Muffler, Resinator or straight?

[Alan Baker]

Hi,
I think the muffler on my 84 Eagle 6V92 TA is nearing the end of its life.
I noticed several caoches at Bussin' this year with a straight pipe. I remember Dave Galey mentioning that he had to be sure to cut off his Jake when entering his neighborhood as he never ran a muffler.
I think I'm going to try out a straight pipe, all I have to loose is a couple of hours of my own labor.
What do you think of this idea? Has anyone got first hand knowledge of a 6V92 running sans muffler?

Alan Baker
1984 Eagle 10
6V92 TA running 350 HP

[Bob & Tracey]

We ran our 8V71 without a muffler and we would set off car alarms as we passed, too loud for me.

[Chopper Scott]

The turbo in your setup will help but as Bob stated, I also tried the straight pipe on my 8v71n and it was unbelievably loud. I put a straight through 4" muffler on it intended for race cars and now it is unbelievably loud.... Luckily for those staying near me I am never the first to leave!

[baker4106]

Alan:   When my muffler went bad I replaced it with one from AERO company, I think.   It was a 5 inch straight thru and muffled some but the Ohio State Police didn't like it.   Before I installed it I talked to a bus buddy with a 4107 with a 6v92ta and he had one on his and it wasn't that noisey.   The turbo will cut the noise down some.   Saw that same muffler at Perry this year.

[Kenny]

Some what related to this, is there much of a gain in power when running a straight pipe on a 6V92?  Kenny

[Iceni John]

Why not just leave the present muffler in place, even though it may not be working well?   As long as its interior baffles don't get dislodged and block the exhaust flow, what harm would result from running a muffler that's at the end of its life?   It should still muffle slightly better than having no muffler at all (as long as its baffles don't buzz and resonate at certain revs, like what happened with a previous old car of mine that would make a delightfully fruity exhaust sound at 3000 RPM!).   Just make sure that exhaust gases are still being directed where they should, and not out through rust holes and against anything flammable.

John

[luvrbus]

Better check your DD bible they require some back pressure

good luck

[Chopper Scott]

I must have enough back pressure cuz the bus seems to run better. Maybe it seems that way because nobody follows me anymore!!!!

[Tom Y]

If you decide to buy a muffler I have a new old stock 5" inlet on one end and a 5" outlet on the other. Not sure what it will fit. 45.00 + shipping, and it is heavy.  Tom Y

[Alan Baker]

Its my understanding that DD don't need too much back pressure.
My muffler is still muffeling, I'm starting to leakage at seams.
I know the 8V71's make a lot of noise. I tried the same thing Larry did when his bus was mine and went back to stock.

Alan

[pabusnut]

When I transplanted an 8V71N into my GMC transit 5301, there was only room for two shorty mufflers and dual exhaust(without going wild), and it was definitely loud, but not obnixious.  I did notice when the throttle was open wide and I was near the jersey barriers on the highway, that I could easily hear the exhaust rumble in the drivers seat w/windows closed!  BUT--IT DID SEEM TO HAVE MORE POWER THAN IT DOES NOW IN MY GMC 4905(same engine now transplanted into newer coach).

Steve Toomey
pabusnut

[JohnEd]

Better check your DD bible they require some back pressure

good luck

I have heard this many times about DD 2 strokes.  I have also heard that less flow resistance to flow will yield more HP and MPG in the INLET and EXHAUST.  The statement that a DD needs some back pressure and won't run "right" without it seems to fly in the face of that "other" logic.  I have heard both so many times from credible sources I won't argue with either.

Mt only experience is with 2 stroke gas engines.  The straight thru exhaust is whjat we would have called a "blue-eeey" pipe.  It made a sort of bluey sound and it was basically a megaphone on the end of a short piece of exhaust pipe.  It was very loud but not ear splitting.  It was discovered that a properly designed "expansion chamber was a far superior performer to the Bluey pipe.  The thing about the Bluey was that that megaphone part, with it's expanding size, would actually create a "negative back pressure' wave to be reflected back to the ex port.  If properly designed and sized that wave would "scavenge" the cylinder and more completely flush all the spent ex gasses out and allow the engine to breath a fresh and fuller charge with every stroke.  The Bluey had a big advantage over the straight pipe cause the straight pipe never sucked.

THEN.... along came the expansion chamber.  That was a "system" that scavenged the ex gases and "overcharged" the cylinder both. The Ex was pulled out of the cylinder by the megaphone section of the chamber and then the reverse-megaphone section would create a brief positive back pressure pulse that would "stuff" the last puff of scavenged air, fresh by that point in the flow, back into the ex port.  Between the inertia of the intake air rushing into the cylinder and that brief positive (back pressure?) pulse, the air was stuffed into the cylinder and when the ports were closed there existed a supercharged condition in the cylinder.  Voila, and you got a 50% power boost...maybe. All depended on the timing of those suck and blow impulses and their relative intensities and how far apart they were.  There is more to it...isn't that always true....and the math involved is daunting for anyone that isn't well versed in "The Calculus"....but it is comprehend-able. But, "some back pressure is needed and good"....that, take alone, doesn't make sense.  And not that I can't accept a truth without full comprehension cause that would be a lie.  Just look at all the stuff I don't understand but accept as true about "women" that is based on results alone.

So as I understand it:  Free flow to the max....largest diameter ex pipe you can connect....freest flowing muffler you can buy and a straight pipe is the freest.....min bends in the pipe....shortest pipe length you can accomplish and get the gases out of the engine bay.  OK?  Now in conclusion "SOME BACK PRESSURE IS GOOD AND DD SAYS SO".    Feels like an Abbot and Costello skit..."Who's on first?".  This keeps coming up for me and I hope there is an answer lurking out there if Clifford can't help.

And the expansion chamber sound level?  Absolutely ear SPLIT  TING and illegal and should be...at least without a sound suppressing end....that I never used until forced.  Outlaw! But quick about it.

Be gentle with me but WT?...over.

John

[JohnEd]

Steve,

The lower the freq of the ex noye the more difficult it becomes to "silence" the thing.  Witness the V8 with itsd clever little "cross-over pipe right behind the engine.  Its only function is sound suppression as far as I know.  What I am certain of is that if you leave that little jewel out of your system the engine is defining and illegal in all 50.  The old Jags had a "split six ex that had two runs each serving three cylinders each and remember how they roared with that peculiar note?  When you ran a split 8 system you created two 4 cylinder systems and my math says that would be very loud and difficult to control.

Brings up the question of "were the old 4 cylinder and IL 6 cylinders much more noisy in the day?  Where does the term "scream'n Jimmy" come from and why?  I am barely old enuf to remember the noise along the highway but little else about it.

Anybody?

John

[luvrbus]

DD has a min and max and that is based on what injectors your engine has, their not going to make any more power with a straight pipe as they do with a muffler,if your going to do anything with a 8v71 use duals with mufflers like the Eagle bus did.

[JohnEd]

I am a believer in all things "Clifford".  Duals sounds good to me...pun intended.

Thanks

John