91 2.0 to 90 2.1 si??

ludedude63 · #1 (**permalink**) 07-16-2012, 07:35 PM

I have a 1991 prelude 2.0 si i found a parts car that is a 90 2.1 si with 4ws.
My question is. Can my 2.0 bolt directly on to the tranny that ran the 2.1?
Any feedback is greatly appriciated.

TripleLude · #2 (**permalink**) 07-16-2012, 09:12 PM

In short, yes. The following information here applies to a 5-speed transmission..

If you use a B20a5 flywheel, use the B20a5 clutch kit. If you use the B21a1 flywheel, use the B21a1 clutch kit.

I would recommend using the same flywheel & clutch kit that came on the car from the factory. Also, you should spend the $12 and have the flywheel resurfaced at a transmission shop. It takes about 10-15 minutes and will make a huge difference in how the car drives.

Secondly, the speedo is different. The B20a5 uses a cable to drive the speedometer, while the B21a1 uses an electronic circuit. You can remove the speedometer from the B20a5 transmission and it will bolt up to the B21a1 transmission.

IMO, the B21a1 transmission is a downgrade because the gearing is lower. So you will have to shift sooner and also 5th gear will cruise at a higher RPM. Gas mileage may be a hair better at 40-55mph, but gas mileage at 55+ will be worse.

TripleLude · #3 (**permalink**) 07-16-2012, 09:21 PM

And I forgot to add info about the axles. The axles and center shaft may be a little different. I am not sure if the difference had to do with the hub (at the wheel), or the transmission.

What I am saying is, do a search and I promise the info is out there. Here are some resources you should have, but transmission is not yet covered in one of them:
Prelude Bible Repair Manuals Diagrams Part Number
www.prelude3g.com

Lespaul59 · #4 (**permalink**) 07-16-2012, 09:51 PM

I have a 1991 2.0 Si and my speedo is electronic. I took the dash off 2 weeks ago so I know. Now are you talking about an automatic or manual trans? Didn't see anywhere in your first statement which tranny you had.

Lespaul59 · #5 (**permalink**) 07-16-2012, 09:58 PM

Plus the speedo runs out of the tranny so I'm sure you'll be able sleep a lot easier knowing your keeping your tranny. Are you? Are you swapping the engine or tranny in your car?Don't think the axles are different as long as your trans mounts bolt up the same. But if you're putting a 2.0 where a 2.1 is I think the OBD1 HARNESS MIGHT HAVE TO BE LOOKED AT A LITTLE MORE. A OBD0 engine is now gonna go where an OBD1 harness already is, Right? Any body wanna chime in?

Sideswipe SI · #6 (**permalink**) 07-16-2012, 11:52 PM

You guys sure 90's aren't electronic? I remember Prelude 13 had a 90, and it had electronic gauges and OBD1. Just swap and done. Why does this sound more complicated?

1funryd · #7 (**permalink**) 07-17-2012, 01:40 AM

Ok this thread is lacking information.

Here is what is needed:

Ok since there is no real write up on this and we keep getting newbies and oldies alike forgetting stuff, I am putting this fairly straight forward simple write up that will resolve this issue.

I will add data to it as necessary to cover every aspect of the swap to answer all questions.

Here we go:

When getting ready to swap from the B21a1 to any B20a5 or A motor there are basic parts needed to do this.

1. B20a5 or B20A(JDM 88-91 Prelude motor only, no other B20 motor is compatible PERIOD!!!)

Since this is a fairly straight forward swap, you will need all the parts off of your old B21a1 motor to transfer everything over.

When I say everything, I mean:

1. Intake manifold and sensors

2. Distributor and everything attached.

3. All sensors off of the B21a1 Block. They are mostly located underneath the distributor on the block.

4. Entire Engine harness

5. Side Engine mount, specifically the B21a1 bracket that is bolted on the drivers side. This bracket is different than the B20a5/A brackets.
*It is also imperative to note, that should you decide to purchase aftermarket B20a5/A engine mounts, that this bracket does not work with them. You need the B20a5/A engine bracket and chassis bracket to make those aftermarket mounts bolt up.

6. Exhaust manifold and downpipe and EGR pipe. Its is crucial you pay attention to this because the B21a1 is OBD1 and thus the O2 sensor is on the downpipe and the engine harness is going to need to be plugged into the O2 sensor to ready your exhaust gas readings, and the 90-91 EGR pipe is longer than the 88-89 B20a5 EGR pipes.
*Note: The EGR pipe is no longer available at Honda Dealers - Discountinued

7. The one thing that gets left out is that if this a Auto to manual swap, it is necessary to replace the auto water pipe with the manual one as well. The auto is longer and will not work. This is one detail that was discovered and known but was left out for auto to manual swappers.

8. The last common part is the ECU. You are keeping everything off of your old B21a1 which includes the engine management.
This is necessary since the mechanical side of the motor will run just fine, but the sensors which your stock B21a1 ECU will be looking for are different because the B21a1 is an OBD1 motor and the B20a5/A are OBD0 motors.

*If you use a B20a5 flywheel, use the B20a5 clutch kit. If you use the B21a1 flywheel, use the B21a1 clutch kit.

Vehicle Speed Sensor:

B20a5 is cable driven
B21a1 is Electronic driven.

All you need to do is transfer the VSS from your old transmission to the new one to keep your speedometer working.

If you prefer to convert to the electronic VSS, this will take more work for you.

Now you are doing the opposite of the original intent of this swap, so you will doing the reverse for everything.

Sideswipe SI · #8 (**permalink**) 07-17-2012, 02:00 AM

That parts car must be mint to swap an engine into it. If you pull the dash and you see a bicycle brake cable looking thing, that's the VSS cable you have a b20a5. Proceed with above pictures. No cable, OBD1, and life gets a whole lot easier.

Lespaul59 · #9 (**permalink**) 07-17-2012, 03:28 AM

Maybe 1991 was the first year they switched to electronic vss for the B20A5. Cause that's what I've got. Don't know if it was done in the beginning of the year or what.

Kenpachi · #10 (**permalink**) 07-17-2012, 06:58 AM

Quote:

Originally Posted by TripleLude

IMO, the B21a1 transmission is a downgrade because the gearing is lower. So you will have to shift sooner and also 5th gear will cruise at a higher RPM. Gas mileage may be a hair better at 40-55mph, but gas mileage at 55+ will be worse.

Your right about gas mileage, but I totally disagree that it's a "downgrade". Why do you think Honda used shorter gearing for the Integra Type R (FD 4.785), and esp. all other Honda performance cars? Because it gives you better acceleration!

TripleLude · #11 (**permalink**) 07-17-2012, 07:04 AM

Ludedude, are you trying to swap the transmission, or the entire engine?

Sean pointed out some info for swapping the engine. I pointed out info for swapping the transmission. Please clarify what you are trying to do.

Lespaul59 · #12 (**permalink**) 07-17-2012, 08:42 AM

Acceleration is good but really don't wanna be doing 4000 rpm's at 60. My stock B20A5 WHICH IS REALLY A JDM B20A does 3000 rpms at 60 mph 5-speed manual.

itsdatoneguy · #13 (**permalink**) 07-17-2012, 12:27 PM

This seems like a lot of effin work my friend. Is your tranny toast?

luzer · #14 (**permalink**) 07-17-2012, 03:37 PM

There is some mis-information in this thread. First of all, the clutch kit you use has little to do with which engine you have. It all depends on the year. All 90/91 3rd gens used the same transmission, and would use the same clutch kit and flywheel. Same with the axles. And since the 90/91 2.0 Si came with a b20a5, it would use the same clutch parts and axles as the 90/91 Si. For example, if you have a 90 Si (b21a1) and are wanting to install the b20a5 from a 2.0 Si, they will both use the same clutch kit, flywheel, and axles. But if your donor engine is coming from an 88 or 89 2.0 Si you will want to make sure that you use the clutch kit, flywheel, and axles from your 90/91.

Bottom line here is to match the clutch kit and flywheel to the year of the car for the transmission being used (88/89 vs 90/91), not the engine. The axles must be matched to the chassis you are putting them into.

TripleLude · #15 (**permalink**) 07-17-2012, 06:36 PM

Quote:

Originally Posted by luzer

There is some mis-information in this thread. First of all, the clutch kit you use has little to do with which engine you have. It all depends on the year. All 90/91 3rd gens used the same transmission, and would use the same clutch kit and flywheel. Same with the axles. And since the 90/91 2.0 Si came with a b20a5, it would use the same clutch parts and axles as the 90/91 Si. For example, if you have a 90 Si (b21a1) and are wanting to install the b20a5 from a 2.0 Si, they will both use the same clutch kit, flywheel, and axles. But if your donor engine is coming from an 88 or 89 2.0 Si you will want to make sure that you use the clutch kit, flywheel, and axles from your 90/91.

Bottom line here is to match the clutch kit and flywheel to the year of the car for the transmission being used (88/89 vs 90/91), not the engine. The axles must be matched to the chassis you are putting them into.

That sounds good to me. I've only ever owned 89 2.0 Si auto, 88 2.0 Si 5sp, 88 2.0 S auto. I remember replacing the transmission on my 88 2.0 Si and the clutch kit and flywheel had to match together. It was possible to use either setup as long as they matched.

Luckily, I ended up with a low-mileage imported D2j5, which has high gearing. Believe it or not, the 88 S model 5-speed had the highest 5th gear of them all. However, it is rarely discussed since most people do not consider it as an option.

1funryd · #16 (**permalink**) 07-18-2012, 12:49 AM

And just for clarify my post, this is to show you what parts you need to swap when swapping between either motor.

ludedude63 · #17 (**permalink**) 07-18-2012, 02:24 PM

Ok to clarify i have a 91 2.0 si the tranny in it is toast. I found a 90 2.1 si with 4ws and all power options but the motor is bad. So i want to know if i can just put my 2.0 si outta my 91 in the 90 2.1 si. They both are 5 speeds. Can it bo done fairly easy.

luzer · #18 (**permalink**) 07-18-2012, 06:15 PM

Quote:

Originally Posted by ludedude63

Ok to clarify i have a 91 2.0 si the tranny in it is toast. I found a 90 2.1 si with 4ws and all power options but the motor is bad. So i want to know if i can just put my 2.0 si outta my 91 in the 90 2.1 si. They both are 5 speeds. Can it bo done fairly easy.

That would be a direct swap. Keep your intake and exhaust manifolds to use on the 2.0. Everything will bolt up the same. Both cars should have the same D2A4 transmission unless a previous owner has replaced one of them with something else.

ludedude63 · #19 (**permalink**) 07-18-2012, 08:16 PM

Ok good. are you saying use the 2.1 exhaust and intake manifolds on the 2.0, and are the wiring harnesses going to be the same?

TripleLude · #20 (**permalink**) 07-18-2012, 09:52 PM

Use the 2.1 (aka B21a1) intake and exhaust manifolds on the 2.0 (aka the B20a5). The ECU and some wiring is different for the two engines, so the easiest thing to do is replace the engine and use the intake and exhaust systems that originally came on the car.

If you want to make a bit more power, use the B21a1 block with the B20a5 head. This will increase compression to like 10.5:1, which is great. Just make sure to use the B21a1 head gasket for the setup. I recommend going ahead and replacing the t-belt, water pump, cam seals, front main seal, and t-belt tensioner while you have easy access.

luzer · #21 (**permalink**) 07-18-2012, 09:56 PM

Quote:

Originally Posted by ludedude63

Ok good. are you saying use the 2.1 exhaust and intake manifolds on the 2.0, and are the wiring harnesses going to be the same?

Yes. The most of the sensors are on the intake and exhaust manifolds. Those that are on the coolant neck should be the same. Same with the distributor. Keep the wiring harness that is in the car now.

1funryd · #22 (**permalink**) 07-18-2012, 10:47 PM

Quote:

Originally Posted by TripleLude

Use the 2.1 (aka B21a1) intake and exhaust manifolds on the 2.0 (aka the B20a5). The ECU and some wiring is different for the two engines, so the easiest thing to do is replace the engine and use the intake and exhaust systems that originally came on the car.

If you want to make a bit more power, use the B21a1 block with the B20a5 head. This will increase compression to like 10.5:1, which is great. Just make sure to use the B21a1 head gasket for the setup. I recommend going ahead and replacing the t-belt, water pump, cam seals, front main seal, and t-belt tensioner while you have easy access.

Joe is this correct?

Quote:

If you want to make a bit more power, use the B21a1 block with the B20a5 head. This will increase compression to like 10.5:1

Have you done the measurements and verified this with a machine shop?

TripleLude · #23 (**permalink**) 07-19-2012, 07:35 AM

Quote:

Originally Posted by 1funryd

Joe is this correct?

Have you done the measurements and verified this with a machine shop?

Yes, but I did not verify it myself. When I had my engine at the machine shop they did the calculations before milling the head and block down. Some others on PreludePower verified this information as well. It is well-known and was quite popular about 5-6 years ago.

Also, remember, I have a B20a5 bored out to 83mm with B21a1 pistons and a B20a5 head.

1funryd · #24 (**permalink**) 07-19-2012, 06:28 PM

Quote:

Originally Posted by TripleLude

Yes, but I did not verify it myself. When I had my engine at the machine shop they did the calculations before milling the head and block down. Some others on PreludePower verified this information as well. It is well-known and was quite popular about 5-6 years ago.

Also, remember, I have a B20a5 bored out to 83mm with B21a1 pistons and a B20a5 head.

The reason I ask, is because we need documentation posted up not just words. That is the single biggest problem with going off of just someone's words on the net.

I know of those guys who said that it was that compression, but if you could post the paper work that states that from your machines shop, that would go a long way for everyone.

TripleLude · #25 (**permalink**) 07-19-2012, 06:37 PM

I was lucky to get the work finished at all. My block sat there for 2 months before I got it back from the machine shop. They do awesome work, but don't even use Quickbooks to keep logs. No computer for accounting.

ludedude63 · #26 (**permalink**) 07-25-2012, 07:32 PM

Ok so the guy selling the parts car isnt responding to my emails anymore. Again i have a 1991 honda prelude 2.0 si.5 SPEED TRANNY Does anyone know whAT KIND OF TRANSMISSION IT HAS IN IT. also does anyone know were i can get one??

Kenpachi · #27 (**permalink**) 07-25-2012, 08:09 PM

It's either a D2A4 or D2L5, it should be stamped on the front of the transmission.

Woodfins Guaranteed Used Auto Parts - Used Engines - Transmissions - Wheels - Bumpers - Lights My friend just dropped a 3rd gen off to these guys, they might have what your looking for,

luzer · #28 (**permalink**) 07-26-2012, 10:14 AM

^^Agreed, look at the transmission housing near the starter. There should be a tag there with the engine code.

I may have posted some incorrect information earlier. I had always read (in forums) that all 5 speed 90/91 3rd gens had the d2a4 transmission. After doing a little research, it appears that the 90/91 2.0 Si models had the D2L5 and the 90/91 Si models had the D2A4. I've never owned a 90 or 91 2.0 Si, and I rarely have seen them in junkyards. So I have no first-hand knowledge of this. The best thing you can do would be to identify your transmission by looking at the tag on it. This link shows where the tag should be located...

http://www.preludebible.com/service-...on-numbers.pdf

Another source for used parts is Car-Part.com--Used Auto Parts Market

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