tweaking about ignition (plug reading etc.)
Posted: Sat Oct 25, 2008 1:16 pm
Hey there. I just figured I would move over here so as not to Hijack Almost's issue, but still delve into discussion about ignitions.
A 4s running at 16krevs has equal coil saturation times as a 2s running at 8krevs.
My car electronics guru friend, Dave (did F.I. and ign. development for Roush for years) assures me that waste spark was an economic issue initially (less parts-which spilled over into engineering time and dev.) and also worked as a stopgap in the emissions wars. The waste spark has/had the interesting side-effect of slightly ionizing the outgoing charge and improving catalyzer life and performance. And, with low rev limits and comparably long times between firing in auto (and old bike) engines the limits of waste spark were negligible.
Two strokes I have owned have responded well to the elimination of waste spark with more usable power higher in the rev range than the same engine with waste spark. Part of that is coil dwell/saturation allowing a denser spark. a) a two stroke running at 11k revs has combustion spark events occuring at the same rate as a (same cylinder#) four stroke at 22k revs. b) a 2s has it's waste spark occuring at bdc and then 180° later(assuming parallel 2cyl) it needs to fire for real. That is a really short re-sat time at 11krevs(again as short as a 4s at 22krevs). My recollection of the switch to v-twin TZ's was also individual spark on those engines) and the Suz gammas that i dealt with (race-not street engines) had individual pickups for each cylinder(and corresponding coils).
With the advent of full spectrum closed loop engine management (fuel and ignition tailoring to suit a suite of sensors) full and individual ignition control became desirable. This was seen early in BMW's 'eta' engines( 325e, 528e '84/'85?) with individual crank triggers and coils per cylinder.
Now it is common for automotive engines to have coil-on-plug setups for the same reason. C-O-P has been on Yamaha(and other brands') dirt/atv engines for quite a while now. I am not sure but I do suspect that this is the current norm in fuel injected sportbikes. If it isn't, it will be.
C-O-P is the way to go (at least until laser controlled combustion). All it requires is 4 'bumps' for the hall sensor and a clocking cicuit in the ign module. And, is the result of progress.
Yamaha_george wrote: RR,
I must admit that "waste spark" has always been a bit of a niggle but having asked several Yamaha JP & venemoto engineers all I got was shrugs and economics as an answer. It seem they thought the extra engineering of a having one shot per cylinder was too much. Thinking now about it it may have had to do with the limits of revs & the speed of electronics in those days as compared to the switching frequencies we can do now.
Lets face it 2 stroke bikes (street) had what 11K top end revs before they grenaded. now we see 4 strokes with 16K revs and no problems the world has moved on , do yamaha R1 / R6 use wasted spark these days ?
If they do it is probably to keep the coil numbers down for space saving ???
A 4s running at 16krevs has equal coil saturation times as a 2s running at 8krevs.
My car electronics guru friend, Dave (did F.I. and ign. development for Roush for years) assures me that waste spark was an economic issue initially (less parts-which spilled over into engineering time and dev.) and also worked as a stopgap in the emissions wars. The waste spark has/had the interesting side-effect of slightly ionizing the outgoing charge and improving catalyzer life and performance. And, with low rev limits and comparably long times between firing in auto (and old bike) engines the limits of waste spark were negligible.
Two strokes I have owned have responded well to the elimination of waste spark with more usable power higher in the rev range than the same engine with waste spark. Part of that is coil dwell/saturation allowing a denser spark. a) a two stroke running at 11k revs has combustion spark events occuring at the same rate as a (same cylinder#) four stroke at 22k revs. b) a 2s has it's waste spark occuring at bdc and then 180° later(assuming parallel 2cyl) it needs to fire for real. That is a really short re-sat time at 11krevs(again as short as a 4s at 22krevs). My recollection of the switch to v-twin TZ's was also individual spark on those engines) and the Suz gammas that i dealt with (race-not street engines) had individual pickups for each cylinder(and corresponding coils).
With the advent of full spectrum closed loop engine management (fuel and ignition tailoring to suit a suite of sensors) full and individual ignition control became desirable. This was seen early in BMW's 'eta' engines( 325e, 528e '84/'85?) with individual crank triggers and coils per cylinder.
Now it is common for automotive engines to have coil-on-plug setups for the same reason. C-O-P has been on Yamaha(and other brands') dirt/atv engines for quite a while now. I am not sure but I do suspect that this is the current norm in fuel injected sportbikes. If it isn't, it will be.
C-O-P is the way to go (at least until laser controlled combustion). All it requires is 4 'bumps' for the hall sensor and a clocking cicuit in the ign module. And, is the result of progress.