re: to cat or not to cat

[jkerouac@xxxxxxxxxxxxx]

re: To Cat or Not to Cat.

     Years back I had an '84 318i that went through various states of
tune and degrees of modification.
     This included cat, hollow cat housings, and 2 1/4" straight pipe
replacements.

Here are my emission results:

The factory sets these cars so that they will pass emissions even in a
bad state of tune.  There needs to me a faulty component, such as a
coolant temperature sensor, for the car to run really dirty.
     If dialed in precisely, the car ran below .015 CO.  The HC was way
down, don't recall the numbers.
     With the cat removed, CO went up to about .04.  HC increased
slightly.  Still way below limits.

The most evolved the motor got was up to 2 liter displacement, retarded
stock cam, timing set to 40 degrees total advance, Stahl header with 2
1/4 outlet and straight pipe to any cheap free flow muffler, Mallory
Voltmaster coil, NGK wires for a Honda 1500 and BP6ET plugs, IVC and ICU
removed, larger throttle, 60psi fuel pressure, etc.

The car still ran less than .05 CO.

What's the key?
They key item was the O2 sensor.  If the O2 sensor is good and the loop
is connected, the engine will run more than clean enough, as long as all
the sensors around the injection system are in good working order.  The
O2 sensor I used was Pep Boys' as listed for a Rabbit.

So go ahead and remove the cat.  You will still run cleaner than most
else of what's out there even if they do have a cat.

Good Luck,
'jk

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