No Burble/Popcorn on Decel

[1stgear]

I have a ROW '85 Carrera with a NA 3.2. I'm running Fabspeed headers with no heat exchangers and a dual outlet muffler with very little packing.

My question is this - every other 3.2 I've had (3) that I ran without a cat would make that nice popcorn sound on decel. This car doesn't. Any ideas as to why?

I know that sound comes from unburnt fuel in the exhaust. I currently have the car in for leaky injectors and intake gaskets. We're trying to fix all the vacuum leaks. Could this be the source of my missing sound?

Thanks for any help!

[Trakrat]

I've heard that it isn't just an exhaust that adds this burble on decal... it's a combination of air/fuel mix.
Are you running an open CAI kit in place of the factory enclosed airbox?
Do you have a custom tune?

[Arne2]

Carreras with Motronic shut off the fuel during off throttle decel, and because it is a more effective system in other ways, there is little unburnt fuel during decel. It's a better tuned system, and I don't think you can make it pop without changes to the engine management software.

[1stgear]

Are you running an open CAI kit in place of the factory enclosed airbox?
Do you have a custom tune?

I'm running a stock air box and tune.

Carreras with Motronic shut off the fuel during off throttle decel

My previous '85 and '87 had stock chips and they popped like crazy. So did my '95 993.

[evan9eleven]

You want my CIS injection setup? With SSI's and Dansk muffler, I have enough popcorn on decel to feed an 18-plex movie theater!

[1stgear]

Originally Posted by evan9eleven

You want my CIS injection setup? With SSI's and Dansk muffler, I have enough popcorn on decel to feed an 18-plex movie theater!

POP POP - Talk to me, brother! LOL

[evan9eleven]

Originally Posted by 1stgear

Talk to me, brother! LOL What's a CIS injection system?

The slow-throttle-response fuel injection system that you can't get parts for anymore, or modify much, or run hot cams with, that was replaced by the motronic in your car. Its not an upgrade just to get popcorn. JMHO

[1stgear]

Originally Posted by evan9eleven

The slow-throttle-response fuel injection system that you can't get parts for anymore, or modify much, or run hot cams with, that was replaced by the motronic in your car. Its not an upgrade just to get popcorn. JMHO

LOL! Hey, Evan. I looked it up and changed my reply. Thanks for your insight into the system, brother!

[Arne2]

Originally Posted by 1stgear

I'm running a stock air box and tune.

My previous '85 and '87 had stock chips and they popped like crazy. So did my '95 993.

Really? My '84 does not pop at all, either with stock or Steve Wong chip; with either the stock cat or M&K premuffler. While I don't mind a bit of burble on over run, if mine started doing that now after 5 years of driving it, I'd be concerned.

[douglas bray]

All kinds of popcorn now on my car:

https://www.instagram.com/p/BFSRl5Yv9h5/

[sugarwood]

I thought that burble was air/fuel igniting in the exhaust, meaning it's running too rich.
I used to get burble on decel with my Welt. chip.
When I changed it to a Wong chip, the burble went away.

[s5uewf]

decel burble and popping is due to a lean condition usually on decel. The gas/air is not ignited in the cylinder and passes into the exhaust header, where it accumulates with discharge from other cylinders and is ignited by the hot headers or by a spark in one of the cylinders.

backfires are usually from rich mixtures. They are different.

CIS generally does not burble and pop because the catalytic converter burns up waste and also muffles a lot of the noise when combined with the muffler. Remove the catalytic converter or swap in headers and you will likley get some popping depending upon how your WUR is adjusted.

If Motronic shuts off fuel on decel, there is no fule to burn in the exhaust, so no popping.

[NY65912]

Lean condition causes the popping on decel, and you don't want that.