Single cam sync pulse for sequential control.
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Author:  Vdubber [ Sat Nov 12, 2016 2:01 am ]
Post subject:  Single cam sync pulse for sequential control.

I have an idea to generate a cam sync pulse from the fuel pump cam on the dizzy drive. This gives one pulse per dizzy revolution.

My assumption is that for sequential control all that is needed is a way to differentiate which cycle any given cylinder is on, a single pulse is theoretically all that is needed.

I have searched and found a few references to it but none that empirically state 'yes-this-will-work'.

So, assuming that the signal is suitably conditioned and reliable...

- Will this work?

- What are the drawbacks?

- Does the current firmware has this capability?


Author:  Fred [ Sat Nov 12, 2016 7:18 am ]
Post subject:  Re: Single cam sync pulse for sequential control.

Will it work? Upload a photo! I'm not familiar with the chunk of metal you're talking about.

No drawbacks, I guess. I'd be inclined to put an optical or hall sensor in the hole where the dizzy usually goes with a cap over it like a typical 90s CAS unit (mx5, evo, some toyotas, etc).

With even non-missing tooth wheel on the crank, yes. With missing tooth on the crank, no, but it's pretty easy to do... hours, not days.

What's your attraction to sequential? Hopefully not from this: viewtopic.php?f=54&t=1954 See point 5 :-D

There are valid reasons, but... :-)


Author:  Vdubber [ Sat Nov 12, 2016 11:01 am ]
Post subject:  Re: Single cam sync pulse for sequential control.

Similar, but just stick a VR sensor in there to pickup directly from the cam then use some signal conditioning to turn that signal into a nice readable pulse.

There's no real attraction for me with sequential, I'm happy to use batch fire + wasted spark on my own stuff, VW engines generally don't rev high enough to warrant using sequential.

I'm just thinking ahead and planning out my hardware build. Joe public like the idea of sequential and it's those guys that I'm trying to please. Everyone seems to herald sequential as a 'must-have' so if it's reasonably easy to implement I'll include it as an option.

Author:  Fred [ Sat Nov 12, 2016 8:14 pm ]
Post subject:  Re: Single cam sync pulse for sequential control.

OK, yeah, as a sales item, it's important. I don't think like that - yet. :-)

If the sensor is VR then the conditioning is MAX9926. But the shape of the wave generated needs to make sense.

I thought those holes were A narrow B slotted? Coming up out of the hole into a housing gives you the ability to more precisely position your signals at a larger diameter. At lower diameter your metal would have to be custom shaped a lot, and then you'd lose signal all together. Can you find/supply a photo looking into the hole?

Keep in mind that VR is terrible at low RPM, non existent at a stop, and pretty bad at cranking. IE, your signal needs to be strong and well aligned enough when cranking so you can gain the sync you want and start quickly.

That's another limitation of single pulse sync: slow starting. By slow I mean peak 720 degrees before the ECU can know what's up, average 360 degrees. This is when it *starts* injecting fuel and firing plugs, so actual combustion begins after this time. How long is 2 revolutions at 120 RPM? 1 second longer cranking, worst case. Keep in mind, I'm spoilt, I have owned a couple of Nissans with insta-start. There are other designs similarly good, but single pulse is worst case.

Maybe another phone call, however if you want to remain compatible with other systems my top-secret ideas are out of the question for you.

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