Ever wondered what was inside your muffler?

[Ron]

<FONT face="Comic Sans MS">In my quest to understand Vipers more fully, I acquired a "donor" stock rear muffler assembly and cut it open. What I expected was a maze of baffles forcing the voluminous exhaust gases along a tortuous route. What I found however, was a straight through design, completely unbaffled and unrestricted, with a crossover of sorts in that the inner tubes were perforated thereby allowing a balancing of exhaust pressure between the two cylinder banks. The only apparent muffling effect was the gun silencer type of fibrous packing material stuffed around the pipes (but not in the exhaust flow).

My question is, does this design of muffler really provide any measurable backpressure and if not why would it's removal provide any horsepower increase? (there have been quotes of up to a 12 horsepower improvement with muffler removal)

As for sound improvement, it would appear that the removal of the fiber and a resealing of the twin skins would accomplish the same result as adding a rear muffler eliminator, i.e. a louder exhaust note.

What am I missing here? </FONT f>

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[C O D Y]

Great pics! Thanks

 

[jeremypittman]

Yes, Very nice shots. Thanks for taking the time....
You think the side mufflers on my car would be the same?

Jeremy

 

[Ron]

<FONT face="Comic Sans MS">Jeremey,

Though I doubt the sidepipe mufflers are similar, I really have no idea.

Perhaps there is a scientific reason why a perforated pipe dimishes flow and creates backpressure, etc. but on the surface it sure seems like this muffler shouldn't hurt performance much....</FONT f>

 

[Hisser]

Excellent pics and thanks. I think the answer to your question concerning why removing the muffler creates the horsepower is because: note the holes throughtout each side, yes some gases go straight through but a lot goes through the holes and creates a turbulance and therefore cannot escape expediently. This is only my opinion, I am sure there will be others.

 

[Rich Detert]

Jeremy,
When I took off the factory mufflers on my 94 I cut the inlet end open so I could save as much as possible of the inlet pipe.

What I found was that about 1-1/2 inches inside the main boby of the muffler the 2-1/2 inch inlet was reduced down to 1-5/8ths. This causes a serious restriction in the exhaust. The muffler is not a straight through design either. I wish I would have taken pics before I threw them away.

I changed mine over to glasspacks for now which definitely improved the sound and reduced the restriction in the exhaust.

The sound is good, but at some point I'd like to put better mufflers on it yet, probably Borlas. I got to drive Rob McPhee's 93 with Borla mufflers on it. I liked the sound better than mine, they both have some resonance but at different frequencys. The drone on the Borlas is at a lower tone than with the glasspacks.

 

[Kurt 97 GTS]

Jeremy,

Rich is right on the money in his description of the mufflers. I took a good look at mine when I removed them and was amazed at how restrictive these mufflers really are!! I immediately noticed increased throttle response, which was great. Also, I don't know the exact weight, but the stock Gen 1 mufflers seemed very heavy.

I'm still thinking about the borla's. Rich, do you really like the sound over your glasspacks?

 

[JonB]

"THE YEAR MATTERS" a lot !

The USA Gen-II (different from export) is exactly as Ron kindly posted, and the little holes act as "vortex generators" as Tom describes, creating slower velocity due to turbulence and expansion. Lose the rear muffler (alone) and get 9HP. Add the K+Ns (or MoparPP) and smoothe hoses and gain a total of 15. (20 if lucky.) Remember, Gen II ALSO has baffeled resonators in each sidesill, and a moderate-flow OEM cat.

And the 1998+ OEM tube headers do flow a bit better, with NO "claimed" HP. But conventional wisdom says they should provide 3-4 HP.

Gen-I step-down mufflers are by comparison a cork! This is why, in relative terms, Gen-I gets a HUGE bang-for-buck benefit from a simple, inexpensive, hi-flow cat and/or a hi-flow muffler, when coupled with the same hoses hoses/filters.

Great sound aside, the recent dyno results of the brand-new 3" CORSA system, vs. the 2.5" systems out there, pretty much prove that SOME backpressure near the motor is needed to achieve max torque and max HP in "less-modified" or stock motors.

JonB

 

[Rich Detert]

Kurt,
I do like the sound of the Borlas better, the lower frequency drone was easier on my ears. On contrast to that Rob McPhee said he liked the higher frequency of the drone that my glasspacks had, it bothered his ears less.
Part of that could be that I know there are some frequencies that I've become deaf to (my wife just thinks it's selective hearing

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).

I'd like to hear what the Dynonax bullet mufflers sound like on a Viper, otherwise I'll probably go with the Borlas.

 

[Tom and Vipers]

Why a perforated pipe reduces flow .... my 2 cents:

If you draw a control volume around a straight pipe, there are no reactions, only piping loses.

If you draw a control volume around an elbow, the change in direction results in a constant reaction on the elbow, that reaction is a net pressure profile on the elbow surface so that means delta P. So now we have a delta P associated with the elbow that wasn't present with the straight pipe. This is backpressure.

Think what happens to the flow when it goes thru the perforations. If you could see it with smoke for instance you would see radial jets relative to the pipe axis.

These are 100's of little elbows with associated delta P's.

Note that there is no net flow in the muffler body, however, the pressure pulse results in a higher velocity jet going out of the perf with a lower "backwash" jet going back into the pipe. The reaction force is proportional to velocity squared. So there is still a net reaction like the elbow analogy.

Any of you piping engineers may be able to expound on this.

I may be completely wrong, of course.

Tom

 

[9 seconds]

What goes out of the perforations will have to go back in somewhere.