Mono injector or port injection for a bike engine

[coyoteboy]

Looking at a new project - a 600cc, old bike engine - removing the carb from a bike engine and replacing it with injection of some sort. Currently it has a short set of runners and a plenum, a cack carb stuck on it - that is all. I'm torn between picking up some bike injectors and doing multipoint injection at the ports (more manifold fabrication needed) or replacing the carb with a mono injector which would just require essentially making an injector mount and sizing suitably. Thoughts? I'd be fine if it were a car, but this is a little different to my usuals! One larger injector may make idle control harder? It has to run a plenum anyway, for info.

Looking at sizes - its a <100hp 600cc - individual injectors I'd say ~100CCs would be right (based on the assumption that 200hp bikes run ~200s?) but mono injector would need to flow 4 times as much so something like a 430 from a toyota engine?

Thoughts?

[insanezane]

how many cylinders is it 2 0r 4

[coyoteboy]

Sorry, vital info missing here

4cyl, 4 stroke, MS1-hires, not sure of max RPM but I'm starting to assume that in order to reach the powers it is hoping for, a single injector would need to be pretty large and so wouldnt deal with idling properly. Large, fast injectors tend to be uber-expensive too, whereas small bike engine ones (230cc) can be picked up for $50, but require manifold machining.

[Matt Cramer]

I suppose you could use automotive TBI injector(s); the main problem would be fuel distribution instead of lack of resolution. After all, four tiny injectors with the same flow rate as one large injector would also have the same pulse width. I suspect there's a reason virtually all injected bikes have independent throttle bodies and port injectors, though - high performance TBI car engines are quite rare "in the wild," and a mild sportbike engine is in about the same state of tune as an all out racing engine for automotive applications.

[coyoteboy]

Fair points Matt, I've been looking in more detail at the honda CBR600 setup, they seem to have primary throttle injection followed by secondary port injection , presumably to deliver the rest of the fuel and trim the cyls individually, presumably both will be relatively small flow rates too . This is never going to be a flying machine, primarily due to having a bloody great restrictor in the inlet, but I'd like it to be in a fairly good state of tune. The thing is it is for some people learning to tinker with cars/engines and if it gives them something to look at improving then thats fairly acceptable, so long as it runs and can be driven fairly well in the mean time then its a start. My thought was to machine up a block directly after the restrictor/throttle area that just sink two car injectors into it, pointing into the plenum, firing on alternating/2 squirts, or maybe alternating 4. Although feel I'm going to run into trouble with high RPM if I run multiple squirts.

I'm a bit torn now, having found the ideal option is (as usual) quite a bit more complex!

I could throw in some small car engine injectors, rather than bike ones I suppose.