Black Bandit

Hey Guys, I have an 02 Mustang Gt Vert Auto., that so far, I have installed a CAI, and noticed a difference in performance, but just yesterday I decided to pull the trigger, and have Flowmaster AT's installed inluding a new dual exhaust system from the cats back. Although I like the sound, I noticed a significant drop in performance, actually seems sluggish. I had the work done at a small Performance muffler shop that came highly recommended. Anyone have an idea what happened?? Thanks for your input.

Lance

sonicx

I find it hard to believe that you can feel a CAI on new edges since actually have a similar sort of CAI on them already except they don't look fancy. Alot of people instead drop in a K&N reuse filter and it's the same thing. Now if you said a 05+ mustang different story entirely. Does your car have/had a tune before? I can't see you losing performance for FM AT's unless the shop were goofing around with your 02 sensors. Otherwise without numbers from the strip or dyno it's hard to fathen your losing HP from what you've given.... Could be something entirely different; however causing an issue. Any leaks, how many miles on the clock?

Dragonus18

The only thing that comes to mind that I say out of experience is perhaps an exhaust leak.

cliffyk

There is nothing (other than if it were plugged up) about a catback system that would affect engine performance--except the psychological effect of it being louder making you think it should be going faster.

This may sound silly. but it is often true--in part evidenced by that you "noticed a difference" after replacing the stock CAI with an aftermarket assembly. In fact no aftermarket intake system (other than one driven by a belt or the exhaust gases) makes a bit of difference, other than in the tone and loudness of the intake noise...

BLKSTANGER

Removing back pressure from an engine will move the torque curve to the right. Meaning the torque you felt by the seat of the pants will now come at a little higher RPM. I have been into heavily modified Harleys for the past ten years and have noticed it many times. Put a big old open pipe on and it feels sluggish till you romp on it.
So hows it feel when you get on it and mash the go pedal?

Black Bandit

Thanks for the input Guys. Maybe its all in my head, LOL! I was under the impression that anytime you increase the amount of cool air to a combustion engine, and relieve back pressure of a stock exhaust system, you allow the engine to breath better, therefore increasing HP. Have not found a shop that has a Dyno yet, but am still looking. I was hoping for at least a 25HP increase with what I've done so far, but based on your replies, I guess not. Yes, I have aleady floored it, and it just seemed sluggish to me. Oh, and the car has 56,000 miles on it. Thanks again for your input.


Lance

JC316

Everyone here hopes for a 25HP increase from a cat back and CAI, but it will never happen. I doubt you even picked up 5HP from that.

cliffyk

That is true, but you didn't change anything that would increase either the intake or exhaust flow to any great extent.

The comments about the impact of larger exhaust plumbing are correct, however it's not backpressure but rather the velocity of the exhaust gas pulses in the system that is affected by pipe ID.--here's a good white paper dealing with "backpressure".

BLKSTANGER

Good read cliffyk. Makes perfect sense to me. The same principal can be applied to head porting as well. Hogging out the ports and using huge valves can ruin a motors performance.

cliffyk

Absolutely...

It is the concept of intake and exhaust moving in pulses that is the missing ingredient in people's way of understanding both. I know it was not until that got through my thick head that I really began understanding what "tuned" intake and exhaust meant.

This is another good read too, not as well formatted but it gets into multi-cylinder engines and scavenging.

Regarding headers, this is perhaps the best Headers 101 paper ever written. It was done by S&S Headers, no longer with us after many years of making the best there were...