I have a 91 b21a motor
I also have a 5 sp trans out of a carb b20a3
Will the b20a3 trans bolt to the b21 ?
If it will, will the flywheel off the b20a3 fit ?
Also the b21 currently is bolted to an automatic
Will the motor run right with an auto ecu and a manual trans ?
Thanks

 

All B20/21 5 speed transmissions bolt up the same, however you will need the flywheel and clutch setup for the B21 for it to work right.

The automatics are different though, you will need the correct auto flywheel and torque converter. The B21a1 has four lock up soleniods so they will not transfer over if you try and use a B20a3 auto transmission.

 

Sounds like you're planning a 5 speed swap. The a3 trans will work fine. Get the clutch, flywheel, pressure plate, and midshaft from the B20A3. Axles should be the same on the tranny side, but the hubs are different between the 88 and the 91. You also need the 5 speed tranny mount, you'll have to drill holes in the frame rail for it to work. ECU for the auto should work fine for a 5 speed swap. It did on my B20A5.

 

Ok cool.
I put the auto trans in a prelude that was a 5sp so my friend welded the motor mount to rail for trans. Lol
But i still have the whole a3 motor and trans. So if want to do the 5sp i can. When you swapped yours did you just leave your vss unplugged ?

 

I was dealing with an 88 trans in an 89 car, both sensors were cable operated. IIRC you can swap the top half of the electronic VSS onto the older bottom half and your speedo should work. I'm not positive on that tho.