I want to make a custom cross member to tuck my dual exhaust up a bit and I've seen it done many times on Horsepower TV so I think it's time to give it a shot. Any tips as far as what to avoid and what gauge steel I should be using? It's for about a 350 hp car with a 700R4.

 

I made mine similar to a Spohn crossmember.

Support the tranny at the height you want it. Remove the old crossmember. Cut some angle iron and drill holes to mount it to the underside of the floor where the original crossmember was. There's extra holes for different crossmembers. Use whatever ones work best. Get some 1" steel tubing with a thick wall. Cut and trim 2 pieces so they fit between the angle iron and are on the front and rear of the tranny mount. Weld a plate between the 2 tubes for the tranny mount to attach to.

The underside of the floor isn't flat and the angle iron mounts are slightly staggered. It's not practical to make a real wide crossmember because there isn't any frame rails to attach it to. If you have SFC that run closer to the driveshaft tunnel, you could attach the crossmember to them. If they run along the rockers, that means an extremely wide crossmember.

I don't think you're going to gain very much for exhaust. You can't tuck the crossmember up any higher than what it already is without some custom bending of the tubes

 

When I make mine (information in a thread below) I used 1/8" wall 1" x 2" tubing. I used a peice of 7ga (3/16" steel) bent in a u for the trans mount. If you look in the thread below 1982 silver state project. I have extra of all of the parts that I made. I'll be happy to sell you some if you see something that you might find usefull.

Send me a PM if you need something.

Have fun. It is easy and great to say I built that.

 

With the 700R being wider than the t5 and t56 you may want to look into adding clearance in the other direction.....what I mean is to drop your cross member down in two spots so you can run the exhaust over it.......if you search you will find some have used the stock cross member and just added to it.....a couple of things to remember when welding under you car.......watch the fuel and brake lines on the driver side.....also take into account the speedo cable on the driver side of the tranny........good luck and make sure you post up some pics....as far as material it will depend on the design.
Mike

 

Thanks for the tips, I'm going to look at it when I can get it in the garage and get a game plan.

 

Ya, that sounds about right but I think mine is just 1" x 1/8" round tubing. You could use a single tube if the tranny mount was gusseted or braced to the single tube. Sort of bend it in a U shape similar to an old G-body style tranny mount. It can hang off the front or back of the tube depending where you position the crossmember tube in relation to the mount on the tranny.

 

I know others have posted a few pictures that might give you some ideas.
Some look like a 3" exhaust pipe that was sliced down the middle, using only half of it per side.
I think Evilcartman did one that looked really weird, like Spohns apparently. Used square tubing on that one.

 

Here is mine....
Mike
https://www.thirdgen.org/forums/fabr...ossmember.html