Hi guys, I found the 76cc heads on my 327 were giving me around 8:1 compression with the forged pistons that are in there, so I swapped a very clean set of 461 305 heads on this week, after lapping the valves and installing new springs and seals. I now have true 10:1 compression w/ the 58cc chambers on a 327, and I have had to back my total timing way down from what I used to get away with running low compression. I have also started using highway mode fuel/spark, which I had not used before. I have up to 8 degrees timing added in highway mode, and cruise around 40-41 relative to TDC in the main table, so I see a max of around 49 degrees rel. to TDC cruising now w/ highway spark. Here's the problem -- I have the min. speed set to 55mph for highway spark. If I am driving down the road, I can watch the +8 deg timing kick in right as I crest 55 mph. So far so good. However, if I drive around enough I notice that the +8 highway spark kicks in even at low speeds , even 20, 30 mph. Is this normal? I am not getting any knock counts when I am observing the added highway spark, and the car kicks out of the high spark timing mode when I get into the gas, but I figured that the car should not be allowed to enter highway spark mode ever below its minimum speed. Is that minimum speed not the ONLY criteria that is used for highway spark? IE at low loads, low rpms, but below the minimum speed, can the car still enter highway spark mode?

 

Problem solved - I am retarded. Highway FUEL mode has a minimum speed, highway spark mode uses separate parameters. Highway spark mode can enable at any speed given the correct low load and temp conditions. Yeay!

 

I'd say your beginning to advance

 

Don't rely solely on the knock sensor for picking up pre-ignition. It'll detect detonation but pre-ignition it will not... and pre-ignition can do damage. At low air flow like cruising the pri-ignition won't lead into detonation if the combustion chambers are being cooled down. Look at your spark plugs for too hot of a temp and also look at the MAP vs a holding mph cruise. The lower the MAP the closer you are to a perfect AFR/spark. I was running about 45 degrees in highway mode until I got a bad tank of gas and was having it detonate every few seconds, pull timing, back and forth. I finally took out 4 degrees and disabled the highway SA all together (kept the highway fuel) and my problem went away and gained 1 whole mpg. It wasn't a HUGE difference in the MAP so take an average. I used Excel to find the perfect AFR/spark combo for highway cruising.
Good luck with it and if it needs/wants 49 degrees, well so be it , whatever makes the engine happy.

 

JPrevost, I just went back to my calibration earlier tonight because I got to thinking, 49 degrees is an AWFUL lot of timing. I have true 10:1 compression now with the 58cc heads on a 327 -- so much compression that I am running 32 degrees total timing after getting KR running any more (I was able to run 40 total with the old 76cc heads, which yielded only 8:1 compression and no KR anywhere, ever). I realized why I had soooo much timing in highway spark mode -- I based the general shape of my timing map on a bin file that had highway spark "disabled" from the factory- the cruise mode spark advance was built into the main table. I then used the highway spark table from a calibration that did not have the extra timing built into the main table. What resulted was cruise spark added to more cruise spark. I backed the highway spark advance down so I have 42-44 degrees max total now at light cruise.