The Stovebolt Site Forums The Shop Area Engine Shop 216 w/ HEI Distributor, Spark Plug Help and Other

I bought a HEI distributor of eBay for a Chevy 250, modified it, and installed in per the instructions I found on here.

I didn't think it would really improve the drivability of the car, just the reliability, but it actually idles better and accelerates better.

Have a couple of questions.
1) What would you set the base timing at, I set it at 5° advance.
2) What would you set the vacuum advance timing at? I left it alone for now; need to source a vacuum pump to check it.
3) How about spark plugs? Currently have the stock plugs in it which have short threads. I looked at pics of the plugs on Rock Auto and it looks like the plugs from a 1978 Nova 250 which had HEI would fit. Correct me if I’m wrong but selecting a plug is first its dimensions, resistance, heat, then gapping it. Do you think I should stick with the stock style plugs or do you think I would get better spark with a plug that went into a vehicle that had HEI?

Thanks in advance!

A spark plug is a spark plug, the only difference is the heat range ( the plugs ability to retain or give off excess heat) A hotter heat range will keep the tip of the plug hotter, good for oil burning engines, a cooler plug is better for high compression or lean burn engines, no hot spots in the combustion chamber. Stick with what it came with, you can open up the gap to .045" to .050" for more spark.

Set the timing as high as you can but still have the engine perform as it should. Advanced timing gives better fuel milage, up to a point! Step it up a few degrees at a time and test drive it.

Vacuum advance is not adjustable unless you installed a aftermarket unit. Same thing on it as with the base timing, set it high if adjustable and test drive.

Your main problem will be compression, you don't have enough to really tell when the timing is to high. At 7 or 8 to one compression, you should never hear it ping under a load even with crappy fuel. Ideally you want the timing just below or right at the point of detonation.

Joe

Stick with the stock plugs for the 216, and set the gap at .045". Set the initial timing to the BB just like the point-type distributor, disconnect the vacuum line, and rev the engine to about 2,000-2,500 RPM and use a delay-flash timing light to check for the maximum centrifugal advance. The combination of initial and centrifugal should top out at around 35-36 degrees. You might have to install a set of different springs in the centrifugal advance to allow the advance to max out at that speed, usually slightly weaker springs than standard. If the initial/centrifugal total advance is too low, adjust the distributor housing to get that number at cruise speed, and let the initial fall in there wherever it will. The total advance is more important than timing on the BB, as long as the engine doesn't kick back when starting. Connecting the vacuum should add about 8-10 degrees more advance at light-throttle cruise.
Jerry

One other consideration is the spark plug wires. When I got my HEI from Tom Langdon, he told me to go get a good set of HEI compatible wires. If you do a net search on HEI spark plug wires you'll get lots of good info. I bought a universal set of Taylor wires and they've given trouble-free service for many years.