90CB7EX

Since parts for the block of the F20B are so hard to come across, I was close to buying a set of 86mm forged pistons from Bisimoto to place in. I'm going to have the block bored the extra mm. However I was told by someone not to waste the money on those since they are actually made by Arias and they are stock compression (the motor will be fully built before going into my 90 Accord). I was recommended to just get a set of STD bore K20 pistons with a bump in compression and use those. I'm wondering if they will work with the stock rods and pins in the F20B. I'm also a little concerned about to valve clearance. Any input or experiences would be greatly appreciated.

Aradin

Yes, they work, or else I wouldn't have told you that to begin with. They need to be flipped around in the opposite direction because the engines spin in opposite directions. The dot on the piston you would normally put towards the timing side of the engine will point towards the transmission in the F20B.

As for the compression, you will need to check the compression height and dome cc then plug that info into a compression calculator to see exactly where you'll be with the K series pistons you choose. I recommend the zealautowerks calculator as it's pretty accurate and has most of the data already there.

Also, pins and rods don't come together. Pins come with pistons. The rod has to have the correct bushing to use that pin. I believe if you use a forged piston you will have to have the stock rod small end hogged out a little to fit the pins. Valve clearance shouldn't be an issue unless you're running crazy cams. In which case you should be claying the whole assembly anyway.

IMO, if you're gonna go through all that trouble of having the block bored and switching pistons you might as well just get an F23 crank and H beam rods and stroke the motor while you're at it. For an extra $500 or so it's definitely worth the huge torque gains.

If you're planning to just do a basic all motor build...you're not going to gain much by just going 1mm over and adding a very small amount of compression. If that's the case then I would advise just sticking with the stock 11:1 compression for reliability and longevity. You can make very good power on an F20B without ever touching the bottom end.

lilrider250

Well from direct expeirience , it's very possible , the k20a2 pistons work perfectly ,bore the block, the Ross hve to be shaved 2mm on each side of the small end, but the piston pins from the k20 are identical, ten the pistons backwards when u install them,my f20b built in beginning of 2016 is still alive, made 189whp with porting an polishing the cylinder head , hondata , larger injectors, the engine is now boosted an it just over heated An melted the pistons to the cylinder walls because my cooling system was not good enough, An temps spiked at 140mph, I hade 12k miles all motor , An about 100 with boost, but that was my fault, I've ordered a new set of pistons an rod bearings for a b18, it will go back toegther this weekend, An will be on our in house dyno here at mnr racing in Parker Az, looking to make 350+ on 8lbs , any questions just hmu or call the shop well

dpine

K20 pistons have a 30 mm compression height. H, and f20b have 31mm. Even if you do all the work needed the pistons will be in the hole 1mm. That s not very efficient. People put k20 pistons in f23a blocks because the f23a has a 30mm compression height.

And I just realized that this thread is over a year old...

CyborgGT

^ Still solid information for future searchers

lilrider250

It's plenty efficient , a lot of engine come factory between 8-1 and 9-1 compression An this setup places u in a calculated range of 8.4-1 static compression ratio, An from experience driving the car, I couldn't even tell it had lower compression, n/a it still made 189whp an 145tq , An pulls 155 on flat ground in a full interior h2b integra