81' exhaust conversion
Thread Starter
Burning Brakes
Joined: Dec 2002
Posts: 1,205
Likes: 1
From: "Too Low, Too Fast, Too Loud" TX
81' exhaust conversion
Morning all, a quick question to those that have done this mod on the 81's. I have a stock engine/exhaust set up. I would eventually like to go with the "true dual" setup. My first question is when the car is of age to be emission legal for me to do this, is there any harm in removing the cat? Will I start getting the "check engine" light coming on? Secondly, has anyone removed the heat riser valve from the passenger side of thier vette, if so what did you do with the vacum line that runs to it and can these be tested off the car to see if they are actually opening up....thanks in advance for the info!!
Joe :seeya
Joe :seeya
Le Mans Master
Joined: Mar 2002
Posts: 7,456
Likes: 2
From: Coming home from Luckenbach Texas
Re: 81' exhaust conversion (81' Corvette Guy)
You have 2 years before the car goes exempt. Mine just went exempt as of Jan 1. But it looks like we're gonna dodge the emissions testing bullet...at least for now. Worst case scenario is you'd have to retrofit cats for 1 year...
The main issue you face is the configuration of the pipes and the tranny crossmember. If you look in the Mid-America catalog, you'll see there's a different pipe layout for '80-'82 cars -- in a dual setup, both pipes go to one side of the x-member.
I know an exhaust shop that could do a decent job for you relatively cheap. Drop me an email if you're interested.
The main issue you face is the configuration of the pipes and the tranny crossmember. If you look in the Mid-America catalog, you'll see there's a different pipe layout for '80-'82 cars -- in a dual setup, both pipes go to one side of the x-member.
I know an exhaust shop that could do a decent job for you relatively cheap. Drop me an email if you're interested.
Pro
Joined: Oct 2000
Posts: 740
Likes: 0
From: Republic of TEXAS
Re: 81' exhaust conversion (81' Corvette Guy)
I went to true duals (no cats) last year on my '79. I was going to just chance it on nights and weekends when I do most of my driving without a sticker. My mechanic told me to try getting it inspected and see what happens. I did.....it passed! (They don't do a visual) Got my Antique plate now...... :hurray:
Safety Car
Joined: Mar 2000
Posts: 4,078
Likes: 27
From: Northeast South Dakota
Re: 81' exhaust conversion (CaptainMike50)
You should not get a check engine light from switching to true duals. You will need to make sure that you put the O2 sensor in one of the pipes relatively close to the manifold, or even better yet go to a heated sensor. Either way an O2 sensor absolutely needs to be there. What will happen is you will notice an immediate power increase. Best bang for the buck mod you can do in my book. And why remove the heat riser? It really works just as designed on cold starts and there is really nothing to gain by removing it.
-Justin
-Justin
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Re: 81' exhaust conversion (81' Corvette Guy)
Good evening!
When I got my '81 the previous owner had already removed the cat (replaced it with a pipe) & the heat riser. The valve in the p'side pipe had been removed & the 2 holes in the housing for it had been welded up. The vacuum lines had been removed/disconnected & plugged. No problems with check engine light due to these mods & the engine started & warmed up OK. Even without the cat fitted on mine, changing to dual pipes made a big seat of the pants difference in power. If only all mods made that much difference.....!
Hi Justin & Page :seeya
:cheers:
[Modified by UKPaul, 11:32 AM 1/22/2004]
When I got my '81 the previous owner had already removed the cat (replaced it with a pipe) & the heat riser. The valve in the p'side pipe had been removed & the 2 holes in the housing for it had been welded up. The vacuum lines had been removed/disconnected & plugged. No problems with check engine light due to these mods & the engine started & warmed up OK. Even without the cat fitted on mine, changing to dual pipes made a big seat of the pants difference in power. If only all mods made that much difference.....!
Hi Justin & Page :seeya
:cheers:
[Modified by UKPaul, 11:32 AM 1/22/2004]
Race Director
Joined: Jan 2003
Posts: 15,177
Likes: 90
From: State of Confusion
Re: 81' exhaust conversion (UKPaul)
Anybody here have any 'definitive' before & after numbers, either from a dyno or drag-strip, when performing this mod on a late-C3?
I swapped the 2.87 gears to 3.73s, and my ETs went from 15.90 to 15.20 (how much of the improvement was due to 50* lower temps is unknown...)
I hope to install the M-A-D kit soon, and am curious how much quicker/faster my '82 will run.....
:confused:
I swapped the 2.87 gears to 3.73s, and my ETs went from 15.90 to 15.20 (how much of the improvement was due to 50* lower temps is unknown...)
I hope to install the M-A-D kit soon, and am curious how much quicker/faster my '82 will run.....
:confused:
Burning Brakes
Joined: Jan 2001
Posts: 1,218
Likes: 2
From: Plainfield IL
Re: 81' exhaust conversion (Pauld)
I removed the catalytic from my '81 and installed a test pipe. The pipe included a fitting for the hose that normally attached to the cat. As stated above, you won't get a check engine light from switching to true duals without a catalytic. Just be sure to locate the O2 sensor in one of the pipes relatively close to the manifold.
Unfortunately, my car would never pass Illinois emissions testing. I've therefore decided to leave my exhaust stock with the exception of the test pipe, which can be easily removed (on testing day) thanks to the flanges.
Unfortunately, my car would never pass Illinois emissions testing. I've therefore decided to leave my exhaust stock with the exception of the test pipe, which can be easily removed (on testing day) thanks to the flanges.
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