to bore, or not to bore....

[s13-t]

Im wondering what the hp and torque differences between stock and 86.5mm bore would be. I did the math and I think its a mere 2 percent increase in displacement and if the displacement to power is a dependent ratio then it would only be a 5hp increase. but I want a second opinion. This is assuming I keep stock compression. so, if the cylinders are perfect and don't require an over bore then is a .5mm even worth doing?

[Hijacker]

You're not going to see a massive increase in power/throttle response from a .5mm overbore. Usually the overbore is done to clean out pock marking on the bore.

[s13-t]

Thats what I figured. So the Money spent on the machine work isn't worth the 2% increase. Ok well thank you hijacker. One more question though and I know it has been covered but I want to hear it from an engine builder, like you, rather than random people that cant prove their experience. So, how does increasing the comp. ratio affect the stock hp? Im planning on running a s15 spec r turbo at 15lbs with bigger injectors and an Enthalpy tune. How likly is it that that set up would ping with 9:1 CR. And is that Increase in CR worth it? I just havnt read anything that goes in depth about CR and their affects on the sr.

[Hijacker]

You'll have better response at 9:1 without sacrificing top ceiling boost on that turbo.

[s13-t]

sweet, thanks.

[s13-t]

sry for bumping an old thread but im finally about to buy pistons and I needed to know for sure...

I want around a 9:1 CRBoth the head and block have been resurfaced- minimalI want to buy a cosworth head gasket. 1.1mm or 1.5so which size head gasket combined with what CR piston, 8.5 or 9:1, would put me around a 9:1 CR?

[Justin35ll]

I'm in the same boat as you. Had the block decked 4 thousandths over. And the head wasn't resurfaced.

I just ordered a cosworth 87mm bore 1.5mm thick gasket. I had my block bored .5I'm hoping to keep the stock 8.5 : 1 ratio.

I really don't know what it's going to be though. So any help for us is appreciated.