Okay, just how good/bad is this computer command system? How far can one go with the cam/heads, etc without making the computer take a crap?

I've recently picked up an '86 SC with a stock LG4/4bbl. Of course, I have no intentions of making the engine suffer being stock for longer than nessacary.
I'd LIKE to keep the computer controlls on the carburetor if possible, for better controll of part-throttle A/F mixture.
So, if I go and do some porting, upgrade the intake, exhaust, and cam (nothing too wild - yet) would I just go and adjust idle, rejet, and fiddle with the secondaries like normal, or would the CCC system just try and screw me over?

are there any good sites/articles on this system out there?

 

Intake (dual planes only!), exhaust, and heads really won't affect the carb much. The problem is in the camshaft. Try to stay under 220* dur @.050 for the stock setup. If you want to go wilder, JET Performance can modify both the ECM and carb to suit your needs.

 

cool, don't think I'll be going past 220* cam timing anytime soon on this car. It'll be keeping its 305 for some time while my '77 gets running.

So, what needs to be reprogrammed in the ECM for larger cams? does low vacuum confuse it, or does the timing curve need to be significantly adjusted at that point?

 

I don't think there is much at all that you can do with a CC QJet. The only thing the computer controls is part throttle primary mixture, trying to achieve that mythical 14.7 to 1 air fuel mix. The secondaries work exactly the same as an ordinary QJet. You just find a nice rod/hanger combo and it comes on according to the tension of the AV spring. Usually a B hanger and DR rods work very well.

Go to www.thirdgen.org and look in the Tech Article section. There is an excellent column on tuning a CC QJet for performance.

 

As far as the ECM and PROM, do not go with an off the shelf unit. Instead, see if you can find an L69 ECM and PROM. Can't find one in a Camaro or Firebird? Monte Carlo's had them too.

Better yet, go with the GM ZZ4 ECM and PROM. That would be a little harder to come by, and more expensive, but it would perform the best.

You could also go with an ECM and PROM from a 350 Caprice...

The main problem with large cams and the CC QJet is the primary metering of the carb is EXTREMELY sensitive to vacuum. And if you mess with the primary system on a CC QJet it will never run right again. The main problem with the stock ECM and PROM is the timing curve, or uh, lack thereof They have very weak curves which will keep power levels down, regardless of what performance parts you throw at it.

 

I agree with Mark about the timing curve on the cc-carb setups. LG-4s had weak curves. L-69 HO motors had reasonably good ones.

The cc-carb setup is FAR more adaptable to engine changes than an equivalent FI system. The carb itself, being still a carb in it's operation, is naturally about 80% self-adjusting to changes in engine airflow due to larger diplacement, intake, heads, modest cam changes, etc. The ECM can compensate for the rest. I still wouldn't go totally crazy with the cam, though. Under 220* duration @ .050 is probably still a valid recommendation.

Heck, I ran a cc-QJet sytem with a Weiand roots blower under it once! Other than losing some of the emissions-related stuff it ran great under control of the stock chip!

You can push these system further than many think.

 

In his book, Doug Roe makes it sound like the CC system just works on a feedback loop between the mixture solenoid and the O2 sensor, and goes to wide open on the rods when there is low vacuum.
So, what happens if I re-jet? Can I break open the caps, and adjust the idle screws without fear?

I'll have to look around for an ECM/PROM. Do I need both, or would just a PROM swap do? Junkyards here suck (they want $75 for a mecnahical Q-jet ) so I'll likely have to have it shipped from somwhere, or just get the ZZ4 setup...

 

Do you have a dwell meter? Do you feel confident enough to try and tune it yourself?

I was going to suggest getting Doug Roe's book, but you've already got it!

Just a PROM swap might help - what year is your car?