Stock Intake manifolds

[SSC's76]

It's a double edge sword kind of deal. The inert gas from the EGR system does increase intake charge temp but decreases combustion chamber temps. This cooling effect of combustion gases allows more spark advance under cruise and increases combustion efficiency. That’s why the auto manufactures went with electronic spark control and an array of sensors to monitor and adjust for proper operation. In pollution controlled vehicle with all the sensors intact it does work especially with a computer controlled carb or fuel injection system. In a dumb system it does very little to effect fuel economy but can hurt drivability since the EGR will only be metered by vacuum and the levels of advance that would yield better cruise economy will bring detonation without constant adjustment. So for performance or non emmision use toss it. If your running a CCC or FI setup keep it.

BTT.

Lots of GM cars came with an aluminum intake manifold. For weight savings it might help but for a good seal your not going to beat a cast unit and there is no flow difference between the peices unless you get ahold of a ZZ3/ZZ4 intake which are both nearly identical to a performer.

[79blazer]

Yeah I noticed I can have the timing more advanced at night when it is cool, but during the day, It will knock a lot easier. Now I am seeing why they had CCC. I have a year to go before It has to be emission tested, So I think I'll go with the intake I have. And will be keeping an eye out for a #3701 intake.

[jimfulco]

I wouldn't use a Performer on a stock or nearly stock 305. Too much volume in the runners that you can't use, and which can diminish the signal to the carb, causing poor driveability and, I suspect, gas mileage. The Performer reduces the performance of even a 350 up until 3000-3500rpm, according to an Edelbrock graph I saw a few years ago. Bigger is not always better.

EGR or non-EGR depends on carb calibration, and vice-versa. Disconnecting EGR with a carb that's calibrated for use WITH it can cause pinging at part-throttle due to a lean mixture. You can recalibrate the carb to be a little richer at part-throttle, and the pinging will disappear. EGR is not in the circuit at full-throttle, so WOT performance might not be diminished by it, but part-throttle efficiency is a different story. I'd be tempted to use a pre-'73 intake and carb, if possible, just to keep away from EGR problems.

Be sure of a couple of things when you go to pick a manifold. Does your air conditioner compressor use a rear brace that mounts to two holes straddling the crossover port on the driver's side of the intake? Not all intakes have those holes. The alternator brackets have a rear hole that mount to a hole near the top front of the intake. Early long-water-pump engines had the hole in a different place than the later ones. This may be addressed by getting an alternator bracket that matches the intake. The changeover was sometime in the '70s, but I don't know which year. I found a late-style non-EGR cast iron intake without EGR but with A/C bracket holes on a '77 Chevy van.

I'd be a little leery of the factory aluminum intakes, what with the fine quality control they had back then. Not to mention they didn't use any kind of anti-seize compound when they bolted stuff to them. Check all the bolt holes for threads, and hope like heck it's not warped.