190 or 255 lph?

[svodad]

I have a leaky gas tank and need to drop it so figure time to change the fuel pump (86 comp prep). I hope to build the car to about 300 hp. I have heard various things about how big the pump should be (assume the stock is aound 100 lph). Motion Dynamics recommends only going with the 190lph, says the 255 recirculates too much, just adds heat to the tank. Most others (and threads I've read) say go with the 255 and forget need more pump in the future. Sure could use a tie breaker on this.

Second question, Walbro high pressure or standard?

Thanks

[svobud]

1. Do it once and get the 255lph. Too many people doing this way with EXCELLENT results vs one person having an opposite opinion on the matter. Heat to the tank? New one on me.

2. The high pressure. No ifs. No ands. No buts.

[Gator]

I could go on and on about the 190 vs 255 in regards to 300HP at the wheels.

But I dont feel like typing and the end result would be the following sentence: Do the job once and get the 255High Vol. Its only a couple bucks more than the 190 ( literally,) and you will never have to worry about having enough fuel.

[mutant]

I dare to be different.

The stock pump is 88lph.
As boost pressure goes up, so does your fuel pressure because of the fuel pressure regulator. As fuel pressure goes up fuel flow goes down. How much pump you need depends on how much boost you are going to run. I personally think that the 255 is way overkill. According to a fuel pump test in one of the recent Mustang magazines, even a 155 lph pump will supply enough fuel at 20 psi of boost to make 300 hp. Another consideration is pump noise. The 190 will be quieter.
If you plan on running 30+ psi of boost with 9.5:1 AFR at 8000 RPM then a 255lph might be warranted. anything less will be handled by a 190 with ease.
-Dana

[SVOeric]

actually, my 255 is quieter than the stock pump I removed. I have to listen closely to hear my 255.

now -- on to 300 hp with boost,

to run this much HP on stock injectors, most people are running 40-45 psi base fuel pressure.

now add 1 psi per psi boost, and wow -- at 25 psi boost , you are looking at roughly 70 psi fuel pressure.

the ONLY fuel pump I've seen that would hold that is the 255 HIGH PRESSURE pump.

now -- on top of that, in 10 years, when my 255 is worn out, it should still outflow the 155

[Gator]

Originally posted by SVOeric
actually, my 255 is quieter than the stock pump I removed. I have to listen closely to hear my 255.

That may have been due to the fact that the stock pump may have been on its way out. They have a tendency to get "loud" when they get old and they start to "strain" ( if you will. )

But I will say that the 190 Motorsport pump that I had ( which is basically the Walbro pump with some sort of deadening material around it and a new cage. Its a complete "drop in.") was just as loud as my 255 Walbro.

I have done 292 to the wheels on the 190 and the lean condition was more than likely related to another component of the car.

Im just sayin for the couple extra bucks, ( for me )to have the ability to say "If I want more HP, at least I know I have the fuel for it. "

[140cilx]

Gator, whereabouts are you now on HP to get that lovely 12.7?

[svodad]

Decision time

First thanks for all the great input.

I thought I would try to work backward into the solution. First was to determine max fuel pressure. Taking a lead from SVOeric, I would agree that 45 lb at the rail plus 25 lb max boost would say 70lbs required.

Going to the spec sheets provided by APE, the outputs of the pumps in gpm at 70 psi and 12volt and 13.5 volts are

190 = 28 & 38
190hp = 31 & 41
255 = 40 & 50
255 hp = 46 & 56

This of coarse is output at the pump, some % should be deducted for line and filter loss etc. This is also an average of 10 pumps at random and without knowing the standard deviation (where did that come from) I would assume you want to be a little conservative.

Ron Gregory posted a formula of dividing crank hp by 12 to get gpm, applying this to the flows each pump supports the following hp at 12 volt and 13.5 volt

190 = 336 & 456
190hp = 372 & 492
25 = 480 & 600
255hp = 552 & 672

Conclusion so far is , wow, really pays to improve electrical system (Charlie at Evergreen stated a high output alternator made a world of difference on the performance of the car, 14volt+ now instead of 12 volt, this now seems believable). Also is seems to say the 190hp should support 300rwhp but must stay factory fresh in performance. Ron at APE did also say that too big a pump will circulate a lot of fuel, heat the fuel up, and that is not good.

STILL undecided.

[Gator]

Originally posted by 140cilx
Gator, whereabouts are you now on HP to get that lovely 12.7?

Dunno to be honest....I'll say that last time she dyno'ed was 322HP / 349TQ. I just havent been to a dyno in 3 years, and that was my second time on a drag-strip in 2 years.

Originally posted by svodad
Conclusion so far is , wow, really pays to improve electrical system

100% correct. Stock SVO electrical sytems are J - U - N - K as far as performance is involved...( not to mention the nice and "crispy" connections it will eventually provide for you in the stock harness . ) One of the FIRST things you should do is swap to a 3G alternator.

You cannot honestly appreciate that statement until you try squeezing every ounce of power out of your car. For example: when I was more into "playing" on the street, i was notorious for running at night with my headlights off.

As for the 190 - 255 pump debate, i just dont understand the debate. Its not like your going to be full throttle all the time ...but when you are, its nice to know that you have what it takes to dish out whatever it is that you throw at it.

Not so sure about this "heating the fuel up" jazz ( not that i dont believe it ) but I suspect that you are not going to build a car that rides the fine line in tuning to validate the statement " I lost 1.7 horsepower due to the fact that the temp in my fuel raised 3 degrees. "

IMO, your making this waaaaaaaay harder than it really is.

[Pat_in_L.A.]

When you get to that ragged edge where the fuel temp makes a difference, try an old showroom stock trick. Stop by the local ice cream store (Baskin Robbins, Ben & Jerry's, etc.) and get some dry ice from them. Now just stick all the small pieces of dry ice down the fuel filler (or into a 5 gallon gas jug, fill with gas and pour into the tank).

Make sure to wear gloves to avoid major frostbite.

[jayG]

Definetly get an adjustale fuel pressure regulator what ever you do. My stock one was bad and caused the fp to jump to 90psi under boost! And thats with a stock fuel pump! Caused all kinda havoc on the dyno...can I get an amen Todd?

[mutant]

More than you wanted to know: 2 speed pump

Don't forget that your '86' was manufactured with a simple 2 speed control circuit on the fuel pump. There is a .68 ohm resistance wire going to the pump. This keeps the stock pump spinning quietly during normal operation off-boost. When you get into boost the pressure operated switch shorts across the resistance which speeds up the pump. This switch is in the engine compartment directly in front of the driver. You will see a hose coming from the vacuum tree that ends in a wrapped-up bundle that has 2 wires coming out of it.
Because of this 2 speed arrangement, there are 2 potential problems with doing a fuel pump upgrade. The first problem is the resistance wire. The resistance that Ford put there is correct for the stock pump and the amount of current that the stock pump draws. Your replacement pump willl undoubtedly draw more current than the stock pump. This will lower the voltage that the pump sees. I don't know the pressure that the pressure switch switches at( no std. dev. on that either!). So the potential problem is the engine going lean just before boost gets up to that switch point. The second potential problem is the current rating of the pressure switch's electrical contacts. My guess is that the current draw of the 255 lph pump could be about 3 times the draw of the stock 88 lph pump. Are you going to bet your engine that those contacts will reliably carry 3 times the current? How many things in the car are made to handle 3x normal load? Certainly nothing in the electrical system that I can think of!
You would go very lean under boost if those contacts fail.
What to do? You have 3 choices: 1. Do nothing. 2 Re-engineer the 2 speed setup. 3.Permanently short out the resistance wire.

-Dana

[SVOeric]

hey dana -- I believe you have the 2 (84 & 86) setups confused slightly

the 86 has the switch, with no resistance wire, the 84 (and 85) has only the resistance wire, with no switch.

[mutant]

The 86 has the switch, I'm 100% sure of that. If there is no resistor then there can be no speed change. If there is no speed change then there would be no need for the switch. I think Ford is smarter than that!
My schematics show the switch and a .68 ohm resistor.

[SVOeric]

I think we are saying the same thing---

the 84-85 actually has resistor WIRE that runs to the ground of the fuel pump

the 85.5 - 86 has the switch, the switch itself is the resistor, there is no resistor wire.