Building mandrel bent exhaust
 

Have any of you guys built your own mandrel exhaust? I had the Mid America Direct bolt on dual exhaust, but have plans for a full mandrel system. I have the Dynomax Ceramic coated headers and they hang kinda low(I have fiberglass springs on front and back and I have it lowered to a nice stance). I'm thinking I'm going to need a 15 degree upward bend right off of the collector. I'm also going to go with an X-pipe. Most exhaust systems have pipes that slip into each other, but on "Cut, Chop, Rebuild" they butted a system together and welded it. Seems that the welds would go through the pipe and glob up defeating the purpose of the mandrel pipes. I have a good Mig welder, and I plan to decide what bends I will need and probably order them from Jeg's or Summit-or if anyone can suggest a better priced retailer. Any advice?

Yup, done it myself. With Dynomax headers you'll need a 15* bend to bring the exhausts level, as you say. The only other bends I needed were right at the back for the mufflers & were 85* (I think? Check the archives, I put a full description in a post). Rather than describing it all I can send you a picture (IM your email address if you want one). I expanded the pipe ends so that they slotted together (& allowed for some "fine tweaking" when fitting). This also allows me to remove sections to give access to things without having to take the whole system off (taking the whole system off isn't difficult, but getting it back on with the mufflers sitting level, pointing straight back & symmetrical is fiddly, especially with 4 tail pipes).
The lowest part of the system is below the driver seat pan & gives 3" clearance to the ground. It will be better for earlier years as my floor pan is lower due to an electric seat (some would say that I should have an electric chair fitted :lol: ).
I used an "H" pipe instead of an "X" mainly because it was easier to make. Additionally, the exhaust gas has a more or less straight run out of the collectors through to the fierce bends to the mufflers with an "H". With an "X" there would be a more tortuous route, which may negate the advantage an "X" has over an "H" (well, that's my story & I'm sticking to it!!!! To be honest, an "X" would have been a lot more work). The x-over pipe also helps keep the whole system locked rigidly in place (my one ****le with the MA system for the '81 is that it jiggled around a bit & occasionally "clang" loudly over bumps).
My bends were done by some people that make the exhaust systems for some F1 cars (you should see their stuff - pure art in pipework, the Headers for a Ferrari were incredible) & they made such a nice job of the bends that I polished the entire lot. If you want the pic you'll see how much mess one small oil leak can make in a year :mad:
:cheers:

I built my stainless exhuast out of pieces. The 90's can be cut down to any angle you want. I did tig mine together, being stainless but it is the only way to get a really tight mandrel bent exhaust.
I have access to a very very good mandrel bender and we couldn't get the tight back to back bends we needed.

I can't find the thread you put up about your exhaust UKPaul. Hey Norval, did you butt the pieces together?

Good thread, Paul if you send any pic's out include me too and send the crosmembe again with it. I can't find that file anymore.

Norval, while we are on the subject. Would you use the Camaro headers again or the Corvette?

Thanks Y'all, jim

TTT

Have I sent pics to everyone that needed them??? Sorry if I've forgotten anybody, things are a bit manic at the moment. Post or IM me if you want pics.
Mike, the bends at the rear are 85* & there's one immediately after the collectors of 15* that bring the system up level with the underside of the car. As I used a pipe expanding tool to expand the ends of the pipes I had a bit of adjustment when slotting the pipes together, so 15* & 85* are approximate bends as the pipe joints could easily have added/subtracted a few degrees from these angles. If you need any more info just email me again.
:cheers:

You have to butt weld the peices together. I had a whole series of 3 inch madrel bent 90's and just cut out the pieces I wanted with a chop saw, butted them together and tig welded them.
Came out really nice

Norval, while we are on the subject. Would you use the Camaro headers again or the Corvette?

The problem with corvette headers is the collecters are turned inward towards the transmission. I wanted to keep the heat as far from the transmission as possible plus I was not going to use the existing cutouts in the crossmember. I wanted them outboard more and 1/2 moons so the exhaust can pass underneather.
Camaro headers run the collecters stragiht back, which is desirable in my case or if your existing headers are not plated cut the collecter on a slight angle just back from where the 4 tubes come together and rotate the cut until the collecters point in a better direction and weld it back together.
I would never keep a stock set of corvette headers if I could not modify them for a better angle.

I wouldn't worry about the weld 'glob' inside the pipe unless you are a real hack welder. I made my headers and exhaust all out of butt welded U bends and the insides are plenty smooth. And thats using a torch. ( not stainless obviously)

Summit is not the cheapest place to get U Bends / L bends. Shop around a little.

Also Slip fit pipes are a pain. I have flanges on all my removeable joints. I only loose about 1/4" of ground clearance and they actually come apart when I want them to. With an aluminum gasket it's a piece of cake.

Good info :thumbs: