mark944turbo

Does anyone know the max pressure that the stock fuel pump could in theory maintain without problems? Im just brainstorming ways to maximize the delivery rate of my current injectors without exceeding 80% duty cycle.

Plus, more pressure = more atomization = less knock = more boost= more air = power.

I would like to run 70 psi at WOT, which is 20 lbs boost, meaning idle would be around 30 at idle would be nice to maintain.

Another side note, what are the causes of failure in a fuel pump? Do they spin so fast that they become ineffective or overheat or what?

Thanks for any input.

Danno

The problem is that as you increase pressure, the total flow-volume goes down. So at 3-bar, it may deliver X gal/min. However, if you bump up pressure to 3.5-bar, the pump will only deliver 80% of X. So it's a criss-cross function. While you may be able to decrease the duty-cycle on the injectors, you'll get to the point where the pump will run out of capacity when the injectors are only at 70%.

With the stock pump, I wouldn't go over 3-bar. What you can do is run a Walbro pump ($100) with 100% more flow-capacity than the stock pump, 60% more than the 928GTS pump, 80% more than the pump Lindsey sells. Then you can bump up the pressure to 50psi for about 10% more flow than you're getting now without worrying about reducing pump-flow below what your injectors can flow at that pressure.

mark944turbo

I guess a better question would be at what point is this criss cross function maximised? 3bar? I would rather push the pump than the injectors, for atomization purposes.

It is cheaper to buy an adjustable fpr than injectors, and that extra percent form maximising the function just may be enough to save me.

Danno

On the stock pump, from all the data I've been able to gather, it's good for about 375rwhp @ 2.5-bar, 350rwhp @ 3.0bar and 310-320rwhp @ 3.8-bar. Your injectors are good for about 350rwhp @ 100% duty-cycle, so it's matched up pretty well right now. You can go up to 3.8-bar and program in -12% to -15% in the MasterAFM to cut back on the duty-cycle. Or I can do that in the chip I'm gonna send you for 25psi. I'll set the FQS as follows:

FQS FUEL IGN
---------------------
0 55#-15% 0
1 55#-10% 0
2 55# -5% 0
3 55# 0

4 55#-15% ignition-retard for 25psi
5 55#-10% ignition-retard for 25psi
6 55# -5% ignition-retard for 25psi
7 55# ignition-retard for 25psi


This will give you the most flexibility. You can use either 3.0- or 3.8-bar FPR with the same chip. And you can make quick incremental changes in fuel to match boost as well. When the pump & injectors are closely matched like this, it's difficult to figure out which one is maxed out first. Using a duty-cycle meter would help here.

mark944turbo

I looked into duty cycle meters, pretty pricey! Im on a serious budget. I think I am going to cut open a stock fuel pressure regulator and see if I can modify it to maintain 3.8 bar when referenced to a 20 psi signal, which I will get with an air compressor using a compression guage to get an exact reading. I do need a fuel pressure guage though. Or does the factory have one for small pressure change variations in the fuel rail? It would be nice to hack into that if possible.

I believe Jon Milledge used to get fuel pressure regulators to flow a higher pressure by squeezing them in a vice. Has anyone done this or maxed one out before it broke? Any info would be awesome. Squeezing one of my 3bar ones might get me a little more pressure, if not 3.8 bar.

Danno, any chips you send that do not have any overboost protection at all would be awesome. Mine now keep cutting me off under WOT due to that 3 seconds over the boost vs rpm graph threshold. Eventually I would like some of those fancy ones with multiple options, but for now overboost removal along with a single map of high boost fuel would be the best.

Asarus

Interesting thread

I have one question. What would be the fuel pressure under WOT ? Is that the same as the one you set up with the motor off and the fuel pump on (2.5 bar stock and 3.0 bar for Guru chips) ?

Danno

Fuel-pressure is a function of manifold pressure. The FPR uses manifold-pressure to adjust the baseline fuel-pressure of 2.5-bar or 3.0-bar. Then manifold-vacuum or boost is used to lower and raise pressure. So with stock FPR at idle, fuel-pressure is about 1.8 bar. Then under 1-bar of boost, it rises to 2.5+1.0=3.5-bar (add 0.5bar for 3.0 bar FPR).

BTW - can anyone confirm the fuel-pressure used in the TurboCup cars? Is it 2.5 or 3.0 bar???

Mike1982

Well, what happens danno if I ran your chip set at 15psi (where it is suppose to be) with the 2.5bar instead of the 3.0? Would I be running lean then? You said with increased pressure, you get less flow but what is the major advantage of going higher? Better mix in the motor of the gas itself?

special tool

You should be VERY careful about listening to whoever did your chips as far as the fuel pressure.
.1 bar (1/4 turn on Paragon AFPR) wll raise or lower my AFR about .3. That is it would go from say 12.3/1 to 12.6/1. You can see the danger.

Obviously, fuel pressure moves the entire curve - if you want to adapt certain points along your curve, you have to adjust inj. duty cycle.

Asarus

Thanks Danno

Sure...

250 bhp cup cars : 2.5 bar FPR
300 bhp cup cars : 3.0 bar FPR