ss454327

iTrader: (10)

I just removed mine and did some data logging runs and I can assure you the engine didn't lose any power. Anyone claiming you need them for backpressure doesn't understand the concept of that term. Having correct "backpresure" means you have 0 resistance while also having constant velocity. I can tell you I did get some KR at the top of my 2-3 shift because of the resonance of the exhaust without the cats. We found it to be false knock so we dialed the sensativity back a bit and didn't get it again.

Most people claim to have lost power down low because it sounds louder at lower RPMs so when it sounds like it's winding out most people remember it going faster when it was that loud.

JYount

Like he said, backpressure is a misnomer, everyone says bp but the only effect of exhaust being free flowing is less scavenging, cause theoretically the velocity of the exhaust should increase. Unless you put a pipe through it though, gutting alone can hurt flow. This is why
Exhaust in cat, expands to fill area that used to be glowing hot honeycomb, then has to shrink back down to go out the exit. It has been verified with water flow rating, gutted cats flow worse than cats with the junk in em, straight through pipes are obviously the best.

ss454327

iTrader: (10)

So this guy gutted his cats instead of cutting them out and putting in pipe? That I can believe would cause a loss in power because of the added turbulance.

JYount

doesn't read that way, now that i go back. its been a couple days since the thread started

jeforton

iTrader: (3)

no, i cut the cats off and welded in some pipe. would a small exhaust leak cause the loss in power? when i went to the drive through, i could hear and exhaust leak echoing off the wall. i can't be very big, but would that screw with anything?

p.s.
sorry for the stupid questions, i always figured after the headers(or exhaust manifolds) it was all about sound. so be patient while i figure out the ins and outs of exhaust tuning.

ss454327

iTrader: (10)

A leak could cause a slight loss in power but it's more likely resonance causing false knock or the simple fact that it sounds louder at lower RPMs so you feel it should be accelerating faster than it is.

jeforton

iTrader: (3)

it's not that it feels slower, it is slower. my 0-60mph time was 9.78 with the cats. 10.2 with out the cats.

camochevy21

I went from a Y pipe to true duals with no mufflers and stock cats and my truck was slower off the line but had more at top end. I think if I still had that exhaust a tune would have made it better all around. I think it sounds like a tune is what you need then go from there. Correct me if I'm wrong.