If I attempt to do a B20 Vtec conversion with a B18C or B16A head then do the the combustion chambers on the cylinder head need to be rebored to 84mm or can it stay 81mm stock? I'm guessin that its doable and will promote a tighter sqeeze because its like adding qench to the cylinder head, the fuel and air mixture will get a more efficent burn and higher compression pistons won't be needed, thus less worry of piston and valve clashing against each other. I have heard that the B20Z has a higher compression ratio so the vavles might touch the cylinder head if you use a VTEC head and attempt to play with the cam timing, but what if you use the lower compression B20B block? Wouldn't there be a reduced chance of piston to valve touching, thus you can use more aggressive high lift and duration SKunk2, Spoon, Mugen or Toda cams and now you can also play with the cam timing? Anyhow this is my B20 Vtec theory so if anyone out there knows somethin then lemm know.

 

I've done a CR-VTEC/B20-VTEC build, and boosted it in my 90 CRX. The reason for the higher compression numbers on the B20Z lies in it's pistons. Instead of being "flat" like the B20B, they dome up a little bit. This creates a higher compression ratio. Even with the B20B block/pistons, you will still have to do a little bit of modifying to the valve reliefs on the pistons, as the B20 heads pistons are far smaller in diameter. It's even worse with the the higher compression pistons of the B20Z. Cam timing does become key with the higher compression pistons, and may cause valve-piston clearance issues. As far as the head is concerned, it does not have to be milled out to 84mm. However, I think that if you don't at least "clean up" the quench area by smoothing it out, the rough edges might cause resistance/fluttering and cause the air-flow to become less efficient.

You can read up on the CR-VTEC more in depth about it here:

http://www.c-speedracing.com/h...c.php

HTH

Dan P.