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Right - been looking into fuel pressure, pumps and flow curves recently. Wanted to capture some basic info here and confirm some thinking with the more experienced (officially learned) folk...
The fuel pressure regulator (FPR) used on turbo engines like ours has the job of maintaining the *SAME* pressure across the fuel injectors. It does this by increasing the input pressure at the fuel rail in a linear fashion with boost pressure so that the effective pressure across the injectors is the same.
Eg The FPR in an ABY is rated at 4bar at ambient pressure. At idle, when the engine pulls ~0.5bar vacuum, the FPR reduces rail pressure to 3.5bar. At 1.2bar manifold boost pressure, the FPR provides 5.2bar fuel rail pressure. In all cases we maintain the 'baseline' FPR rating of 4bar across the injectors.
ABY injectors flow 320cc per minute at 4bar with 100% duty cycle - you'd never achieve that reliably in the real world with max duty cycle around 80-90%. So even at a notional 2bar boost, we still only flow 320cc per minute as the FPR lets the rail pressure increase to 6bar to compensate for 2bar of boost. Right ?
So for this spec, knowing we only fire one injector at a time on the S2, we need a fuel pump easily capable of flowing 320cc of fuel per minute. We need to know the fuel pumps pressure/flow characteristic in order to determine that it can flow this amount of fuel at the increased rail pressure as demanded by the FPR.
It is my understanding that an electric fuel pump's flow rate decreases with pressure - RIGHT ?
Nominally the ABY fuel pump is spec'd to deliver 2 liters of fuel per minute with the engine not running - ie 4bar rail pressure and assuming worst case of 10V across the pump terminals. We need the pump's flow graph to determine how much fuel it flows at higher boost levels. All that excess fuel runs back to the tank by the return line of course.
Based on that figure, my gut feel is that a healthy S2 fuel pump (and clean filter of course) has plenty of margin for RS2 applications which flow higher amounts of fuel on account of larger injectors, but its easy to see how a monster fuel pump (such as the Bosch motorsport spec'd one) can buy a good amont of insurance against poor fuel delivery in modified engines.
If anybody has the Bosch reference and can post the flow/pressure graph for the S2 and RS2 pumps it would be mighty interesting.
Paul
The fuel pressure regulator (FPR) used on turbo engines like ours has the job of maintaining the *SAME* pressure across the fuel injectors. It does this by increasing the input pressure at the fuel rail in a linear fashion with boost pressure so that the effective pressure across the injectors is the same.
Eg The FPR in an ABY is rated at 4bar at ambient pressure. At idle, when the engine pulls ~0.5bar vacuum, the FPR reduces rail pressure to 3.5bar. At 1.2bar manifold boost pressure, the FPR provides 5.2bar fuel rail pressure. In all cases we maintain the 'baseline' FPR rating of 4bar across the injectors.
ABY injectors flow 320cc per minute at 4bar with 100% duty cycle - you'd never achieve that reliably in the real world with max duty cycle around 80-90%. So even at a notional 2bar boost, we still only flow 320cc per minute as the FPR lets the rail pressure increase to 6bar to compensate for 2bar of boost. Right ?
So for this spec, knowing we only fire one injector at a time on the S2, we need a fuel pump easily capable of flowing 320cc of fuel per minute. We need to know the fuel pumps pressure/flow characteristic in order to determine that it can flow this amount of fuel at the increased rail pressure as demanded by the FPR.
It is my understanding that an electric fuel pump's flow rate decreases with pressure - RIGHT ?
Nominally the ABY fuel pump is spec'd to deliver 2 liters of fuel per minute with the engine not running - ie 4bar rail pressure and assuming worst case of 10V across the pump terminals. We need the pump's flow graph to determine how much fuel it flows at higher boost levels. All that excess fuel runs back to the tank by the return line of course.
Based on that figure, my gut feel is that a healthy S2 fuel pump (and clean filter of course) has plenty of margin for RS2 applications which flow higher amounts of fuel on account of larger injectors, but its easy to see how a monster fuel pump (such as the Bosch motorsport spec'd one) can buy a good amont of insurance against poor fuel delivery in modified engines.
If anybody has the Bosch reference and can post the flow/pressure graph for the S2 and RS2 pumps it would be mighty interesting.
Paul
to maintain flow pressure must go up- flow dynamics and pump ineffiencys count for the loses. if you spin the pump at higher speed (increase voltage) the rollers are forced out centrefugally and this increases efficency by stopping flow reversal.
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