what are the differences between a b20b head and a b18b head i found some b20 heads for 75$ a peice and that just sounds scetchy to me. if sombody could tell me why that particular head is so cheap warn me befor i waste my money.

 

Same AFAIK. Might be a duration difference on the cams but that's it.


For that cheap I expect it'll be warped or need surfacing/milling.

 

I have seen B18B heads go for cheaper, I picked my extra one for $50 and it wasn't warped.

The demand for B18B heads is pretty low, and probably less for B20's as no one realizes they are the same.

 

any way to tell if theres anything wrong with the head?
either immediately evident from just looking at it, or actual tests you can do to pinpoint leaks or warping.

 

nothing immediately evident. only way to be sure is to disassemble it and spec everything.

 

Instead of using tems like B18a/b and B20b/z lets use terms like PR4 and P75.

P75 heads have noticeably larger intake ports and matching manifolds than PR4 heads on B18a motors. I have not compared late B18b motors with PR4 heads so do not know how the port size compares. It is well known that the P75 head is the best stock head for the L/S motor.
I have seen the smaller B18a manifold used on the P75 head. When the owner switched to the low rise Integra P75 manifold there was a noticeable seat of the pants hp increase as well as better driveability. Obviously the port mismatch of the PR4 manifold on the P75 head lost some power. The P75 head will likely have better cams stock than the PR4 head.

PR4 heads were used on B18a/b motors. There is said to be some port size increases through the years mostly from 91 B18a to 92 B18a and possibly again from 93 B18a to 94 B18b. During these years there were also manifold and cam changes that more likely account for the hp diff.

P75 heads were used on newer B18b motors (starting year is unclear and often argued about) and to the best of my knowledge all B20b/z motors also used the P75 head. I believe the B20b was first used in 96. The 96 B20b in my car has the P75 head.

Stear clear of older B20a motors found in 91 Preludes as parts interchangeability is questionable at best.