Im rebuilding a motor out of a gta a recently bought and when I pulled the heads off I found scratches in 3 of my cylinder walls that I can catch my nail on. Since it has to go to the machine shop Iknow Im going to need to buy oversized pistons but what else should I do to ensure long life and peak performance. My sig shows the topend of the motor so heres my Q's about the bottom end

1. how much should I bore out .030, .040, .060
2. highest compression ratio I can safely run without meth injection and using 93 octane, heads are 64cc and boost is 6psi
3. can I stick with stock crank and rods,, if I use arp hardware
thanks for any help

 

Since you are boosting, bore it as little as possible. Hopefully it has not been rebored already. 30 over will have a big piston selection, but 20 over should have some good selection too.
I run 21.5:1 compression in the 6.2L out of my truck, its going to the machine shop this week, I am only having it bored 20 over to save wall meat. Its not boosted but its compression is up there a bit.

 

Its still a 4" bore,,,, did you mean 12.5:1 ?

 

Diesel. They have absolutely silly compression ratios.

 

what trans are you putting behind this, and i dont have a clue what aftermarket is available piston wise for your combo

 

the previous owner is very sick and hospitalized and his son sold the car for him. Unfortunetly the son is not a car guy and doesnt know an alternator from an ac compressor. He said his dad had something done to the trans but not sure what. With all the mods to the l98 in my sig he insisted it was a stock l98 corvette engine put into the car, the seats were made by recaro, and the "digital guages" were aftermarket or very very rare. So you see what I was dealing with trying to get info about the car.

 

I had the day off and did alot of research about boost and compression ratio. I found this website and it gave me the effective compression ratio at 12.95 with 9.3:1 being my stock static CR. Powerdyne says 12.5-13.10 is good for a centrifugal supercharger. Hope this site helps someone


http://www.rbracing-rsr.com/compression.htm