Help needed - strange exhaust note
Thread Starter
Cruising
Joined: Apr 2010
Posts: 11
Likes: 1
From: Newport
Help needed - strange exhaust note
Hey guys, - got a headscratcher for you !
Bit if a strange one this so I need the forums help. I have a 74 s/b - mildy modded engine, (Edelbrock heads, cam, and inlet man., headers, roller rockers, holley 600) and a dual stainless exhaust system with just the 2 mufflers at the back . My problem is the sound - it sounds like the rotor blades on Bell helicopter at idle !!. Really, woolly and fluffy. The idle quality is regular and smooth however. My wife goes as far as to say it doesn't even sound like a V8 - major problem which needs to be changed!.
Anyone got any experience of similar or any ideas/pointers to offer as to what might be the culprit ?.
My gut tells me its the system - what does everyone think.
Cheers in advance
Larry
Bit if a strange one this so I need the forums help. I have a 74 s/b - mildy modded engine, (Edelbrock heads, cam, and inlet man., headers, roller rockers, holley 600) and a dual stainless exhaust system with just the 2 mufflers at the back . My problem is the sound - it sounds like the rotor blades on Bell helicopter at idle !!. Really, woolly and fluffy. The idle quality is regular and smooth however. My wife goes as far as to say it doesn't even sound like a V8 - major problem which needs to be changed!.
Anyone got any experience of similar or any ideas/pointers to offer as to what might be the culprit ?.
My gut tells me its the system - what does everyone think.
Cheers in advance
Larry
Melting Slicks
Joined: Mar 2009
Posts: 3,126
Likes: 15
Do you have a crossover pipe that connects the two pipes together? Did you block off your heat crossover under the intake manifold? When I ran my under the intake heat crossover plugged, it greatly changed how the exhaust sounded. The two pulses coming from the exhaust were much more distinct, not blended together. After removing the block off plates at the intake manifold gasket everything sounded normal again. Just an idea. mike...
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
I'm not quite sure how to interpret "woolly and fluffy". Your best chance for help from us would be to post a video of it if possible. That would pretty much tell the story without words. 
Thread Starter
Cruising
Joined: Apr 2010
Posts: 11
Likes: 1
From: Newport
Thanks for the replies guys - all much appreciated.
Let me address the points you raise.
The system doesn't have a crossover or X pipe, and the mufflers are not a "brand" name - they were put on by the system manufacturer when I had it fitted.
I'm intrigued about the point about blanking plates which was raised. The car has an aftermarket inlet manifold so I gues standard features are deleted now, but tell me a bit more about these blanking bits please ?. Are they the metal plates that come with the aftermarket gasket ? - as I think I fitted them when doing the engine rebuild.
Now then, the reference "woolly and fluffy" !: - its an attempt to describe the type of sound I'm getting. If you imagine blowing out of your mouth like whistling - without the sound ! - and holding your index figure horizontally over your lips and quickly moving it up and down (as it you were cleaning your teeth), but with out hardly touching your mouth, this is quite a good reproduction. It sounds bizarre I know but its quite close - took me ages to think up this decription !!
Cheers,
Larry
Let me address the points you raise.
The system doesn't have a crossover or X pipe, and the mufflers are not a "brand" name - they were put on by the system manufacturer when I had it fitted.
I'm intrigued about the point about blanking plates which was raised. The car has an aftermarket inlet manifold so I gues standard features are deleted now, but tell me a bit more about these blanking bits please ?. Are they the metal plates that come with the aftermarket gasket ? - as I think I fitted them when doing the engine rebuild.
Now then, the reference "woolly and fluffy" !: - its an attempt to describe the type of sound I'm getting. If you imagine blowing out of your mouth like whistling - without the sound ! - and holding your index figure horizontally over your lips and quickly moving it up and down (as it you were cleaning your teeth), but with out hardly touching your mouth, this is quite a good reproduction. It sounds bizarre I know but its quite close - took me ages to think up this decription !!
Cheers,
Larry
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
Thanks for the replies guys - all much appreciated.
Let me address the points you raise.
The system doesn't have a crossover or X pipe, and the mufflers are not a "brand" name - they were put on by the system manufacturer when I had it fitted.
I'm intrigued about the point about blanking plates which was raised. The car has an aftermarket inlet manifold so I gues standard features are deleted now, but tell me a bit more about these blanking bits please ?. Are they the metal plates that come with the aftermarket gasket ? - as I think I fitted them when doing the engine rebuild.
Now then, the reference "woolly and fluffy" !: - its an attempt to describe the type of sound I'm getting. If you imagine blowing out of your mouth like whistling - without the sound ! - and holding your index figure horizontally over your lips and quickly moving it up and down (as it you were cleaning your teeth), but with out hardly touching your mouth, this is quite a good reproduction. It sounds bizarre I know but its quite close - took me ages to think up this decription !!
Cheers,
Larry
Let me address the points you raise.
The system doesn't have a crossover or X pipe, and the mufflers are not a "brand" name - they were put on by the system manufacturer when I had it fitted.
I'm intrigued about the point about blanking plates which was raised. The car has an aftermarket inlet manifold so I gues standard features are deleted now, but tell me a bit more about these blanking bits please ?. Are they the metal plates that come with the aftermarket gasket ? - as I think I fitted them when doing the engine rebuild.
Now then, the reference "woolly and fluffy" !: - its an attempt to describe the type of sound I'm getting. If you imagine blowing out of your mouth like whistling - without the sound ! - and holding your index figure horizontally over your lips and quickly moving it up and down (as it you were cleaning your teeth), but with out hardly touching your mouth, this is quite a good reproduction. It sounds bizarre I know but its quite close - took me ages to think up this decription !!
Cheers,
Larry
Burning Brakes
Joined: Dec 2003
Posts: 1,004
Likes: 7
From: Adelaide South Australia
Uhhhh, sorry Larry- my family already thinks I'm about 1/2 nuts so there's no way I'm going to play "motorboat" to figure out this sound.
I have a better idea- if you don't want to take a video of your car how about you do a video of you making this noise of yours and post it here. We promise we won't laugh at you.
I have a better idea- if you don't want to take a video of your car how about you do a video of you making this noise of yours and post it here. We promise we won't laugh at you.
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Thread Starter
Cruising
Joined: Apr 2010
Posts: 11
Likes: 1
From: Newport
Bravo Les - great reply
It was a daft thing to post I know - but hey, got the message across ! - kinda !!
I can't post a vid I'm afraid - don't have the techno.
I've had a crap day in work today so thanks for making me laugh
Still doesnt get me closer to solving my prob tho'.
Thanks for confirming the bit about the blanking plates Mike - can discount them I guess.
Cheers, Larry
It was a daft thing to post I know - but hey, got the message across ! - kinda !!
I can't post a vid I'm afraid - don't have the techno.
I've had a crap day in work today so thanks for making me laugh
Still doesnt get me closer to solving my prob tho'.
Thanks for confirming the bit about the blanking plates Mike - can discount them I guess.
Cheers, Larry
Le Mans Master
Joined: Jul 2000
Posts: 6,664
Likes: 162
From: columbia city in
if everything is working well and this change did not happen all of a sudden .i would make the wife happy with a new set of mufflers from any of the top brands .flowmaster ,magnaflow, turbos ,thrush ,cherry bomb.
Race Director
Joined: Dec 1999
Posts: 11,096
Likes: 990
From: Sierra Foothills CA
Larry,
I'm sorry you had a bad day at work today- I've been there a time or two myself. Glad you got a chuckle though. I do wish I could help. Have you eliminated the possibility of an exhaust leak or a vacuum leak at the carb/intake? If that couldn't be it, did this sound begin after you made any changes to anything at all? Does the engine run right once it's above idle or could it be related to a problem you're having there?
I'm sorry you had a bad day at work today- I've been there a time or two myself. Glad you got a chuckle though. I do wish I could help. Have you eliminated the possibility of an exhaust leak or a vacuum leak at the carb/intake? If that couldn't be it, did this sound begin after you made any changes to anything at all? Does the engine run right once it's above idle or could it be related to a problem you're having there?
Thread Starter
Cruising
Joined: Apr 2010
Posts: 11
Likes: 1
From: Newport
Hi guys - thanks for the replies.
Carrying on the points you've raised- I cant say that I noticed as to when I became aware of it not sounding quite right. But yeah Les, I've changed loads of things since the exhaust was added (nudging 10 years ago) - when it was first put on, the car was an anaemic 74 with about 180hp, - now its probably over 300 hp. The pulses out the back are really strong and raw tho' - loads more than my 400bhp Jag.
I think this is the crux of it - the prob seems to be right at the back. The car drives fine, with no noticeable air leaks, idle screws are 1and1/2 turns out and seem fine and performance is strong through the rev range. Could timing etc alter exhaust tone ?, as I set it at 15 before (all in 34 by 2800).
What do we think ?
Cheers all
Larry
Carrying on the points you've raised- I cant say that I noticed as to when I became aware of it not sounding quite right. But yeah Les, I've changed loads of things since the exhaust was added (nudging 10 years ago) - when it was first put on, the car was an anaemic 74 with about 180hp, - now its probably over 300 hp. The pulses out the back are really strong and raw tho' - loads more than my 400bhp Jag.
I think this is the crux of it - the prob seems to be right at the back. The car drives fine, with no noticeable air leaks, idle screws are 1and1/2 turns out and seem fine and performance is strong through the rev range. Could timing etc alter exhaust tone ?, as I set it at 15 before (all in 34 by 2800).
What do we think ?
Cheers all
Larry
Racer
Joined: Oct 2010
Posts: 474
Likes: 0
From: Bishop CA
Hi guys - thanks for the replies.
Carrying on the points you've raised- I cant say that I noticed as to when I became aware of it not sounding quite right. But yeah Les, I've changed loads of things since the exhaust was added (nudging 10 years ago) - when it was first put on, the car was an anaemic 74 with about 180hp, - now its probably over 300 hp. The pulses out the back are really strong and raw tho' - loads more than my 400bhp Jag.
I think this is the crux of it - the prob seems to be right at the back. The car drives fine, with no noticeable air leaks, idle screws are 1and1/2 turns out and seem fine and performance is strong through the rev range. Could timing etc alter exhaust tone ?, as I set it at 15 before (all in 34 by 2800).
What do we think ?
Cheers all
Larry
Carrying on the points you've raised- I cant say that I noticed as to when I became aware of it not sounding quite right. But yeah Les, I've changed loads of things since the exhaust was added (nudging 10 years ago) - when it was first put on, the car was an anaemic 74 with about 180hp, - now its probably over 300 hp. The pulses out the back are really strong and raw tho' - loads more than my 400bhp Jag.
I think this is the crux of it - the prob seems to be right at the back. The car drives fine, with no noticeable air leaks, idle screws are 1and1/2 turns out and seem fine and performance is strong through the rev range. Could timing etc alter exhaust tone ?, as I set it at 15 before (all in 34 by 2800).
What do we think ?
Cheers all
Larry