66 327 Engine Troubles

[Dan White]

The 327 in my 66 is running very poorly. First off, it misses on acceleration, and on deceleration or coasting, it pops loudly out the rear (the sound is very loud with the chambered under car system I have). It will occasionally pop like this under acceleration, but rarely. With a vacuum gauge on the carb's vacuum port, I get a vey erratic needle (it sweepes rapidly back and forth over a range of 3 to 4 inches). Besides this, it idles very rough. The car was recently brought out of a 20 year storage. The valves were adjusted, and a new edelbrock manifold and carb were installed. The distributor was checked, including the points and timing, and that checked out fine. One thing I knoe is wrong is the carb is running rich, and the plugs are getting a little black, but it doesn't seem like that would cause all these problems. I figure I might have a bad lifter (but there is no excessive noise) or a stuck or rusty valve??? Thanks in advance, Dan

[Duke W.]

Re: 66 327 Engine Troubles

The first thing I would recommend is a compression and leak down test. You never know what might happen to an engine that has been in hibernation for 20 years.

Assuming compression and leakdown indicate no internal problems,your problems could be both fuel and ignition related. Is it a 300 or 350 HP engine? I don't know why you installed a new carburetor and manifold. Most aftermarket carbs are "one size fits all" and may not be properly calibrated for the engine.

My suggestion would be to overhaul the original carburetor and install it on the original manifold with the correct PCV system. While the carb is being worked on pull the distributor and disassemble it for a thorough inspection. Check the bushings and regrease the upper well. Install a new breaker plate and insure that it is snug and wobble free. Test the vacuum can and replace it with a new OEM equivalent spec can if it is not to spec. Check that the centrifugal advance functions and shim up the end play to two to seven thou when you assemble it. Use the high breaker arm tension points if it is a L-79. You should also check the wires, and if they show more than about 5000 ohms per foot they should be replaced. Look at the date code. They might be original, which is good for judging, but they have probably broken down electrically.

My approach is to always repair/overhaul the original components as necessary to restore OEM performance. The mid-sixties small blocks were the pinnacle of pre-emissions engine development. Chevrolet spent a lot of time calibrating them, and they are very good as-is, but time takes a toll.

A lot of times if you start "re-engineering" an engine with off-the-shelf once size fits all aftermarket parts you will be required to finish all the development work to get them working synergistically with the rest of the engine, so you're better off restoring the original components to original design performnce.

The wear parts you need are readily available, and the AIM and Chassis Service Manual are your guide to putting everything back together the way it was originally built.

You could also check lobe lift with a dial indicator, but a really flat lobe would be evident to visual inspection and will show up as low compression if its an inlet valve.

Duke