Ian964

My car as always done this, it sounds kinda cool I guess but I'm not sure if its supose to be doing it. If I rev the car up and then let it rev back down i get a pop-pop-pop like noise. It kinda sounds like a race car or something. It only does it when the car is losing revs.

maverick

Mine does the same thing. It is a function of unburnt gas in the exhaust stream under deceleration meeting the hot exhaust system. It ignites as it passes through the hot exhaust pipes, litteraly small 'explosions'. If the car has a catalytic converter this does not happen.
Maverick

Sameer

It's normal.

SonnyV

Mine '92 C2 Turbo does it all the time just as described above. I do have the Cat in place without the final muffler though. It did not do that before I removed the final muffler.

Regards,

Sonny

Ian964

Hmm wierd. I have the cat too.

Staffan

My car had a popping sound, it dissapered when I changed to a working CBV. Somone more technical could probably explain why it pops more when the CBV isn't working.

Vince5

Mine does it as well. CBV is relatively new (10 000 km) with cat but no muffler

BTW 12 000 km in 10 months <img border="0" alt="[ouch]" title="" src="graemlins/c.gif" />

johnfm

This 'poping' sound, was it in Latin or Polish............

Kevin Ross

Hello Everyone

A topic close to my heart... I have a similar popping from my car. But, if you'll allow me the creative lattitude, I'd like to divide the popping into two distinct but seemingly interelated noises...

One sounds like: pop-pop-poh-pop-poh
The other like: tsih-tss-tss-tsihhh

They occur together, and happen under the same set of circumstances, ie - lifting off the throttle. The first is definitely a wonderful sound. Throaty and an attention grabber as... especially the looks one gets from people waiting for the bus near a stop street.

But, the second sounds like somethings wrong... like the acoustics are wrong somewhere and the pohhh is turning into a tsihhh.

My car is stock. and I mean stock... no mods at all!

Any ideas?

John McM

A bit of a guess here, but could the second sound be your compressor bypass valve working? In NZ we have a lot of turboed Japanese cars and they make this noise every time they come off the throttle. I figure it's the same thing but designed to make more noise and be noticed. Almost sounds like a steam train.

fc-racer

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Kevin Ross:
<strong>Hello Everyone

A topic close to my heart... I have a similar popping from my car. But, if you'll allow me the creative lattitude, I'd like to divide the popping into two distinct but seemingly interelated noises...

One sounds like: pop-pop-poh-pop-poh
The other like: tsih-tss-tss-tsihhh

They occur together, and happen under the same set of circumstances, ie - lifting off the throttle. The first is definitely a wonderful sound. Throaty and an attention grabber as... especially the looks one gets from people waiting for the bus near a stop street.

But, the second sounds like somethings wrong... like the acoustics are wrong somewhere and the pohhh is turning into a tsihhh.

My car is stock. and I mean stock... no mods at all!

Any ideas?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">The "tsih-tss-tss-tsihhh" sound is from your mixture being a bit on the lean side. Not dangerously lean (well, you can't really tell if it is by looking at only the overrun). If you richen the mixture a touch, you'll find that it greatly reduces that sound.

I'm not sure what that sound is, but I can consistently stop it by richening the mixture a touch.

fc-racer

Actually, I'm going to change that The noise you describe if I try to make it sound how you've written it would be the compressor bypass valve failing.

The noise I refer to above is more like a click/pop noise on deceleration that happens even after the intake has released excess pressure (the job of the CBV).

Ian964

FC: did you get the 993TT

fc-racer

Ian, nope

I was C$5k (about US$3.5k) away from getting it, but the owner of the twinner is a good friend of mine so I wanted him to get max dollar for it. He sold it for C$115k or US$84k. I was willing to go to C$110k for that car.

I will now continue to enjoy the 964 Turbo and when the opportunity comes up again, I will get the twinner. For now, I am enjoying the 964T a lot. Did some minor tweaks to it and am enjoying the car a lot, it's such a beast

Kevin Ross

FC....

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by fc-racer:
<strong>Actually, I'm going to change that The noise you describe if I try to make it sound how you've written it would be the compressor bypass valve failing.

The noise I refer to above is more like a click/pop noise on deceleration that happens even after the intake has released excess pressure (the job of the CBV).</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Well, honestly, it is kinda hard to 'write' the sound accurately... and your click/pop probably is more accurate than my Tss.

However, I can say for sure that it comes from the exhaust, occurs all the way DOWN the rev range (ie on lift off it keeps occuring until the car almost stalls), and that it seems to be 'mixed in' with the normal pohpohpoh that one expects from the Porsche exhaust note...

I also have read the CBV thread with interest... I might have a combination of two issues, lean fuel delivery and a failing CBV...

Comments?

I'll get Porsche to check it out and comment too... will report back.

<img border="0" alt="[bigbye]" title="" src="graemlins/xyxwave.gif" />