Single point injection - pulse frequency?

[NDT]

Does anyone know the injection frequency on a typical SPI set up?
I'm interested in whether I can use a sequential EFI ECU to drive an SPI injector.

[stevieturbo]

Be more specific.

Injectors simply get powered on to open, and off to close regardless of system. Frequency is irrelevant.

Some might use different control strategies whether P&H type or saturated, but that's a different matter.

So exactly what ecu, and why ?

[GreenV8S]

I don't know what OEMs would have used, but for my upstream fueling at the throttle body I use eight events per engine cycle i.e. four times crank frequency. I was concerned that might be too low, but going to a higher frequency has its disadvantages too. In practice the distribution seems excellent - in fact it seems better than when it was on port injectors alone, all the way from tickover up to the point where the upstream injector maxes out. (It's really cool to see frost forming on the throttle body in a hot engine bay.) I think that wall wetting is probably why this works at such (relatively) low frequencies, but I'd be wary of going any lower than that. One tip I was given is to put an angled slot at the edge of the throttle plate so that the air flow is focused here at low air flows and makes a jet blowing over the injector - this also induces a high degree of swirl at the injection point so the air speeds are nice and high to get everything mixed.

[NDT]

stevieturbo said:

Be more specific.

Injectors simply get powered on to open, and off to close regardless of system. Frequency is irrelevant.

Some might use different control strategies whether P&H type or saturated, but that's a different matter.

So exactly what ecu, and why ?

Frequency is highly relevant if you:
a) want to use it on a Siamese port engine (which I do)
b) want to drive it with an easily available ECU (and I don't care which, really) which uses four injection events per cycle

By frequency I mean how often they open and close.
So, does anyone know, is it many times the engine speed or something more akin to once per firing event?

[NDT]

GreenV8S said:

I don't know what OEMs would have used, but for my upstream fueling at the throttle body I use eight events per engine cycle i.e. four times crank frequency. I was concerned that might be too low, but going to a higher frequency has its disadvantages too. In practice the distribution seems excellent - in fact it seems better than when it was on port injectors alone, all the way from tickover up to the point where the upstream injector maxes out. (It's really cool to see frost forming on the throttle body in a hot engine bay.) I think that wall wetting is probably why this works at such (relatively) low frequencies, but I'd be wary of going any lower than that. One tip I was given is to put an angled slot at the edge of the throttle plate so that the air flow is focused here at low air flows and makes a jet blowing over the injector - this also induces a high degree of swirl at the injection point so the air speeds are nice and high to get everything mixed.

really helpful, thanks.
So ideally I want an ECU that either has multiple injection events per cylinder, or run it in V8 mode (on a 4-cyl) or just fool the 4-cyl ECU that it's running twice as fast as it really is.

[GreenV8S]

NDT said:

So ideally I want an ECU that either has multiple injection events per cylinder

I don't know which ECUs you're considering, but the ones I have looked at seem to be based on the idea of injection events per engine cycle rather than being tied to the number of cylinders. I think you'll find that most ECUs will let you set this as high as you want (within reason), and the limiting factor will be choosing a multiplier that lets you stay within an acceptable duty cycle across the whole rev/load range.

[stevieturbo]

NDT said:

Frequency is highly relevant if you:
a) want to use it on a Siamese port engine (which I do)
b) want to drive it with an easily available ECU (and I don't care which, really) which uses four injection events per cycle

By frequency I mean how often they open and close.
So, does anyone know, is it many times the engine speed or something more akin to once per firing event?

How often any injector opens depends on how often you ask it to open and how you configure the ecu. So again, it is largely irrelevant. If you want once per cycle...you fire it once per cycle. If you want it 4 times per cycle that's a little more crude and essentially 2 stroke batch fire sort of thing.

Most ecu's should allow this.

Or some of the Mini guys and Megasquirt have dedicated "Siamese code" as they call it for proper port injection on such engines.
I think Specialist Components also offer something similar.

But for a wet manifold and non timed, single ( or even multiple injectors ), almost any ecu would cover it

[NDT]

stevieturbo said:

How often any injector opens depends on how often you ask it to open and how you configure the ecu. So again, it is largely irrelevant. If you want once per cycle...you fire it once per cycle. If you want it 4 times per cycle that's a little more crude and essentially 2 stroke batch fire sort of thing.

Most ecu's should allow this.

Or some of the Mini guys and Megasquirt have dedicated "Siamese code" as they call it for proper port injection on such engines.
I think Specialist Components also offer something similar.

But for a wet manifold and non timed, single ( or even multiple injectors ), almost any ecu would cover it

thanks, that's helpful.
It's for a Mini, but I want to avoid "Theaker" injection where the pulse gets split between the siamesed cylinders.

[stevieturbo]

NDT said:

thanks, that's helpful.
It's for a Mini, but I want to avoid "Theaker" injection where the pulse gets split between the siamesed cylinders.

The dedicated setup with port injection is just timed for each cylinders valve events, to remove the charge robbing element.

Obviously a wet manifold and untimed injection is a bit simpler.

If you arent already there, go over to Turbominis. Various guys there have tried most setups out there.