930 Exhaust sounds like a fart - Help
 

Hello,
I have a 35k mile 79 930 with an Andial rebuild on the motor done a few thousand miles ago to stock specs. The car made some really terrible fart noises out of the exhaust when it came on boost so I figured I would toss on a fabspeed supercup. Well, it sounds better at idle, makes some great rumble noises, and still a very loud fart noise that continues as you are on boost, then stops when off boost. Yes, it sounds as I described it - Not a pleasant growl, howl, rumble or scream, just a loud ripper of a fart. I have and have had plenty of 911s and Turbos, so I know how they really should sound but this is the first stock 930 I have owned. Any ideas on how to mitigate this a bit? Headers, new turbo, something else that I may not even be thinking of?

Thanks,
Seth

How is it running? Do you have an afr gauge? Is it on boost onset?

It is running very well. Super healthy, no smoke, smooth power and plenty of it. The noise just throws me off... I can't quite pin it.

No, I don't have an AFR but that could be a good start.

Do you think it might be a vacuum/boost leak or something? Flutter from a flimsy rubber comes to mind. Other than that I’m stumped.

I guess anything is possible, but it doesn't sound like a leak of any sort. I will try to get a video soon and post it here.

Broken head studs can allow the a head to walk/vibrate under boost
and
it sounds bad when it happens

I hate to say it, but that's what immediately came to mind for me. :eek:

I remember when it happened on my SC (thankfully the turbo is fine, I check the head stud torque every year when I check the valves and do the annual maint).

When I got on it the head/cylinder would separate and made a weird raspy noise. When you hear it, you know it ain't right.

Are you sure the wastegate piping has not been modified to vent to the atmosphere rather than through a muffler?

Yes, check wastegate routing and possible leaks as well...

trunk monkey?

naaa, not head studs. don't scare the guy yet

could be you have a bad over boost sensor making the "rev limiter" kick in.

you can ground the wire going to the OB sensor and drive it.

check the vac hose to the WUR. make sure it is connected.

start with the easy stuff

I don't know what one is, but I want one! :D

This was my initial thought as well. Because it only happens under boost it may not have damaged anything yet. When you hear that noise off-boost things are bad. Pull the valve covers and take a look, if this is the problem you want to know about it.

The overboost switch cuts the pumps and gives the dash-in-face response which is unmistakable. Over-rev and you get a machine gun sound.

Also, as a side note, I would never have sold you a muffler to cure an unidentified noise. A conversation would have taken place first to find the problem.



.

Thank you all for the feedback.

Yes, the head issue could be a concern but I sure hope that isn't the case. I could see how the noise of this type could be a result. Crossing my fingers for the best.

The waste gate shouldn't be it as the factory muffler would have muffled it, and now with an open to atmosphere setup it is still there just louder.

T77911S -The boost and revs continue upwards with throttle, so wouldn't that prove to not be the boost sensor?

RarlyL8- I actually had a return to Fabspeed from a 964 cat with gave me credit with them, and that was the reason for going with the supercup. I actually just installed your 2 in 2 out sport muffler on my 69 over the weekend. It sounds great (I had megaphones) and if anything I could have had it even louder. Very pleased with it so far.

I took a quick video of the exhaust list night while driving. Check out the Honda fart sounds

<iframe width="560" height="315" src="https://www.youtube.com/embed/CV9A7ErdW4o" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

You're sure it's not tire rubbing?

Sure sounds like exhaust drone.

Checked youtube for some Fabspeed exhausts. They seem to have drone too.

Surprisingly many make fartcan -exhausts and youtube is full of comments they sound awesome, which I find funny, but guess that sells.

Think your ears are working good, and it is right to be annoyed at that sound.

https://www.youtube.com/watch?v=Rx6WB5YJia8

I don't hear anything unusual

OMG!

THAT.

IS.

AWSOMEEEEEEE!!!!!!

Now I really want one :D