No cats=No torque?
Thread Starter
TECH Resident
Joined: Sep 2002
Posts: 803
Likes: 0
From: Charlotte, North Carolina
No cats=No torque? I recently had my car dynoed a few months back. When I was in the shop talking to the owner I was telling him how I would be getting headers soon. He told me that I better get a catted y-pipe because without the backpressure from the cats these cars are absolute dogs on the low end. Is this true, all you guys without cats did you feel a difference down low? It seems like more people are running ORP then catted y's.
Well, I don't have a low end (my converter winds
up over 3500RPM at WOT). But I did look at two
of my log files, from before & after swapping on
gutted (stock) cats and there was no midband
difference and a slight improvement at the big
end, in the Delivered Torque - Engine PID (though
this is not a "hard measurement").
To me it feels like it's pulling stronger when I
really open it up, gutted. But maybe a stock-
converter car would see its VE messed around a
bit and have some more mixture related issues,
stuck in the low end and without a chance to
kick down (stock PCM shift program is lame).
up over 3500RPM at WOT). But I did look at two
of my log files, from before & after swapping on
gutted (stock) cats and there was no midband
difference and a slight improvement at the big
end, in the Delivered Torque - Engine PID (though
this is not a "hard measurement").
To me it feels like it's pulling stronger when I
really open it up, gutted. But maybe a stock-
converter car would see its VE messed around a
bit and have some more mixture related issues,
stuck in the low end and without a chance to
kick down (stock PCM shift program is lame).
I feel like I lost some torque down low with my orx. You see alot of people running with off-road pipes because it is much cheaper than a catted one, plus some of us don't have inspections to pass 
Cats or no cats...in the low rpm range you'll never be able to tell the difference. All these people who talk about needing backpressure is BS. Backpressure is a measure of resistance. I have driven my car with and without cats with several different setups and never noticed a low rpm power loss. I am running cats now, but not for that reason.
Staging Lane
Joined: Jul 2004
Posts: 61
Likes: 0
I know everyone says that backpressure = bs, but I'm not so sure. Back when I had an Impala SS, I did a before and after race with a buddy of mine. Initially, I had full exhaust. Then, I yanked everything and ran straight pipes with no cats or mufflers.
With the exhaust, I could beat him, easy. Without the exhaust, he'd pull a good car on me until we got to a decent speed. I had no low end at ALL.
If not backpressure, why would that be? I'd really like to know...
With the exhaust, I could beat him, easy. Without the exhaust, he'd pull a good car on me until we got to a decent speed. I had no low end at ALL.
If not backpressure, why would that be? I'd really like to know...
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Launching!
Joined: Jul 2004
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From: Gainesville, Florida
Originally Posted by Dr. Juris
If not backpressure, why would that be? I'd really like to know...
On second thought, yeah backpressure is good. When its caused by a turbo which makes more intake pressure than exhaust pressure
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!LS1 11 Second Club
Joined: Apr 2003
Posts: 7,133
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From: Miami
When removing cats, or opening a cutout, your peak torque moves up in the rev range.
The peak number gain increased also, it's just up there and no longer down low.
I'd take more peak TQ up high than less peak TQ down low any day.
The peak number gain increased also, it's just up there and no longer down low.
I'd take more peak TQ up high than less peak TQ down low any day.
TECH Fanatic
Joined: Oct 2003
Posts: 1,655
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From: Northern Va
Originally Posted by Dr. Juris
I know everyone says that backpressure = bs, but I'm not so sure. Back when I had an Impala SS, I did a before and after race with a buddy of mine. Initially, I had full exhaust. Then, I yanked everything and ran straight pipes with no cats or mufflers.
With the exhaust, I could beat him, easy. Without the exhaust, he'd pull a good car on me until we got to a decent speed. I had no low end at ALL.
If not backpressure, why would that be? I'd really like to know...
With the exhaust, I could beat him, easy. Without the exhaust, he'd pull a good car on me until we got to a decent speed. I had no low end at ALL.
If not backpressure, why would that be? I'd really like to know...
Tuning!
TECH Fanatic
Joined: Oct 2003
Posts: 1,655
Likes: 0
From: Northern Va
horsepower is a function of torque, when you remove the cats, you down lose any power, it just moves it, like south was saying...
(Torque x Engine speed) / 5,252 = Horsepower....so plug in some numbers and do some math...
can't beat the sound. if the car is running worse without cats, try having it tuned
(Torque x Engine speed) / 5,252 = Horsepower....so plug in some numbers and do some math...
can't beat the sound. if the car is running worse without cats, try having it tuned
Like they said, it moves it up the power band. Before headers/ory I would shift at like 16-1700 in everyday driving. Now I shift like 2600 in the traffic. The cars barely moving now where I used to shift at so yeah it seems like I lost some low end but definately made up for it on the top end (which is what matters).
The freed up exhaust flow might possibly lean the fuel mixture in a similar manner like when headers are installed.........
jimmyblue: Did your ported exhaust manifolds make a difference? I see there's a good 1/8" restriction around each port.
jimmyblue: Did your ported exhaust manifolds make a difference? I see there's a good 1/8" restriction around each port.
TECH Fanatic
Joined: Oct 2003
Posts: 1,839
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"When I was in the shop talking to the owner I was telling him how I would be getting headers soon. He told me that I better get a catted y-pipe because without the backpressure from the cats these cars are absolute dogs on the low end."
People like this need to produce time slips or STFU.
People like this need to produce time slips or STFU.
