Larger exhaust made my car slower?

[lancerswimmer89]

Hey guys, so i just added a catless midpipe to my car the other day, and it kinda feels like i've lost power. So i am now running a Weapon R secret weapon intake w/ the metal intake box, a speedyracer header, tsudo catless midpipe w/ resonator, and a 2.5" catback magnaflow exhaust.

Does anyone know how I would get the power or torque back? does it need a tune? or do i need to turn off my rear o2 sensor now that the catalytic converters are gone?

Any and all help would be greatly appreciated.

[grayguy]

is it throwing a check engine light?

[lancerswimmer89]

yes it is, but to be fair, it was throwing one before i pulled the cat's off

[Perkul8r]

yes it is, but to be fair, it was throwing one before i pulled the cat's off

Have you rechecked it though?

I had a check engine light for egr on my 99 for awhile. for some reason another issue arose and I never rechecked the codes. But than when I did, I had multiple codes.

[Kevlar_07]

Could have to do with the cat being removed causing a check engine, also n/a engines need backpressure to an extent. Back when I had my supercharged cobalt I ran across this thread that explains why little better

http://www.cobaltss.net/forums/general- ... ion-68523/ (http://www.cobaltss.net/forums/general-cobalt-68/simple-explaination-intake-exhaust-resonating-camshafts-operation-68523/)

Chances are your intake is causing your issues, install your factory intake back on and go for a drive. A tune will help but will only mask the problems caused by running a CAI/SRI Heres another thred about the intake issue

http://forums.nasioc.com/forums/showthr ... ?t=1471819 (http://forums.nasioc.com/forums/showthread.php?t=1471819)

[86bratman]

This is not a 2 stroke engine, backpressure is needed on a 2 stroke. The term you are looking for is scavenging effect.

While the intake losing you a little bit of power is always possible, I would look at things like the knock sensor first. I've never had a car lose power eliminating the converters. One possible issue I see is the exhaust size, more specifically how it steps up from 2.25 to 2.5 from the track pipe to the cat back. To keep exhaust velocity at its best you need to have the piping size the same all the way back. Thermal dynamics would suggest stepping it down slightly smaller as you move closer to the rear of the car, exhaust gasses are cooler back there, and will move slower as such.

[lancerswimmer89]

It was explained to me, and it kind of makes sense, that by eliminating my cats, and widening the exhaust, i have moved my powerband a bit, and increased my mid to upper range torque, while decreasing my low end torque.

[Wiscon_Mark]

Definitely get the CEL codes checked out.

It's worth mentioning that a faulty front o2 sensor can cause A/F mix issues while a rear o2 sensor is only to measure the effectiveness of the cat, so a rear o2 code will not be affecting engine performance.

Other things like knock sensor codes can put your car into limp mode and really affect performance.

But if it's a slight reduction in performance, it's likely the 2.5" exhaust.