I've seen setups where 3" piping is run under the Dana rear end. I've also seen them split and run under the inside of the rear control arm. (I suppose it's possible some have even been 3.5" on major builds?)

My question is mostly about clearance advantages of either routing? Doe people choosing to split and go under the control arms do so to avoid contact with the diff in some way? Seems like straight down the middle would get it up the highest so I'm probably not thinking of something for those who split it apart -- and ran it under the control arms.

(Note: One reason might be to lessen 90 or near 90-deg bending)

 

In my opinion it is better to avoid moving parts like the control arms. I run dual 3" under Dana 44 and no problems at all. With camber relocation brackets the control arms move down and then it is much more space under the rear end.

 

I got some 3" round to 3" oval transitions with V-band clamps on one side, welded a couple of 3" oval pie cuts, and routed under the diff so that the ground clearance was increased. Not cheap and you need to weld stainless, but I think it worked out well, especially with the rest of the exhaust system. Learned to weld 0.050 thin 304 stainless tubes, backpurging, fun stuff... then I ran a 1/8" thick diffuser panel underneath (best place for ballast, a heavy aluminum diffuser low and near the rear axle)

https://www.summitracing.com/parts/grn-313532
https://www.summitracing.com/parts/vpe-13170
https://www.summitracing.com/parts/vpe-13571

Probably didn’t gain all that much for the effort, but at least the rest of the 3” exhaust was also tucked up a little bit better as I could aim it closer to the two areas of the diff that provide a little more room

 

 

Instead of a pair of 3" pipes I run a single 4" on my '84 turbo and my '69. The four inch pipe flows well and is lighter and packages better than two three inch pipes. On the '84 I just run that single pipe out to under the license plate for track usage, but on the '69 I wye the four inch to two three inch pipes under the spring and up to the mufflers.

 

Mine drops to 2.5" right at the axle and goes out the rear that way. It probably doesn't hurt anything but with more power wouldn't be ideal. My 84 is very low for whatever reason even though it measures to the manuals ride height specs... but that section of 3" hits a lot. Probably the **** NJ roads.

 

Part of the reason I was curious is a diagram of a Vizzard exhaust that (tho low-rez and shadowed), appeared to split and run under the control arms. It MIGHT have been 3.5" tubing though as the setup put out 700+hp in a C4 (20yrs ago). Looking at mine I didn't see the reasoning for that routing.

I recognize the j-piped mufflers in your picture. I almost bought a set of those but (from early calculations) thought the j-tubes were too short. How do they work for you? ***

***I've actually spent a TON of time listening to exhaust setups and [recently] looked into j-pipe formulas. Apparently, there's somewhat of a lack of concensus or lack of understanding. I'm still not clear and have wondered where to create a meaningful throad on the topic. Why? I get the measureable frequency to eliminate AND the 1/4 wave theory. The confusion comes in the conflicting opinions on the lengths necessary for cancellation on the number of cyinder (vs not) and (IMO) whether that changes if placed after a balance pipe. If my recent assumptions are born out, a shorter pipe (as in your picture) probably works OK and could even be a hair too long? The other interesting behavior is a harmonic 75% of the target frequency to be attentuated should also be affected. (Closed pipe harmonic resonance). In short, I could see 17", 34", and a shorter pipe length where the harmonic is cancelled/lowered -- by using a smaller/shorter "package".

 

I don't know yet. Haven't quite reached the engine-run stage of the project. I figured I try it and evaluate the most offending frequencies, and then it may be easy to change the length. Most issues are indeed at lower frequencies, but I didn't test (I just needed an exhaust system for now) I've purchased some stainless 3" straight through resonators from them (1320) in the past, and was very happy with the quality, materials, performance, price.

The best sound would likely be a large/long oval shaped 2 into 2 resonator right there I suspect, rather than the individuals, and the length of the resonator sort of works the same way as Helmholtz but 3rd wave. I figured I try this instead and it may be easy to change the length. I suspect it will be VERY obnoxious, and after break in, I have some high flow 4" cats to install behind the header, we'll see how that sounds.

Point was a 3" oval... it's basically a 3" round that's squished to an oval shape, let's say approximately 2" by 4" so it shouldn't flow as much as a round 3". Therefore it's a fitment excercise to provide a 1" additional clearance at the diff, and 1/2" additional ground clearance for some of 3" round in front of it (essentially the same as the OEM 2.5").

 

On the J-pipe thing... my muffler eliminators are two pipes Yed together where the inlet of a normal muffler would be. I plug one outlet per side (effectively giving me a single 2.5" outlet and the other acts as a J-pipe.) And end up with an interior as quiet as a corolla... depending how you want to measure it it comes out to ~16 inches. I haven't run the numbers but that's about 200hz which sounds about right?