cremaster

iTrader: (1)

hello all. i currently have the borla cat back system on my 09' isf, w/ the resonator cut out and straight pipes in place.

i called borla and asked them, if i were to now remove the rear, two muffler cans, would there be any adverse consequences. (so, then the set up would be primary cats in place, no secondary cats, borla X pipe, and straight pipes all the way back.) the borla guy said essentially:

- bc i already removed the borla resonator, i would have too much exhaust flow, which would mess w/ my O2 sensors. this would cause all sorts of problems including limp mode.

- bc the exhaust would flow too freely (w/o enough back pressure), the O2s would not have a chance to read the air/fuel mixture bc it's flowing out the car too fast; which would ruin/damage my O2 sensors.

- i would lose both HP and torque across the entire power band.

basically, my car would shut down and i would not be able to drive it anymore AND i would cause damage that would be very costly to reverse.

how much of this is true? i know one member is running no muffler cans on his borla cat back, but he's still got his resonator in place.

LOLM3

iTrader: (3)

Your borla resonator doesn't restrict flow actually most resonators don't restrict flow. All it is, is a perforated tube with fiberglass packed in it. I think you have the term back pressure and exhaust velocity mixed up. The o2s are really only working when you are at idle or at a constant speed, so having an exhaust or not, the o2 sensors won't be able to keep up with you flooring it. I really wouldn't worry about your car shutting down and causing costly damage.

USB_F

iTrader: (11)

Do you have any vids of your current setup?

I'm thinking of removing the mufflers since they slip right off to see how it sounds.

cremaster

iTrader: (1)

good points, thanks for your input. yeah, i figured the guy might just be trying to scare me. he was obviously biased in the fact that he didn't want me to hack up or further modify the system. and of course he had to add comments like, "you have a nice car, why would you want to make it sound obnoxious like that?" "you paid a lot for that system; you're going to mess up and reverse engineer the hard work that went into designing the system." etc.

i have two vids on youtube of my current set up but i have not removed the mufflers. so, just the cat back w/ reso delete.

caveman

^ sounds great. Did you notice more drone after the resonator delete? Did it change the tone? Volume?

lorenr

iTrader: (1)

The best way to work with any exhaust system is to use a good dynamometer, seat of the pants does not count. Just because it is loud, doesn't mean a thing.

I went to college with Gale Banks, who did everything the hard way. He would build it, race it and then decide if it worked. He builds some quality and efficient exhaust systems. So does Borla. I installed one of their cat back systems on my F. I think it makes a little more power but have not done a before and after on a dynamometer.

I would bet that changing any part of the Borla system would cost power, and just make it much louder. I just roll my eyes when I see these cars made unnecessarily loud with slanted wheels from goofy coil overs. I just does not work.

I know for sure that the Borla representative is correct about back pressure. Building an efficient exhaust system is quite difficult. You want it to work all the way through the power band, including down low where it is driven the most. A high RPM stepped exhaust system with 3 inch exhaust is useless if the car is driven at 2000 RPM.

Loren

cremaster

iTrader: (1)

yes, yes, and yes. i'd say the system sounds about 30% louder overall. the drone increased as well but i didn't mind, as i was expecting that. also, the tone became slightly more raw. if you notice from the vid, you can hear a slight rasp towards the higher rpm range, which i really like, and which is not present w/ the original cat back system.

in thinking about removing the rear mufflers, i wanted to do it purely for noise/sound purposes. i wouldn't expect to gain any power but also didn't want to lose any significant amount, esp low end hp and or torque. i'll probably just leave the system as it sits now.

VtotheJ

iTrader: (2)

An ISF owner drove 8+ hours with his entire rear section removed from DES exhaust, and he didn't have CELs or limp mode. If you're doing it for sound purposes, I don't see how it would be an issue. Hit the dyno now and after you remove mufflers to see if there is a real performance difference. You will need to ensure it is done in the same conditions and on the same dyno.

I8ABMR

I'd say listen to the Borla guy. The car is loud enough. I guess you could try and if there is an issue then go back to original set up

LOLM3

iTrader: (3)

I had a Borla and immediately took out the resonator. I also then ran it with a muffler delete for a few months until I got my HKS. I had ZERO problems, if deleting a muffler would cause issues everyone on here with a muffler delete would have a thread talking about how their cars o2 sensors are fried...Like I said you should be fine.

This is a video of the borla with a delete and Sikky headers

This is my Borla with mufflers and PPEs

cremaster

iTrader: (1)

i just had another Borla rep email me back. he said i might gain some upper end HP but lose bottom end torque. he said NOTHING about limp mode or the exhaust gasses moving too quickly for the O2 sensors to read the air/fuel mixture, nor anything about detrimentally ruining my car.

his only concern was if i did not fabricate any extended pipes off the rear Ypipe towards the rear outlets on the bumper, that i might smell some of the exhaust fumes, which i don't really care about. i just wonder how significant the bottom end torque loss will be; if enough to be felt on the butt dyno.

EDIT: thanks LOLM3 for the vids!

lobuxracer

iTrader: (2)

Backpressure? Again?

Some people just don't understand simple physics. Bigger pipe, more backpressure, not less. "Too free flowing" is utter BS, there is no such thing. There is velocity loss from energy dissipation because the pipe is too big, but surely there is no such thing a "too little back pressure." Anyone saying that doesn't understand simple gas physics.

tmf2004

iTrader: (15)

man those vids sound great...