Lets talk mufflers

[Road_Runner]

I'm not sure what you mean by "back pressure velocity", but scavenging is a function of velocity and mass flow rate.  To get good scavenging, you've got to keep the velocity up. Cooler gas means higher density which means a smaller diameter pipe is required for the same mass flow rate at the same velocity.  Twenty years ago I could have done the fluid mechanics equation to show this, but brain rot has set in.

That being said, you get into restrictive compression bent tail pipes, this theoretical stuff pretty much goes out the window.

Interesting idea about stepping down to 2 1/2 tails, I had thought about doing this on the Roadrunner at least right before I plugged them into some NOS tips I have.  How did you accomplish the drop in pipe size: are mufflers available with 3" in 2 1/2" outs or did you put some kind of 'step' pipe in after the mufflers?

Thanks, Jim

[PlumCraZRT]

Trying to gain power by putting a 2.5" tip on a 3" exhaust is a wasted effort.  A 2.5" exhaust will provide superior torque for the reasons 471_Magnum mentioned: you get a higher velocity for the same volume/mass of air through a smaller pipe dia (mass flow rate=density*area*velocity).

The exhaust pulses which are responsible for the increased scavenging will have an "amplified" velocity with a smaller diameter pipe, giving you greater torque (at the expense of high-RPM power).  Putting a small(er) diameter tip on will do nothing to the system since the exhaust pulses have largely normalized in the mufflers.  I doubt it really adds any back pressure, and it certainly will not increase exhaust velocity.

[MJS73]

I have the Accurate Exhaust repro exhaust system (with resonators) from the headers back and it sounds nice without being obnoxious.

[ntstlgl1970]

I have 3" all the way out the back through stock tips with magnaflow mufflers and while it sounds really good, it's borderline too loud. I'm going to try 2 1/2 pipes after the mufflers and see if that helps - if you get the preformed flowmaster ones from summit, they are free shipping right now...