CatBack Systems Losing Power

[Budwise]

I've seen several reports of people saying they're losing power with catback systems on the 5.0 S550's. One guy dyno'd before and after going with Stainless Works and he lost 10 HP and 5 ft/lbs and it also caused his A/F mixture to run super rich at higher RPM's. Just a heads up for those with the early itch to start modding before the aftermarket really knows what the heck they're doing.

 

[ArabianOak]

I gained 5rwhp and tq with my Gibson.

 

[Dcrypter]

The FRPP catback stayed 2.5", I would guess there is a good reason for that.

 

[Supernova]

I saw the thread on Mustang6g about the SW catback losing 10hp... I didn't read all 20+ pages, but supposedly the car wasn't dynoed back to back on the same day. That's could introduce some variance, though I'm not sure if it would account for a 10hp difference. I haven't seen this issue with any other aftermarket manufacturers, but I admit I haven't been combing the forums...

 

[Voltwings]

I dont really see how changing the catback would throw off the AFRs ...

 

[HEMI LOL]

go read that thread. its full or more AED magic.

 

[ZWilson07]

Anyone got the link?

Haven't found it yet.

 

[Deranged2013]

I had SW on my 13 gt and the sound was amazing but,,,,,, it looked like the resonators and mufflers neck down to 2.25"ID. But that still shouldn't effect the AFRs.

 

[Blazer707@TBR]

Link to thread?

 

[SID297]

My guess would be that it doesn't have anything to do with the exhaust. It's the ECU pulling timing/adding fuel to save the cats.

 

[Blazer707@TBR]

My only guess besides that would be maybe with the bigger exhaust valve the motor is already opened up alot on the exhaust side and with the added catback its too open.

 

[SID297]

My only guess besides that would be maybe with the bigger exhaust valve the motor is already opened up alot on the exhaust side and with the added catback its too open.

I don't see that being an issue at all. Opening up the exhaust too much can reduce tq, but should show at least minimal HP gains on the top end.

I forgot to mention that the ECU will close the throttle blade too.

 

[STL5OHSLOW]

I agree with blazer. If the car is tuned around the exhaust being 2-1/2 inch and were throwing 3 inch catbacks on them they would loose power. Just my opinion as well but I said it as soon as the car came out and I Actually saw the exhaust in person. These cars will need a tune for a catback like some other cars on the market today. 2-3/4 to 3 inch was one thing on the 11-14 but the fact that this is jumpin up a whole half inch I think is what is making the difference

 

[Voltwings]

I don't see that being an issue at all. Opening up the exhaust too much can reduce tq, but should show at least minimal HP gains on the top end.

I forgot to mention that the ECU will close the throttle blade too.

This ^^

I agree with blazer. If the car is tuned around the exhaust being 2-1/2 inch and were throwing 3 inch catbacks on them they would loose power. Just my opinion as well but I said it as soon as the car came out and I Actually saw the exhaust in person. These cars will need a tune for a catback like some other cars on the market today. 2-3/4 to 3 inch was one thing on the 11-14 but the fact that this is jumpin up a whole half inch I think is what is making the difference

Torque is a derivative of velocity; how fast air both enters and leaves the cylinder. A larger exhaust will cause velocity to slow, which will lower torque, BUT it allows the higher end to flow at a greater velocity (where the smaller pipe was previously a "restriction") which should allow greater top end torque. HP is a derivative of torque, so more torque at a given point = more HP. On paper there is no reason for the car to be losing horse power.

Secondly, air coming into the system is still measured at the MAF, and the Catback is far enough downstream of the o2s that nothing there should be effecting them as well. This is the ECU stepping in and doing some funky stuff.

 

[Derek@Lethal]

My only guess besides that would be maybe with the bigger exhaust valve the motor is already opened up alot on the exhaust side and with the added catback its too open.

That wouldn't make sense because with the smaller valves in the 11-14, the 2-3/4" exhaust was a restriction. Adding larger cams and valves would then make the 2-3/4" exhaust even more of a bottle neck, and to close it down to 2-1/2" would do it even more so. I'm sure there's more to this than just changing the cat-back, something to do with the tune most likely, but going from 2-1/2" to 3" on these 15 motors would actually net some really good gains.

 

[Deespeed99]

I can tell you over at Revolution Automotive we did extensive back to back testing and we did verify that the SW catback is a restriction. We picked up 15-20rwhp from dropping the catback and running through the SW headers/cats. We did a few things to test it but it's legit that it cost HP.

 

[beefcake]

it has nothing to do with that. the ONE car that dyno'd at a loss, had a/f ratios of a full point richer.

what does this mean. it means that the cats are getting too hot and the car is going into cat overtemp protection and dumping fuel.

PERIOD, that's it.

It amazes me in this day and age of one person dynoing a car, and posting a/f ratios of a full point off, knowing what we know about the coyotes and how they work. That this information spews.

Put whatever catback you like the sound of the most on your car and enjoy it.

/THREAD

 

[beefcake]

I can tell you over at Revolution Automotive we did extensive back to back testing and we did verify that the SW catback is a restriction. We picked up 15-20rwhp from dropping the catback and running through the SW headers/cats. We did a few things to test it but it's legit that it cost HP.

That is complete misinformation.

Dynoing a cat back vs open headers is not a valid comparison at all. Now, if your extensive testing involved testing a factory connect headers setup with the stock exhaust vs the sw fact connect exhaust. that would be a valid comparison.

Open headers will obviously have 0 restriction. That's why we run essentially that type of setup on our race car as does everyone. Why do you think big turbo cars aren't running through factory systems and run bull horns or the like

 

[Deespeed99]

I have more information then just that comparison. I also have a comparison with stockings off as well. It definitely called a loss of horsepower. Let me know what information you need to see it and I'll gladly post it.

 

[Deespeed99]

Stock exhaust not stockings lol