76 carbs any good?

I have a pretty decent carb off a 1976 Buick 455 (17056240). Is this thing any good for any type of performance use or just a bag of worms?? (I know the mid and wot changes are easy to make, what about idle, I am assuming its gonna be real lean for a cammed engine and need passages drilled)...I know parts won't interchange with earlier ones too...

Anybody been there, done that??

Thanks
Tim

 

There are so many variations of Q-Jet that you might as well say there is no parts interchangability, period. Then when you discover something does interchange, it's a bonus.

Nothing inherently wrong with the '76 carb. It is the general basic design of the Edelbrock Performer RPM 1910 carb, in that it uses the newer style (Mod Quad) castings having the part throttle mixture adjustment, and space for the plastic "shot glass" or aneroid bellows.

You are right, you'll probably have to drill the idle mixture passages larger. Easy money. Same with changing jets and metering rods.

You could do a lot worse.

 

Anyone know what an aproximate CFM rating is on a 1976 Rochester M4MC?

 

It's probably an 800, although they may have gone back to 750s by then????

See this article on telling the difference

Although you can't see it in the pic, the 800 has a "bump" on the outside edge of the circumference of the venturi. Hard to describe, easy to spot once you've seen it.

http://www.buickperformance.com/qjet.html

 

Actually, considering the advanceemnts made to the Q-jet through the years made the late '70's and early 80's Qjets very reliable, and easy to service, even the electronic units. You are correct, however, regarding the metering. They were actually somewhat richer than the early 70's units, as with the advent of the convertor, the metering actually made the engines tolerable to drive. What seriously affected the engines of the late 70's was the slow timing advances, aggresive EGR calibrations, and restrictive exhausts caused by the early convertors. The tall gearing to reduce engine rpm did not help, either. Since the cams had a lot of overlap to encourage NOx reductions, and slow timing advances for the same reason, when tuned, they actually run very well, especially if geared for the cams, and have the emission controls defeated. No, wait, I didn't say that. What has brought back performance of late is the advances in electronic controls, and their integration into the overall performance. Ray

 

Wow, I never would have guessed it to be that high. My 460 Lincoln only has a 600cfm on it, I think.

 

Ray- What is required in removing the EGR system on a car? I have a car that had the EGR removed (not by me).

 

Simply not connecting vacuum to the EGR valve will "turn off" the system. You can't really "remove" the EGR system as it is mostly passages within the motor. You can unbolt the EGR valve and replace it with a block off plate, for looks...

 

I see, I guess that's what the recirculation part of EGR is. So would turning it off positively affect the performance?

 

If it's working properly, it won't be active at idle or WFO. It would be nearly seamless when it is active.

The only thing you'd notice is that you'd need to recurve the distributor if you disable it, 'cause the engine is going to ping like there's no tomorrow. EGR is one of the best cures for part-throttle ping.

End result: Make it functional, and the reduction in pinging will allow you to run cheaper gas or more timing or both. OR go all the way to non-emissions compliant carb and timing specs, more compression, more cam, etc. DO NOT just disable the egr and think you've accomplished something.

 

Though in theory, the EGR is seamless, it is actually responsible for the hesitations, and surging at part throttle experienced at the time of its introduction. It seems that its calibration was a nightmare, rarely correct, and usually sticking, causing its share of rough idling, and stalling. You are correct regarding its operation range, from just off idle to heavy throttle maneuvers, being off at idle and at WOT. At this time, however, it rarely created a need for extra advance; its elimination did not typically require ignition timing recurving. There were times, however, when cheap fuels or short trips using the EGR created its share of carbon, and the necessary cleanouts. Eliminating its input typically eliminated the surging and tip in sags, and typically resulted in much improved driveability and idle quality. It tended to foul plugs when cheap fuels were used, causing its share of required tune-ups. Though its elimination raises NOx emissions, they are typically not checked on vehicles prior to 1986. They need to be connected, appearing to operate correctly. A BB in the hose works well here. Do I sound experienced? I do not advocate the elimination of emission controls, especially in vehicles built after 1985, however, before that time, the controls were typically add-ons, and driveability typically suffered with their operation. I worked for GM as a driveability expert, assisting them in the integration of the computer controls seeing their advent in the '80's. I would be happy to answer any question you may have.