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Hi guys! So I finally restored my 1990 4WS Prelude that had the B21A1 engine swapped out about 4 years ago with a B20A5. My problem is that the downpipe/ flexpipe coming from the manifold is rotting away and I need to replace it. It still has the 1 original O2 sensor attached to this pipe right after the 2 pipes fuse into 1 since the ECU still recognizes the older B21A1 engine (it's the 1 O2 sensor system). It has been working well without the CEL going off. I am having a hard time finding a replacement downpipe that fits (Honda doesn't make them any more and an aftermarket one I bought from MAC didn't fit and didn't even have the bung hole for the O2 sensor on the pipe!
So is there anyway I can get a OEM style downpipe for my B20A5 engine or is there an aftermarket header system that will work well, give me a little more power and still be able to have the O2 Sensor attached to the pipe? OBX seems to make a header and downpipe system that might actually fit but doesn't seem to have the bung hole for the O2 Sensor. Am I right about that? Any suggestions will be most appreciated!!! I have a Magnaflow Cat ready to be attached to this downpipe once I get something. Thanks guys for any help at all!
 

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Hi guys! So I finally restored my 1990 4WS Prelude that had the B21A1 engine swapped out about 4 years ago with a B20A5. My problem is that the downpipe/ flexpipe coming from the manifold is rotting away and I need to replace it. It still has the 1 original O2 sensor attached to this pipe right after the 2 pipes fuse into 1 since the ECU still recognizes the older B21A1 engine (it's the 1 O2 sensor system). It has been working well without the CEL going off. I am having a hard time finding a replacement downpipe that fits (Honda doesn't make them any more and an aftermarket one I bought from MAC didn't fit and didn't even have the bung hole for the O2 sensor on the pipe!
So is there anyway I can get a OEM style downpipe for my B20A5 engine or is there an aftermarket header system that will work well, give me a little more power and still be able to have the O2 Sensor attached to the pipe? OBX seems to make a header and downpipe system that might actually fit but doesn't seem to have the bung hole for the O2 Sensor. Am I right about that? Any suggestions will be most appreciated!!! I have a Magnaflow Cat ready to be attached to this downpipe once I get something. Thanks guys for any help at all!
A b20a5 downpipe will not have an o2 sensor bung. You'll want to look for a downpipe or header/downpipe for a b21a1, not a b20a5. There are some headers on ebay occasionally. I'm not sure if there are any there right now and I can't look from my work computer. If you find one that doesn't have the o2 sensor bung, just take it to a muffler shop and have one installed. Shouldn't cost more than $20 for that. If you go the header/downpipe route you'll also need to make sure the header has an egr bung for a b21a1. There is enough of a difference in the b21a1 and b20a5 egr pipes that you'll want the correct one.
 

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bosal makes a b21a1 replacement downpipe. I think it is still available. It was last I knew. Amazon sells them but not sure if they have one in stock. Rockauto.com might sell it but I don't remember. You might find the bosal on ebay too.
 

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I tried Walker exhausts and they list part numbers for just about every piece of the exhaust, except the downpipe.
http://www.walkerexhaust.com/catalog/walker-exhaust-systems/e-catalog-lookup

I had a check on Bosal's website and they're showing the downpipe as out of stock; shown as a bit expensive in their catalogue too, with O2 sensor it's US$342.98, without the O2 sensor it's US$163.70. Bosal also describe them as "Except 4WS", I'm not sure what difference 4WS makes to the downpipe.
http://www.qcsonline.net/bosalb2b/products/

Just because a company lists a part does not mean they have it available, but I did a quick search for the Bosal downpipe with O2 sensor, part# 882-551:

Premium Autoparts have them up for US$291.53.
http://www.premiumautopartsllc.com/...checkfit=y&make=honda&year=1990&model=prelude

Autozone show the Bosal part.
http://www.autozone.com/1/products/394988-exhaust-pipe-882-551-bosal-882-551.html

CARiD show them for US$123.41
http://www.carid.com/bosal/front-exhaust-pipe-mpn-882-551.html

Car Part Kings show them for US$140.10
http://www.carpartkings.com/bosal-front-exhaust-pipe-882-551.html


Another option is to find the Bosal downpipe without an O2 sensor (part# 882-861) and have a bung welded in.

Autozone.
http://www.autozone.com/1/products/357808-exhaust-pipe-882-861-bosal-882-861.html


Amazon (for some reason it says it doesn't fit)
[ame]http://www.amazon.com/Bosal-882-861-Pipe/dp/B00180NAX0[/ame]


CARiD US$62.40
http://www.carid.com/bosal/front-exhaust-pipe-mpn-882-861.html

Car Part Kings US$72.66
http://www.carpartkings.com/bosal-front-exhaust-pipe-882-861.html


It would seem your options are:

1. Hunt down an exhaust supplier that has a Bosal downpipe part 882-551 on their shelves.

2. Hunt down a bosal downpipe part 882-861 and have a O2 bung welded in.

3. If you can't find the Bosal part, try a local exhaust shop. You may find they can custom make you a downpipe. Could be expensive.

4. Go with 1funryd's OBX suggestion and have an O2 bung welded in. Luzer makes a good point about the EGR pipe, but I'm guessing having a 'hybrid' pipe made to connect your B21 inlet manifold to a B20 exhaust manifold is quite possible, and probably cheaper than having a new downpipe made.
 

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Down pipe

Tried the OBX header system, (Jet-Hot coated) and wish I'd never done it !
Melting anything plastic even after exhaust wrap.
Can't find down pipe either to switch back.
If you find one let me know. !!!
Then there'll be an OBX system for sale.
I also made a heat block plate to go between the alternator and the #4 pipe as it was only 3 in from the pipe and I'm sure the heat would sooner than later do damage to the alternator.
The damage is the foam wrap on the a/c return hose around the cooling fan was getting deformed and every time I get out I can smell hot plastic.

Cheers
nigel
 

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Tried the OBX header system, (Jet-Hot coated) and wish I'd never done it !
Melting anything plastic even after exhaust wrap.
Can't find down pipe either to switch back.
If you find one let me know. !!!
Then there'll be an OBX system for sale.

Cheers
niogel
88SE Lude fitted an OBX header and downpipe to Grey Lude before I bought it off him, it is covered in exhaust wrap from the block to beyond the sump, but I've had a quick look around and nothing appears to be melting. Can you tell us where the damage is being caused on your car? I just want to make sure I haven't missed something.
 

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88SE Lude fitted an OBX header and downpipe to Grey Lude before I bought it off him, it is covered in exhaust wrap from the block to beyond the sump, but I've had a quick look around and nothing appears to be melting. Can you tell us where the damage is being caused on your car? I just want to make sure I haven't missed something.
I'm curious as well. What plastic parts are near your exhaust system? I had an OBX on my previous 3rd gen for several years with no heat issues. It was stainless, with just the header section wrapped. No wrap on the down pipe. It was the system that Sean posted a link to above.
 

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If your staying with the B20/21 then just pay the money and get that Bosal if you can find it.

But honestly its more than likely going to be cheaper to get the OBX and modify it.
 

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88SE Lude fitted an OBX header and downpipe to Grey Lude before I bought it off him, it is covered in exhaust wrap from the block to beyond the sump, but I've had a quick look around and nothing appears to be melting. Can you tell us where the damage is being caused on your car? I just want to make sure I haven't missed something.
You haven't missed anything at all Matt.
I've used 3 OBX systems on 3Gs and know of 3 more personally (not counting the many on here who have them), not one of them have ever had any issues with them melting anything. And only one of them was wrapped, and you have that one Matt. So the others are more likely to do it, and haven't.
They are no more likely to do this than any other downpipe made for the job.
 

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Exhaust

Just left the Auto Zone site and it says they have Bosal #2 flex pipes.
I'll be stopping there on my way from the airport today.
More later.

Cheers
nigel
 

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Discussion Starter #12 (Edited)
bosal makes a b21a1 replacement downpipe. I think it is still available. It was last I knew. Amazon sells them but not sure if they have one in stock. Rockauto.com might sell it but I don't remember. You might find the bosal on ebay too.
Ha! Already tried the Bosal route. Found one on eBay. After they took my money they discovered it was no longer in stock. I called Bosal directly and they don't make them anymore! At least I got my money back from the eBay vendor! They apologized for the screw up. And of course I now realize I ordered the one for the B20a5 engine which is the wrong version anyway! I need the original downpipe for the B21a1.
 

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Discussion Starter #13
A b20a5 downpipe will not have an o2 sensor bung. You'll want to look for a downpipe or header/downpipe for a b21a1, not a b20a5. There are some headers on ebay occasionally. I'm not sure if there are any there right now and I can't look from my work computer. If you find one that doesn't have the o2 sensor bung, just take it to a muffler shop and have one installed. Shouldn't cost more than $20 for that. If you go the header/downpipe route you'll also need to make sure the header has an egr bung for a b21a1. There is enough of a difference in the b21a1 and b20a5 egr pipes that you'll want the correct one.
Thanks for that info regarding the EGR pipe! A local Meineke muffler shop I asked about installing an o2 sensor bung (if I find a downpipe) said it would cost me about $80!!! Thanks but no thanks Meineke!
 

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Discussion Starter #14
I tried Walker exhausts and they list part numbers for just about every piece of the exhaust, except the downpipe.
http://www.walkerexhaust.com/catalog/walker-exhaust-systems/e-catalog-lookup

I had a check on Bosal's website and they're showing the downpipe as out of stock; shown as a bit expensive in their catalogue too, with O2 sensor it's US$342.98, without the O2 sensor it's US$163.70. Bosal also describe them as "Except 4WS", I'm not sure what difference 4WS makes to the downpipe.
http://www.qcsonline.net/bosalb2b/products/

Just because a company lists a part does not mean they have it available, but I did a quick search for the Bosal downpipe with O2 sensor, part# 882-551:

Premium Autoparts have them up for US$291.53.
http://www.premiumautopartsllc.com/...checkfit=y&make=honda&year=1990&model=prelude

Autozone show the Bosal part.
http://www.autozone.com/1/products/394988-exhaust-pipe-882-551-bosal-882-551.html

CARiD show them for US$123.41
http://www.carid.com/bosal/front-exhaust-pipe-mpn-882-551.html

Car Part Kings show them for US$140.10
http://www.carpartkings.com/bosal-front-exhaust-pipe-882-551.html


Another option is to find the Bosal downpipe without an O2 sensor (part# 882-861) and have a bung welded in.

Autozone.
http://www.autozone.com/1/products/357808-exhaust-pipe-882-861-bosal-882-861.html


Amazon (for some reason it says it doesn't fit)
http://www.amazon.com/Bosal-882-861-Pipe/dp/B00180NAX0


CARiD US$62.40
http://www.carid.com/bosal/front-exhaust-pipe-mpn-882-861.html

Car Part Kings US$72.66
http://www.carpartkings.com/bosal-front-exhaust-pipe-882-861.html


It would seem your options are:

1. Hunt down an exhaust supplier that has a Bosal downpipe part 882-551 on their shelves.

2. Hunt down a bosal downpipe part 882-861 and have a O2 bung welded in.

3. If you can't find the Bosal part, try a local exhaust shop. You may find they can custom make you a downpipe. Could be expensive.

4. Go with 1funryd's OBX suggestion and have an O2 bung welded in. Luzer makes a good point about the EGR pipe, but I'm guessing having a 'hybrid' pipe made to connect your B21 inlet manifold to a B20 exhaust manifold is quite possible, and probably cheaper than having a new downpipe made.
Good advice. The OBX looks appealing but my auto mechanic friend said it is very hard to cut and weld a bung hole into a stainless steel downpipe which is what the OBX is. I just found a European car repair guy who says he can make me a downpipe since he has the equipment for this kind of fabrication. Might cost more than the car though!
 

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Discussion Starter #15

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Discussion Starter #16
Ha! Already tried the Bosal route. Found one on eBay. After they took my money they discovered it was no longer in stock. I called Bosal directly and they don't make them anymore! At least I got my money back from the eBay vendor! They apologized for the screw up.
 

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Discussion Starter #17

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Discussion Starter #18
Good advice. The OBX looks appealing but my auto mechanic friend said it is very hard to cut and weld a bung hole into a stainless steel downpipe which is what the OBX is. I just found a European car repair guy who says he can make me a downpipe since he has the equipment for this kind of fabrication. Might cost more than the car though!
Just saw that the Bosal 882-551 might still be available from some parts dealers online that you sent me. Wish me luck. That would solve my problem!
 

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but my auto mechanic friend said it is very hard to cut and weld a bung hole into a stainless steel downpipe
Swap that friend for either just a friend or just a mechanic ;-) Because that advice is complete crap.
Any self respecting exhaust shop or welder could do that without any issue.
 

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Discussion Starter #20
I tried Walker exhausts and they list part numbers for just about every piece of the exhaust, except the downpipe.
http://www.walkerexhaust.com/catalog/walker-exhaust-systems/e-catalog-lookup

I had a check on Bosal's website and they're showing the downpipe as out of stock; shown as a bit expensive in their catalogue too, with O2 sensor it's US$342.98, without the O2 sensor it's US$163.70. Bosal also describe them as "Except 4WS", I'm not sure what difference 4WS makes to the downpipe.
http://www.qcsonline.net/bosalb2b/products/

Just because a company lists a part does not mean they have it available, but I did a quick search for the Bosal downpipe with O2 sensor, part# 882-551:

Premium Autoparts have them up for US$291.53.
http://www.premiumautopartsllc.com/...checkfit=y&make=honda&year=1990&model=prelude

Autozone show the Bosal part.
http://www.autozone.com/1/products/394988-exhaust-pipe-882-551-bosal-882-551.html

CARiD show them for US$123.41
http://www.carid.com/bosal/front-exhaust-pipe-mpn-882-551.html

Car Part Kings show them for US$140.10
http://www.carpartkings.com/bosal-front-exhaust-pipe-882-551.html


Another option is to find the Bosal downpipe without an O2 sensor (part# 882-861) and have a bung welded in.

Autozone.
http://www.autozone.com/1/products/357808-exhaust-pipe-882-861-bosal-882-861.html


Amazon (for some reason it says it doesn't fit)
http://www.amazon.com/Bosal-882-861-Pipe/dp/B00180NAX0


CARiD US$62.40
http://www.carid.com/bosal/front-exhaust-pipe-mpn-882-861.html

Car Part Kings US$72.66
http://www.carpartkings.com/bosal-front-exhaust-pipe-882-861.html


It would seem your options are:

1. Hunt down an exhaust supplier that has a Bosal downpipe part 882-551 on their shelves.

2. Hunt down a bosal downpipe part 882-861 and have a O2 bung welded in.

3. If you can't find the Bosal part, try a local exhaust shop. You may find they can custom make you a downpipe. Could be expensive.

4. Go with 1funryd's OBX suggestion and have an O2 bung welded in. Luzer makes a good point about the EGR pipe, but I'm guessing having a 'hybrid' pipe made to connect your B21 inlet manifold to a B20 exhaust manifold is quite possible, and probably cheaper than having a new downpipe made.
Great info! I will check out the Bosal 882-551 online and hope for the best.
 
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