that sound a little optomistic
cut out cats
Thread Starter
Drifting
Joined: Sep 2004
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cut out cats
So what will be the effect on my engine if I just cut out the cats in the stock exhaust and replace em with straight pipes? I'm running a ZZ4 with a stock exhaust - I assuming I can do better!
Carl Johansson
Carl Johansson
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Joined: Aug 2000
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From: San Pedro CA
you don't say where you live.
I would not just gut the cat... the L98 exhaust is so restrictive.
Consider this:
1) remove the exhaust from the manifolds back.
2) install a custom exhaust, more like the LT1 style, with a pair of bullet cats located about where the old pup cats used to be.
3) x-pipe
4) mufflers.
This can be modified to accept headers at any time. This type of update is worth, I would guess, about 30-40 hp. and will still pass any sniff test, and won't smell of raw fuel.
I would not just gut the cat... the L98 exhaust is so restrictive.
Consider this:
1) remove the exhaust from the manifolds back.
2) install a custom exhaust, more like the LT1 style, with a pair of bullet cats located about where the old pup cats used to be.
3) x-pipe
4) mufflers.
This can be modified to accept headers at any time. This type of update is worth, I would guess, about 30-40 hp. and will still pass any sniff test, and won't smell of raw fuel.
Thread Starter
Drifting
Joined: Sep 2004
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well guys - i do live in california - but i just 'sold" the car to my brother who lives in Michigan - we actually share the car -- really!
So all of a sudden - no need to worry about cal smog. The air pump is gone - along with the tubes that seemed to be recirculating exhaust back into the cylinders.
carl Johansson
So all of a sudden - no need to worry about cal smog. The air pump is gone - along with the tubes that seemed to be recirculating exhaust back into the cylinders.
carl Johansson
Team Owner
Joined: Aug 2000
Posts: 40,156
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From: San Pedro CA
Originally Posted by Carl Johansson
well guys - i do live in california - but i just 'sold" the car to my brother who lives in Michigan - we actually share the car -- really!
So all of a sudden - no need to worry about cal smog. The air pump is gone - along with the tubes that seemed to be recirculating exhaust back into the cylinders.
carl Johansson
So all of a sudden - no need to worry about cal smog. The air pump is gone - along with the tubes that seemed to be recirculating exhaust back into the cylinders.
carl Johansson
you don't have to pass a test, but if CARB sets up the highway testers, they can nail an outta state car... especially if it has been in CA beyond the DMVs threshold.
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From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Just deleting the cat and putting in a straight pipe should net about 10hp.
It will be noticably louder.
It will be noticably louder.
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
I don't think GM left that much on the table. I don't see what's so bad about a dual 2.5 to 3 to dual 2.25 system on a motor that only revs to 4800, except maybe the cat.
The LT1 exhaust has about 35% more cross sectional area, and revs about 30% higher.
The LT1 exhaust has about 35% more cross sectional area, and revs about 30% higher.
Last edited by CentralCoaster; Apr 1, 2006 at 04:26 AM.
Team Owner
Joined: Aug 2000
Posts: 40,156
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From: San Pedro CA
Originally Posted by CentralCoaster
I don't think GM left that much on the table. I don't see what's so bad about a dual 2.5 to 3 to dual 2.25 system on a motor that only revs to 4800, except maybe the cat.
The LT1 exhaust has about 35% more cross sectional area, and revs about 30% higher.
The LT1 exhaust has about 35% more cross sectional area, and revs about 30% higher.
Once you do the intake, the exhaust is mandatory.
Team Owner
Joined: May 2002
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
I'm not trying to play devil's advocate here, but all the reports I've seen were with SOTP dynos.
What do you think of:
stock shorties with port work,
stock 2.5" catless front Y to 3"
high flow carsound cat (same flow as random tech)
dynomax 2.5" rear Y
Muffler elims
What do you think of:
stock shorties with port work,
stock 2.5" catless front Y to 3"
high flow carsound cat (same flow as random tech)
dynomax 2.5" rear Y
Muffler elims
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by CentralCoaster
I'm not trying to play devil's advocate here, but all the reports I've seen were with SOTP dynos.
What do you think of:
stock shorties with port work,
stock 2.5" catless front Y to 3"
high flow carsound cat (same flow as random tech)
dynomax 2.5" rear Y
Muffler elims
What do you think of:
stock shorties with port work,
stock 2.5" catless front Y to 3"
high flow carsound cat (same flow as random tech)
dynomax 2.5" rear Y
Muffler elims
Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
Removing the stock L98 exhaust and replacing it with a 2.5-3-2.5 exh, carsound pre/main cats and aftermarket muffs netted me about .2 and 3 mph in the 1/4 mile. Results are muddled just a tad as my 60 ft varied by just under a tenth on before/after runs. MPH on each was a solid 3 mph diff.
Thread Starter
Drifting
Joined: Sep 2004
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Originally Posted by bogus
actually, you do.
you don't have to pass a test, but if CARB sets up the highway testers, they can nail an outta state car... especially if it has been in CA beyond the DMVs threshold.
you don't have to pass a test, but if CARB sets up the highway testers, they can nail an outta state car... especially if it has been in CA beyond the DMVs threshold.
regardless - so I pull of the stock pipes where they join up to the manifolds - correct ?- then not worrying about cats - I would take 2 pipes back to an X pipe - then continue to the rear where I would run em through some elcheapo muffler - is that correct?
Carl "vroom Vroom" johansson
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Joined: Aug 2000
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From: San Pedro CA
but you are missing the point... if you are caught in CA without cats, you are violating a federal law, which CARB enforces. You will get a ticket. And a loud car will attract that kinda attention you don't want.
The mobile units use some kinda infrared to scan the air for high concentrations. If it finds a problem, in theory at least, they issue tickets to all vehicles in that pack, via photo radar, requiring them to go in for a sniff test.
The otherside of this is the noise... the last thing anyone wants is greater attention drawn by the local LEO. And with so many towns passing tighter and tighter noise restrictions, tickets are a way of life. Why expose yourself to them?
Then comes my selfishness... I like my air to not smell like raw exhaust gases.
The mobile units use some kinda infrared to scan the air for high concentrations. If it finds a problem, in theory at least, they issue tickets to all vehicles in that pack, via photo radar, requiring them to go in for a sniff test.
The otherside of this is the noise... the last thing anyone wants is greater attention drawn by the local LEO. And with so many towns passing tighter and tighter noise restrictions, tickets are a way of life. Why expose yourself to them?
Then comes my selfishness... I like my air to not smell like raw exhaust gases.
Team Owner
Joined: May 2002
Posts: 24,337
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From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Roadside testing, I can't wait to see this disaster. And you thought the redlight camera lawsuits were bad... 
So tell me what happens when a perfectly clean car shifts right at the sensor and spits out those unburnt HCs. Honestly where the hell would you put one anyways? In the road surface? On curbs?
They'd be better of hooking all the cars onboards to the carb communist air resources board home office so they can issue tickets everytime the ecm detects a misfire.
So tell me what happens when a perfectly clean car shifts right at the sensor and spits out those unburnt HCs. Honestly where the hell would you put one anyways? In the road surface? On curbs?
They'd be better of hooking all the cars onboards to the carb communist air resources board home office so they can issue tickets everytime the ecm detects a misfire.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Originally Posted by CentralCoaster
Roadside testing, I can't wait to see this disaster. And you thought the redlight camera lawsuits were bad...
So tell me what happens when a perfectly clean car shifts right at the sensor and spits out those unburnt HCs. Honestly where the hell would you put one anyways? In the road surface? On curbs?
They'd be better of hooking all the cars onboards to the carb communist air resources board home office so they can issue tickets everytime the ecm detects a misfire.
So tell me what happens when a perfectly clean car shifts right at the sensor and spits out those unburnt HCs. Honestly where the hell would you put one anyways? In the road surface? On curbs?
They'd be better of hooking all the cars onboards to the carb communist air resources board home office so they can issue tickets everytime the ecm detects a misfire.
It looks like LA and SF Bay area are the target areas.