Nice this gets asked alot lol

 

Great write up Sean, very straight forward and simple! :smilejap:

 

Might want to add if they swap in a b20a5 or a b20a they need to get the clutch for the trans they have not the engine. Might help more towards the auto to manual swap guys, I know that the info is covered in the auto to manual swap thread but it wouldn't hurt to throw it in here I guess. Just my opinion....Great thread by the way, simple and to the point!

 

as someone who just asked this thanks man! im not a newbie to hondas just a newb to preludes!

o and maybe an eventual sticky for this thread since its such a common question but not a link in the FAQ's?...

 

It is already in the FAQs. Its under my 3rd gen performance upgrade thread.

And you are all welcome.

 

i guess the "upgrade" would be the less amount of oil burned after the swap? because from from what i have been able to find on here, doesnt the b20a5 have less power? obviously without any boost/forced induction

 

You will not really be able to tell the difference. Once you change the stock header to an aftermarket one and the intake and catback, then it is all irrelavant.

If you are just trying to stay stock, then doing this is pointless. But if your B21a1 is dying and you do not want to rebuild it, then this is the way to go.

I will note, that there are some B21a1 owners who swear by there beloved B21a1. I know quite a few that love them, and I know a majority that do not.

The main reason for swapping to the B20a5/A is simply because it does not go through the piston ring lands like the B21 does.
So to fix the issue of not have not having to rebuild there motors, with the possibilty of doing again in about 10,000+ miles the B20a5/A have proven themselves to be the more relaible motor in this department.

Lets all face it all of our ludes need to rebuilt at this stage in the life of our cars, and since rebuilding motors is such a bad word for the enthusiasts who just want to buy it and go, then we all came up with this swap.

Since the majority of the B20a5/A motors do not burn through ring lands due to their Factory pressed in Iron sleeves, it is a cheap block to turbo charge and has been tested without any modification to the block to handle up too 400whp(Thank you to TonyBaker12 for that dyno), while on the other hand the B21a1 will eat through ring lands way before 5000 miles on boost.
To make the B21a1 just as reliable, all that is needed to be done is to take the block and have the FRM sleeves removed and have iron sleeves installed and you have yourself a block that is not going to eat the ring lands; however, since you will want to have the new sleeves bored out to the OEM specs of the B21a1, it will not leave much room for over bore and will put the new sleeves in the danger zone for breaking due to the fact that the FRM sleeves are much slimmer and stronger than iron sleeves at the same bore specs.


Most of us who have owned these cars all know the ups and downs of both motors, and it has been proven and determined that the B20a5/A motors are the most reliable with regard to the burning up of the ring lands at the same mileage.


But there are the very rare who own the B21a1 that have low mileage and have not seen a drop of oil burned because they were take well cared of.

I say this to put the whole debate to rest.

For you newbies, swapping from the B21a1 is not a power upgrade, its more of a reliablitly and financial factor for regular NA power, and also turbo charging potential in the future so as not to spend $1500 to replace the FRM sleeves in the B21a1 with iron sleeves for more reliability, since its much cheaper to find a B20a5/A long block to fix that issue.

One last note, If you put a B21a1 head on a B20a5/A block, you will lose compression.
This is good if you are going to turbo charge.
This is bad if you are wanting to build NA power.

 

Do you really need to swap distributors? I never heard that until now...Just want to clarify, Will the B20A dizzy work?

 

they are the same for the b20a,b20a5,b21a1 and all other 3g si models. the carb model 3g's have two different distributors.

 

got it. thanks again

 

So after reading this you need to swap the drivers side motor mount bracket that attaches to the engine from the old B21 motor onto the B20 motor and then use the B21 motor mount? Is that correct? If that is true I am going to need a B21 motor mount bracket because my dad sent his back with the old motor..

 

the perch(on enine)mount, and cage(mounts to chassis) for the b21 is different than the b20 version. if you have all three components from either one, you will be fine. preferred mount would be the b20a/5 setup as the aftermarket we do have will have you reuse the cage and perch with their mounts.

 

Good info, gonna be starting my project soon and this is one of the jobs up and coming!

 

what are the differences between the intake manifold for the b20a5 and the b21a1? why is it necessary to keep the b21 IM?

 

Emissions and ECU will affect the result of using the wrong intake. Also, the B21a1 head ports match the B21a1 IM better, while the B20a5 head ports match the B20a5 IM better.

 

Ok, the ECU and emissions part makes sense.

But are you saying that when i put the B21a1 IM onto the B20a5 head, it wont fit/match correctly?

as an FYI, i have everything for both engines because i have 2 preludes, one of each engine. the b21a1 block is damaged, hence the needed b20a5 drop in swap

 

^^question regarding after market header, should I get one for a b21a1 or modify and b20a?

 

If you are going with OBD0 stick with the B20a header.

If you are going with OBD1 stick with the B21a1 header.

Just so you are informed, the B21a1 header was thicker in the primaries than the B20a5 header.

 

i know this has nothing to do with B series, but it does have to do with rebuilding. when i fully rebuilt my SiR H22A for the 4thy i thought i was gonna mess it up, it took me 5 days to tear down and rebuild. (Excluding Machine Work) and it was the best experience/learning curve to be on. you get to see every detail on how everything works, not only that YOU rebuild it so that YOU know its reliable. also i bought the motor for 400 and spent 900 on the rebuild (all new gaskets, seals, bearings, rings ect ect). download a HELMS, buy a beer, and rebuild. youll enjoy it.

 

What happens if sensors or alternator is not swapped. Also I did a b21a1 to an 89 b20a5 but I have problems no spark changed coil and ignitor any idea what it is.

 

You need to Keep your original engine harness and swap over the sensors or else the ECU will not understand. The B21a1 is OBD1 and the B20a5 is OBD0, but as long as you keep everything from the original motor, then you will be just fine.

 

just wanted clarification ty :smilejap:

 

soooooo the B20B wont work..?



"The answer to this question has been updated now as of (2019):

1. https://www.preludepower.com/threads/88-91-prelude-b20b-z-swap-awd.440074/#post-4043370

2. https://www.preludepower.com/threads/1funryd-88-91-prelude-b20vtec-swap.462080/#post-1986650640
..."

 

soooooo the B20B wont work..?

Are you serious dude?? we already answered you in the other thread.... it will not work without tons of modifications... stop reviving threads and asking the same damn questions.

 

Don't need the attitude bro, just getting clarification due to the fact I already bought the damn motor... What "MODS" are needed and what "OTHER" thread are you talking about. Thanks

Tabs got closed and I haven't received any emails about replies except this one.. Can you remind me what link it was so I can move forward..

 

http://www.preludepower.com/forums/showthread.php?t=325385

 

Great Info

This is pretty much identical to my current situation. I have a B21A1 installed in my 91 4WS that is dying after 60K on a .25 over bore and rebuild with OEM pistons and rings. It puts out a pretty good puff of smoke on start and after idling at a stop light. Overall it does not use much oil, its just that annoying puff of smoke coming off of idle. There is some blow by witnessed by removing the CCV from the valve cover. There is a steady stream of air coming out at idle.

Being stubborn I had to see for myself the truth about the FRM issue almost like conducting my own experiment. I did get 6yrs and 60k out of it. Is that acceptable for rings? Absolutely not. Re-ring and go again? Even if I were to want to, rings for the .25 OEM pistons are no longer available. So this time I am doing what I should have done the first time.

I just got my hands on a good B20A5 block shipped to me from Oregon that will be bored to B21A1 STD specs. Everything will be swapped over to it. When I'm done it will be the same as though I have a B21A1 with iron sleeves.

Getting the best fit bearing size is the last thing I have to figure out. I really don't want to have the crank ground. I will try to stay with the Honda OEM color coded bearings as they do seem to still be available at Majestic Honda.

Question: :questionmark:
Would you re-use the B21A1 head?
I have a B20 PK2 head that is all checked out and re-surfaced. I am debating on whether or not to use it for the slightly higher compression. What Head Gasket would I use :questionmark:
Feel free to comment

 

Damn, that's some mods I don't even wanna deal with. Time to hit Craigslist for a trade.

 

Which Head and Which Head Gasket?

Question:
Would you re-use the B21A1 head :questionmark: The reason I ask is because I am fortunate to have an option. On an unrelated occasion I acquired a B20 PK2 head with the cams that is all checked out, new guide seals and re-surfaced. I am debating on whether or not to use it for the slightly higher compression. I am reluctant because the water passage shapes are different and from what I understand the B21A1 intake won't port match to the B20 PK2 head. The other question is: What Head Gasket would I use :questionmark:

I want to hear all opinions but I am leaning towards using the B21A1 head just because it will be easier than messing with the B20 head and the port matching issue. I don't have access to a B20 intake and don't know if the sensors and plugs will match up. Is it worth it to gain the extra compression :questionmark:

Since I have the cams from the B20 head someone suggested using the intake cam on the B21A1 head because the duration is a little longer. Is this true :burnout::questionmark:

Feel free to comment :?

 

Question:
Would you re-use the B21A1 head? The reason I ask is because I am fortunate to have the option. On an unrelated occasion I acquired a B20 PK2 head with the cams that is all checked out, new guide seals and re-surfaced. I am debating on whether or not to use it for the slightly higher compression. I am reluctant because the water passage shapes are different. What Head Gasket would I use :questionmark:
Feel free to comment :?

You use the HG of the head that you are going use.

And I would use the B20a5 head for higher compression, and then use the B21a1 intake manifold just port match that way the harness is just plug and play.

I believe that is all you need to do for the head.

 

I had the block checked. It has some abrasions in cylinders 3 & 4. If boring was in my price range ill see about that. This sucks man what was a week project is turning into a month event, not to mention were about to have a baby any minute.

 

couple questions

I read somewhere that the stock head gaskets are composite and won't hold much power, is that true, and who makes cams for the b20a5, I've looked around without any luck. Is there a difference between the cams for an auto and a stick? Thanks for any help, I have an auto trans, it's a dog til 3k, then screams like you stomped its tail!

 

I read somewhere that the stock head gaskets are composite and won't hold much power, is that true, and who makes cams for the b20a5, I've looked around without any luck. Is there a difference between the cams for an auto and a stick? Thanks for any help, I have an auto trans, it's a dog til 3k, then screams like you stomped its tail!

You can call www.deltacam.com or www.webcamshafts.com or www.coltcams.com and ask about building you a set or regrinding yours to your power specifications.

The cams in the motors are all the same, it does not matter if its auto or manual.

Yes the headgaskets are composite. Just email me at: 1funryd@comcast.net

And I can sell you the new cometic MLS headgasket to rid yourself of blown headgaskets.

I worked with Cometic to produce their MLS gasket for our motors.

 

Wow!

Thanks for the info. It's my dd/ therapy, I drive a big truck all day, she's such a blast to blow off a little steam after 14 hrs. on a SLOW ROLL! I've had it for almost 2 yrs, I always had Honda bikes, this won't be my last Honda car though. Despite the lag to 3k she runs awesome!
Thanks again for giving me some direction. :headbang:

 

Ok, so I'm swapping my b20a5 into a 90 obd1 chassis. i have about 3-5 sets of everything harnesses, sensors, plugs, etc. what i am wondering, is that on my b20a5 all of the sensors on my intake manifold are blocked off. can i simply plug in the obd1 sensors from the b21? i currently have no check engine light on my 89 with all the sensors blocked off.