Hi, I'm a rookie when it comes to cars so I need some input.
I just bought a 90 Prelude SR with a B21A1 engine and one of the values has very little compression, which we have concluded from reading on the internet that it's the piston rings and possibly the value sleeves. And in the end there is really no guarantee that this fix will last either if we do it.
So what I was thinking of doing is swaping the engine for a B20A5 (90 or 91) and was wondering if anyone has done this before or if the B20A5 will fit properly without any headaches? I was also wondering if there would be any modifications that would need to be done to the computer, wiring, etc because of this swap?
Engine Swap from B21A to B20A Question
Moderators: RedRacer, spiffyguido
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tprelude
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spiffyguido
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tprelude,
Thanks for stopping by. Don't worry about being a rookie around here. We don't flame people. I'm actually in the process of getting a B20A5 ready to swap into my car in place of my B21A1 so this topic is of interest to both of us.
A B20A5 will absolutely fit into your car. All the mounts are the same, and the transmission that you already have will bolt to it perfectly. By the way, keep the B21A1 tranny because it has better gear ratios in my opinion.
You will need to get an ECU for the B20A5 most likely. The B20A5 uses an OBD0 ECU whereas the B21A1 uses an OBD1. The ECU plugs will be different. As far as I know, the big difference between the OBD1 and OBD0 system in this case is the distributer unit. On the OBD1 system I believe that it has more wires than on the OBD0. Most other things should be much the same. If possible at all, it may even be easier to just convert the distributor on the B20A5 to an OBD1 style unit and go from there. I'll help you research this because I'm going to run into this as well.
Thanks for stopping by. Don't worry about being a rookie around here. We don't flame people. I'm actually in the process of getting a B20A5 ready to swap into my car in place of my B21A1 so this topic is of interest to both of us.
A B20A5 will absolutely fit into your car. All the mounts are the same, and the transmission that you already have will bolt to it perfectly. By the way, keep the B21A1 tranny because it has better gear ratios in my opinion.
You will need to get an ECU for the B20A5 most likely. The B20A5 uses an OBD0 ECU whereas the B21A1 uses an OBD1. The ECU plugs will be different. As far as I know, the big difference between the OBD1 and OBD0 system in this case is the distributer unit. On the OBD1 system I believe that it has more wires than on the OBD0. Most other things should be much the same. If possible at all, it may even be easier to just convert the distributor on the B20A5 to an OBD1 style unit and go from there. I'll help you research this because I'm going to run into this as well.
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tprelude
- Lude Dude
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Spiffyguido or whoever,
Just a little confused about the distributor unit - Will I need the distributor unit off the B20A5 motor, or how would I go about converting the distributor unit from the B21A1? I would prefer to do this the easiest way possible as I am not out there to modify my prelude, just get it in working order.
Also is the tranny from the B21A1 compatible with the ECU unit for the B20A5?
If you have found out any other information on this engine swap could you let me know. I'm going to look at a motor today and if it's good I'm buying it and will be doing the swap within the next month, but want to make sure that this will work without a lot of headaches.
Thanks, tprelude
tmaxmaxx@hotmail.com
Just a little confused about the distributor unit - Will I need the distributor unit off the B20A5 motor, or how would I go about converting the distributor unit from the B21A1? I would prefer to do this the easiest way possible as I am not out there to modify my prelude, just get it in working order.
Also is the tranny from the B21A1 compatible with the ECU unit for the B20A5?
If you have found out any other information on this engine swap could you let me know. I'm going to look at a motor today and if it's good I'm buying it and will be doing the swap within the next month, but want to make sure that this will work without a lot of headaches.
Thanks, tprelude
tmaxmaxx@hotmail.com
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spiffyguido
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- Prelude Model: 1991 SE-SR
- Location: Alberta, Canada
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tprelude,
When I said in my last post that it might be easier to 'convert the distributor on the B20A5 to an OBD1 style unit and go from there' what I was getting at is that it might be easier (and cheaper) to just keep your B21A1 ECU and try to convert the B20A5 parts that are incompatable. As far as I know, this means swapping the distributor unit. I'm going to research this more too, as I'm faced with this dilemna as well.
It is possible to convert the whole system to OBD0, but running all the new ECU wires or making a conversion harness will be difficult. That's why I'm convinced that swapping out any parts on the B20A5 that are non-OBD1 compliant is the easier route. When it comes right down to it, the engines are very similar, so most of the parts are interchangeable. For example, I would plan on keeping your intake assembly and exhaust from the B21A1. Many agree that the intake runners on the B21 are the superior design. Really all you need from the B20A5 is just the block and the head and you should be able to make it work. This is what I'll be doing.
Let's both keep working on this.
When I said in my last post that it might be easier to 'convert the distributor on the B20A5 to an OBD1 style unit and go from there' what I was getting at is that it might be easier (and cheaper) to just keep your B21A1 ECU and try to convert the B20A5 parts that are incompatable. As far as I know, this means swapping the distributor unit. I'm going to research this more too, as I'm faced with this dilemna as well.
It is possible to convert the whole system to OBD0, but running all the new ECU wires or making a conversion harness will be difficult. That's why I'm convinced that swapping out any parts on the B20A5 that are non-OBD1 compliant is the easier route. When it comes right down to it, the engines are very similar, so most of the parts are interchangeable. For example, I would plan on keeping your intake assembly and exhaust from the B21A1. Many agree that the intake runners on the B21 are the superior design. Really all you need from the B20A5 is just the block and the head and you should be able to make it work. This is what I'll be doing.
Let's both keep working on this.
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tprelude
- Lude Dude
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Not sure if this is good information or not, but I have found ECU harnesses to convert from OBD1 to OBD0.
http://rywire.com/store/obd1-obd0-conve ... 19f359abb8
Of course their expensive though, but this could make things easier.
http://rywire.com/store/obd1-obd0-conve ... 19f359abb8
Of course their expensive though, but this could make things easier.
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spiffyguido
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You can make that harness if you wanted. I've seen the wire match up diagrams before on the web.
I'm going to stick with OBD1 and just make my B20A5 work. Here's what I've found so far:
The OBD1 compliant distributor has 4 wires. If you go and look at your B21, you'll see this. OBD1 also requires a 4 wire O2 sensor. If you just keep your exhaust manifold from the B21A1, this won't be a problem either.
More to come...
I'm going to stick with OBD1 and just make my B20A5 work. Here's what I've found so far:
The OBD1 compliant distributor has 4 wires. If you go and look at your B21, you'll see this. OBD1 also requires a 4 wire O2 sensor. If you just keep your exhaust manifold from the B21A1, this won't be a problem either.
More to come...
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Prelude4Lyfe
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Ok After reading this I had to sign up and post my thoughts. The swap is a complete drop in. Take the b21a1 out. Keep the Intake Mani, Exhuast mani, the ecu, everything except the engine. Its a straight drop in replacement. Dont say im wrong, me and a friend just did the swap with nothig wrong. If you dont have a new tranny keep the old one BUT you will need the flywheel, clutch, and presure plate from the old engine to use with the old trany if you keep it.
Jared
Checkout my prelude forums to at
projectprelude.6.forumer.com
Jared
Checkout my prelude forums to at
projectprelude.6.forumer.com
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tprelude
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Re: Engine Swap from B21A to B20A Question
spiffyguido,
It's been awhile, but wondering how your engine swap came out? I've had no luck with my 90 prelude as of yet and wanted a first hand experience of someone who has done the engine swap to a 2.0L.
Did you need to change the ECU or did it work fine without it like the last post had mentioned? I'm inquiring as I have found a 2.0L JDM engine and just wanted to drop it in - if possible.
Any advice on your experience would be helpful.
Thanks, tprelude
It's been awhile, but wondering how your engine swap came out? I've had no luck with my 90 prelude as of yet and wanted a first hand experience of someone who has done the engine swap to a 2.0L.
Did you need to change the ECU or did it work fine without it like the last post had mentioned? I'm inquiring as I have found a 2.0L JDM engine and just wanted to drop it in - if possible.
Any advice on your experience would be helpful.
Thanks, tprelude
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spiffyguido
- Moderator
- Posts: 2196
- Joined: Fri Nov 11, 2005 2:55 am
- Prelude Model: 1991 SE-SR
- Location: Alberta, Canada
- Contact:
Re: Engine Swap from B21A to B20A Question
tprelude,
Good to see you on here again. Been a while.
I'm still working on rebuilding my B20A5 to swap in. I don't have enough free time to work on it as much as I would like.
I'm going to stick to my original plan and keep the OBD1 system (including dizzy, etc) from the B21 when I complete the swap. This just seems easier to me, and it should work just fine. The B21A1 is just a bored out B20A5, so things should match up rather nicely.
Is the JDM engine you got a B20A? If it is, this is not the same as a B20A5, and you're going to have to do more research. If the engine is a B20A (notice, no number), you are very lucky as they make wicked power.
Instructions on a B20A swap into a 3rd gen are here: http://www.harleyc.com/prelude/writeUps ... fault.html
Good to see you on here again. Been a while.
I'm still working on rebuilding my B20A5 to swap in. I don't have enough free time to work on it as much as I would like.
I'm going to stick to my original plan and keep the OBD1 system (including dizzy, etc) from the B21 when I complete the swap. This just seems easier to me, and it should work just fine. The B21A1 is just a bored out B20A5, so things should match up rather nicely.
Is the JDM engine you got a B20A? If it is, this is not the same as a B20A5, and you're going to have to do more research. If the engine is a B20A (notice, no number), you are very lucky as they make wicked power.
Instructions on a B20A swap into a 3rd gen are here: http://www.harleyc.com/prelude/writeUps ... fault.html
