Advanced Engineering Tech - Exhaust Volume/Back Pressure Question

Is it possible to run a rectangular tubing for an exhaust? If it has the same flow volume as a 3" round exhaust will it have the same type of back pressure? The reason I ask is because im lowering my car and I have custom side pipes and they have issues with scraping the ground at current height. So I figured if I lower the car 1 3/4 in the rear 2" in front I can make it back running a 2"x4" (equivalent to 3"?) rectangular tubing instead of running the 3 1/2" round side pipes.

I doubt you would see a difference in performance going to the square tubing, but I did read a good writeup a while beck about square vs round tube flow, and the same size volume round tube outflows the square tube

Back pressure is NEVER a good thing. You gain low end torque from scavenging, a process in which after a section of gas leaves the head the vacuum behind it helps draw the next section through. I hear a lot of people say open headers is no good because their is no back pressure, this is incorrect. Open headers cause a loss of low end torque due to a lack of this scavenging effect. So the real question is how will switching to rectangular pipe effect scavenging? I would assume that you would lose some power from the exhaust gas and the vacuum behind it mixing, especially at the transition from round to square, however if you use square pipe for only the last 1/4 of your exhaust system the power loss would be negligible.

I believe what you want is oval tubing, correct?

I ended up crushing 3" pipe down to oval on a front wheel drive car one time to run under a flat floor for ground clearance...wasn't a performance beast though...1.7liter V4 with a wopping 78 HP

I believe what you want is oval tubing, correct?

Good idea, I completely for got about that, oval will yield better results then square. In fact I may end up using some for my 300zx, to minimize the chance of scraping before the exhaust splits in the rear.

As long as the hydraulic diameter is the same you should be just fine.
HD=4*Area/perimeter.

The only down side is Oval Mandrel Bends are rather expensive.