5 to 10 compression ratio, this would work great for under 10psi of boost.
Of course an intercooler and/or methanol always helps too.

 

If you run good pistons and not junk you can get away with it. Like MikeGyver said an intercooler and meth/water injection will make it pretty safe.

 

Good pistons = Mahle?

 

I looked at them and ended up going with diamond.

 

When they say good forged piston they mean one out of 2618 alloy which is more tolerant to detonation than a 4032.

So if you get into detonation with a higher CR, you might not grenade the pistons. Detonation still is very hard on other engine components - head gaskets and bearings - It is not wise to operate any motor while detonating!

You wont lose much of any driveability comparing 10.5 to 9.5, or even high 8's. Efficiency goes down with lower compression ratio, but it is also important to lower CR with increased load.

Gains will be minimal running a 'high' compression ratio on pump gas while the risk of damaging engine components goes up. At 10psi you could probably run 9.5-10.0 ok, but I guess my point is why not just build the motor to handle boost?

-Scott.

 

Well the whole boost/CR is new to me, so pardon me coming off as an idiot. Any advice is greatly appreciated. I just don't want to get worse gas milegae than I do now.

 

Hey no problem. It's good to see new people interested in supercharging and turbocharging on this forum.

You're adding a turbine wheel in the exhaust path out of the engine, so in theory you will lose gas mileage even at cruise. You will certainly lose mileage when your foot is in it - which will be quite often with a turbo

-Scott.

 

Ok, another question for you guys, the turbo that comes with the STS kit, is it a GT40? If so how much would a rebuild cost?

 

you can get a couple different turbos with the STS kit, best bet is to get the part number off the turbo and call a shop.

 

Well I don't have the kit, so I am kinda in the dark here. But in general how much is a turbo rebuild and is it possible to do by yourself?

I am trying to weigh a rebuild versus a new turbo.