Slower top speed with aftermarket exhaust?

[bryan_giovana]

I recently put on an aftermarket exhaust (Aeroturbine) and since then my top speed has gone down.

Before the mod I topped out at around 128mph. After the new exhaust I can't get it past 120mph.

Has anyone had this same problem? I'm thinking that it has something to do with less back pressure. Now that the exhaust is opened up I get more power on the lower end, but then it tops off earlier.

Any comments would be appreciated

 

[Minishotglass]

I heard Aeroturbine only makes mufflers. What is your exhaust setup?

 

[2k2s4]

I haven't looked under the car yet, but it's possible that the factory exhaust system was designed to blend into the shape of the underside of the car (it's like this on my S4), thus helping air flow under the car. Aftermarket systems are almost always just a generic canister, and not designed to explicity fit the underside of the car. It's possible that your new exhaust is causing enough drag to lower the top speed. At high speeds, don't discount aerodynamic effects.

 

[leungwingkei]

You test for top speed?

 

[bryan_giovana]

2k2s4,
Have you seen size of the stock muffler? It's HUGE. I doubt that any aftermarket muffler would create more drage than the stock one.

OH,,,I guess I just installed a muffler and not the whole exhaust.

 

[mp5jeff]

by adding a different muffler and nothing else only thing i can see changing is the sound. you still have the stock piping.

 

[2k2s4]

2k2s4,
Have you seen size of the stock muffler?

Sorry, just picked up the P5 today.

 

[Subghetto]

Aeroturbine? please don't tell me you got an exhaust w/ a built in turbine those mufflers are garbage and do more harm then good.

 

[Minishotglass]

bryan_giovana, are you sure the only modification before your lower top speed is just the muffler?

 

[Douggie]

Did you reset your ECU after the mod? Might explain the difference.

 

[2k2s4]

Has anyone had this same problem? I'm thinking that it has something to do with less back pressure. Now that the exhaust is opened up I get more power on the lower end, but then it tops off earlier.

Any comments would be appreciated

Less backpressure should actually hurt low-RPM power output and help high-RPM power output. Looking at Aeroturbine's web site, it looks like a lot of snake oil techno-babble to me. I'd like to see one cut away of their "jet engine technology". My knowlege of fluid dynamics is almost non-existant, but I still can't figure out how that thing would work; it sounds as credible as the tornado fuel saver.

My guess is that any power felt by your butt-dyno is purely a placebo effect and the lower top speed is empirical evidence that the Aeroturbine muffler doesn't work.

 

[Mxyzptlk]

Tell you what since no one is really answering this I will try out the top speed next week when I get mine done.

 

[bryan_giovana]

Yes, I did reset my ECU. If you look at the stock exhaust system it's about 2 1/2 in diameter. THE SAME AS A MAGNAFLOW OR FlowMaster catback. And yes, by changing just the muffler you will have a difference in power. It's not much, but it's there. The stock muffler is extremely restrictive, meaning power is restricted.

And yes I did buy the Aeroturbine. I'm very happy with it except for the lost top end which could be from something else. They didn't install a turbine inside of it. It just directs the flow of air out better. Supposedly...
After researching Flowmasters, Magnaflow, Skunk2Racing, Ractive, etc.....WHERE'S THE DIFFERENCE?????????

 

[Mxyzptlk]

Stock system is not 2.5 more like 1.75