Header for the B20a3 (PGM-CARB SOHC)

15875 Views 45 Replies 18 Participants Last post by 1funryd, 10 d ago

TripleLude

Discussion Starter · Jan 8, 2012 (Edited)

4

Remember, the B20a5 header does not fit on a B20a3 cylinder head. We need a readily available performance header for the B20a3 and other SOHC 3rd gen Prelude cylinder head.

As I was poking around online, I stumbled across this:
OBX RACE EXHAUST HEADER 84-87 HONDA PRELUDE 2.0L A20
http://www.erzperformance.com/ProductDetails.asp?ProductCode=OBXHONDA-14

I know there are a lot of similarities between the A20 and B20a3 cylinder heads and PGM-CARB setups. It would not surprise me if they are almost identical in a lot of ways.

So I invested $10 in a Felpro exhaust manifold gasket made for a 86 Prelude PGM-CARB.

Guess what?!?!?!?!

It fits like the regular B20a3 exhaust manifold gasket. Exact match. Now the only thing to figure out is if the header angle is compatible with the angle the B20a3 sits at. If the angle is right (or close enough), we have a bolt-on performance header options. If the angle is too far out, we could possibly modify it to work.

____________________________

Adjustable Cam Gear too:

Also a side note, here is a F22 adjustable cam gear I bought off eBay for my B20a3 build. I took a gamble on it and found it is an exact fit with the B20a3 cam gear. The only questionable remark I have is regarding the quality of design. The generic eBay cam gears suck.

In any event, even if this cheap cam gear slips, the B20a3 is a non-interference engine. Meaning under any stock circumstances, a valve will never be able to kiss a piston.

In my particular engine build, I am milling the engine block and head surface down for performance, so I don't know if it will change anything.

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21 - 40 of 46 Posts

othermike

· #21 · Oct 3, 2012

manifold

What's wrong with your B20A3 intake manifold?

TripleLude said:
I have a spare head and manifold, but they are already screwed up. The head has a crack in it. oh joy

Cptn. Shankz

· #22 · Nov 17, 2013

Soooooo, which one will fit my b20a3?

preludefan

· #23 · Nov 17, 2013

Looks like a goer...just change the flange if you cant get the a series one to fit, dont think they gain would be worth it unless you add some webbers and a good cam. ..

shawng22

· #24 · Nov 22, 2013

I have a new ish b20a3 head. I bought it new when I was building an oval car. It has about 1000 miles on it before I took it off for the pgm-fi swap. I am willing to sell the complete head including distributor, cam, intake, and carbs.

Cptn. Shankz

· #25 · Dec 1, 2013

Ay shawng22... Can u Post up a couple of pics. Did u have the b20a3 headers too

LudicrousSpeed

· #26 · Nov 7, 2014

Reviving the 2yr old thread as my very first post to preludepower forums!

Did the OBX exhaust header fit the B20A3 without difficult/costly modifications?

How about that adjustable cam gear for the F22 engine? Did it work out?

Any news at all regarding B20A3 performance parts?

frijoles

· #27 · Nov 7, 2014

LudicrousSpeed said:
Reviving the 2yr old thread as my very first post to preludepower forums!

Did the OBX exhaust header fit the B20A3 without difficult/costly modifications?

How about that adjustable cam gear for the F22 engine? Did it work out?

Any news at all regarding B20A3 performance parts?

All of that info is more or less covered in this thread.

None of it fits without some slight modification. Or major modification.

LudicrousSpeed

· #28 · Nov 7, 2014

frijoles said:
All of that info is more or less covered in this thread.

None of it fits without some slight modification. Or major modification.

"more or less covered", "slight... Or major modification" -EXACTLY. I was trying to find out if it was slight OR major modifications required to make it work. Sure seems like you are just trolling along.

mg:

I am hoping someone who actually used that OBX header and did (or paid someone to do) the modification required would shed a bit of light onto the level of difficulty (or cost).

And for clarity's sake, I'm also trying to figure out if it would be easier to send my cam for a regrind, or if that F22 cam worked out.

I don't think these are foolish questions to ask... or am I too foolish to notice that I am asking foolish questions? Haha.

frijoles

· #29 · Nov 7, 2014

LudicrousSpeed said:
"more or less covered", "slight... Or major modification" -EXACTLY. I was trying to find out if it was slight OR major modifications required to make it work. Sure seems like you are just trolling along. mg:

I am hoping someone who actually used that OBX header and did (or paid someone to do) the modification required would shed a bit of light onto the level of difficulty (or cost).

And for clarity's sake, I'm also trying to figure out if it would be easier to send my cam for a regrind, or if that F22 cam worked out.

I don't think these are foolish questions to ask... or am I too foolish to notice that I am asking foolish questions? Haha.

If you read through you will see that the types of modifications needed are explained in pretty good detail.

It isn't the whole cam. Just the cam gear. That, I do believe fits without modification, but someone else said it did require modification so, I don't know for sure.

Cptn. Shankz

· #30 · Nov 18, 2014

Iv bought the obx header and did some modifications but have not gotten around to fitting it yet... and its also its the easiest header to work with

LudicrousSpeed

· #31 · Nov 19, 2014 (Edited)

Cptn. Shankz said:
Iv bought the obx header and did some modifications but have not gotten around to fitting it yet... and its also its the easiest header to work with

COOL, thanks Cap'n (salute)! I was really hoping for a reply exactly like that one. -Hope you slap it on there soon and post some pics

-especially a bit specifically showing your mod to that obx!

I found a place nearby that does custom race fabrication stuff specifically on honda/acura's..gonna call them to verify they can mod it to fit (apparently just needs to be bent 30 degrees somewhere along the downpipe). Then with a high-flow cat and slightly bigger exhaust pipe..seems I could get a modest performance boost!

Cptn. Shankz

· #32 · Nov 20, 2014

Yes, you have to bend the down pipe. And the header as well (the header is a lot harder to bend). Yo also have to fabricate a piece to go between both the header and the downpipe because they wont meet otherwise... the only problem im having now is a ground clearance because the header down pipe is a 4 tube instead of a 2tube

4lvin

· #33 · Feb 17, 2015

So... has anyone successfully modded any headers to fit their A3 yet? I've yet to see any photos or write-ups on it.

othermike

· #34 · Feb 22, 2015

I've been searching for a practical solution to the B20A3 header problem for a long time. As far as I can see, the A20 header has to have a ton of mods to make it work, and then has ground clearance issues.
Wouldn't it be easier to modify a B20A5 header, as the physical dimensions would be the same, with the exception of the flange shape. How about plasma cutting a new 3/8" flange using the exhaust manifold gasket as a template. Some minor reshaping of the pipes would be required where they meet the flange, but that sounds a heck of a lot less hassle to me.

carotman

· #35 · Feb 23, 2015

With all the modifications involved, I would just put a B20A5 head on your B20A3. The performance gains will be a lot greater than just changing the exhaust manifold.

Of course, you would need to convert to EFI but this isn't that complicated.

Cptn. Shankz

· #36 · Feb 28, 2015

othermike said:
I've been searching for a practical solution to the B20A3 header problem for a long time. As far as I can see, the A20 header has to have a ton of mods to make it work, and then has ground clearance issues.
Wouldn't it be easier to modify a B20A5 header, as the physical dimensions would be the same, with the exception of the flange shape. How about plasma cutting a new 3/8" flange using the exhaust manifold gasket as a template. Some minor reshaping of the pipes would be required where they meet the flange, but that sounds a heck of a lot less hassle to me.

Yeaaa, this would be the more practical way to go about doing this... cut the a5 header flange off and an a3 on should weld on with little modification

othermike

· #37 · Mar 2, 2015

carotman said:
With all the modifications involved, I would just put a B20A5 head on your B20A3. The performance gains will be a lot greater than just changing the exhaust manifold.

Of course, you would need to convert to EFI but this isn't that complicated.

The blocks are different, as the B20A5 has 2 cams, the tensioner mount, etc are different. It's not that simple to stick a 2 cam head on a block designed for a one cam head.

What is probably the simplest solution for guys with limited equipment is to get a Pacesetter header (70-1250) meant for a 2nd Gen, as the head ports match the header. Cut the bottom flange off of it, and reattach it in a better angle, so it fits the 3 Gen piping. If I hadn't already started on the other header for my race car, that's what I'd be doing. It's simple, and effective.

4lvin

· #38 · Mar 2, 2015

othermike said:
The blocks are different, as the B20A5 has 2 cams, the tensioner mount, etc are different. It's not that simple to stick a 2 cam head on a block designed for a one cam head.

What is probably the simplest solution for guys with limited equipment is to get a Pacesetter header (70-1250) meant for a 2nd Gen, as the head ports match the header. Cut the bottom flange off of it, and reattach it in a better angle, so it fits the 3 Gen piping. If I hadn't already started on the other header for my race car, that's what I'd be doing. It's simple, and effective.

The B20A5/B21A1 head would bolt up to a B20A3 block just fine. The only differences is the pistons, rods, and crank journals because they are smaller on an A3 block.

Wouldn't the placement of the EGR piping and air suction valve piping on the Pacesetter header be an issue as well? Unless one were to completely delete those of course.

othermike

· #39 · Mar 3, 2015

4lvin said:
The B20A5/B21A1 head would bolt up to a B20A3 block just fine. The only differences is the pistons, rods, and crank journals because they are smaller on an A3 block.

Wouldn't the placement of the EGR piping and air suction valve piping on the Pacesetter header be an issue as well? Unless one were to completely delete those of course.

Yes, you're right. That could be an issue. Not for me because it's for tack use only, but yes it could be for others.

othermike

· #40 · Apr 4, 2015

B20A3 SOHC Header

So I bought a Pacesetter Header kit for a 2nd Gen (#70-1250). It just arrived, so I haven't had a chance to modify the lower flange to fit my 3Gen B20A3. I will take some pix and try to post them (I have no idea how to do that).
Should have it all done soon. The fit to the engine is perfect. The only problem is the A20 engine tilts forward, so I'll have to do some cut & paste to get it to fit. But I'm sure it will fit without a whole lot of hassle.

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