Welcome to the Corvette Forums at the Corvette Action Center!

84 Exhaust changeout question



I am going to switch the stock dual-single-cat-single-dual pipes with Corvette Centrals true dual no-cat system. My question lies in the tube running from the check valve.

1: What the heck does the check valve have to do with the cat?

2: Do I need to bypass it or trick it into thinking it has a cat?

3: Can I twist the tube into an animal shape and forget it was even there?

4: Will I ever fix my windows so they work properly?;)

BTW Here is my car!
and one of my custom rear speaker covers/grill:bang
...now time to do something about the dash grills:bang

Bill C

The check valves allow the AIR pump to inject air into your exhaust manafolds. The air pump either pumps air into the CAT or the exhaust manifolds. The check valves keep the exhaust from blowing back into the AIR injection system. If you eliminate the emisions i.e. the AIR injection system, then you can block off the tubes, get rid of the pump (install a pump eliminator pully) and remove the CAT. If you live in or plan to live in a state that checks emissions, you better keep all of that stuff (Then the animal stuff would be out of the question!) so you can re-install it if needed. Nothing in the ECM needs to know or cares that you made this MOD.
The manifold air injection only happens when the engine is warming up and the CATs are coming up to temp.
There is an electronic air deverter valve near your A/C compressor that will need to remain hooked up to the ECM to keep it happy.


Well said!

Thank you! I was worried about that, and yes, California emmisions would not like this mod so I think Ill keep all of that stuff!


1984 Exhaust

Bill C pretty much answered your questions about the exhaust. I was more interested in your concern about getting your windows to work.
I recently replaced the window motor and drive on my '85. Now this is a car which I bought with 37K on the clock. But that plastic drive broke one day and the motor was already making noise. I bought a motor from Ecklers and the previous owner gave me the track. Turns out he had already replaced the other one. I guess they don't last long in storage. Anyway it was not near as bad as I envisioned it. My one peeve was that both the instructions that came with the motor and all of the manuals I have only showed the right door. Now why they show the right door when it should be pretty obvious that the driver's door, the left door, would be the one most likely to need repair is beyond me.
Anyway I want to encourage you to dive into them they look a lot worse then really are.

Good luck with it...............


Thank you!

I just tried to replace the outer weatherstrips that I got from Corvette Central and they were the wrong ones! :hb
I looked at the window mechanisim and you are right, they dont look exceedingly difficult to change out. Ill let everyone know how it goes. Chances are Ill need some help tho!:gap

Bill C

Just get a high flow cat and keep all of the other stuff. It doesnt suck that much HP out of the engine.

Bill C


Exhaust changeout

Well if you start by removing the center hardware, door lock, etc. first you will save a lot of time. There are several screws right around that area that are not noticed at first. once those are out the rest of it is not so hard.
One thing to rememer is that the glass comes out the top of the window (Well Duhh!) unlike some pictures seem to indicate or ignore altogether. And the window mechanism comes out through the middle of the door panel once it is unfastened from the bottom of the door as well as along the side. The hardest part for me was pop riviting the new motor in after I drilled out the old rivets. Try hard not to make the holes too big when you drill out the old rivits. That can make it a long afternoon. Then you have to washer it up, etc.

Yeah when I got the window wipes, the rubber on the outside of the windows. They gave me 2 left hand sides. It was easy to exchange though because it was a local vendor. But it was a show stopper!

Have fun, if you come up with any questions let me know while it is still fresh in my mind. I just did mine about 2 months ago. It's much easier to do then it looks, as you have surmised.

It sure is nice to have TWO windows that go up and down fast. Well as fast as a Corvette window goes. :)

Have fun with it............


Well-known member
Dec 9, 2001
2001 red convertible, 1985 wht
exhaust changeout

Just one caution on your exhaust changeout. I dont know about other states but in Colorado if you fiddle with your exhaust system especially with your cat you run the risk of failing the emmissions requirement and once you fail that here its really a pain to bring it back into compliance. With thier fancy dyno and all that rot. Also in Colorado if you sell a car you are liable to bring it into compliance with emmissions unless you sell it as a tow away.


84 Exhaust changeout

I think almost all states are different in the way they comply to the emmisons standards.
Most of the state of Oregon does not even get tested. However most of the greater Portland area is one that is tested. Every car that does not have OBD II gets dyno'ed. This happens once every two years. If you remove the CAT('s) you can expect to fail. However you can get by with high flow cats or removing the precats on the later model C4's. Mufflers do not seem to enter into the equation. My '85 got through with essentially no mufflers. It has those ZR1 pipes from Mid America. The '86 got through with the pre-CAT's removed and those Targo mufflers from Mid America. I used to run my Fiero without a CAT until inspection time then remove the spacer pipe and install the CAT for the inspection. On a Fiero that is about a 15 minute job. Don't think I would want to do that on a Vette. Tiring of that procedure I finally just got a high flow CAT and left it in place. I was doing it mostly for the tone anyway.

You should be aware of your DEQ details before you venture into the project. Like billd indicated it could effect how or if you modify it........

Good luck with it..........


I dont think Ill have that much of a problem...

But it might be safe to throw a hi-flo cat on there instead of the dual pipes. I would expect the dual pipes to perform much better though. California is the crappiest state to screw with your car, emmisions wise. But you can get by with simple change out stuff like pipes and what not. Now when it comes to the X-ram manifold, which I would love to have, it gets pretty crazy. I would not like to have to change that thing out every two years just to pass smog.

Whats the best place to find a hi-flo cat? Ecklers-MidAm-Corvette Central?

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors


MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!



Advertise with the Corvette Action Center!

Double Your Chances!


Top Bottom