The Stovebolt Site Forums The Shop Area Engine Shop Testing Stage! HEI for the Stock Distributor

Check your manual. My 1946 Factory manual says set points to .018. Though read a bit farther the manual says that when putting in new points set it to .022 because the points wear down.

My Motors manual says .022 with no reference to the points age.

So for me the ideal setting would be .022. The larger the gap allows for better coil field saturation and a stronger spark. Now I do not know what year engine you have though I can look up your engine in my Motors manual.

I have seen HEI spark plug gaps up to .060 to .080. I do not see why you would limit your test to .045.

Also you have to use a spark plug that will fit yet is designed to have a wide gap for the ground electrode end has to be above the center electrode as when using a regular plug and gap.

Though you have to find out is there enough clearance between a large gap plug an the top of the piston.



As to the old codgers 1940 to 1948 SP gap was .040. points were .022.

1949 to 1953 SP gap was .035. points were .016, except corvette was .015

This points out that there was more to just a difference in point gaps and may yield questionable results.


Test one: Points Distributor (.016 points gap) with stock coil using ballast resistor with plugs gapped to .035.

Test two: Points Distributor (.016 points gap) with stock coil using ballast resistor with plugs gapped to .040.


I agree on the first two tests.


Test three: HEI Distributor (.007 reluctor gap) with HEI coil (45,000 volt) no ballast with plugs gapped to .045.


To me test three would be more valid with using stock plug and gap of .035 because you will be testing apples to apples. You will have one variable. The HEI ignition. By having everything else constant you can show exactly how much HEI compares to points.


Test four: HEI Distributor (.007 reluctor gap) with HEI coil (45,000 volt) no ballast with plugs gapped to .050.


Test four to me is tying one of HEI's hands behind its back and then tell it to get into the ring and show me what you've got. As said 1981 Buick 231 V6 had a SP gap of .080. Now if there are clearance limitations then maybe you will have to run a SP gap of .060.


Test should be done at idle RPM, for no advance, minimum throttle opening.

Then at RPM to do 30 MPH in 3rd/direct drive, for partial throttle, light load condition simulation.

Then at RPM to do 55 MPH in 3rd/DD, for wider throttle opening, increased load condition.

The reason for different RPM's is to show if there is any changes at idle. Where low RPM and low engine load may show the stronger spark of HEI may not be a benefit if there is no change or very slight change.

Now the 30 MPH and 55 MPH tests are important for as engine RPM increases the dwell from point gap does not change though the time the points get to saturate the ignition coil decreases and the voltage available for the spark will be reduced.

Now when doing the 30 MPH and 50 MPH test the second time with the HEI you will get very valuable numbers to compare not only is HEI better but at which operating ranges.

You are testing how much which way uses the least amount of fuel. Though nothing wrong with taking vacuum readings and RPM readings. For they can provide supporting data for your tests conclusions.

Though say HEI allows your engine to pick up RPM's without touching anything. That is ok. However do not readjust anything on the engine because you are adding unknown variables and may not be able to see how you are then providing advantages that will skew the test results.


As to your shop being climate control you still need to record climate conditions.

One you are running an engine indoors so there must be an exhaust system. So your shop will not be air tight. Then even if your humidity and temp is constant in the shop weather outside changes and that means barometer change. Like a valve opening an closing pressure differential moves air through an engine. Every time your shop door opens even into just your house nature will try to balance out the pressure differential between the inside and outside.

Though recording the Baro reading or not for the day of you test will not effect the reliability of your test results.

Though it will take away your ability to do further testing if your were bored on a cold rainy late fall day to test how air temp, humidity, a baro effect air density and it's relationship to engine performance. Jeffrey