2-cyl 4-stroke bike: injector sequencing without cam sensor?

[MattMooseZ400]

Hello, just getting started with DIY EFI here.

I wanted to add EFI to my twin cylinder 4-stroke engine, but can't think how injector sequencing could be achieved if there is only crankshaft sensing readily available. It uses wasted spark ignition; would that mean it has to use 'wasted squirt' as well - is this the done thing, or unheard of?

Anyhow I'll aim to get a cam sensor installed if I have to, it would seem to make more sense.

Many thanks,
Matt
NE Wales, UK

[grippo]

You don't have to have a cam synch to run - probably most run without it. The spark gets synched by the wasted spark coil and the fuel is injected either alternating or simultaneous, your choice. The key is that fuel timing is not important for running an engine the way spark timing is.

[MattMooseZ400]

Thanks, it's very interesting and surprising that you say fuel injection is not so sequence-dependent. I guess the worst it can be in my case is that the fuel pulse has to hang around in the throttle body until it gets sucked in, so long as it doesn't bounce back out again. I really thought the whole essence of fuel injection was to provide only one fuel pulse per intake, right when it's needed. However if the engine is happy to suck in a calculated fuel/air mix that's aggregated, rather than timed, then so am I.

Doesn't the MegaSquirt calculate dynamic fuel requirements on a per-cylinder basis then? Or am I complicating things far too much as usual with my ignorance?

Please can you recommend any further reading on how different injection sequence schemes compare?

Best regards,
Matt

[EWflyer]

You're not the first person to ask this question.....

It's funny that the moment somebody pulls the carburetors off an engine and starts working on fuel injection they forget that up till the carb removal it was running pretty well on a steady stream of not-very-well-atomized fuel delivered by engine vacuum alone to cylinders that were everywhere and anywhere in their 4-stroke cycle.

it's very interesting and surprising that you say fuel injection is not so sequence-dependent

Sequential injection is a "nice-to-have" rather than an "essential" item (think about all those early '90s cars that had throttle body injection, they ran much better than the carbureted ones they replaced). Sequential injection is just a further perfecting of the system, gaining every possible efficiency that fuel injection can offer (the icing on the cake), but the real magic of fuel injection is that the fuel is very finely atomized, the airflow through the intake and throttle body is unimpeded by all that carb monkey-business, and the extreme accuracy, flexibility and agility with which the fuel is metered to the cylinders.

I really thought the whole essence of fuel injection was to provide only one fuel pulse per intake, right when it's needed

Well, that's what you'll have. The mega or microsquirt will be delivering a precisely metered amount of finely atomized fuel to each cylinder one time for every 4-stroke engine cycle.

Doesn't the MegaSquirt calculate dynamic fuel requirements on a per-cylinder basis then? Or am I complicating things far too much as usual with my ignorance?

If you set up your motorcycle's fuel injection system with one injector per cylinder (for a total of two in your 2-cylinder bike) using a dual throttle body (which has two injector ports, one in each bore of the throttle body) then during your setup of the system you will configure the fueling at a per-cylinder level/amount.

However, you could choose to use a single throttle body (with a single injector) and an intake system that splits into two separate runners (one for each of your two cylinders). In this case you would program the fuel requirements on a whole-engine basis rather than a per-cylinder basis.

Good luck with your project. I'm a 2-cylinder, 4-stroke, microsquirt project guy myself (Kawasaki EX-250).

[Bernard Fife]

Please can you recommend any further reading on how different injection sequence schemes compare?

MM..,

There's the FAQ: http://www.megamanual.com/MSFAQ.htm#sequential

and the manual: http://www.megamanual.com/v22manual/mfuel.htm#batch

or you could use the forum or manual search functions at the top of every forum page.

Lance.

[grippo]

There is really quite a lot to it. I gave you a short answer because you sort of seemed to think the engine would not run well without fuel timing. It will, but if you were to purposely time the fuel to inject during valve overlap, and you had a wild cam, then it would run noticeably poorer, although you could cover over this to some extent by dumping in more fuel. This is the only way fuel gets wasted and its just a small amount. Fuel on sequential port-injected V8s can stay in the port for up to 7 cylinder firings, then it all gets sucked in with no waste if timing is not at the bad spot.

[MattMooseZ400]

Hi all, very glad to get so many questions answered, cheers

@EWflyer: Thanks for a great explanation of the difference between carb vs injection, regarding mixture. Helpful picture, very quoteable. I feel drawn to the dual throttle body + 2-injector solution initially, having heard of intake unevenness issues on simple old BSA 1:2 inlet manifolds. One injector per cylinder seems better, although I wonder how the EFI would cope from a tuning point of view with say a difference between left/right compression? Of course I'd be starting with fresh rings, bores, gaskets etc... once a replacement bike finally turns up. What's your experience of injection on your EX-250 so far?

@Lance: Links and tips greatly appreciated.

@Grippo: Brilliant, I had no idea that injected fuel was allowed to hang around for some time until it's inhaled by the cylinder. That simplifies everything. I was mistakenly fixated on the idea that injection had to coincide with an open intake valve. I hadn't realised how far away from the intake valve the injection point can be. Will and once I've understood a bit more then I might make some simple animations.

regards
Matt