Im buying my fuel pump today and I want to know if a 255 walbro will be an overkill for a fp big 28 setup? I can get the 255 for $99 from dejon and thats the best price ive seen so I just wanted to know. Thanks.

Anyone?

I've got the setup you described and to tell you the truth, the car runs the same as before except the loud whine from behind the passenger seat.

actually i have that same loud whinning noise but i do feel a little better top end .. but i think will only be effective if you upgrade your turbo.

You will need an aftermarket fuel pressure regulator reagrdless if you ever plan to tune your fuel trims(ex. AFC). That pump will overrun the stock pressure regulator and you will not get linear fuel pressure. I just had the same issues first hand with a 255hp FP on my own car. I rewired it too, so that was even more overkill. I got myself an aftermarket FPR and now I can tune with consistancy. The B&M FPR is not an option because it uses part of the stock regulator and it will not be able to lower the pressure. You need one that replaces the whole stock unit and allows you to lower or raise the pressure.From what I have gathered from reading the forums, is that the 190 is enough to support what you plan to do without having to replace the FPR. But then again not all cars will get the same results and the 190 might still need an aftermarket FPR. Good luck.

^that is exactly what I wanted to hear!

Ill stick with the 190 then because I really dont know if Ill end up doing injectors. This is what I was thinking. I would get an intake, hard intercooler piping, bov (recirculated of course), exhaust mani, t28, 2.5 turboback, and the 190 as far as the engine goes. This is stage one for me. Stage 2 will involve a new engine, big turbo, fmic, complete fuel system with dsmlink, lsd, 2 step, all the fun stuff. But thats much farther down the road. Thank you for the useful info!

Originally posted by FearceDSM
You will need an aftermarket fuel pressure regulator reagrdless if you ever plan to tune your fuel trims(ex. AFC). That pump will overrun the stock pressure regulator and you will not get linear fuel pressure. I just had the same issues first hand with a 255hp FP on my own car. I rewired it too, so that was even more overkill. I got myself an aftermarket FPR and now I can tune with consistancy. The B&M FPR is not an option because it uses part of the stock regulator and it will not be able to lower the pressure. You need one that replaces the whole stock unit and allows you to lower or raise the pressure.From what I have gathered from reading the forums, is that the 190 is enough to support what you plan to do without having to replace the FPR. But then again not all cars will get the same results and the 190 might still need an aftermarket FPR. Good luck.

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Good advice but not exactly true. This is true only if using a High pressure 255lph fuel pump. The standard 255 lph fuel pump will work within the stock system's fuel pressure limits. The standard 255 lph pump is just larger capacity not higher pressure. The stock fuel pressure regulator is diaphragm operated by pressure not flow. The pressure of the fuel system is supposed to be higher than what is required of the injectors as the fuel pressure regulator will ensure constant fuel pressure at various loads. Ignition is controlled by pulsing the injectors in accordance with intake air measurements and firing the spark plug as timed. Higher flow will not overrun the regulator, higher pressure will. The higher flow just helps prevent lean conditions when the injectors are constantly being pulsed (full throttle).

HeavyD,

The fuel pressure regulator creates pressure by restricting the flow. The problem is that even when the stock fuel pressure regulator is wide open it can't flow enough fuel back to the tank and the pressure rises.

The pressure in the fuel rail is exactly what causes the injectors to spray a given amount of fuel. The reason for a reference tap in the FPR is to maintain a constant pressure difference between the outlet of the injector and the inlet so that the same amount of fuel is delivered for a given unit of time at idle or at full boost. As long as the fuel pump can deliver more fuel than the injectors can spray the fuel pressure regulator can maintain a given pressure.

I've never looked but perhaps the key difference between the 255 and the 255hp is that the hp version is able to support higher fuel pressures than the non-hp versions. Normal pumps have relief valves to limit the max pressure to around 70 psi. If someone was running 45 psi base fuel pressure and 25 psi boost the pump would start venting at a bad time. Flow also falls off as pressure increases so maybe the hp pump is better able to keep the flow up at high pressures.

Steve

Regulators don't create pressure, they just regulate it as the name implies. An orifice such as an injector nozzle restricts flow and creates a pressure drop. That is how the fuel atomizes into a spray. The fuel is high presure liquid before the orifice and after the orifice it is a vapour state due from the pressure drop. Restrictions cause a pressure drop. Flow is calculated by differential pressure across an orifice.

The pressure from a fuel pump will pulsate and the job of fuel pressure regulator is to ensure that pressure after the regulator is constant. If the pressure is lower than the diaphragm/spring pressure setting, you have no control as the fuel pressure can be anywhere between 0 psi and the regulator setting (eg. 34 psi). That is why the pressure is higher before the regulator. So the regulator can reduce it to a constant known rate that the car's ecu uses in its air/fuel ratio controller algorithms.

Our fuel pressure regulator is on the end of the fuel rail. It's doesn't regulate the pressure after it like an inline regulator would but regulates the pressure by restricting the flow of fuel out ot the rail. I said it creates the pressure in the rail because without it or some other restriction the our fuel pump won't generate sigificant pressure on it's own. But you right the regulator doesn't create pressure on it's own, the pump has to be pushing fuel into the rail faster than it gets out to have any pressure. http://www.stealth316.com/2-fuelpumpguide.htm
Without a doubt, there is a pressure drop after the FPR but in our case it's unimportant until the return line becomes a restriction.

Our FPR has a manifold reference port to allow the fuel pressure to track manifold pressure and maintain a constant pressure delta over manifold pressure so that the flow rate of the injectors doesn't change. As you point out their flow is calculated by differential pressure across an orifice. the pressure drop you speak if the in fact the base fuel pressure setting.
This simplifies the ECU task of computing the injector pulse width and keeps the injector flow from dropping off when you need fuel the most, during boost.

I can't comment on how effective our injectors are at producing a vapour state due from the pressure drop. It's recognised that in direct port injection on high rpm engines full atomization of the fuel can be a bad thing since the fuel in a vapor state moves slower than a high pressure stream or droplets.and can limit your ability to get the fuel into the combustion chamber. From the papers I've read spraying the fuel on the back of a hot intake valve causing vapourization can inprove delivery and lower charge temps .

Back to the thread topic, have you measured your base fuel pressure with your 255. With the stock FPR I've seen a small rise in the base pressure with a ND 180 lph pump but since I don't have a fuel pressure guage in the cockpit I can't say it impacted the 1:1 rising rate tracking like a pump that sigficantly overruns the regulator will.

Steve

I just know that my car runs better now with the aftermarket AFPR and the 255 FP as opposed to when I just had the 255 FP alone.