Safe limit for ign adv? Stock top end.

[edfmaniac]

I've been experimenting with the curve on my Ignitech programmable ignition again and am now just beyond the 38 degree cutoff of the stock ignition. The bike seems to be liking it and is still pulling up to the 8500rpm cutoff that I have set. Any educated guesses as to when I should expect the performance gain to stop and how far beyond that do I need to worry about detonation? Here's my current curve numbers.

6 degrees - base advance
13 degrees - 500rpm
15 - 1500
19 - 2300
23 - 3000
30 - 4000
36 - 5000
38 - 5600
40 - 6500
41 - 7600
41 degrees - 8400rpm

[samandkimberly]

With a stock motor, I think it's safe to assume that the stock timing is at least close in relative advance. Typically 4 stroke timing curves retard slightly past peak HP or higher, but I'm not exactly sure why. I believe Bill's experience has been that retarding the ignition across the board improves things. Really, the only way to tell for sure is lots of seat time and dyno time, but for a stock motor I'd stay pretty close to stock timing, just raise the RPM limit.

One thing worth doing is verifying that you're getting the actual advance the Ignitech is showing. Program a broad range of the RPM for the same advance as the flywheel mark - I think it's 12 degrees. Check your timing with a strobe on that. Until you *know* you're getting the timing you think you are, you're shooting in the dark.

Another thing for the more technologically adventurous would be to put a MAP sensor on the intake, and start tuning for engine load as well as RPM - every modern engine control system does this as it is both more efficient and can improve drivability. This way you can have relatively high advance at low engine loads for better throttle response, but retard under maximum load to eliminate preignition and maximize power. The Ignitech has inputs for a standard 5V sensor.

Now that I have a motor apart my plan is to add a couple of marks on the flywheel so I can verify 100% what the Ignitech is giving me. I'm still not sure what the correct base advance is, and that impacs the whole range.

[edfmaniac]

So far my best results have been to mimic the published stock curve of the Skorpion oem box up to the 24 degree @ 3000rpm mark. My next point is 39 @ 5000rpm and then a linear curve up to a maximum advance of 43 degrees @ 8500rpm. I could probably squeeze a little more juice out of the top end as is but why push it. The ole gal is hauling my 300lbs around pretty darn good for having 40+ thousand miles on the original top end. I have a new 686 cylinder, 11:1 piston and stage 1 cam to put in but haven't had the heart to crack open a perfectly good running engine just yet.

[edfmaniac]

I stumbled across this thread and thought I'd give it a little update. I don't think I can offer any final answer to my question other than it didn't blow up at 43 degrees. The dyno testing we did said the engine was very rich up until the stock petcock fuel flow limit was reached and the engine started starving for fuel. So any data we retrieved above the 6500 to 7000 rpm range wasn't really useable and the tech said he didn't know whether or not all of the horrible noises that he heard when the engine started running out of fuel contained any definitive signs of detonation. As a result of what info we did gather at lower rpms, I dropped both needles one notch when I got home. Next step was to replace the petcock with the Acerbis universal(a very tight fit and the valve faces the front of the bike) and retarded the max. advance to 40 degrees. She is really purring now. I should be real close to the 50hp mark at the rear wheel and won't do anymore tuning before the top end gets upgraded and the major chassis and wheel work are complete. Of course I'll have to retard the advance back to Bill's recommendations after the piston and cam go in. I'm sure the 11:1 won't like 40 degrees.