WyattH

You can put an AP1 ECU on an AP2 to get 9k if you want. I wouldn't do it. It's like removing a rev-limiter and getting your AP1 to 10k.

The difference in the bottom-ends is the crank, I believe. They changed the stroke, not the bore. THAT cannot go to 9k, while the AP2 head sure can.
If you want more TQ and 9k, bore it out.

12:1 CR is silly on a street block because you would need to retard the timing so much to avoid pre-detonation. You would need a higher octance fuel to maximize the gains of those pistons. So with 92 octane, you wont see many gains.

Bore it out (never heard of this done on an S2, actually), get some aggressive cams with 11.5:1 CR pistons that can provide for valve clearance, P/P the head, and get some upgraded valvetrain parts (valves, springs, retainers, etc). Then tune her to rev up to 9300rpm and I would predict 250+ whp on 92 octane.

newspeed

are you implying that with this combination the CR will raise to 12:1? i thought the heads from F20 to F22 were the same and just the cams and springs changed.. how would that increase CR?

I assumed that hybrid motors would just be asking for trouble, just wanted to confirm... I dont agree with reving a F22 to 9k but the point of this thread was to determine if the limitation was in the block or the head. Apparently its the block.

WyattH

I didn't imply that. The OP mentioned 12:1 and I assume he was going to put in some new pistons with the 2.2L AP2 crank.

AusS2000

This is one of those threads where many of the people giving the answers know as little or less than those asking the questions.

The thing that limits an AP2 is the ECU. If you use an AP1 ECU on an AP2 F20C (or install an AP2 block in an AP1) it will rev to 9K. There are those that say you can't do, and there are those that are doing it. The reason the F22C ECU limits the revs is because the piston acceleration and sidewall pressure increases with stroke and exceed Honda's recommended limit. My take is that you can do it, but you are increasing your possibiity of engine failure. How much is yet to be calculated.

The AP2 has a longer throw (the crank journals are further off center) and shorter rods. What this means is that the piston reaches the same height in the cylinder but travels further down.

You cannot bore the F20C block much. The cylinders are very close together and the factory liners (fibre reinforced walls) are very thin so any major bore would leave you with thin bare aluminium walls. For maintenance purposes Honda only offer a 0.025" oversized piston. Any more than that and they suggest a replacement block.

All that said, I am after an F22C crank and rods for my low compression turbo built engine.

abominablehitman

I certainly didn't say you COULDN'T do it, I simply said that it is not recommended. Of course the ECU is what is preventing the higher redline. That is the same in pretty much every car, and if you chip it/ get a different ECU you will be able to rev higher. That doesn't make it safe. I will be the first to say that I am no mechanical engineer, but this has been gone over enough in other threads, with pictures, documentaries, receipts, etc. to prove to me that it definitely wouldn't be worth it in a daily driver. I am sure the occasional trip to 9k on a 2.2 wouldn't kill it, but it surely wouldn't be something I would do every day.



Believe it or not, I think we were kinda saying the same things....

tbonesteak

there are literally TONS of rsx-s folks running hondata ecu reflash on their k20s that raises the redline to 8600. They've been doing that for years on a daily basis with not a single engine failure coming from the "overrevs". They've also seen amazing results with the setup as well. I am aware that honda places their redline quite a few rpms lower than the motor can take, but i am not sure with the s2ks since they come so well tuned already. I honestly would not feel safe taking the ap2s over 8k.

steven975

you can't bore it out. the walls between cylinders are already ultra thin.

you can only bore out a couple thousands of an inch...which is what you would do on a rebuild. That won't add any notable displacement.

OyATL

Why stop there. Might as well do 13:0 compression. I heard its 300 to the wheels easily. Honda-tech misses you.

OGPackin

Im running a stock ap1 block with an ap2 head (springs & retainers). My car seems to really like the setup.

Wisconsin S2k

You start saying one thing and end with another. The RSX has NOTHING to do with this subject in any way, shape, or form, so what those owner's do with their cars has as much relevance as whether or not you wore red or blue to work.

Let me just point out that AusS2000 had the best post in this thread, and there was a LOT of misinformation given in some other posts.

That said, this has been discussed ad nauseum, and is also in the wrong forum.