Question about trigger wheel choice...

[EWflyer]

Hello Ignition Control Experts,

I'm beginning my second motorcycle fuel injection project. The first project was a fuel-only conversion of a Kawasaki EX250 (250cc parallel twin engine). Now I've got a Suzuki GSF400 Bandit (400cc inline four cylinder engine) and this time I want to do both fuel control and ignition control.

The stock GSF400 ignition control setup uses a 4 inch diameter trigger wheel (it's one of those crazy Denso corporation long-tooth wheels). I have found that a 4 inch 36-1 trigger wheel is available at DIYAutoTune which seems like just the thing for me. However, the wheel is cut with perfectly triangular teeth (it looks like a saw blade). This is the first trigger wheel I've ever seen with triangular teeth. Every other trigger wheel I've seen so far has perfectly square teeth or slightly tapered square teeth.

The GSF400 is a high-revving motor, with a redline of 14,000. I'm just concerned about being able to configure an ignition setup that can be accurate at these engine speeds. Would it be asking too much for a Hall sensor to reliably read a triangular toothed 36-1 wheel at 14,000 rpms?

Any advice would be appreciated.

Greg

[kjones6039]

Just curious........
What is the configuration of the existing wheel? I'm not a m/c kind of guy, but why would you not want to use it?

Ken

[DonTZ125]

Without seeing one, I'd guess it's a 3 short 1 long, like so many Japanese bikes of that era. There is a code patch and adaptor circuit for the MS2/Extra code that seems to work; I was working on an all-hardware solution but haven't gotten to the point where I'm satisfied enough to starting printing boards and clipping leads.

FZR_ignition_slides_flywheel.jpg

[kjones6039]

Point well taken!! Certainly not something I would want to take on!

Good luck with your solution!

Ken

[EWflyer]

Hey Don,

Would you believe that there's a wheel out there that's even stranger than the "3 short 1 long" wheel? Well how about this little starfish right here? Yep, this "5 short 1 long" is the stock wheel out of a Suzuki GSF400. This is why I'm asking about the 4 inch 36-1 wheel.

[DonTZ125]

Yuk - what a mess ... I think Matt's circuit and code would still work, although it would obviously have to be modified for 6 teeth. One point to be confirmed with the Extra devs, now that I think of it - CAN the Extra code do a 4 cyl with 6 teeth ...

[EWflyer]

Yuk - what a mess ... I think Matt's circuit and code would still work, although it would obviously have to be modified for 6 teeth. One point to be confirmed with the Extra devs, now that I think of it - CAN the Extra code do a 4 cyl with 6 teeth ...

Once again, thanks for the input Don, that is a very good question. I'd jumped right to the assumption that I would have to replace the stock Suzuki trigger wheel and hadn't even considered the idea that the simple modification of this "1 long 5 short" wheel into a "6 minus 1" wheel could be the answer to my ignition control needs. I'd love it if this could be a workable and supported solution.

A quick check of the MSExtra Manual gives me this quote:

For wasted spark you require a minimum of single "missing tooth" crank wheel, only engines with an even number of cylinders being supported. You need at least 4-1 for 4cyl, 6-1 for 6cyl or 8-1 for 8cyl. However, the 36-1 wheel is probably the easiest to obtain. The MS2 ECU can drive up to 6 seperate spark outputs, meaning it can run up to 12 cylinders in wasted spark mode.

So if I'm reading this correctly it sounds like I could run a 6-1 wheel for my 4 cylinder wasted spark coil-on-plug engine. Except... I also found this quote in the MSExtra Megasquirt-3 MS3 Trigger Wheel description page:

The Megasquirt-3 code benefits from a reasonable number of teeth (hence 36 or 60) for best ignition timing accuracy. Low tooth count wheels such as 4-1 are not advised.

Do you think that a 6-1 trigger wheel can work?

I guess I'll need to go over to the MSExtra forum and ask a few questions about the pros and cons of using trying to use a trigger wheel with so few teeth. Any further thoughts on the issue?

Greg