4000 Quattro Exhaust/Cat. Help! Help needed!

[Bruce Bell]

Ricky,

You are lucky to get 3 years out of that Ansa. My OEM system
lasted 6 years, the Ansa replacement about 18 months. The Stebro
exhaust has gotten pretty good reviews in the past.  A couple of
thoughts for you: 1) Listen to Hew, the pulses are very
important, especially if you are running a big cam. Cam's really
need a tuned exhaust system to work properly on a NA car. 2) The
cat in a 4kq has the same ID as the cat in an urq. BTDT. (they
are different lengths) 3) Stock, the 4kq has about the best
exhaust system you can find and very well balanced for proper
backpressure. 4) Upgrading the 4kq with Schrick cam to an urq
exhaust (2.5" VS 2.25") does not appreciably help power output
other than a small gain near 5300 rpm. Most everywhere else power
is down and the torque curve is multi-modal rather than smooth.

A last thought. You mention a lot of lope with a large cam.  The
fact your car doesn't idle well with the O2 sensor plugged in
tells me you may have way too much cam for CIS. Intake pulses
caused by too much overlap interfere with the metering plate
causing the motor to rapidly fluctuate between rich and lean. I'd
also think, with that much overlap, you would be hitting the rpm
limiter right in the middle of the fun.

Bruce