4.1, what compression ratio?

[6SENSE]

Have a 4.1 build in the works (although not sure when it will all come together ). This is the "later" version of the 4.1 which I pulled from a '84 Riv. I have a good set of used .020 forged pistons , turbo crank checked out great and will stay std/std, 2dot rods, yada, yada.
Question now is what compression ratio to shoot for? With my current combo I went with thicker gaskets (GM 87s on the undecked 84 block: about .060 thick compressed compared to original steelshim @.017 or .019 ). When Im on it and running a ton of boost its a bat out of hell but all other times a bit sluggish before it kicks in for me to really enjoy it.
My machinist seems to think we should deck the block (which Im not opposed to because after all 86/87 blocks are decked and used thicker gaskets). However he also thinks I should go with a 10:1 compression ratio which sounds a bit high to me. I know I would like to up the ratio from what I have been dealing with [heck if for nothing else to get better gas mileage ] but need opinions on what to shoot for. I guess cometics would be in order, although I have always heard good things about felpro 1000s which I think are about .035 thick compressed right? Any suggestions would be appreciated. I have never blown a head gasket (knock on wood) and have beat the heck out of my motors so I want to plan this right and not start going the other direction because all of a sudden I cant run much boost without BOOM!

 

[Ormand]

If you go to 10 to 1, you may either have to run the boost really low, like less than 10 psi, or to use alky/race gas at all times. If you use something like 9 to 1, then you can go higher on the boost, or use less expensive fuel.

 

[thunderace31]

10.1 is way to high for a Turbo car plus running race gas is a pain and you would have to with that comp. just to drive the car on the street
Find a new eng. builder that knows about turbo cars would be my next thing to do but that just me

 

[JeremysGN]

compression

I asked this maybe a month ago when I was building. Can't remember who it was but they had an article about a VW that continually gained HP as they lowered compression and raised boost. Personally I though a lot of the article as you are charging your cylinder with already compressed air. High compression is needed on engines to pressurize the ambient air. I wouldn't double up. Besides, when you think about the volume in your cylinder you are actually flowing more air with lower compression do to the increase in volume. I think lower comp-more boost = more HP,but haven't finished mine yet.

 

[Scott Atk]

Although its true that ultimately you will achieve higher total horsepower with lower compression. But too low and the car is just not any fun to drive on the street. I think 9 to 1 is a good compromise. Make sure if you deck the block, keep it at the minumum necessary to true it up. The 4.1 blocks have thinner decks to start with.

 

[6SENSE]

Thanks for all the response!