Popping During Deceleration

[Tony Hanna]

I'm running a mitsu with a 2.5" downpipe connected to a 3" Dynomax race bullett and 3" side exit. I'm happy with the sound level. With the windows up, you barely hear it as a background noise. The only problem I have is that it pops like crazy on decel. I'm curious as to what causes the popping and what can be done to eliminate it or reduce it significantly. I'm sure going with a different style muffler would do the trick, but I'm short on cash at the moment so I'd like to try a different option. I'm thinking of making an anti-reversion cone similar to what they sell for Harleys with drag pipes, but I'm not sure if it would do any good, or if reversion is even an issue with the turbo smoothing out the exhaust pulses.
Any thoughts and advice would be appreciated.
Thanks,

[iTurbo]

The only time I get loud popping on decel is when the speed sensor and/or wiring has failed. Are you getting a code 15? Could be a clogged AIS passage too.

[turboaddict]

my 87 doesnt have a decel lean out as most newer fuel inj. cars have. basically on decel the engine is still being given fuel which burns n the exhuast system. i like the sound of it.

[Mario]

The only time I get loud popping on decel is when the speed sensor and/or wiring has failed. Are you getting a code 15? Could be a clogged AIS passage too.

That's what I was about to say.

But most of the time when I've had a speed sensor fail, the engine would want to die when I let off the throttle/came to a stop unless I played with the throttle. He didn't mention anything of the sort.

[iTurbo]

I have two cars right now, both with bad speed sensors. Idle does go a bit low when coming to a stop, but they don't stall, mainly just snap crackle pop out the exhaust on decel. Not annoying enough to fix yet though. Might be worse with auto trans, but I have manuals in all my cars.

[Tony Hanna]

That might be it then. I'm running an auto trans computer on a manual trans car. Might be the sds too as it does idle a bit low when coming to a stop. It's never stalled though. Would a bad sds cause a check engine light or just set a code? I'll check for a code 15 and clean the ais passage later this evening.
Thanks for the suggestions!

[Tony Hanna]

Ok, just pulled the codes. It's all clear, nothing but a 12.
I'll check the ais passage later this evening after it cools off some.

[tryingbe]

My 89 Daytona Shelby pops all the time when I'm decelerating with using the cut out.

It's normal, to stop it, put a muffler on it or shift out of gear.

[Dave]

It's normal. Just raw fuel being burnt in the exhaust system instead of the combustion chamber.

[Garret]

unplug the AIS and set your idle manually and the problem goes away, just gotta blip the throttle more when you slow down

[butchsuppe]

Advancing the timing a tad at a time got the popping out of my car - 2.5" mendral bent, no cat + ultra flow muffler.

[Tony Hanna]

Thanks for all the help. I think the biggest issue is that this computer doesn't have the decel fuel cut. Maybe because it's an auto computer? If I ever get a cal done, maybe I can get that fixed. For now I'll try out some of the suggestions here and if all else fails, I'll just try to find the best flowing quiet muffler I can.

[shadow88]

Do you run a cat? Mine made alot of popping without one, and nothing noticeable with one.

[Darkapollo]

naw. my auto pops all the time.. i love it. scares little children.

[Tony Hanna]

Do you run a cat? Mine made alot of popping without one, and nothing noticeable with one.

Nope, no cat, but it popped with the stock one in place (exhaust was rusted in half before the muffler).

[Tony Hanna]

naw. my auto pops all the time.. i love it. scares little children.

That's what I'm trying to get away from. That which scares little children usually attracts the attention of the cops. The Sundance is pretty low-key and I'm trying to keep it that way. It even still has the luggage rack on the trunk. The only thing that even remotely looks sporty on the car are the 16" pumpers. Crap, I think I've just talked myself into trying to find a decent flowing quiet muffler.

[GLHNSLHT2]

it's the fact that the fuel isn't being totally cut when you drop the throttle. The S60 is really dumping fuel at idle and decel vac levels. Anyway it's normal for these cars. If you want to get rid of it you need to recalibrate the puter and turn the fuel off in decel.

[86Shelby]

get a regular old straight through type muffler. Those race bullets are horrible about that.

[Tony Hanna]

get a regular old straight through type muffler. Those race bullets are horrible about that.

What are you calling a regular old straight through type muffler? AFAIK, the race bullet is a straight through muffler. The construction is almost identical to a cherry bomb or other straight through type glasspack. The only difference is that the race bullet is shorter and stays 3" through the core. All the other ones I looked at necked down considerably inside the muffler. The 2.5" cherry bomb I had on the Daytona looked to be closer to 2.25" core size.

After going back over my goals for the car, I'm thinking more about switching to a chamber style or "turbo" muffler. Any suggestions on something that would be really quiet but still flow well?

For reference, I'd like to eventually turn the Sundance into something capable of running mid 12's in the 1/4 and still carry my butt back and forth to work every day and make the occasional trip to GA to visit the parents.
If I could do that and keep it looking and sounding like something that grandma would drive to church, that would be perfect.
Thanks,

[86Shelby]

Ok, the bullet type mufflers I reffered to are pretty much race-only style mufflers, just enough muffling to pass as mufflers at the track. Supercrackerbox had one on his CSX-T, it was very loud and harsh sounding. Especially during decel in gear.

I believe I have a Magnaflow on my R/T, not quite straight through style, more of an angled -\_ type. It stays the same inner diameter all the way through. The main difference is that it has several times the sound deadening material around the core than bullet or glasspack style mufflers do. Typical bullet muffler in my experience has about 5/8-3/4" of material around the core, figure 1.5" or so larger outside diameter around the core. My muffler an oval style with a 3" core with 3" I/O. It's got a good exhaust note, reasonably quiet on the highway(resonates a bit though) and around town and doesn't let any of those decel backfires come through loudly at all. They are just little burbles in the note. Not brash, or harsh loud sounding exhaust. Check around with Magnaflow, they are usually a straight through design and come in 3" I/O, they should be the same diamter inside, but ask to verify.

Bullet style IMO:


Not bullet but straight through style: