Hey guys.
Trying to learn as much as I can about turbos as it may be a possibility for me in the future.

I am running a zz1 crate engine which is a 5.7L with forged crank, forged rods, and hyper pistons. With the aluminum heads on it now, which have 58cc combustion chambers, I am seeing 9.8:1 compression. I would like to run a nice safe amount of boost and know that compression ratio is going to keep that number low. However, I was planning on buying a pair of AFRs anyhow. My first question is, is lowering the compression ratio by increasing the combustion chamber size a no no? Turbulance probelms? I was told that the combustion chambers on GNs were below 40ccs but no one else has backed this statement up. I can get myself either 68cc combustion chambers or 72cc from AFR. Smaller than that, and its another 250 to get them milled down to the size i want. 68cc would put me at about 8.8:1. I haven't calculated what the 72s could give me but i guestimate around 8.5.

I am only considering turbos as a do-it-yourself project with custom log headers. I have access to a turbo from an 82-83 Riviera. ITs a GARRET T3 and a/R is .63 ( its the bigger one) not the smaller .40. I was going to setup a single turbo system with just this but I have been told this will not be enough to keep my engine happy. I now agree for the most part. What are the best turbos that I would find in a junkyard and could rebuild that would support my engine? If I am running two turbos, should i look for a turbo from a 2.9L engine and then find two of them for about 5.8L total?

BTW, I will be running a siamesed tpi system with this setup. I have some questions about the computer too but I will get there once I know more about the turbos and whether I can actually lower my compression in a good way to support the turbos or not.

Thanks
I noticed my posts are always long but I tried to give as much info as I could so you wouldn't have to ask me much to clear things up.

 

I'm not the smartest guy so don't take everything I say to seriously, but anyway. For the compression ratio I'd try to keep it around 9:1. Any less and it'll be a little soggy when not under boost. One thing to mention, a lot of people don't like using hypers with boost. If you're going to have the engine out you may want to replace the hypers with a set of forged pistons, but I guess it really depends on how far you want to go with everything. If you're really careful about the tune the hypers would probably be okay for a while.
One turbo off of a Riviera is too small. If you could get a second it might work. A lot of guys like the .60/.63 T3's found on the mid 80's 5-speed turbocoupes. Those are actually the turbo's I have and am planning to use on my own project. Some of the Ford guys have done pretty well with things, getting well into the 10's and sometimes the high 9's. HTH's.

 

Don't worry about too low a compression, it will let you run more boost, timing and make the intercooler not as critical, and most of what you'll find at the junk yard will be small enough that you'll build boost almost instantly making up for any sagging... You'll have more low end then you'll know what to do with.

the riv turbo if its a 60trim/.63AR (the smaller one had a .48AR, but I could have sworn that they were both 50trims), will be fine for a twin setup.