Hey guys and gals,

I'm rebuilding an Evo 8 engine that had the valves hit the pistons. There are scratches on the cylinder wall linings. I plan on over boring the engine by .25mm or 0.5mm, haven't figured out which is better. When you overbore a block do you have to modify the cylinder head at all?? All knowledge tells me no but I just want to make sure.

Lastly, If I go with oversized Wiseco Pistons they specify that the compression ratio is 9.0:1. Stock compression ratio is 8.8:1. My goal with this build is more so a reliable daily driver/street car hence I'd like to maintain stock compression ratio as much as possible. If I increase the compression ratio to 9.0 will I have to tune the car in order to avoid engine knock issues or can I run on stock ECU??

Thanks

 

Modding the cylinder head is not needed.

the compression ratio, in short, It's not a big deal.

In long...
The Evo pretty much already needs a tune in stock form LOL. And not for more power, they already run too much timing for the fuel we have. I would just tune it. For $500, it'll run better, and make more power. You can even have the tuner keep power closer to stock if you want...

 

Alright, I've actually never driven an Evo. I bought this one with a blown engine to fix. Does the stock tune knock more as result of too much timing advance?

 

Yes. These cars are tuned for better gas than what we have available in the states. If you have 93 octane, they're ok, but still fairly knocky. They can still be tuned to where they make more power, yet the tune is safer and knock free.