going with larger pistons in an F20 rebuild to gain HP
 

So it appears I may need a rebuild. I wanted to stick as close to OEM as possible to maintain the 9k redline and reliability. Talking with a reputable builder they suggested the possibility of slightly oversized pistons to up the compression to 12.5:1. I could still go to 9k, but would pick up 10-15whp. So I am curious if anyone has any experience with this and if there are any downsides as opposed to trying to staying near or at OEM depending on what the cylinders look like. My thought is that there has to be a downside or everyone would do it?

honda sells a +0.25mm piston, which is the max overbore for a FRM cylinder f series block. that all there is for OEM

if you are talking about boring more than that you will be installing sleeves at that point you can have pistons made to any size/compression you want!

bumping compression to 12.5:1 you are going to need a aftermarket ecu so you can effectively tune timing/fuel

Well that wouldn't be a huge deal, I have a VAFC, but could ditch it and go Kpro. Is there a downside though? The builder was a inline pro and he just suggested it when I said I wanted to make a bit extra HP, but wanted to stay as close to OEM as possible and keep the 9k redline. I just don't see many people going this route, it seems OEM or Stroker are all I see.

if your f20c is toast just buy a used f22c long block and throw it in and use your ap1 ecu. rev it to 9k, its not unheard of.

adding 1 point to the compression ratio will net you about 2.5% so from 11 to 12.5 expect about 3.75% Using my head that's about 7-8whp so 10-15 may be optimistic. It will force you to use the 9k redline as the jdm 11.7cr raises the max power from 8300rpm to 8600rpm so expect peak power to be above that some where if using 12.5cr

Bigger pistons are heavier and with more surface area, adding more rotational mass, this is offset by the benefits of more overall power, but there is still going to be some slight inherent loss of that free revving feeling. A light weight flywheel will more then compensate and highly recommended. Agreed that the 12-15whp is quite optimistic, more realistically its 12-15 engine hp.

A f22 with the stock ap1 ecu is something ive employed with great success in the past long term. If you start getting into lowering vtec though, you need fuel, either mechanically through a adjustable rate fpr or some type of ems that increases injector duty, not a vafc.

That's something that i'd like to ask many times!So,how is the f22 with the ap1 ecu?Got any problems?You rev it all the way to 9000rpm?How you compare it with the f20?And how about reliability?Got any video with the f22 all the way to 9k?

I went with the .25mm hone and OEM piston/ring setup on my first S2000 and it turned out great. I would do it again in a New-York-Heartbeat.

An added note. I was going to go aftermarket with sleeves. When the parts came in the speed shop tore down my motor and then called me in for a meeting. When they compared the aftermarket to the OEM, they favored the quality of the OEM and the simplicity of OEM route. I took their recommendation and it saved me a lot of money and turned out just great.

Its 100% pnp, no problems. The F22 due to the stock cams only really is worth revving to 8400-8500 rpms and drops off in power too drastically after that, which is good in a way as its easy to tell when to shift, unless your supercharged, and then it doesn't matter. But there are times on the track where having the over rev is certainty beneficial. In my experience the f22 will take 9k rpms reliably, but it cant be great for longevity compared to stock rev limit. Norule that says you have to bounce it off the rev limiter every chance you get just because you can. 8500 rpm in the f22 is the equivalent piston speed of the f20 at 9k just fyi.

That's exactly where I have my fuel cut off set on my KPro for my supercharged F22.