I have an 80' Corvette w/ZZ4 crate engine, I am looking to upgrade the exhaust system. Which headers and exhaust system do y'all recommend? I know I will have to replace the crossmember with an earlier model in order to get true duals. I am in the market for a TH350 crossmember also.

 

I may be wrong but I don't think you can use an earlier crossmember in a 79-82. I think the 700R4 vrossmember from Bowtie Overdrives would allow dual exhaust in a later C3.

 

First off, welcome to the forum !!

I also did the ZZ4 swap in a 1980, so I can help you out with plenty of personal experience.

I see you live in Texas, so you have to pass emissions, and so will need to run catalytic converters.

The 1980 has a crossmember that does not allow for true dual exhaust. The '68-'79's with automatics all had a crossmember that did allow for dual exhaust. The problem is, that you need to find a crossmember from a pre '80 Corvette with a turbo 350. Now, the next problem is it is not a direct bolt in. There are 6 bolts that hold the crossmember in. 4 from below that go into the frame and 2 long cross bolts that bolt it to a pair of hangers that mount on the top edge of the frame. None of these line up correctly with a pre '80 crossmember. You can either re-do the brackets, or open up the holes until they line up, or get someone to make a custom crossmember.

Bow Tie overdrives makes a really nice tubular unit that allows dual exhaust, but it is set up for the 700R4 transmission. If you don't plan to go to the overdrive transmission (another great improvement for that ZZ4, way better than that Turbo350C that you have now), then you will have to get one made similar to it. Below is the picture of their crossmember for some ideas.



The next step is the exhaust. If you have to run the full emissions such as the A.I.R. pump, you will need the right headers. Hedman headers #68301-6 is the part number. From Summit or Jegs for about $475 for the set. They fit perfectly !! Use the Stage 8 locking header bolts and the stock gaskets and you won't have problems. From there, you will do dual 2 1/2 pipes past the transmission and then to under the battery and jack compartments. In that area you can have the converters installed. Behind that, look to get a "H" pipe installed. From there, out the back to the mufflers.

Here are pictures or my installation.









Hope this gets you started ..... let me know if you have any other questions.

 

Thanks for the info and great pics! I ordered a set of Hooker headers. I also ordered a complete chambered exhaust system from Allens Stainless Exhaust. Wish me luck!!

 

I hope the exhaust works for you. Do they have a provision for converters? Is it dual?

 

I am not gonna use cats, this is the last year the car will have to do the emission thing and I will get it inspected before I change the exhaust.

 

on a similar note...
my mechanic told me that if a production model was made without a cat the year of a car...the car didn't need a cat...?
any input on this?
ie if chevy made a 1975 vette without cat, any pre75 wouldn't be required to have one to pass emmissions (maybe this is just for MS?)

if this is true...anybody know when the last year a vette was made without one?

 

If the car left the plant without cats then it will never require them. 74 was the last year before cats i believe.


[Modified by Stewart's74, 4:21 PM 12/2/2003]

 

So yall are saying that I can't put a true dual exhaust system on my 81 unless I change out my tranny crossmember?

 

If I am not mistaken, you can use a tubular BTO crossmember made for the 200R4 that will fit for the th350. I will sell my stock crossmember from my '79 if anyone is interested.

 

Well, there is a way to do it, as long as you do not want to run converters. That is to have both pipes go under the crossmember under the passenger side. As it is now, you have 2 pipes from the engine. The drivers side turns behind the trans and meets with the passenger side exhaust in a screwed up "y" pipe before going into the converter. You could run two pipes side by side through that route and then split them at the back where they split now. You would have to replace both pipes all the way from the manifold / header back, and the two pipes under the passenger side will be a tight fit, but they do work.

I would recommend at some point the two pipe are either connected by an H or X pipe or that the two pipes be siamesed together so they have a connection between them. The purpose is to help increase some flow and scavenging effect but it also helps the exhaust tone. By putting a H or X pipe in you get a more mellow tone and helps to eliminate the popping and banging when you let off the gas at higher speeds.
I would also recommend that the pipes have a heat shield over them or use header wrap all the way from manifold back to behind the passenger area. The stock system has some shielding to use as an example.

Mid-America makes a system that supposedly bolts in that does dual exhaust from the factory manifolds back down the passenger side as I mention above. I however have not heard any good words about this system. Many complain of fit and having to have an exhaust shop doing most of the work any way (doesn't save any money then).


If you want to run converters, your S.O.L. with the stock crossmember.

 

I chose to modify the existing cross member on my '80.

Notch the cross-member in the desired location to allow clearance of the exhaust tubing. Fill the void by welding in a short section of sliced exhaust tubing. This setup makes removal of the exhaust system much easier. This cross-member was also modified to accept the 700R4. Making it pretty is optional.
These modifications were easy to do and the only cost was a little time.