450 Electronic Ignition

[vt450scr]

Hi graeme,

A day late and a dollar short, perhaps, but just something to consider.
I wouldn't agree that ignition curves aren't too important, especially on a dirt/playbike, where the revs often run wide in use.
As an 860GT owner I can testify as to the effects of "steep" ignition curves: The original system on these early
squarecase motors ran 0 ATDC from idle until 2000 RPM, then BAM...28 BTDC. No curve whatsoever.
With relatively gentle use, this lack of "ramping up" the power didn't create much problem, but when the motors
were hammered, so were the big end components. Failure of these components has been put down to the combo
of the increase in engine capacity (without a corresponding upgrade in big end parts, from the 750's) and the rapid
incease in power from the "lightswitch" change in spark lead.
You may wish to try the gentler curves first, seeing as the 450 engines are already noted for decent low end torque.

Have fun,

cliff

[Jordan]

That sounds reasonable, but I have another view on why 860s chew up their big ends. They are simply not up to the sort of low rev, high torque that these engines are capable of. Instead of revving them in a traditional Italian way, riders tend to flog them along in too high a gear.
Just a thought!

Jordan

[graeme]

Thank you for your comments,

I don't like anything below 4000 revs on any Ducati especially a 450 when under power.
Before I get shot down, cruising with little throttle down to 3 1/2,, and below that it's in a car park or taking off.

I've only had '74 year singles which had the red Ducati electronica ignitions. I've never had a problem with any of them. I have no idea what sort of advance they have, I must strobe it one day and see.

I'll try the Sachse and see what it's like. (once I get the carb problems sorted)

Thanks
graeme

[Jordan]

More thoughts on advance curves-

A sudden jump in advance timing, such as on some Ducati twins, isn't the problem. It's the fact that it occurs at too low engine speed. 2000 rpm could be too low for a caged roller bigend (but maybe OK for a crowded roller or plain bigend). A gradually rising curve up to too low an engine speed would be just as harmful as a sudden jump. Actually even more so, because at some points along the curve it would already be too far advanced.

If the jump occurred at a higher engine speed, that could avoid overloading. But then it would be retarded for too much of the lower speed range, and that would mean less power over that range.

A rising rate of advance, to a high enough engine speed that avoids overloading, would give good power and also safety.

Spring loaded centrifugal advance units can provide that. Also inductive pickups inherently provide that. Digital techniques could also do it.
Ducati mechanical advance units as on our bikes are well designed and reliable. They can be used in conjunction with an electronic ignition unit that doesn't have inherent advance action, such as those triggered by Hall Effect, optical or points type pickups. Not necessary with inductive pickups, such as with standard Ducati CDI.

I do not think that slight variation of shape of curves would matter, unless the nth degree of efficiency and performance is the aim. It's not likely easy to measure any change in performance anyway.
Many racing bikes have fixed ignition.

Jordan