Modifying subframe for exhaust

[super_kev]

Hi all,
I didn't see a chassis section on this forum, so I posted this here since it would be dealing with the way the car handles. This forum seems for those who modify their cars more than the usual motor and suspension upgrades, so hopefully I'll find someone with some experience or knowledge of this area. Basically, I'm looking to notch my 3rd gen (Trans Am) subframe and install a couple short sections of 4" tubing with 1/8" or 3/16" wall, and bracing it with 1/8" plate. The reason I am doing this is because I need to run exhaust tubing through the subframe in order to save precious ground clearance due to the T56 transmission crossmember.




There are plenty of pictures and sketches in my original LS1Tech thread to help illustrate what I want to do. I didn't feel like posting everything with the replies and such, and your forum here won't allow me to display attached images in the post itself (displays them as links instead), so I said forget it. Modifying subframe for exhaust. I am not sure if you have to be a LS1Tech member to see the pictures, so let me know. No need to post your replies there, you can go ahead and post them in this thread.

Thanks.

[MrQuick]

From the looks of your, drawing is the dual pipes going to go into a "Y" pipe then to one pipe? Good idea but over engineered . An easier way to go would have the "Y" pipe before the frame then one pipe through or pass along the trans or through the frame. is the x member that large?

[super_kev]

Yes, dual to Y to single. The crossmember isn't as large as it is tall. The way it's built (and the way the T56 sits in the tunnel) leaves no room to pass the pipes along the transmission and over the crossmember, and there's not a lot of room for a pipe to go under the transmission, hook up to the other and then go out the subframe on one side. It would be easier for dual subframe outlets and then a Y after the tranny to the single going through the tunnel.

[MrQuick]

Are you running full length headers?

If you are running emissions style shorties the how about running the pipes around the frame near the lower control arm bracket similar to what was done as stock. But then you would most likely run into problems with your subframe connectors.

[super_kev]

I'm running stock '02 manifolds & cats. The LS1 oil pan is equally as low as the stock k-member, and is wider than the std. 350, so I can't run the x-over pipe there or pretty much all the way back.

[Norm Peterson]

Is there enough room to run a crossover under the front of the transmission / immediately behind the bellhousing? That's sort of the way my '79 has been plumbed ahead of the single cat (and under the Tremec 3550). Although you don't get completely equalized exhaust pulsing in/after the Y, it's arguably better than straight duals and enough different to have a distinctive sound. Being that close to the engine, you'd ideally have a short flexible length similar to what you find on many OE FWD systems, particularly with headers.


Norm