3" exhaust in a 79

Belgian1979vette

Well-known member
Joined
Apr 4, 2008
Messages
1,706
Location
Koersel/Belgium
I'm converting from a 2.25" system to a 3" system and ran into an issue I'm not quite sure how to solve.

The current system is a dual system with the original transmission bracket for a dual exhaust.

I run full length headers, so I need to be able to remove the pipe. This entails making sure I can move the pipe coming off the header and going through the transmission crossmember a little bit back for removal.
In my 2.25" system, I solved that with a 2.25" ID diameter pipe welded at the end of the pipe coming from the header and there were no issues as the 2.25 ID fits through the crossmember just fine.

With a 3" this is a problem. A 3" ID will not pass under the bracket and through the crossmember. Even a 3" OD is hitting the crossmember.

I've been looking at modifying the bracket some (cutting the edges and bending it upward so the pip sits somewhat higher (I still have clearance on the top of the bracket) but on one side the reverse rod seems to be in the way. How did you guys solve this one?
 
On my 2 1/2" system, I have a pipe joint immediately behind the crossmember. It's female-to-male (backwards) because of how close my x-pipe is to it, but if you have room it could be male-to-female. I poke bits of header wrap into it and then shove exhaust pipe cement into it before I clamp it with 3" long wraparound clamps.

My support bracket is just a flat steel piece (supplied by SST with my tranny) which I bent a little to get the location right and then I formed it to fit the pipe radius using the regular exhaust pipe clamps.

I undo the header flanges & clamps and wiggle the short sections out by pushing the rest of the system back by undoing the hangers at the back of the car and supporting it there and around the driveshaft (at the x piece) with baling wire, without having to remove the whole system.
 
i switched cross members for the 700r4 let me find a picture.... i bet it would work with your set up with some massaging

mine was a 2.5 system from corvette central and a new crossmember from bow tie overdrives

00000165.jpg

getting close let me keep looking

00000321.jpg

00000322.jpg

00000947.jpg
 
Last edited:
Meanwhile I have massaged the bracket and so far it seems to work. On to the next issue, fitting a lambda sensor bung to each primary and getting the magnaflow X to fit somewhere.

Why is there always not enough room on these cars.
 
Meanwhile I have massaged the bracket and so far it seems to work. On to the next issue, fitting a lambda sensor bung to each primary and getting the magnaflow X to fit somewhere.

Why is there always not enough room on these cars.

I used an H pipe. just couldn't get the clearance figured out for an x pipe
 
Why a lambda bung on each primary? Or do you mean collector? A 2.75" pipe should be more than enough for most anything you can throw at it and these cars are super easy to build exhaust for, it's almost a straight shot back.
 
The EFI is currently a sequential. So basically you have the ability to tune each cyl seperately.

I've built an airbox around my stacks so I could use an airfilter. This causes some pulsations in the inlet tract and what I witnessed was imbalances in flow between various cyls, depending on load, rpm, etc. Not one cyl is equal.
This is not counting other small things like small differences in flow between injectors etc.

With 8 WB's you can easily assign each cyl to each individual lambda and have the ecu do ego making them all equal.

All it takes is welding in the bungs, using an IO-extender for MS and 14point7 WB's.

I'm still a bit uncertain if I will go to the 8 WB's as there might be a trend in the deviations between cyls and I might as well be able to use the trim tables. But, that will still require some extra WB's and the bungs in each primary to see what that cyl is doing and then switching the lambda to another cyl etc.

As for the exhaust : not exactly a straight shot back. Want to go through the holes in the crossmember and then below the diff to prevent the tubes from touching the camber arms in the rear.
 
Last edited:
This is 2.75"

24ddeab6aa7554.jpg

24ddeab6c37045.jpg

That's more than enough exhaust for about anything you can throw at it.
 
While I'm done fabricating/welding on the exhaust. Have a bullit style muffler (4") in the middle and the magnaflows in the rear with an X-pipe below the rear axle.

Have not had much chance to ride with it, but at idle it is doable, but if I step on the throttle just a bit it's becoming loud, like scarry race car loud.

The good news is the VE has improved some 7% at idle alone.
 
Top