Budget friendly Bosch EV14 Injectors??
09-11-2017, 11:48 AM
#22
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(peak duty cycle of 64% on my non-X id1000s at 340)
I think there's something wrong with the pump on the car in question. IME, restrictive NB factory regulators result in fuel pressures that are way too high/unregulated at idle (thus varying with system voltage and stuff like that), they actually work fine at WOT where the injectors are dumping enough fuel that the regulator can handle what's left.
--Ian
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09-11-2017, 11:56 AM
#23
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No need for additional data, folks. It's really simple math. Injectors flow X fuel, car makes Y power at Z air fuel ratio. If your setup deviates from the math in any meaningful way, you have a pump/filter/FPR issue.
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09-11-2017, 12:07 PM
#24
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I have to find the thread where this was discussed, but my main take away was that the stock FPR doesn't listen to boost.
Okay found the info. https://forum.miata.net/vb/showthread.php?t=503389
On the '90-'97 cars, the FPR is referenced to manifold pressure, so the fuel pressure will always be roughly 42 PSI (median) above manifold pressure. Or put another way, the pressure differential across the injectors will always be ~42 PSI, and therefore the flowrate of the injectors will be a constant.
On the '99+ cars, the fuel pressure is not manifold-referenced, so the flowrate of the injectors does drop as MAP increases. This isn't really a problem, you simply size the injectors accordingly, and scale the ECU's fuel table to represent this nonlinearity. It's actually harder to describe than it is to do.
On the '99+ cars, the fuel pressure is not manifold-referenced, so the flowrate of the injectors does drop as MAP increases. This isn't really a problem, you simply size the injectors accordingly, and scale the ECU's fuel table to represent this nonlinearity. It's actually harder to describe than it is to do.
Last edited by ByteVenom; 09-11-2017 at 12:41 PM.
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09-11-2017, 12:09 PM
#25
NB stock returnless should be a higher static fuel pressure ~60 vs what most people rate injectors by at mid 40s. This makes the injectors more like 700cc on our setups and if you aren't configured like that in MS you'll see inflated duty cycles despite not really being there (unless my old rusty logic is way off).
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09-11-2017, 02:39 PM
#32
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No, that's not what I said. What I said is that the FPR is not increasing fuel pressure enough once the engine reaches boost. Once you hit 20PSI, the FPR isn't raising fuel rail pressure by 20 PSI to account for the increase in manifold pressure. Thus effectively lowering the capacity of the injectors.
NAs can run more boost on the stock FPR because they have a 1:1 reference. NBs need something like a Fuelab 535 and a manifold reference if they want to run more than 16.5psi without excessively sized injectors (and even then, it's not advisable). My own high-boost NB runs a Fuelab 535, 60psi base, with a manifold reference.
Having said all of that, most decent setups can flirt with 280-300whp by the time you are at 17psi, so my original general statement still applies in most cases: If you max the injectors before 300whp, something else is wrong.
NB stock returnless should be a higher static fuel pressure ~60 vs what most people rate injectors by at mid 40s. This makes the injectors more like 700cc on our setups and if you aren't configured like that in MS you'll see inflated duty cycles despite not really being there (unless my old rusty logic is way off).
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09-11-2017, 03:28 PM
#33
I've posted this before but worth mentioning in this discussion. I installed a fuel pressure sending unit and found that the factory NB FPR can't cope with more than ~190 to 200 LP/hr, I was seeing 6 to 10 psi above set pressure with a 255 walbro. The pressure was also all over the place until you opened up the injectors enough to get it down to the 60 psi set pressure.
With a 190 I see about a 5 psi drop from 60 Psi at ~250 HP worth of fuel flow, but is a smooth consistent drop and I've tuned around it. I chock this up to pumping losses from the regulator to the rail.
Return style fuel systems are needed at much past 250hp in my humble opinion.
With a 190 I see about a 5 psi drop from 60 Psi at ~250 HP worth of fuel flow, but is a smooth consistent drop and I've tuned around it. I chock this up to pumping losses from the regulator to the rail.
Return style fuel systems are needed at much past 250hp in my humble opinion.
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