If you are using a VTEC head that is matched for a 81mm bore originally, how do you go about matching that up with the CRV 84-84.5mm bore? Or do you just slap the head on and have no problems. Can anyone clarify this for me?

 

You don't have to do anything to the head because the stock head on a b20 is a 81mm head(LS). Supposedly matching the bore of the head with the block will give better performance but like I said before you don't have to.

 

That's kind of wierd that Honda used a 81mm bore on the b20 head with a 84mm cylinder bore, isn't it? I always thought the b20 head was slightly different that the LS head and that it's quench area is supposed to match the cylinder bore.

 

If you try it by hand with a drummel you better have a very good guide. Blue the head in the area to be machined. Then bolt the head to the bare block (already bored) but without the head gasket. From the bottom of the block scrib the outline of the bore onto the head and remove the head. Now you know what needs to be removed. Or, the better way is to have a machine shop do it by getting the center of the bore by referencing off the head bolt holes. Then you'll want to blend the area cut into the rest of the chamber.

 

Go to this webpage.
http://hybrid.honda-perf.org/tech/b20/b20tech.html

They measured everything and found the head to be 81mm with the gasket and block being 84mm.

 

I think it was done that way for cost cutting measures just like the stamp steel manifold. If you look at the picture of the chamber, there's the proof of why the chamber should be opened up to match the bore. Burn quality is not good when the flame has to go around a corner.