Originally Posted by gsr converters
ive been looking at piston kits for my car, looking at a wiseco kit. but on the size it says 81 or 81.5. think my motor is 81 stock so would it be bettr to go any bigger? If i get bigger what else would i have to do to make it fit. also some of the compression numbers are 8-7-1, 9-8-1, and 12-0-1. what do these mean and if im going turbo which do i want?
Stay with the stock bore dimension if you're turbocharging the motor without reinforcing the cylinder bores. You need cylinder wall thickness to contain the increased cylinder pressure when the motor is under load.
The compression numbers must be 8.7:1, 9.8:1 and 12.0:1 respectively.
The higher the compression ratio (CR), the greater the mechanical "squeeze" on the air-fuel mixture within the cylinder.
12:1 is suitable for a naturally aspirated build, while 8.7:1 is better for a high-boost turbocharged application. My advice is to stay relatively close to the B18C1's stock CR, and go with the 9.7:1 pistons. It will lower static compression enough to provide and additional margin of safety, but without compromising low-rpm power production.
The bigger question in my mind is, if you're going to tear down the block and install forged rods & pistons, why not commit to either:
a) aftermarket sleeves (Darton) or
b) at least a cylinder bore brace?