I recently got my hands on an F20B short block that I plan on building N/A. I came across a set of Forged Pistons made by Bisimoto with a bore of 86mm. Bisi's site says it's completely compatible with stock F20B sleeves which has a bore of 85mm. I know the F20B has one of the strongest blocks that Honda has ever made and also iron sleeves, however I'm still a little weary about 1mm overbore on stock sleeves. Most info I've read says that's completely fine but I've also seen a few people said it's not. I do know that Bisi makes some great products. Any input or experience with 1mm overbore?

 

Anyone?

 

Service limit is .5mm, but the aftermarket does offer up 1mm overbore slugs.
The only way to be sure if the block can accept such an overbore is to have it sonic checked at a machine shop to verify that there is enough material concentrically for a safe overbore. The F23 blocks are already 86mm bore, you may be able to simply drop your rotating assembly into the F23 block with a hone, spare yourself the cost of machining.

 

It will be fine NA. There is a guy in the all motor forum that has gone 87 without issue. I ran a stock sleeve 86mm F22 @ 450whp for 7 months until it split a sleeve due to a wrist pin bending. NA will last forever at 86mm. IMO I would skip the bisi(they are actually Arias) pistons and use a K20 wiseco.

 

Now that is an interesting idea. So I could get a set of 11.5:1 compression K20 pistons and just bore the F20B block to 86mm and throw them in??

 

Yup