i have a 1989 prelude si beater car with a b20a5 motor with a recently rebuilt head; new valves, seals, and guides. i recently purchased a 1990 prelude si with a b21a1 motor that i am going to be rebuilding with all new bearings, rings, gaskets etc etc, and need a lil b-series tech advice. havent pulled the b21a1 motor apart yet, but was curious if the b20a5 head is able to be bolted up to the b21a1 motor retaining the factory b21 intake manifold. also, i did some research on the two heads and found the b20 to have 9.0:1 compression while the b21 has 9.4:1 compression. as far as differences between the heads, the only stat i can find is the fact that the b20 has 47.3 head cc's, while the b21 has 51 head cc's. can someone tell me what the new compression ratio might be if i put the b20 head on the b21 block? i dont need any knocking goin on in the '90 due to using 87 octane gas lol. and last but not least, if i put the b20 head on the b21 block will i run into any interference issues as far as the valves with stock cams and/or mild cams? keep in mind my 89 b20 is a beater car, and the 90 b21 i just bought is in absolutely flawless condition, so the 89 will become my parts car for the 90. thanks for any help i can get. oh, also, i am an experienced mechanic and am completely comfortable doing full rebuilds on just about any motor, as i have hundreds of times.


Modified by motoxxxman at 11:03 PM 3/13/2005


Modified by motoxxxman at 11:03 PM 3/13/2005

 

oh, and i will not be racing this b21a1 lude, for all who wonder. the most i may do for mods is a 4-2-1 header, a mild cam, and removing the air box for a FREE factory cold air intake as the factory cone filter is clamped directly to the main rubber intake pipe.

it shouldnt matter as far as a head swap question, but the b21 and b20 are both auto, the b20 auto slips in first and fourth, and the b21 auto works flawlessly. i do have a 5spd out of a lude si, although i am unsure if its from a b20 or b21, i believe its from an 89 or 90. i was told it will work for both motors, but am not sure. an answer to that would also be appreciated; whether a 5spd from a b20 will work with a b21, and whether a 5spd from a b21 will work with a b20. thanx.

 

where did you get your headers? i'm having trouble finding parts for our 3rd gen ludes. and how did you get a free factory cold air intake?

 

i havent gotten the header or cam yet for my 90 b21. im not too familiar with the 3rd gen ludes, but i know the 88-91 ludes inside and out. if im correct the 88-91 is 2nd gen as there was an earlier body style dating back to 1980. in my 89 and 90, for a free factory cold air intake its as simple as removing all the factory intake piping and airbox up to the filter. as the 88-91 factory air filter is a cone filter clamped directly to the main rubber pip which is clamped to the intake manifold. nothing showy, but does remove a lot of restriction and some heat.

 

can i get a lil tech help on my post? it seems either noones viewing this, or noone knows enough about the b-series motors to answer it. NEED ADVICE!

 

doesn't anybody know anything about b20's and b21's??? come on people, i need some advice on this so i dont just go and try it and blow the head off lol. so im replying to my own thread seeing as noone else is so it gets put back at the top so the KNOWLEDGABLE people might actually see it and give me proper advice. thanx