disconnecting precats?
Thread Starter
Racer
Joined: Nov 2004
Posts: 265
Likes: 0
From: Angleton Tx
disconnecting precats?
do the precats on a 1990 really help the emissions much?
If I replaced them with a flanged straight pipe, will there
be a noticable difference in power and sound? Is the center
a cataytic converter or a resonator.
I have one of the precats making a ringing sound as is.
Is this repairable?
If I replaced them with a flanged straight pipe, will there
be a noticable difference in power and sound? Is the center
a cataytic converter or a resonator.
I have one of the precats making a ringing sound as is.
Is this repairable?
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The cats are not repairable. You have to replace them with new cats. Chance sare one of them has rust and corrosion and the stuff inside is just bouncing around. This can lead to clogging of the exhaust pile and disruption of exhaust flow.
The various catalogs have replacement assemblies with and without the precats. If you don't have to do a sniffer test for emissions, then going without the precart will definitely help. And a set of Hooker long tube headers instead of the pipe will be a big help!!
The various catalogs have replacement assemblies with and without the precats. If you don't have to do a sniffer test for emissions, then going without the precart will definitely help. And a set of Hooker long tube headers instead of the pipe will be a big help!!
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Precats really dont affect the sniffer test unless the engine is cold. Once the engine warms up theyre of little use for emissions.
If you remove them entirely, and just replace your main cat with a Random Tech cat, you'll still pass the sniffer test and make a bit more power.
The catalogs will sell the replacement front Y-pipe with cats if you believe you still need it to pass visual, but you dont need them for the sniffer.
If you remove them entirely, and just replace your main cat with a Random Tech cat, you'll still pass the sniffer test and make a bit more power.
The catalogs will sell the replacement front Y-pipe with cats if you believe you still need it to pass visual, but you dont need them for the sniffer.
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Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
we are... precats, by definition, are designed to heat up fast and help cold start emissions.
They do that, but after that, they don't do much for air quality, but do slow down the flow a lot.
Once the car reaches op temps, the factory single cat is up to snuff and all is right in the world.
I would be STUNNED if a warmed up car didn't pass the sniff without precats.
They do that, but after that, they don't do much for air quality, but do slow down the flow a lot.
Once the car reaches op temps, the factory single cat is up to snuff and all is right in the world.
I would be STUNNED if a warmed up car didn't pass the sniff without precats.
Racer
Joined: Mar 2001
Posts: 312
Likes: 0
From: Mesa Az
I cut my front y-pipe right below the cats and then used an air chisel to break out the catalyst and rewelded the pipe back together. I have a Random Technology cat in place of the stock cat and I have passed Az emissions test with no problem. I have turned a 13.77 with my "stock" exhaust (including stock mufflers). Go for It.
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Indeed you can replace the stock front Y pipe with a 2 1/2" mandrel bent precatless Y pipe and a modern hi-flow main cat.
This setup is 49-state legal (sorry Left Coast).
I have run such a setup on my '88 for 4yrs now and every 2 years she easily passes the dreaded OH E-Check dyno sniffer test. BTW, that is while running a 160deg T-stat & fan switch in late Feb.
This setup is 49-state legal (sorry Left Coast).
I have run such a setup on my '88 for 4yrs now and every 2 years she easily passes the dreaded OH E-Check dyno sniffer test. BTW, that is while running a 160deg T-stat & fan switch in late Feb.
Safety Car
Joined: Apr 2003
Posts: 3,793
Likes: 9
From: VA
Originally Posted by vader86
Precats really dont affect the sniffer test unless the engine is cold. Once the engine warms up theyre of little use for emissions.
Originally Posted by 65Z01
Indeed you can replace the stock front Y pipe with a 2 1/2" mandrel bent precatless Y pipe and a modern hi-flow main cat.
This setup is 49-state legal (sorry Left Coast).
This setup is 49-state legal (sorry Left Coast).
I don't know if the NE CARB states enforce the picky visual that Ca does. If they don't then no precats should pass emissions there. Should have no problem passing in any non-CARB state.
Originally Posted by prodadiv
I assume you can't buy just the precats?
I live in Texas and unfortunetely there is a sniffer test
for emissions here.
I live in Texas and unfortunetely there is a sniffer test
for emissions here.
