I'm not sure if this is true, but someone told me today that running my car w/o the cat (race header or off-road pipe) would be really bad for my car. Supposedly, there would be greater flow (good) resulting in a drastic drop in backpressure (bad) which would in turn tell my car to run lean constantly (bad). Has anyone experienced any problems running either of these with the o2 cheater? Would there be any long term damage to anything? My stock cat just got wasted and i'm considering alternatives to just getting another stock cat that will break again.
backpressure on race header?
Saleen317
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I'm not sure if this is true, but someone told me today that running my car w/o the cat (race header or off-road pipe) would be really bad for my car. Supposedly, there would be greater flow (good) resulting in a drastic drop in backpressure (bad) which would in turn tell my car to run lean constantly (bad). Has anyone experienced any problems running either of these with the o2 cheater? Would there be any long term damage to anything? My stock cat just got wasted and i'm considering alternatives to just getting another stock cat that will break again.
I was told that if you reduce backpressure at lower RPMs (<4000) the valves open slightly too early and you lose power. I've always wondered this about exhaust systems, surely they're only going to improve matters at higher RPMs when gas flow is more important?
Joined
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7,439 Posts
I'm in the same boat with you. After about 29,000 miles I got a Hedman Hedder. It is CARB legal.
![Image]()
When I put it on I decided to take a look in my CAT and discovered it was collapsed and falling apart. So rather than leave it like that I gutted the rotten CAT to preven my Borla Exhust from going bad and to keep my car running.
So right now I have a bad CAT that is gutted.
It pulls alot harder than it did before. Butt Dyno of course. It sounds loud but good IMO. (I like race car sound).
Well I'm in the process of getting it fixed. I would like a higher flowing CAT. The Random Tech looks nice. Very expensive though.
I can probably get a factory CAT under warranty from Ford but I really would like a high flow one.
1 week and my CEL light has not turned on. Everthing seems fine.
My car no longer stumbles when idling. It used to stumnble a little. I really like how it is running. The stock CAT even gutted probably doesn't flow as good as a Random Tech. The pipe on the stock CAT is very narrow.
A little more gas probably wouldn't hurt. Maby some bigger injectors. It really seems to be running good though.
I would like at least a 2.5" pipe. 3" would even be better.
I still don't know how fat the Random Tech CAT is.
I have to get this fixed. Fast.
[ 08-02-2002: Message edited by: S. on Da 5 ]</p>
When I put it on I decided to take a look in my CAT and discovered it was collapsed and falling apart. So rather than leave it like that I gutted the rotten CAT to preven my Borla Exhust from going bad and to keep my car running.
So right now I have a bad CAT that is gutted.
It pulls alot harder than it did before. Butt Dyno of course. It sounds loud but good IMO. (I like race car sound).
Well I'm in the process of getting it fixed. I would like a higher flowing CAT. The Random Tech looks nice. Very expensive though.
I can probably get a factory CAT under warranty from Ford but I really would like a high flow one.
1 week and my CEL light has not turned on. Everthing seems fine.
My car no longer stumbles when idling. It used to stumnble a little. I really like how it is running. The stock CAT even gutted probably doesn't flow as good as a Random Tech. The pipe on the stock CAT is very narrow.
A little more gas probably wouldn't hurt. Maby some bigger injectors. It really seems to be running good though.
I would like at least a 2.5" pipe. 3" would even be better.
I still don't know how fat the Random Tech CAT is.
I have to get this fixed. Fast.
[ 08-02-2002: Message edited by: S. on Da 5 ]</p>
Remember backpressure bad. Backpressure lowered at the expense of pulse velocity (too big of piping)... also bad.
Ignore the advice you got. Race headers work fine. For a NA engine I would get yourself a long tube race header to maximize the benefit (will be loud) if you are willing to ditch the cat anyway.
If you really want an offroad pipe, I might sell mine soon to get SS (since I'm running a turbo).
Ignore the advice you got. Race headers work fine. For a NA engine I would get yourself a long tube race header to maximize the benefit (will be loud) if you are willing to ditch the cat anyway.
If you really want an offroad pipe, I might sell mine soon to get SS (since I'm running a turbo).
Joined
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5,592 Posts
backpressure is an ole' hotrodders tale...read up on ur old physics text bout fluid (and thus gaseous) dynamics.
-Ult
-Ult
you could just slap a Supertrapp muffler on your car and "dial-in" the amount of "back pressured" needed for your driving style! I believe Summit Racing carries them
![Image]()
Remember:
Mid-high back pressure = good low end torque
![Image]()
/poor high end power(hp)
![Image]()
low back pressure = poor low end torque
![Image]()
/good high end power(hp)
![Image]()
Remember:
Mid-high back pressure = good low end torque
low back pressure = poor low end torque
For those that care. Search these keywords in google:
scavenging backpressure
Exhaust pulse velocity
Should yield a decent result for some technical articles that try to dispell the backpressure misconception that the entire world seems to have. Or search this forum. If you are convinced that introducing backpressure can help torque production, go use 5" piping and then put a restricter plate on the end. Infinitely adjustable backpressure. You'll have no top end... and no bottom end power EITHER.
![Image]()
Or, you could read some articles and learn how to maximize scavenging (use almost perfectly straight 2" pipe with a glasspack muffler and expensive mandrel bends for places where you are forced to take sharper turns like around the suspension on the back) and never introduce backpressure in any form for the sake of backpressure. Thats why the "best" muffler from a performance aspect is no muffler, as they don't contribute to the flow of the exhaust in any fashion (only increase backpressure).
I don't like the way this guy words some of the stuff, but it seems 99% right and easy/entertaining to read:
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm
[ 08-03-2002: Message edited by: Ducman69 ]</p>
scavenging backpressure
Exhaust pulse velocity
Should yield a decent result for some technical articles that try to dispell the backpressure misconception that the entire world seems to have. Or search this forum. If you are convinced that introducing backpressure can help torque production, go use 5" piping and then put a restricter plate on the end. Infinitely adjustable backpressure. You'll have no top end... and no bottom end power EITHER.
Or, you could read some articles and learn how to maximize scavenging (use almost perfectly straight 2" pipe with a glasspack muffler and expensive mandrel bends for places where you are forced to take sharper turns like around the suspension on the back) and never introduce backpressure in any form for the sake of backpressure. Thats why the "best" muffler from a performance aspect is no muffler, as they don't contribute to the flow of the exhaust in any fashion (only increase backpressure).
I don't like the way this guy words some of the stuff, but it seems 99% right and easy/entertaining to read:
http://www.nsxprime.com/FAQ/Miscellaneous/exhausttheory.htm
[ 08-03-2002: Message edited by: Ducman69 ]</p>
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