#41299 - 05/08/08 08:35 PM
Re: exhaust note
[Re: Mean buzzen half dozen A.K.A. Hank]
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Ted65Mali
Active BB Member
Registered: 11/04/05
Posts: 62
Loc: Copperas Cove, Texas
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Al, I'm glad you asked this question!! I too have the same dilemma. But it started out with glasspacks. Now I have two Thrush Turbos (Cheapies) and it quieted it down tremendously. But my dilemma is it doesn't sound like I want it to. I was hoping to put in the Flowmaster 50s (knowing they are quieter than the 40s) but now maybe not. I know you like the sound your exhaust gives, but just too loud inside, right? Just curious, how well insulated is your interior? I was thinking of redoing mine to see if it would help. Just a thought.
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#41302 - 05/08/08 10:37 PM
Re: exhaust note
[Re: Ted65Mali]
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$UM FUN
Active BB Member
Registered: 03/03/07
Posts: 92
Loc: Nor Cal
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The longer MAgnaFlow mufflers are very quiet. Wen we did dyno testing of mufflers and found that the Maganflow mufflers also increased some HP. When we put the Flowmasters on we lost HP. They just do a beter job of marketing. Last year I called Flowmaster to get the CFM rating on their mufflers and they told me "that they don't rate them that way", I am not sure what other way would be relevant. Maybe they have changed since, but I have never checked. Tom Hand wrote a book on building Pontiac's for the street and strip. Great book. He also tested 54 different mufflers on the flow bench, engine stand (with professional noise measurements) and at the drag strip. He found the Flowmasters one of the least desirable mufflers available. Kinda backs up my experience on the dyno.
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#41305 - 05/09/08 03:29 AM
Re: exhaust note
[Re: $UM FUN]
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Nexxussian
Active BB Member
Registered: 06/12/07
Posts: 1335
Loc: Anchorage
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If you are just trying to eliminate the drone at cruise and like the sound you have now here are a few things you can try.
Make sure the trunk seals well, any holes in the floor or leaks in the trunk lid gasket will make the drone louder.
If you don't have sound deadening, get some (I have been using the foil faced bubble wrap from Home Depot and Lowes, cheap, better stuff is available, but I gotta start somewhere and for what it costs it works good enough).
If all that is good, try a different exhaust tip. We have pencil tips on one of our cars (FWIW 2 1/4") and we had to extend the pipe quite a ways past the back of the car to eliminate a resonance like you describe (you could try the same). A friend has a similar setup with what I call meat grinder megs. They are straight till about the last inch or so then flare out like the 'meat grinder' velocity stacks. It seems to do a better job getting the noise away from the car.
You could try a small glaspack just forward of the bumper as a resonator.
The H pipe will make it quieter, it will also take some of the rasp and rap away and make more of a gurgling sound.
I have Dynomax super turbo mufflers on my A with a bent 8 in it (OT I know) they are quiet at cruise and have a nice tone when you blip the throttle (or are screaming up through the gears) and don't drone. We mounted them as far back in the pipe as we could.
Are you sure it's exhaust drone? I have a friend that chased an 'exhaust resonance' problem for over a year, before he figured out it was the intake that was droning (not too likely in what you describe, but woth checking out).
This is not conclusive or end all be all, and I'm no acoustical engineer. It's just stuff I have tried or seen/helped friends try.
_________________________
My, what a steep learning curve. Erik II#5155
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#41414 - 05/14/08 06:54 PM
Re: exhaust note
[Re: dmw]
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tailgate
Bulletin Board Only Member
Registered: 12/08/07
Posts: 1
Loc: Victoria, Australia
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If the problem is only at cruising speed in 5th its because the engine revs are at the right frequency to set up a resonance in the exhaust. If so you should find that it will be the same in any gear a those revs with a constant throttle, but because you are accelerating though the band in the lower gears it is not a issue. Adding a couple of resanators will most likly help if not fix the ploblem. Take a look under any car on the street you will see two mufflers, usually the last one is a resonator to fix this same problem.
Pete 
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#42885 - 08/09/08 10:04 AM
Re: exhaust note
[Re: Al]
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Leif
Active BB Member
Registered: 04/08/04
Posts: 154
Loc: Northern California
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Somebody needs to write a book about this stuff, but maybe it's too complicated and the people who know consider it a trade secret. I travel and rent cars a lot. It amazes me the difference between manufacturers. Some (like Dodge) seem to be able to make the base engine sound really good (even if it doesn't go) and others (like Ford), must save the good vibes for top end mustangs. I know BMW actually has some one in charge of "sounds" and is responsible for everything form the exhaust note to the "thunk" when you close the door. It seems like a lot can be done if you just keep trying.
Leif
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