just like the title says looking for some people that have run 3.5" dual exhaust. specifically in the area around the front inner subframe. also going around a th400 trans mission. plan on building an custom crossmember to give me as much room as possible.

and before it gets said yeah im going to need some big pipe down there to allow a 540 bbc to exhale. as much as I like the idea of dumping the exhaust out the fenders im not sure how much ill like that on the street.

 

Oval exhaust tubing

 

I know ive looked into it. stuffs expensive tho

 

You would have to cut the trans subframe and notch it to fit 3.5” if you want any ground clearances. I went 3” under and around the subframe for my 555 and i know its killing the na performance but its only temporary as its going turbo soon

 

What kind of power will you be making? You might have to live with a dual 3" and plan on running cutouts when you need the full "go".

 

Oval is about your only good choice around the trans. you can go back to round after.

You also might want to consider a relocated panhard bar

https://www.foundersperformance.com/...v=7516fd43adaa

 

The problem is getting a longtube collector of 3.5-4” with right length and transition to oval by the crossmember. Theres not enough room if you have a big auto trans. Maybe with a t56 or something. I’m not sure.

But on mine with custom fabbed headers i can fit a 3.5” collector with good clearance but have to transition quickly to 3”

 

You can also make your own oval pipe with some 2x4s and a hydraulic press

 

you should look very closely at what the actual gains would be, going from 3" to 3.5", after you do all the mods are you gonna get 10hp? 20? yer gonna have to do a lot of testing to maximize, that costs mucho $. If you have a full drag setup, you wouldn't have to worry about room, so I'm assuming the suspension hasn't been changed much. All that torque is not going to be accommodated by the suspension, so you gotta ask yerself, what is it for? so you can bench race? or just sit and haze the tires? If it's to make noise, get the cutouts, you can make 3" fit well.

 

On a healthy 540 bbc I suspect gains will be pretty healthy. I kinda want to test it on my own 555 as so far the power numbers seem low.

On a 14:1 comp 540 that was making north of 850 flywheel saw 40-50 hp on open 4” headers vs full dual 4” exhaust with mufflers

I have seen 20’s whp on some muffler deletes on late model cammed ls3 stuff. I think the gains are there to be had

 

based on my math im going to need the 3.5 stuff. shooting for 750hp at the crank. suspension is stock style but all tubular also the torque arm will be a little more out of the way its a Midwest 9" with his third gen arm. headers will be custom as well so that should help with collector location. main purpose for the build is drag week and I want to be competitive in street machine eliminator. hence bbc/th400 bracket car lol. it doesn't see much street time but it is nice to not worry about dragging exhaust when loading and unloading from the trailer.
seeing orr's pictures makes me think down and forward out the fenders really might be my best bet.

 

Despite the way it looks the 3” clears well. Cutouts there at collectors would help a ton i think. I want to test it but i likely wont. Starting turbo fab

 

im not sure theres room for a cut out there. I could find room for them with my small block and hooker long tubes with out hitting the frame.

 

3.5" exhaust on my 1988 camaro.