Too bad exhaust systems aren't that simple. The problem is only slightly related to "back pressure." The math that most closely resembles the math of exhaust systems is just about the same as the math that describes radio frequency transmission lines. The pulses that reflect back and forth in the exhaust system end up resembling standing waves in transmission lines. If the engine ran at a nearly constant speed - as a transmitter operates at a nearly constant frequency - it would be much easier. Those resonances in the exhaust explain very neatly the phenomenon of an engine "coming onto the pipe." The intake system is also resonant, and is often tuned to a different resonance than the exhaust to "smooth out" the engine's torque curve. Racing engineers go to great lengths to get intake and exhaust resonances at the same place. The benefit is quite high torque and power, at the cost of a very narrow torque band.

If minimum back pressure were the only goal, you need look no further than the exhaust stubs on the WWII Spitfire. The pipe was only just long enough to get from the exhaust port to the outside air. The absolute minimum back pressure would likely happen by simply removing the exhaust altogether.

Truck,

What size pipe is that that you used?  (great looking pipe by the way)

Yes, very nice work indeed.  I need to practice ... a lot.

justin_o_guy2 wrote on 01/02/10 at 09:08:25:

That's to back fill the weld with inert gases to prevent corrosion and embrittlement.

I plan on changing that boring looking cover. and incorporating an oil cooler in there somewhere.

V, if you're talking about the flange that I think you're talking about, I got two in my garage.  The M50 flanges are identical to the S40.  You can have 'em free if that's what you need.

diamond jim wrote on 01/15/10 at 18:48:52:

I'll keep yours in mind, right now we're checking into what's available straight from the mill and part them off ourselves.