Swap_File

I am looking to swap the Prelude B21A1 head onto the Accord A20 block. The only other person who has ever preformed this swap welded the 3 “extra” holes on the B21A1 head shut, and then had their head shaved to make it smooth again.


Notice the A20 gasket on the B21 head with the 3 holes welded shut.

This seems like a lot more work that it should be.

I thought about using liquid aluminum (block filler) to close up the holes, deep enough in so that it would not require the head to be shaved.

Does anyone have any comments on if they think this method would work, or what other methods could be used to fill these holes?

One of the people on homemadeturbo mentioned that "some dude at honda-tech did it by stuffing the holes with rubber hose and seal it with silicon.", but I do not know how much I would trust doing that, and have been unable to find any posts about it.

ek99

The best way to do it is still to weld it and mill the head. Welding those 3 holes will cost no more than $50 and to mill it another $30. $80 is worth the reliability you will have if its welded. I would not trust any other way. Do it right the first time, and you wont have to take it appart again if it leaks.

Sam1am26

Yeah you should probably just take them time/effort to do it right and have it welded/milled... But just to let you know I put an H22 DOHC VTEC head on an F23 2.3L SOHC block and had to block two holes in the head and all I used was hi-temp silicone and they never leaked... Just something to think about...

Oh by the way I have never head of this swap before? Sounds interesting... Any more details? What is the point? Any specs on the Accord block?

Swap_File

The A20A3 is the SOHC engine found in the older 3rd generation Accords (86-89). It puts out about 120HP at 5800 RPM and 125 ft lbs of torque at 4000 RPM. 82.7mm bore, 91mm stroke.

The JDM Accord had an option for a DOHC B20 from the factory (160HP at 6300 RPM and 190 ft lbs of torque at 5000 RPM, but it is rather expensive to import and is difficult to find parts for in the USA. Also it takes a special transmission. The one benefit is it is a drop in swap, no modifications needed.

The prelude B20/B21 slants in the opposite direction as the Accord B20, so it is impractical (if not impossible) to swap the whole engine in. If the head is swapped onto the A20, it should end up being similar to an JDM Accord B20.

Most people just turbo their A20s for the best “Bang for the buck”, but adding on this DOHC head will allow a turbo A20 to use easily (and cheaply) available adjustable cam gears, and have more exhaust manifold options. The stock A20 head uses non-standard exhaust port spacing. The Prelude B20 isn’t exactly standard either, but it’s a lot closer. The A20 block is cast iron, so it handles boost well too. Forged pistons and rods are available for the A20 too, but most people say you don’t need rods unless you want to go past redline, and you don’t need the pistons until you go past 10 PSI.

(Edit: And the A20's block is cast iron, so you will never have to sleeve it)

Here is the head swap thread on 3geez (its kind of a mess):
http://www.3geez.com/showthread.php?t=47597&page=7

Sam1am26

Awesome... Seems like you are doing it for similar reasons that I put H-Series heads on F-Series blocks... Sounds like a good project

jag

Are the holes round? Could you tap them and thread a plug into them?

Swap_File

I though about that, but I was not sure what I would plug it with.

I would have to tap it from the bottom (the side that mates with the block), but I do not think that would be any problem.

Then a plug would have to be screwed in flush (or deeper) so that it doesnt touch the block.


(horrible image made in paint showing the plug)

Any suggestions as to what could be used for a plug?

Sam1am26

Yeah that would work... Many people have plug holes in heads before.. As long as you have a good seal you should be good...

jag

You need a pipe plug. I would think a brass one would work fine.
Here is a link to a catalog page at McMaster/Carr that has some:

http://www.mcmaster.com/nav/enter.asp?pagenum=19 (look under hex socket plugs)
They also have ones on their website somewhere with a square socket so that you can just use a half inch extension to spin them in (or 3/8 depending on the size of the whole).

You will probably have to drill the hole out to the size that the tap requires (unless it is already the right size for the tap)

WhiteNess

This is very off topic and I know this isn't a sales fourm, but considering the rarity of a B21A1 I think its worth it.

My Best freind has a 91 prelude SI (B21A1). He got His cams reground. He ended up spinning some bearings or throwing a rod or something. The car is just sitting and the cams are for sell. If your interested in them lemme know. They were really bad *** cams and really helped with highend performance on that head. I can find out all the specs and stuff if ur interested.