Fuel pump: 190 or 190hp?

f1monaco

Registered User
I am looking for advice on the best fuel pump to get. I have a 90 SC with a 10% pulley, headers, exhaust, and will likely be going to 76mm MAF, 36# injectors. Right now, I have a stock miata 80 lph pump and pressure is only 29 psi at idle. Looking through the forums, I figured I should go to a 190 lph or 190 lph HP. (Perhaps with an AFPR) Recommendations?
 
Get your self a 255lph high volume pump and be done with it. AFPR is not a requirement for these cars as the stock one does just fine.

Frit
 
This SC engine is in a miata, using the stock miata fuel system. I changed the fuel filter, but I guess that's all it's got.

Is 255 lph overkill for what I need? I hear they are loud and heat the fuel.
 
Is 255 lph overkill for what I need? I hear they are loud and heat the fuel.

theres really no "overkill" when going with a fuel pump. that extra pressure is just there IF u need it later on


so, as it was said before, get a walbro 255lph Hi-pressure pump and be done with it.
 
Thanks for the input. One last question: Can the 190 HP deliver enough fuel at WOT for my setup? I hear they can support 400 hp on NA engines. No future mods are planned.
 
Thanks for the input. One last question: Can the 190 HP deliver enough fuel at WOT for my setup? I hear they can support 400 hp on NA engines. No future mods are planned.

Yes...if you are going to keep the 36# injectors and only do the mods you listed it will be fine.

David
 
If you add additional power and ground wires to the pump, with larger gauge wire and the appropriate fuse and relay, you can get even more output out of any pump. So your 190LPH will perform much better at 13.5V than at 12V.
 
Guys have run ok with the 190's with 42# injectors by the looks of the old old threads. If your replacing your fuel pump now, then get the 255 hv in there and run with it. You say now no more mods, but that can change in a year ;).

Frit
 
As far as the comment about a 255 being loud. Even if it were, which I don't think it is as I don't hear mine, you won't hear it over the SC whine.
 
As far as the comment about a 255 being loud. Even if it were, which I don't think it is as I don't hear mine, you won't hear it over the SC whine.

The 255 high pressure pumps in my cars don't make anymore noise than the stock pump did (can't hear either unless the motor is off). My 91 is also using a KB boost-a-pump with 10% extra voltage for normal driving and 30% extra when using nitrous...doesn't make it any louder.

BTW, my 93 has dual 255 high pressure pumps (in tank) and it's just as quite.

David
 
Duel 255's, wow!

I am caught between two worlds here. This SC is in a miata, where you sit right beside the fuel pump. I could live with some noise, but the miata people claimed it ruined their FPRs and heated the fuel - one guy was even running an oil cooler in the fuel line to reduce the heat from the 255.

Clearly, the 255 hp is the way to go for most SC's. Will running a pump at 13.5V shorten its life expectancy?

Thank you for your considerable knowledge!
 
The additional voltage will spin the pump faster. I am not sure if there would be a proportionate decrease in life expectancy. One benefit of the Boost-A-Pump is that it lets the pump run at lower voltage most of the time, so there is less wear on the pump and less heating of the fuel. Some cars come with a cruder, but still effective setup from the factory (Subaru Impreza WRX, Mitsubishi 3000GT Turbo, Ford F-150 Lightning). That incorporates an additional wire to the fuel pump that includes a resistor, and a switched relay that alternates between the restricted and unrestricted current paths.
 
Last edited:
The additional voltage will spin the pump faster. I am not sure if there would be a proportionate decrease in life expectancy. One benefit of the Boost-A-Pump is that it lets the pump run at lower voltage most of the time, so there is less wear on the pump and less heating of the fuel. Some cars come with a cruder, but still effective setup from the factory (Subaru Impreza WRX, Mitsubishi 3000GT Turbo, Ford F-150 Lightning). That incorporates an additional wire to the fuel pump that includes a resistor, and a switched relay that alternates between the restricted and unrestricted current paths.

My car sits at 13.8 volts when running, and the fuel pump see's about 13.6..... what the heck are you talking about?

If the voltage drop is so bad as your describing, then tuning in the injectors would be a night mare because we would not have the fuel pressure in the fuel rail to run the injectors according to spec. Your describing a situation where if someone switches injectors, they would literally have to run for MANY hours on the dyno to tune it all back in because the specs for the injectors will be totally out of wack and totally useless to use.

I run a 255lph hv pump, and when I dial in my AFPR for 43.5 psi on the rail, thats is what I get. If I use the stock NON adjustable FPR I see 39 psi on the fuel rail with no vac. How much do you wanna bet that I would see the same even if I ran 60 lb injectors. Oh and guess what, even if I was making 15 lbs of boost, the 255 pump I have will easily make 55 psi to support that... and I see 59 psi when I'm running the AFPR at 43.5 at full boost.

Lets keep things simple, and NONE of us are at the point that a hv 255lph pump can't keep up.... except maybe Jim Demmitt

Frit
 
My car sits at 13.8 volts when running, and the fuel pump see's about 13.6..... what the heck are you talking about?

If the voltage drop is so bad as your describing, then tuning in the injectors would be a night mare because we would not have the fuel pressure in the fuel rail to run the injectors according to spec. Your describing a situation where if someone switches injectors, they would literally have to run for MANY hours on the dyno to tune it all back in because the specs for the injectors will be totally out of wack and totally useless to use.

I run a 255lph hv pump, and when I dial in my AFPR for 43.5 psi on the rail, thats is what I get. If I use the stock NON adjustable FPR I see 39 psi on the fuel rail with no vac. How much do you wanna bet that I would see the same even if I ran 60 lb injectors. Oh and guess what, even if I was making 15 lbs of boost, the 255 pump I have will easily make 55 psi to support that... and I see 59 psi when I'm running the AFPR at 43.5 at full boost.

Lets keep things simple, and NONE of us are at the point that a hv 255lph pump can't keep up.... except maybe Jim Demmitt

Frit

According to Walbro data, with 13.5 volts present, the 255 LPH "HP" pump will flow about 70 gallons per hour at 40 psi, and about 63 gallons per hour at 55 psi (interpolated data between 50 and 60 psi). So, 15 psi of boost means you need about 55 psi of fuel pressure. 63 gallons of fuel weighs about 378 pounds. So, on a car running 15 psi of boost, the 255 HP can move about 378 pounds of fuel per hour. Now, we all know that injectors are rated in pounds per hour. I believe that those rating reflect 100% duty cycle. Six 60 pound injectors at 100% duty cycle can move 360 pounds of fuel per hour. So, as you said, with 13.5 volts present, and 15 psi of boost present, the Walbro 255 HP can easily support 60lb injectors. Especially because you would really only want to run the injectors at 80% duty cycle maximum, which would be 288 pounds per hour.

However, Walbro's data indicates that with only 12V present, the 255 HP pump will only flow 53 gallons per hour. That's only 318 pounds of fuel. So that is actually not enough fuel for 60lb injectors running over 88% duty cycle. If the injectors stay at 88% or less (as they should), you will be fine.

Now, you are saying that your car is getting about 13.6 volts present at the fuel pump. However, don't forget that voltage drop increases as current flow increases. You didn't specify under what conditions you tested the voltage at your fuel pump. Was it idling? Or was it under full boost? The pump draws 7.5 amps at 40 psi, but it draws about 8.7 at 55 psi. Of course, if you were only getting 0.2V of drop, then it won't make much of a difference. I wonder if others have gotten similar results to what you got. If so, that's really good news. I hope you're right! :)

I find it interesting that, if we can all get 13.5 volts or more at our fuel pumps while running, then even the 190lph low-pressure pump can pump 44 gallons (264 pounds) per hour at 55 psi. That is enough to support 42lb injectors at 100% duty cycle. It's actually enough to support 50lb injectors at 88% duty cycle.

And by the way, the High Pressure version of the 255lph pump doesn't even start to pull away from the regular version until about 65 psi. Which none of us is likely to exceed "... except maybe Jim Demmitt." ;)

Information gathered from charts at: http://www.autoperformanceengineering.com/

By the way, what are you trying to say about the tuning problems? It wasn't clear to me. The fuel demands at idle and low-rpm operation are pretty small compared to the fuel demand at high boost and high RPM. So a pump like this running at a lower voltage, even turning at half-speed, should have no problem maintaining adequate fuel pressure during those situations. When the load rises (indicated by a signal such as MAF voltage or manifold pressure), the Boost-A-Pump increases the voltage to increase pump output. That allows it to cope with the demands of the injectors at those times. As long as you choose the proper setpoint for your load trigger, fuel pressure will never drop below the desired level.
 
Lets keep things simple, and NONE of us are at the point that a hv 255lph pump can't keep up.... except maybe Jim Demmitt

Frit

Frit,

Mine wasn't keeping up past 5000 rpms, and I corrected the problem by increasing voltage 10% with a KB Boost-a-pump. When using nitrous I have to increase voltage 30% to keep from going lean.

David
 
Back
Top