Swap B21A1 with a JDM B21A questions - Honda Prelude Forum

mandrako3g · 08-06-2009, 05:52 AM

I have access to a JDM B21A with auto trans and less than 50K. The owner says it is a direct drop in for my 1991 Si B21A1. I'd like to confirm that and also know if I just use the intake and exhaust manifolds off my original B21A1 and will the half shafts to the wheel be the same? Any advice from experience would be appreciated.

2nd one · 08-15-2009, 07:53 AM

it is a direct drop in. you shouldn't have to use any of your old manifolds if the motor is complete. the only thing that might not be on that is the egr, which i would mount out of the way and leave it plugged in so you don't throw a check engine light. the jdm manifolds didn't have provisions for the egr system because back then, the car wasn't required to have it. the only thing on your car that you would reuse is the harness. just replace all of the small coolant hoses when you do the swap.

pamelawa1 · 10-25-2009, 07:00 PM

want to swap a b21a with a b20a5. is that a direct drop in?

bulletprfhoodie · 07-02-2011, 08:39 PM

Quote:

Originally Posted by mandrako3g

I have access to a JDM B21A with auto trans and less than 50K. The owner says it is a direct drop in for my 1991 Si B21A1. I'd like to confirm that and also know if I just use the intake and exhaust manifolds off my original B21A1 and will the half shafts to the wheel be the same? Any advice from experience would be appreciated.

i have a 1991 prelude si and me and my buddy recently swapped out the old B21A1 for a JDM B21A and everything dropped right in but now i have an extra vacuum line up on top near the valve cover that has no where to go.. i took it to a mechanic and he said he could look it over and figure it out i just had to bring him up the old B21A1 as a reference.. unfortunately i couldnt because the kid who did the swap scrapped the engine. and when i told the mechanic the deal how my boy steve scrapped it, he said na nevermind sorry he wouldnt touch anything that my buddy had already worked on.. BULL****! the funniest part is i havent gotten the car on the road since the swap. i had the drive from jersey to florida once a month and instead of driving down I-95 doin like 90mph in fifth gear at like 5K RPMs i ended just buying a 1999 nissan maxima to make it easier on myself...

Colfax · 07-05-2011, 03:17 PM

Maybe this will help you. It's from the online service manual...

http://media.honda.co.uk/car/owner/m...f121/6-107.pdf

mandrako3g · 12-19-2011, 12:12 PM

I finished the swap out. I decided to swap the manifolds and the thermostat housing from my original motor. I changed all the little hoses and motor mounts. I also did the timing belt and water pump while it was out. I put a new radiator in while I had the motor out. The motor had the trans attached so i used that. I thought since the new motor/trans only had around 50K it was worth it. Well i have a slow shift between 2 to 3. It winds out a little. My old trans did not do that. The motor is great and no leaks. Not sure what to do about the trans. I wonder if it is a warning.

Colfax · 12-20-2011, 08:56 AM

Great to hear you got the engine change finished and it's running well. I don't know much about auto transmissions. I'm assuming you have fresh fluid in it? It could be a shift solenoid. You might try doing a little research into which one controls the 2 to 3 shift and swap the solenoid from your old transmission onto this one.

mandrako3g · 12-21-2011, 06:26 AM

Thanks, I'll check that out. By the way, this motor is a B21A JDM, not a B21A1, like my original. However, I assume it still has the FRM sleeves.

Colfax · 12-21-2011, 08:51 AM

I'm pretty sure it does, but I'm not 100% about that. You will know if you ever pull the head. It's pretty obvious if you are able to see them. They are more of a grey color and do not rust at all. If you really want to know for sure, rent a fiber optic camera and go in through a spark plug hole. Then post the pics because I'd like to know that too.