im in the process of getting my motor rebuilt. oversize pistons oe honda .25mm, fully balanced, pnp, toda b's, al the other usual suspects. cr of 11.7:1. honda say a clearance of 0.05mm overbore. which is about 2 thou of an inch. for running in purposes. but i'm also wanting to run nitous. zex dry 55shot or maybe 65.tuned with s200. my engine builder is suggesting 3 thou so it doesnt sieze. can anybody help.

 

im just wondering cuz i dont know the benefit for oversized valves doesnt the air have to go around the big *** valve to go in i mite be stoopid but just wondering wuts the advantages n stuff...

 

.003" is fine. My buddy is has a piston to wall clearance on his GSR of .003" with a .020 overbore and he's boosting it (480whp and low 300wtrq)...so you should be fine

 

forged pistons have a looser piston to wall clearance. i forget what stock piston clearances should be.

 

if i remember correctly...i think that stock H22 was 0.0025" to 0.003"

 

https://honda-tech.com/zerothread?id=281812
"the clearance is .0004" to .0016". Service limit of .0020""