Test pipe for an 85
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Joined: Jun 2011
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Test pipe for an 85
I've seen a few threads about this but none with any good links and most of them talking about emmisions and how it's illegal. Can someone tell me where to get a test pipe? I live in Oklahoma and we don't have any emissions. Any help is appreciated!
Racer
Joined: Mar 2011
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From: Derby (Wichita area) KS
Rock auto sells one. I too am considering one for off road use as my old cats are more than likely shot anyway. I'd be interested in hearing others experiences with this but also not interested in a smog lecture.
Team Owner
Joined: Dec 1999
Posts: 34,873
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From: Lacey WA RVN 68-69
NCM Sinkhole Donor
First, your car has 3 catalytic converters. There are two "pre-cats" just below each exhaust manifold; pipe from those becomes a "Y" pipe that attaches to the front of a "main" cat.
The various Corvette accessory catalogs sells a front Y pipe without the pre-cats. You can also buy a true dual exhaust system; it bolts on and replaces the entire exhaust except the mufflers.
Don't ask muffler shops to cut the cats out and replace them with straight pipe. Even though you don't need to have the car tested, it's a violation of Federal law to remove working cats. If a muffler shop gets caught, they can face a 5-figure fine.
You have probably also read that newer cats actually flow very well, you may not see a real increase in power.
One thing you might try is to remove the entire stock exhaust system, pull the plate,s and tow the car to a exhaust shop and tell them you are building a car for "off-road use only". Then they can bend up and install a true dual system add the mufflers of your choice and haul the car back home and put the plates back on.
The various Corvette accessory catalogs sells a front Y pipe without the pre-cats. You can also buy a true dual exhaust system; it bolts on and replaces the entire exhaust except the mufflers.
Don't ask muffler shops to cut the cats out and replace them with straight pipe. Even though you don't need to have the car tested, it's a violation of Federal law to remove working cats. If a muffler shop gets caught, they can face a 5-figure fine.
You have probably also read that newer cats actually flow very well, you may not see a real increase in power.
One thing you might try is to remove the entire stock exhaust system, pull the plate,s and tow the car to a exhaust shop and tell them you are building a car for "off-road use only". Then they can bend up and install a true dual system add the mufflers of your choice and haul the car back home and put the plates back on.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
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From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
The 85 doesn't have precats
the problem with the 85 is that the cat is welded on from the factory. you have to cut it off to make the test pipe fit. On the 86, 87, the cat is clamped on.
You can go to a corvette wrecking yard, and since they can't sell you a used cat legally, they would cut off the cat rear flange and sell it to you for maybe $10. Then you just go buy the appropriate 18 inches or so of 4" diameter pipe, get the muffler shop to flare one end, enlarge the other end to fit over the Y pipe, and bolt it on in place of the cat.
BUT
I would leave your cat on, and just put a gauge on your pipe in place of the O2 sensor, and read the back pressure.
If it is 1-2 PSI, I would leave it alone.
If higher, just get a new cat from Summit racing that is a direct fit.
You would not believe how stinky and eye watering your car will become without that catalytic converter.
It's there for a reason.
the problem with the 85 is that the cat is welded on from the factory. you have to cut it off to make the test pipe fit. On the 86, 87, the cat is clamped on.
You can go to a corvette wrecking yard, and since they can't sell you a used cat legally, they would cut off the cat rear flange and sell it to you for maybe $10. Then you just go buy the appropriate 18 inches or so of 4" diameter pipe, get the muffler shop to flare one end, enlarge the other end to fit over the Y pipe, and bolt it on in place of the cat.
BUT
I would leave your cat on, and just put a gauge on your pipe in place of the O2 sensor, and read the back pressure.
If it is 1-2 PSI, I would leave it alone.
If higher, just get a new cat from Summit racing that is a direct fit.
You would not believe how stinky and eye watering your car will become without that catalytic converter.
It's there for a reason.
Last edited by coupeguy2001; Jul 8, 2012 at 06:19 PM.
Le Mans Master
Joined: Mar 2004
Posts: 5,107
Likes: 171
From: Dublin CA
Yes the 85 cat is a BOLT in. No welds or clamps. I took my old cat when I replaced it and cut off the end flanges and then built my own test pipe. I added a pipe so I could tie in the air tube that would have gone to the cat.
Pictures;
I used 1/2" compression couplings to join the tube to the new cat.
Or unbolt the fitting and attache it to the "test pipe". The 85 exhaust system is very restrictive. When I bolted in the test pipe and installed under-drive pulleys and took it to the track....I dropped .5 seconds off my usual run time thru the 1/4 mile.
Pictures;
I used 1/2" compression couplings to join the tube to the new cat.
Or unbolt the fitting and attache it to the "test pipe". The 85 exhaust system is very restrictive. When I bolted in the test pipe and installed under-drive pulleys and took it to the track....I dropped .5 seconds off my usual run time thru the 1/4 mile.
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Joined: Jun 2011
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Yes the 85 cat is a BOLT in. No welds or clamps. I took my old cat when I replaced it and cut off the end flanges and then built my own test pipe. I added a pipe so I could tie in the air tube that would have gone to the cat.
Pictures;
I used 1/2" compression couplings to join the tube to the new cat.
Or unbolt the fitting and attache it to the "test pipe". The 85 exhaust system is very restrictive. When I bolted in the test pipe and installed under-drive pulleys and took it to the track....I dropped .5 seconds off my usual run time thru the 1/4 mile.
Pictures;
I used 1/2" compression couplings to join the tube to the new cat.
Or unbolt the fitting and attache it to the "test pipe". The 85 exhaust system is very restrictive. When I bolted in the test pipe and installed under-drive pulleys and took it to the track....I dropped .5 seconds off my usual run time thru the 1/4 mile.
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
If you don't have the O2 sensor installed, Heddman makes a collector reducer that has a O2 sensor bung already welded in. Using that keeps you from having to cut a hole in the collector and welding a bung in place. It may take a little longer for the O2 sensor to heat up, but you can also use a heated sensor; just find a switched power source.
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Missed the 85 no pre-cats. :bb
If you don't have the O2 sensor installed, Heddman makes a collector reducer that has a O2 sensor bung already welded in. Using that keeps you from having to cut a hole in the collector and welding a bung in place. It may take a little longer for the O2 sensor to heat up, but you can also use a heated sensor; just find a switched power source.
If you don't have the O2 sensor installed, Heddman makes a collector reducer that has a O2 sensor bung already welded in. Using that keeps you from having to cut a hole in the collector and welding a bung in place. It may take a little longer for the O2 sensor to heat up, but you can also use a heated sensor; just find a switched power source.
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