Ok, some mufflers add about 5-10hp (approx) but if they do, how much torque are you adding? Or do you add torque when you put an aftermarket muffler on?

 

HP = Torque * RPM / 5252
Torque = HP * 5252 / RPM

Can't gain HP without gaining torque.

To really evaluate HP/torque gains, you need to look at the whole dyno plot - not just the peak HP and torque numbers.

 

no muffler is going to add 5-10hp. they probably only add 1-2hp at best. so i assume that torque gains wouldnt be noticeable either.

 

Are you sure about those numbers Billy? For some reason, I thought you could gain one but not the other. How else would those guys be posting those dyno slips with more hp than torque, while the rest of us still have 10-15 more torque than hp? With your equasion, the two affect each other, but if it changes the RPM at which peak hp is reached, then that would allow peak torque to remain the same, be reached at a different rpm, increase, decrease, or any combination of them, as long as the variable fits in that equasion.

 

Brian - To clarify, you can't gain horsepower at a given RPM without also increasing torque at that RPM (with the gain being proportional). It's possible to have a higher peak HP without increasing the peak torque, simply because the peak torque will be at a lower RPM than the peak horsepower.

Example (Lancer):
Peak: 120 HP @ 5500 RPM (=114 lb-ft)
Peak: 130 lb-ft @ 4250 RPM (=105 HP)

Slap on an open exhaust (hypothetical):
Peak: 133 HP @ 5800 RPM (=120 lb-ft)
Peak: 130 lb-ft @ 4500 RPM (=111 HP)

The torque curve has increased after 4250 RPM (or rather, it has shifted and is dropping off slower), leaving the peak torque unaffected but greatly improving top end power. This isn't entirely likely, but possible.

The effect can be more dramatic with high RPM motors (1 lb-ft @8300 RPM = 1.6 HP), and with cars with very broad flat torque curves (the BiTurbo Audi S4 comes to mind).

 

nice breakdown...!

 

math = hard :\