I decided to do some ignition timing tests during a test session on Sat afternoon before our next points race that evening (and to get some practice on the tree after 2 weeks of no racing).

Track testing has some variability, but here are the results FWIW. See attachment. I had been running 34 degrees all year, but maybe a tad less would be optimum. E-85 fuel in a Ron's Flying Toilet mechanical injection system. I did run 33 degrees in all the eliminations, and later that night, I did run:

5.888/114.99, 9.339/141.16

Temperature had gone down, but now the relative humidity was way up at 85% (was ~30% during the entire hot afternoon testing).

Not as much change as I would have thought. Especially with only 30 degrees I expected it to slow down more than that. But years ago using a carb on gas in a different motor, I think it took removing around 10 degrees to slow it down maybe 0.15 seconds.

It's interesting it didn't change ET's more I didn't make back to back changes on mine but picked up a bunch from moving the timing from 32 to 35. I'd have to dig through the log book but I think it was on the order of .05 in the 1/8.

Great post Jim

Based on your results, i assume you will run 32 degrees in the future?

What affect do you think the lower DA you run at has on the timing needed?

We typically run around 4,000 feet DA so I was thinking my combo may want 33 - 34 degrees, but like you did, i will need to test...

Thanks for the real world info!

Cheers,

Arnie

I think your car is stupid, it didn't know you where working on it, did you tell it you where changing things and wake it up befoe testing LOL. Just kidding of course, those changes in the incremental times didn't have much affect on the 1/4 mile times or MPH I wonder why I'm sure the humidity changes has a big affect back there, I know it does out here Thanks for sharing that information I wonder if the E85 doesn't really care about the total ignition timing

Nice post Jim...
looks like the Indy combustion chamber is pretty efficient compared to stock 40 year old stuff. i never understood why guys wanted to run 38-40 deg of timing, never check to see if it needs that much. IMO running the least amount of timing without effect performance really helps the life span of a engine, big inch engines on two steps, running 10 more degree's of timing than needed, and they wonder why it needs bearings every year.
I would love to see a test like this regarding plug gap. More so with Methanol. I have preached a few times to some fellow buddy's about watching plug gap on alky. I have found it very sensitive, in my case...
A


Great info, should be in the tech archive's.

I can only think a few things:

- This combo isn't real sensitive to ignition timing (in this range)
- The flying toilet injection is pretty consistant
- The E-85 fuel is pretty consistant

I do try to keep all the variables as consistant as I can, both for this testing comparison and during bracket racing. Water temp, engine oil temp, trans fluid temp, staging rpm (foot and eye), burn out technique, etc. All those 5 runs were at similar weather conditions, 86 degree, 30% RH, 30.07"Hg. It didn't start cooling off with relative humidity going up until the eliminations in the evening (9pm 1st round)

I talked to Mike at Muscle Motors today and he suggessted 30 - 32 degrees for my new 540 bullet on Alky. He said the high compression needs less timing in general w/ 440-1 heads...

He must be reading Jim's posts !

Arnie

i'm blown away by the fact that timing made almost no diff. although it seems that it didn't like 38*. but still the 1/4mi. mph didn't change at all