So all of the actual HEI testing is complete and you can see the differences in fuel mileage depending on the gap. It clearly shows that gap DOES matter. I didnt stop there. I wanted some comparison data between HEI and Stock systems.
Turns out gapping your stock ignition system to .040 will get you a bit more power and better mileage. I also discovered something totally unexpected. Spark plugs really have an impact on fuel mileage! It turns out those (what I would have called gimmicky) E3 Spark Plugs (part number 52 for our purposes) give you another boost in fuel mileage. The E3 plugs are not gappable and are gapped to .040.
When I did the tests I did them all the same so there is no question about the results. I know you can do the same tests and get the same results.
Another thing I found out was that coils make a great deal of difference when dealing with HEI. An everyday stock coil will get you poor gas mileage with no other variable even with stock gaps! It runs just fine, but at a fuel mileage cost.
These tests were done at idle which is the very same idle that you get in your truck, so the numbers will track. The numbers at 30mph and 55mph were not done with a load, so they will not track, but are offered to give you an idea of the fuel percentage differences between idle and these speeds. As you can see, LOTS of difference in fuel consumption.
The O2 sensor was very important to the tests because I was able to adjust the engine at the start of the test process slightly on the lean side. This way the fuel consumption would be repeatable and similar throughout the process.
It was fun and if there is any way I can improve the data so it makes more sense, please let me know!
http://devestechnet.com/Home/HEIgnitionabout halfway down the page.
