Evo big twin or Sporty ignition advance curves

[Eric.]

Anyone running a Dyna/Dynatek/Ultima/DaytonaTT ignition that is interested in posting their ignition advance curves for comparison?

97" evo, 10.4:1, evl 5025 cam, ported heads.

[Eric.]

Also, wondering if anyone feels my curve is too aggressive (back out 3 degrees across the board?). 

I'm not getting any ping, at any RPM ranges.  On top of my other specs, I'm running a 4" bore, .30 squish, bathtub chamber and come in around 190 CCP. 

Waiting for the weather to get a little hotter before dyno tuning.  It's still early in the season, around here.

[aswracing]

Much depends on the speed of the burn, which varies with things like compression, chamber turbulence, number of plugs, flame front obstructions (like a big dome), the fuel being used, and AFR. For all practical purposes, the only way to know for sure is to dyno test.

That said ... having dyno tested and tuned thousands of bikes over the last 17 years ... what I've basically seen in the vast majority of street hot rod bikes is largely reflected in this one cherry-picked result.

This set of curves, which is from a Dyna 2000 ...



... generated this set of results ...



... on a typical street hot rod 10:1 single plugged motor running on pump gas. Pull 5-7 degrees across the board for a dual plugged motor.

As you can see, the softest curve ran the best. Pulling more timing, via turning the plate ccw, yielded no more gains.

I've seen this basic pattern over and over, on numerous bikes. So if it's possible to generalize, there it is.

The motor didn't ping on any of the curves. This is an important point, because I've seen entirely too many cases where people hurt their pistons by cranking up the timing, under the false belief that more timing gives more power so long as it's not pinging. Even the ignition manufacturers perpetuate this myth in their instruction sheets. It's rarely true, basically I only see this when the motor build is pushing the cylinder pressure limits of the available fuel. Most builds don't do that though, at least not most intelligent builds.

[Eric.]

Awesome.  Thanks for the response, that is good solid data.