Honda Prelude Forum - PreludeDriver.com

Hi, I'm new to the forum. My son and I are considering buying a 3rd gen Prelude with a bad engine and putting in a JDM replacement. I've done it on a few older Accords and have always enjoyed it. I'm glad to see you were successful on yours! We have our eyes on a 91 that looks o.k., but I'm wary of putting in a B20A5 engine into it if it has a B21a1 engine. A few questions:

1. Are all 91's B21a1's or does one have to check to see if it is a B20A5 or B21A1 engine?
2. Is there an issue with the ECU being different? Another post was saying that the ECU on the B21A1 was a OBD1, so it would be difficult (but not impossible) to swap a B20A5 into a B21a1. Did you have any issue with the ECU?
3. Any other issues out there that folks have faced swapping the engine - any advice on this transmission issue?

Thanks for any help anyone can provide!
Ken

Ken,

1 - Not all 91 Preludes are B21A1 equipped. You need to check the engine stamp.

2- The ECUs are different. B21A1s are OBD1 engines, while B20A5s are OBD0. This means that work has to be done on the electrics if you swap either direction. There are several ways to do this. The easy way is to just plug the existing components into the new block (distributor, etc) and run with it. The hard way (but more correct) is to swap out the entire engine harness for the correct one. There are a few differences between the OBD0 and OBD1 ECUs, chief among them being a difference in the distributor.

3- Transmissions between the B21A1 and B20A5 are interchangeable. The B21A1 has shorter gearing, making it better for sport driving.