Okay HT, I'm running out of ideas. I'm going to be running an F20b next season, and the heads are the same as the H22. So I'll be fitting it with Blox b type cams, valves, valve springs and retainers which are all made for the H22 head. Here's my issue: the F20b runs relatively small valves, closer in size to a B series engine than an H series and I'm worried about clearance issues between the valves and pistons. I called Blox and got the specs on their valves and valve train, and its a standard H22 valve size, however they haven't heard of anyone using them in an F20b so they couldn't tell me if I would run into clearance issues. Is anyone running an upgraded valve train on their F20b? Any help would be greatly appriciated

 

I'd be more worried about the valves working properly than clearance issues.

Overall the F20B shared certain "ideas" with the H23A1 (non-vtec), possibly due to racing homologation & K20 development. The F20B has a slightly different valve angle, apparently closer to the H23A1. It also uses H23A1 valves according to the many people that have compared & replaced them. An H22 valve is larger and may fall out because the retainer groove height is different.

The F20B manual uses the Type-S cam, so if anything it will have more clearance to the top of the piston than a normal H22. I've heard from people that a cam up to 0.5" lift will clear H22 pistons, so that much or more in an F20B may be possible. The exhaust reliefs are indeed smaller than an H22 piston near the center of the pistons, so that would be my concern for.

This is a Type-S piston over a F20B piston (less visible), the lower red mark shows the lowest trough of the F20B exhaust relief with the Type-S piston relief visible.