Rising Rate Fpr w/ 380cc

[guitaraholic]

It's said 380cc injectors are good to about 240-250whp at 3 bar. Also 380's can flow enough for 290whp at 4 bar. Now yes you would need an ecu tune for this to work perfect, but,, what if you used a rising rate FPR. At 0psi boost, the fuel pressure would be at ~43psi. However at 14.7 psi of boost, the fuel pressure should be at 4 bar or around 57psi. This would seem to match about perfect, because 14-15lbs of boost (T-28) would give you around 260whp or so maybe a bit more, giving a little bit of head room on fuel. Now I know this isn't the perfect setup, but I would think you would have enough head room from fuel flow to be pretty safe.
Also, 4 bar isn't too much to run on injectors, yes I know once you start getting over 60 psi, things start to get a bit hairy, but 57 psi isn't that bad. This is merely an idea to give a nice alternative to be able to turn up the boost a little bit more and have the fuel flow and not worry about blowing a nice hole in your pistons. Also, yes upgrading your fuel pump is a must before doing this, preferably a something HP, like the Walbro 255hp. Because fuel pumps flow less as the pressure increase.

[Silvia_S13]

how do u plan on starting ur vehicle, because a rising rate FPR will not scale down your injectors at idle.

and a fmu or rising rate fpr is the most useless item in a turbo setup. run a chipped ecu or something. regardless of fuel pressure, or any of that. ur idea wont work.

[hayaimoto]

Good Strategy but I think the best way to figure out fuel delivery is by using a wideband to record where your AFR's are. Most standard japanese injectors start to "overheat" at 80% duty cycle.

Its scary to think that some people still boost 13-15 psi on the stock fuel pressure and stock injectors. I would imagine that the "extra" power that they are obtaining would be from the car leaning out.

Just my .2 cents but if anyone has the proper FPR psi for high boost please post your set up.

[guitaraholic]

Yes, as stated before you are right Silvia, You would need a chipped ECU or some other type of fuel management for it to work properly.
However at idle and normal driving (ie, out of boost), it would act like a normal FRP, because there would be zero pounds of boost, the Fuel pressure will be at the standard 43 psi (stock pressure).

[orion::S14]

2 things:

1) Your STOCK FPR raises the fuel pressure under boost at a 1:1 ratio...so at 14psi, you already HAVE 58psi of fuel pressure.

This is so the injector flow is static.

An FMU would have to be a 2:1 ratio, AT LEAST...to do anything more than your stock one already does.

2) A 2:1 RRFPR would have the fuel pressure at 5bar when running 14psi of boost...that would be as you described.

However, who makes a 2:1 FMU / RRFPR...???

Most are 6:1, 8:1, 10:1, or 12:1

Vortech makes a 3:1...and even that's getting close to dangerous fuel pressure (87psi at 14psi of boost). Keep it at less than 100psi...!!!

- Brian

[guitaraholic]

How about then just getting an adjustable FPR with a 1:1 and set it to 58psi, so it will stay 4 bar above manifold pressure.

[orion::S14]

^^^ That works great, you just have to tune for the 'new' injector size.

Use an online calculator, you can find the new flow of any injector at higher-than-stock fuel pressure.

- Brian

[guitaraholic]

ok, here's a caveat to the question. Under boost, if fuel pressure was constant, did not rise w/ boost,, say 3 at bar of fuel pressure, under boost would you actually flow less fuel because of the increased manifold pressure. So at 4bar under 1 bar of boost,, you would actually only flow 3 bar's worth of pressure though the injectors, again given that the fuel pressure did not rise.

[ronin207]

what does manifold pressure have to do with with injector inlet pressure? I GUESS I"M DUMB. 14.7

[MELLO*SOS]

Originally Posted by ronin207

what does manifold pressure have to do with with injector inlet pressure? I GUESS I"M DUMB. 14.7

Think about this... The fuel injector is just a pipe that connects two pressurized areas, the fuel rail and the intake manifold. Fuel injectors flow a certain rate of fuel, at a certain rail pressure. So whenever the intake manifold pressure changes, you have to add or subtract that same amount of pressure to the fuel rail, otherwise your fuel injectors will flow different rates... Adding 10psi of boost to the intake manifold without adding more fuel pressure would effectively lower the fuel rail pressure to 33.5. This is why we have 1:1 fuel pressure regulators, to bump up the rail pressure by the boost amount and keep the injectors flowing the same rate regardless of manifold vacuum or boost pressure..

Guitaraholic pretty much answered your question here:

Originally Posted by Guitaraholic

Under boost, if fuel pressure was constant, did not rise w/ boost,, say 3 at bar of fuel pressure, under boost would you actually flow less fuel because of the increased manifold pressure. So at 4bar under 1 bar of boost,, you would actually only flow 3 bar's worth of pressure though the injectors, again given that the fuel pressure did not rise.

Why did you put '14.7' at the end of your post??

[ronin207]

Hey Mello88, sounded like a trick ? to me sorry if I was acting like a twat. Also isn't 14.7 PSI, a bar @ sea level? That's why I ended it the way I did. Peace Ronin207