I dont get the problem. SPI is just an electronic carbie - the only varibles are determined by data inputs and varable by the ability to process them - ie ecu.

Should be no worse or better than a good carbie setup.

MPI is a different story.

Single carby... one main jet supplying fuel.
SPI... one injector
Twin carbs... two jets
MPI... two injectors.

How can anyone say that injection is not going to work on a mini when the only difference is the EFI is electronically controlling the fuel.
Carby's are very hit and miss.

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* shrugs *

I guess my explanation wasn't clear.
Carbs = even mixture of air & fuel for the duration of an inlet stroke
Typical modern injection system = mostly air but with a short burst of fuel during the intake stroke except at max revs/power when injector pulse duty cycle approaches 100% if injectors are on size limit for engine.

Time the short burst of fuel wrong on a 5 port head and some of it goes into the wrong cylinder.

Therein lies the problem.

It all depends where the injector is situated...

only at a certain rev range... it's not consistant from 500-10000rpm
not like EFI where you set the fuel needed at any given rev/load

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Oh dear...

Injectors are not valves that open wider and wider as more fuel is needed. If they were, there would be no problem with 5 port injection. They are actually big valves that open for a short time each cycle. As the demand for fuel increases they are opened longer to get more fuel in.

So, at anything but full load the slug of air the inlet valves sees is:

no fuel.... air/fuel mix....no fuel

Get the fuel into the air stream at the wrong time and some of it goes to the wrong cylinder.

Injectors in the combustion chamber or on top of the valve would remove the issue but all feasible locations for the injectors are upstream of the Y in the port.

Carbs are very blunt instruments in terms of getting the right amount of fuel for a given load/speed/temperature point but they mix the fuel in the charge that the inlet valve sees to more like

air/fuel mix....air/fuel mix...air/fuel mix.

If the 5 port issue was just a myth, then there wouldn't be so many issues with the different mixtures between inner and outer cylinders and Rover would not have bothered with sequential injection on the MPi.

It almost makes you wonder why rover didn't redesign the cam to change the firing order to make the system work better.
Okay, I'm sure there's a better reason for not going that way but I put it out there.

The advantage of a carby is that fuel is issued only when the air is going through it. On EFI it gets injected when the ECU tells it; this could be in dead air or in air going to another cylinder (as in 5 port problem). This problem won’t be seen at idle, even on SPI, as you have plenty of time to get the fuel injector timing right (@600rpm there’s almost 200msec to fire the 4 cylinders fuel in).

At higher rpm though it’s a whole different ball game where at 6000rpm you have less than 20msec to get all 4 cylinders fuel in. On the 5 porter you have overlap issues so it’s even less time and this is the reason EFI doesn’t work easily. Conventional EFI theory/set-up can be tossed when it comes to turbocharging the A-series, even the top ECU tuners can’t get it to make decent power.

To say EFI won't work at all though is like calling the earth flat, it's already been proven in some applications but not without significant cost/development or HP/rpm compromise. The argument that "I make xxxHP with a carby, why bother" is just as futile given the significant efficiency gain of EFI in producing equivalent power.

The point is – for simple turbo applications use a carby, it’s much cheaper and there are a lot more people who can tune the engine for you. If you want a reliable daily that has nice power and good economy sans turbo, get an EFI version.

Regards

Daniel

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Videos - Turbocharged A-Series on Dyno & at Wakefield
Mafs waz not my strong subgeckt at skkol

you are assuming that the duration between injector pulses is constant. Many ecus enable you to have variations in injector pulse based on crack angle. So the duration between pulses can be longer or shorter depending where the overlap is on the siamesed ports.

My Jag puleses differently based on which injector is firing to compensate for the inlet manifold length from the butterfly to valve being different for different cylinders so the fuel is injected when the airflow meets the valve, not at a fixed interval.

An SPI can do the same thing is just more complex for the ecu. SPI Camiras worked this way.

I am not assuming that the injector is being fired at the same time for every condition, it simply wouldn't work. At idle you inject fuel for about 1msec and you have plenty of opportunity when you want to do it.

At elevated rpm/load though the opportunity to get this timing in the right place is restricted and the injector is open longer, on top of this you have an overlap issue to deal with on the A-series.....

buztoy wants to know about turbocharging his engine and my advice is to stick with a carby on the 5-porter

Daniel

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Videos - Turbocharged A-Series on Dyno & at Wakefield
Mafs waz not my strong subgeckt at skkol

final destination

im going blow through webber and 5 port head, it will work, i just grabbed the wrong end of the stick with the carby builder.

i looked at the computer + throtles + loom + injectors + extras= way to much. i could nearly do a starlet conversion with that and bit more, I really forgot what i was aiming for and that was abit more power, not huge power.

the reason why i got injection was so good was the fact that a bloke who i know had a 12a bidgey, it was injected and probally better exscrators but he had so much more usable rev range, mine is a 13b bidgey but probally has close to if not more top end. mine at the red lights if your trying to keep it quiet i can take off at around 2500-3500 with out too much trouble but the car will shake and carry on. but his you could all most drive like a normall car and down low you had more tourqe and a snappyer sound and reactoin to your foot,

he had one of those injection perfection throttles that i posted /\ /\. i have a 456 holley. the difference was great. he also had cold start settings which is a better look at the local shopping village rather than i can of "start ya bastard", and the looks you get from families when it back fires at a petrol station.


mind you to say its sad that no one liked the spi/ mpi, 60, 63, 80 and 90 hp marks similar to where i want to be though.

now if you dont mind i only just got back from work and going to bed, nearly 2:30 am

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