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Originally posted by timucin i am just trying to learn, formulas say 720 but real life experts say 511.is there any other formula to calculate this?why there is difference like this
720cc at 80% duty is 80% of 720cc, wich is 600cc
511cc@3.8bar injectors at 6.5bar flows ~668cc, 90% duty on 668cc injectors is ~600cc.
So, with standard fuel pressure and 80% duty, 720cc is needed.
But, with raised pressue and higher duty cycle, 511cc will do.
But, as Albert says, it's better to run bigger injectors at a lower pressure, preferabely the pressure that they are specified at.
The std fuel pump just can't pump that much fuel that fast, so with std pump the fuel pressure would fall, the engine would go lean, the pistons would fry and You would want to commit suicide
Fuel pressure regulator, hmm, dunno, why are You buying one?
Some words about how the Fuel pressure regulator works, in case Your'e not familiar with it:
If you run with 3 bar fuel pressure, and add 1 bar boost to the engine, a stock linear FPR would rise the fuel pressure to 4 bar. Why? because the fuel is beeing held back by the boost. 4 bar fuel and 1 bar boost is so to say the same thing as 3 bar fuel and no boost.
Anyway, one reason to buy an aftermarket one is that you can adjust the fuel pressure on it. Then, you can get a progressive one (I think they mostly are), wich would rise the fuel pressure more than the boost pressure, for example by 1,5 times. (1 bar boost = 1,5 bar more fuel pressure). That way you can have a sickly high fuel pressure at high boosts, and still low or std fuel pressure at easy driving and idling.
I think there is some nonsense being talked here guys... Boost does not have a linear effect on the stock fuel pressure regulator AFAIK.
The stock regulator, or a Bosch motorsport one, that clips into the ABY or RS2 fuel rail runs at two settings. One setting, eg 3bar fuel pressure is available when vacuum is presented on the control pipe (from inlet manifold) and then say 4bar fuel pressure when boost (+ve pressure) is detected on the control pipe.
Maybe I'm wrong, but thats how I remember it - will have to dig out the factory info on exactly how this is tested.
I don't think a rising rate regulator would do anything useful on the S2 Motronic system, as the magic on fuel 'quantity' is calculated by the ECU in conjunction with knowledge of the two-step nature of the stock regulator.
You could just run with one fuel pressure 100% of the time by blanking off the control pipe on the regulator, but you would have to reprogram the ECU with this in mind to ensure that sufficiently higher duty cycle on the injectors was used under boost conditions to provide correct fuelling.
Originally posted by S2central.net I think there is some nonsense being talked here guys... Boost does not have a linear effect on the stock fuel pressure regulator AFAIK.
Sounds a bit strange, have to check that out. Thought it was an ordinary linear FPR.
Read something about testing the fpr at vacuum and at -+0kpa, but can't find it.
If what you're saying is correct, I understand why you would want to change the stock FPR. Running perhaps 2.5 bar of boost and only 4 bar fuel pressure wouldn't give you much squirt from the injectors.
Originally posted by martinjs How about those FSE Powerboost Valves, thats all they are ,an adjustable fpr.
ive never heard of anyone fitting one to an S2 though.
I have one of those that I'm going to use this summer. Mostly to get the car running with far to big turbo for the mapping and stock injectors.
I added a few calculations into a unit conversion program and if anyone do want to use it you are free to do so but please not that all information/values etc are NOT confirmed or verified - so use at your own risc. Look at the last Inline5 tab for the fuel calculations.
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