reasons why carb with cat

[johnny27]

Why do ppl tell you that you can't run a carb with a cat converter? Does it stuff up the cat or does the engine just not run properly? Just intrersted to find ou

[Jack]

The ECU uses an oxygen sensor just ahead of the Catalytic Converter to measure how much oxygen is in the exhaust gases - the Cat needs a certain amount of oxygen to allow the oxidization components to function. Using the oxygen sensor, the ECU can modify the air-fuel mixture to adjust the oxygen level in the exhaust gases and keep the Cat working properly.

Carb engines generally don't have ECU's; so there is no electrical control mechanism to manage the air-fuel mix and oxygen in the exhaust gases. Without this, the Cat could easily get damaged.

This (http://auto.howstuffworks.com/catalytic-converter2.htm) page explains it quite well, and how the Cat functions.

[Adam]

A carb engine would kill a cat in no time.

[johnny27]

great stuff thanks lads. I thought it may have also stoped a carbed engine from running properly also.

[Ste L]

why would you want one anyway, they decrease power output

[Jack]

To pass the emissions part of the MOT :p

But then if the car wasn't designed to have one then it shouldn't really be going through the Cat test

[johnny27]

i bought a nova which was previous 1.2i. Then the previous owner fitted a 14nv sr engine, but did'nt use the sr exhaust manifold, downpipes or system, so he left the cat on the car. I Removed whole exhaust yesterday, and fitted a sportex 4-1 manifold, and custom straight thru exhaust, which i yet have to get a silencer for.

[Adam]

You wont need a cat
if you have a old 14nv engine fitted.

[johnny27]

its a carb fuelled nv, so i guess it never requires a cat by law.

[Jack]

Yup. As its a carb engine, its probably pre-91 - if the engine has been swapped, the emissions test goes by whichever is the oldest between the car or engine. So for example in your case, putting a 1991 SR engine into a 1993 car - the emissions test is run for a 1991 vehicle.