My 89 iroc got a new flowmaster cat back installed and I have now lost all my low end power, the car struggles to take off., and shakes badly if you have it under 1800 rpm while cruising. the only other thing I can think is it has factory 2.73's in the rear and I swaped in a T5. By the way the car is a LB9 originally auto.

 

You clue, right there.

You have a dead hole.

Pretty hard for a muffler to do that. It's just coincidence.

Look for a burnt plug wire.

 

all igniton stuff in less the 200 miles old...coil, cap, rotor, wires, plugs,. O2 sensor.

 

As my dad always told me, "Just cause it's new don't mean it ain't broke"

 

Doesn't matter what's new.

You've got a dead hole.

Find what's causing that, you'll fix it.

It's not the muffler or ANYTHING to do with it.

 

Well, if you get through the ignition with no luck, a large exhaust leak would do something similar IMO. Might check that next.

However my initial thoughts are with the guys above.

 

Did you just swap in the T5 at the same time as the catback?

For one thing, the low end loss of power and bogging can come from being in to tall a gear. Kind of like shifting into 4th at 20mph. Basically, the T5 doesn't have the 1st 3.08 gear the 700r4 has to help launch these suckers. The minumum rear end ratio the T5 got was 3.08.

So with your 2.73 and taller 1st T5 gear you now have, your car's lowend feels horrible. And also, with the nice sounding exhaust you just installed, it will make your car feel slower because the POWER SOUND doesn't make the POWER FEEL.

I hope that makes sense, but I am 99% sure that is where your lack of lowend came from.

Now if you have had the T5 al long time ago and just now added the catback, either it's the power sound issue, or something else entirely.

Good luck.