Does the resonator have any performance function?

[Docwagon1776]

This sounds hinky to me, but I'm curious what the group thinks. Elsewhere, I read the assertation that the resonator on the 6.4L equipped trucks "uses sound waves to help evacuate exhaust gasses" resulting in slightly increased power numbers and fuel economy. This sounds like BS to me for two reasons, one being I could see some claim to low pressure pockets creating vacuum in pulses to do this, but how would sound waves help that? Two, it's so far downstream and after the cat and muffler, could it actually create any pull that would be noticeable through the length of the exhaust?

So I'm thinking this is more internet lore or something they just pulled from their backside, but maybe there's something I'm missing. Anyone aware of any dyno runs with res vs no res being the only difference?

 

[rzr6-4]

For good laminar fluid flow, you want your path to be smooth and consistent. Going from your 3” exhaust pipe to a 5” or whatever it comes out into the resonator, that area will have lower pressure and promote flow, but then you have to squeeze all of those gasses back down into the 3” tail pipe again. I’m sure you would be better off sticking to the solid 3” pipe for max HP. If there was ANY performance benefits, I’m sure racing teams would be all over it.

**I have no evidence for anything I said, but low level physics and racing anecdotes would tent to disagree.

 

[Docwagon1776]

For good laminar fluid flow, you want your path to be smooth and consistent. Going from your 3” exhaust pipe to a 5” or whatever it comes out into the resonator, that area will have lower pressure and promote flow, but then you have to squeeze all of those gasses back down into the 3” tail pipe again. I’m sure you would be better off sticking to the solid 3” pipe for max HP. If there was ANY performance benefits, I’m sure racing teams would be all over it.

**I have no evidence for anything I said, but low level physics and racing anecdotes would tent to disagree.

I think racing teams do this with header tube length, though, right? The exhaust flows through the exhaust system in pulses (vs a steady flow) as the valves open and close and timing the low pressure to the valve opening timing helps scavenge gasses. I get all that and the high view physics of it (as in I get the concept but not the underlying math).

I'm specifically curious as to if there's any truth to the resonator playing any role and if sound waves actually can accomplish anything in this arena. I don't see how it could, but I'm willing to learn something new if it does.

 

[rzr6-4]

I think racing teams do this with header tube length, though, right? The exhaust flows through the exhaust system in pulses (vs a steady flow) as the valves open and close and timing the low pressure to the valve opening timing helps scavenge gasses. I get all that and the high view physics of it (as in I get the concept but not the underlying math).

I'm specifically curious as to if there's any truth to the resonator playing any role and if sound waves actually can accomplish anything in this arena. I don't see how it could, but I'm willing to learn something new if it does.

Yes, there absolutely is a science to the header length and pulse timing. The resonator 10ft down the line after the cats, and the gases already having been merged in the muffler, the resonator isn't seeing those pulses so there's nothing to try and time for any gains.

 

[joesstripclub]

I can't say that I've ever heard of a resonator adding HP. I could see how vs a chambered muffler, a resonator would be less restrictive, but not a claim that it makes more HP on its own.