Dropping the Cat on a 3.0 911sc '83
11-27-2011, 11:36 PM
#16
Agreed...at least in my experience.
The bypass pipe (GHL) definitely adversely affected the low RPM response on my very stock 3.2. Not a lot but I can feel the difference. The throttle response is not as crisp as when the cat was in place.
Interestingly, when I installed a Euro pre-muffler on my '79 SC back in the early '80's, I noticed no drop in low RPM performance. Could that be a function of CIS vs. Motronic?
Interesting theories, interesting thread!
The bypass pipe (GHL) definitely adversely affected the low RPM response on my very stock 3.2. Not a lot but I can feel the difference. The throttle response is not as crisp as when the cat was in place.
Interestingly, when I installed a Euro pre-muffler on my '79 SC back in the early '80's, I noticed no drop in low RPM performance. Could that be a function of CIS vs. Motronic?
Interesting theories, interesting thread!
On my stock 3.0 I didn't notice much loss of crispness at low rpm. and it really sang when on the pipe.
I believe I can tune it for the full spectrum when I put it on an ehaust analyzer.
I do feel the cat is a choke point on the SC as my idle jumped 150 rpm when it was removed....
11-30-2011, 06:40 PM
#17
slapped an exhaust analyzer on the car after about a 75 mile drive to town, so fully warmed up and then some.
With the cat on its CO is leaned out by spec now we fattened it up to 3.5, 3 to 4 is good without the cat says the tech. Should cool the heads better a tad too.
I noticed the low end crispness is back...it had risen to about 3000 rpm before adjustment to feel on the pipe, now it is back down about 1800 rpm. I def notice the dif above 4k, breathes better. 80 to 100 plus just really comes on now.
Maybe the CIS works in this manner with a basically stock exhaust but the Motronic constantly wants to adjust itself....no exp with the Mo so just supposition.
With the cat on its CO is leaned out by spec now we fattened it up to 3.5, 3 to 4 is good without the cat says the tech. Should cool the heads better a tad too.
I noticed the low end crispness is back...it had risen to about 3000 rpm before adjustment to feel on the pipe, now it is back down about 1800 rpm. I def notice the dif above 4k, breathes better. 80 to 100 plus just really comes on now.
Maybe the CIS works in this manner with a basically stock exhaust but the Motronic constantly wants to adjust itself....no exp with the Mo so just supposition.
