Loud exhaust on deceleration

[GhostStalker27]

Specs - 99 Viper ACR, catless w/ borlas, K&N intake

Does anyone know what causes my exhaust to sound basically twice as loud when I let off at a high rpm and decelerate down? It's normally loud idling, driving, and accelerating, but nothing compares to the let of roar from decelerating.

[gage]

I get the same thing but I'm a 97 with no mufflers and smooth intake tubes. Like the borla my car has no crossover exhaust pipe.

Therefore my theory on your noise is the ECU cutting off fuel on decel combined with straight pipes leading to a resonance creating a louder noise than when the engine is loaded/idle. An x-pipe would mitigate some of it.

[Sybil TF]

Do you have the Borla with 2 or 4 mufflers? I have 2 and it does that somewhat but I still have hi-flow cats.

[Loud]

Isn't it awesome

[GhostStalker27]

Do you have the Borla with 2 or 4 mufflers? I have 2 and it does that somewhat but I still have hi-flow cats.

2

Isn't it awesome

Haha yup, curious to the science behind it

[braunstein82]

I have borla 2 mufflers no cats. Mine does the same.

[cfiiman]

isn't it awesome

+1

[v10enomous]

I speed up in my GenII just so I can decellerate K&N intake, no cats or rear mufflers, Random Tech rear X pipe.

[Drummerviper]

You complaining?? My Lambo sounds ridiculous when you back off. Enjoy it . Loud pipes save lives.

[Leslie]

Geez I miss that sound from a GenII!!!
MY car isn't loud enough.

[GhostStalker27]

I speed up in my GenII just so I can decellerate K&N intake, no cats or rear mufflers, Random Tech rear X pipe.

me too lol

You complaining?? My Lambo sounds ridiculous when you back off. Enjoy it . Loud pipes save lives.

Oh hell no, just curious what causes it.. maybe I can replicate it on my DD lol. I rolled with a Aventador once... wasn't as loud as my viper

[Viper Red]

You're running rich, that's why.

[Luisv]

i assume you are hearing that awesome rumble on deceleration. That's basically what some call an after-fire or after-burn. As Viper Red mentioned, it's when the engine is running a bit rich. Most Vipers do this. What causes the sound is that the rich fuel setup tends to burn slower and incompletely. That is usually worse on deceleration or off the accelerator. That unburnt fuel leaves the engine and ignites somewhere in the exhaust. Since it is small amounts of fuel you don't get the flames out the exhaust, but rather the rumble.

Supposedly, the longer the exhaust plumbing, the more rumble you get. A stock Gen 2 GTS supposedly would have a worse rumble than a side exhaust setup. In your case, since you have no catalytics, the unburnt fuel might even accumalate a bit making the sound louder.

[GhostStalker27]

i assume you are hearing that awesome rumble on deceleration. That's basically what some call an after-fire or after-burn. As Viper Red mentioned, it's when the engine is running a bit rich. Most Vipers do this. What causes the sound is that the rich fuel setup tends to burn slower and incompletely. That is usually worse on deceleration or off the accelerator. That unburnt fuel leaves the engine and ignites somewhere in the exhaust. Since it is small amounts of fuel you don't get the flames out the exhaust, but rather the rumble.

Supposedly, the longer the exhaust plumbing, the more rumble you get. A stock Gen 2 GTS supposedly would have a worse rumble than a side exhaust setup. In your case, since you have no catalytics, the unburnt fuel might even accumalate a bit making the sound louder.

Thanks Luis, any idea why Vipers tend to run rich? Is it just a safety precaution necessary for the nature of these motors? Sorry, I'm one of those annoying people who likes to understand everything

[AZTVR]

Thanks Luis, any idea why Vipers tend to run rich? Is it just a safety precaution necessary for the nature of these motors?

I have read that that was the reason; but, don't know the knowledge level of the folks who posted it. I have read that it could be reduced with a tune; but, it is a pleasant, aggressive sound to the ears of even the most mild mannered Viper drivers. LOL !

[Sybil TF]

Thanks Luis, any idea why Vipers tend to run rich? Is it just a safety precaution necessary for the nature of these motors? Sorry, I'm one of those annoying people who likes to understand everything

Speed density type fuel management vs a mass airflow system from what I gather...

[GhostStalker27]

... it is a pleasant, aggressive sound to the ears of even the most mild mannered Viper drivers. LOL !

The look you get when you roll up next to an unsuspecting traveler and let off is priceless

[Sybil TF]

The look you get when you roll up next to an unsuspecting traveler and let off is priceless

The looks I get just sitting at a stop light is priceless...and then when I get out at a gas station lol

[v10enomous]

Downshifting > Upshifting

[Resident Alien]

This thread is worthless without videos...

[GhostStalker27]

Here's mine

[Sybil TF]

Sounds about right^^^

[v10enomous]

Sounds wicked !!! Great colors BTW...

Here's mine

[Luisv]

Thanks Luis, any idea why Vipers tend to run rich? Is it just a safety precaution necessary for the nature of these motors? Sorry, I'm one of those annoying people who likes to understand everything

OK... this is something that will get 100 different answers from 100 different people. However, there are certain "benefits" that a rich NA engine gives you. Some of these are likely why Dodge or any manufacturer would do this.

As a basis, assume there is a "perfect" or "ideal" air to fuel ratio. Running rich means you have more fuel than ideal. Lean, means less fuel in the ratio.

Benefits of running rich:
- Cooler combustion. This equates to less stress on the internal components. Longer lasting engine, in theory.
- Cooler exhaust temperatures. Less heat in the engine bay. Better cooling around engine. Less stress on those pretty parts in bay like the air intake and ECU. Other obvious in a Viper...Touch your side sills lately?
- Less "drastic" engine braking under deceleration. Remember you have 500 lbs of torque in there. Engine braking is drastic unless you "help" a bit with some combustion under deceleration. If you had more engine braking than we do, there would be even more snake bites.

In general, I would say that it is more a matter of longevity and practicality than anything else. If you had a full on race car, stripped of everything except that engine and a seat, you would not care about running hotter and exhaust temps. Also, the engine would not be expected to live for 75K miles or much longer. It would be swapped after a few races or a couple of thousand miles tops.

[GhostStalker27]

^ Good stuff, thanks for sharing