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Exhaust Noise

Hi All
Have a 1988 turbo 930 with dual out B&B exhaust with headers. My concern
is over the high amount of rumbling and popping sound I get when decelerating, is this normal with the dual out set-up and B&B muffler. At this point in time can't really tell if it is an actual backfire but don't believe so, just allot of popping when the gas pedal is let off????

Thanks to all who reply
Old 09-03-2007, 07:20 AM
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The characteristic turbo burble? Normal. Did you purchase the car with these already added? Or is this a mod you've just done, yourself?
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1987 Venetian Blue (really looks like grey) 930 Coupe
Old 09-03-2007, 07:28 AM
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I had a dual-out GHL on my '86 for a while. The popping is likely because the dual outlets let in a lot of air which, combined with a nice healthy rich mixture, ignites in the muffler. This noise was reduced quite a bit when I went with a single-out. The rich mixture is good for a turbo and the popping is normal for a dual-out (or a zork tube for that matter). Enjoy the sounds!
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'86 930 Kokeln IC, K27-7200, SC cams, GHL headers, Fabspeed muffler, Short R&P , misc other mistakes made...
Old 09-03-2007, 07:33 AM
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Noah 930
Purchased the car with the the modified exhaust already so never really had a baseline to compare to, thanks for your knowledgeable replies
Old 09-03-2007, 07:53 AM
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That's the way they are, if it wouldn't that'll be a concern.
Old 09-03-2007, 10:22 AM
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The "cackle" is not necessarily a product of a dual outlet design.
My single outlet muffler cackles quite loudly on decel. The dual outlet prototype that I am running now is actually more quiet and cackles less.

What accents the cackling is a lack of restriction which is a good thing. The more sound deadening material and the more narrow the ID of the system the more quiet (and restrictive) it becomes. Also, a straight through design is more prone to cackle than a baffled design. An empty can, such as the B&B, has potential to be a cackle monster.

You can tune some of that noise out by going more lean on your CO but that defeats the purpose of a performance system. What I do is simply push in the clutch when I don't want to hear it.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8

Last edited by RarlyL8; 09-03-2007 at 10:48 AM..
Old 09-03-2007, 10:45 AM
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Should have heard the old turbo formula one cars. Sounded like gunshots.
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Old 09-03-2007, 12:17 PM
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You might find that you can significantly reduce the amount of popping and banging by not taking your foot completely off the throttle on the overrun - just leave it in 1/8" or so. Worked for me when I had an open pipe.

I think this works because the motor actually burns the fuel then...
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Old 09-04-2007, 12:37 PM
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I believe the sounds you are describing are more a result of pressure waves caused by the exhaust trying to suck back through a spinning turbin than an ignition event. My muffler cackles when leaving the garage with the engine, turbo, and exhaust bone cold. The sound does become more pronounced as the engine warms.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 09-04-2007, 01:36 PM
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makes it kind of hard to let off the throttle to avoid attention when a cop car goes by though. i had one pull in behind me a few day back and instinctivly lett of the gass and looked at the speedometer only to hear a bunch of loud pops and crackles . I was sure I was going to get pulled over but he just kept going.
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Old 09-05-2007, 12:19 PM
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Quote:
Originally Posted by RarlyL8 View Post
What I do is simply push in the clutch when I don't want to hear it.
When do you ever not want to hear it?!

Agree with everything else you've said, as my car does that, too, even when cold.
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1987 Venetian Blue (really looks like grey) 930 Coupe
Old 09-05-2007, 04:34 PM
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Ha! Yes there are times. Most recently it was in a hospital zone. I think Ken911 found a time when you don't want it as well!
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 09-05-2007, 05:07 PM
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