Help Distributor 3 pin plug
- Thread starter gajh
- Start date
This device is reading the serial ouput of the DME computer. Looking at that it is working on M2.1 which would be for the S/S2 and 968 but not the turbo and NA 
Sounds like a usefull bit of kit for you guys with that version of motronic though! Would be great for fault finding.
Sounds like a usefull bit of kit for you guys with that version of motronic though! Would be great for fault finding.
bertelli_1
New member
Good old wikipedia! The injectors on the s2 share a 12v supply and earth (to ecu) so there is no way they can fire in pairs. Interesting point about the turbo injectors, so even though they are paired coming out of the ecu they share a common driver? It seems strange they would wire them up in this manner.
Also the point about injecting against a closed valve is worth expanding on - eary electronic & mechanical systems would fire every cycle, leaving fuel pooling in the intake. However this was still a huge leap over carbs, do we all remember chokes & flooding? Even at low rpms (around 3k) with a very modern efi system fuel is injected against a closed valve - this is due to the lack of time available.
3000rpm equates to 50rpm/sec or 1rpm every 20 millisec. Of those 20ms the intake valve will be open for around 11ms, assume 1ms to open & another 1ms to close the injector leaves 9ms to inject fuel, not enough time! Do the maths at 6000rpm & we get just just 4ms open valve time at a time when we need the most amount of fuel. So the injector HAS to be open while the intake valve is shut. (as an examle my golf injects for 12ms at around 3500rpm).
As my very simple maths shows we do not need sequential injectors as most of the fuel sits in the port before the intake valve opens anyway so the 944 system is absolutely fine with its batch fired injectors. Why have sequential injectors then? Simply for emissions, at low rpm it is possible to more finely control the amount & timing of fuel.
Also the point about injecting against a closed valve is worth expanding on - eary electronic & mechanical systems would fire every cycle, leaving fuel pooling in the intake. However this was still a huge leap over carbs, do we all remember chokes & flooding? Even at low rpms (around 3k) with a very modern efi system fuel is injected against a closed valve - this is due to the lack of time available.
3000rpm equates to 50rpm/sec or 1rpm every 20 millisec. Of those 20ms the intake valve will be open for around 11ms, assume 1ms to open & another 1ms to close the injector leaves 9ms to inject fuel, not enough time! Do the maths at 6000rpm & we get just just 4ms open valve time at a time when we need the most amount of fuel. So the injector HAS to be open while the intake valve is shut. (as an examle my golf injects for 12ms at around 3500rpm).
As my very simple maths shows we do not need sequential injectors as most of the fuel sits in the port before the intake valve opens anyway so the 944 system is absolutely fine with its batch fired injectors. Why have sequential injectors then? Simply for emissions, at low rpm it is possible to more finely control the amount & timing of fuel.
peanut
Active member
injector spray time is not really an issue at the sort of revs our engines run at ie sub 6000rpm The fuel is at 3Bar pressure which forces the atomised fuel out and the forced induction draws the air and fuel through into the cylinders at huge speeds . I'd imagine it might become more of an issue at F1 engine speeds above 18000+rpm though[]
]
peanut
Active member
wern't some of the very early 944 sequential ? I had the impression that those engines which had both the reference sensors on the crankshaft had sequentially firing injectors ?
With the sort of high revving engines we have now I guess the continuous fuel flow is the most efficient system . No firing at all just continuous fuel injection
With the sort of high revving engines we have now I guess the continuous fuel flow is the most efficient system . No firing at all just continuous fuel injection
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
