ok, so maybe a week ago i posted up the results from a back to back run with an evo 8 fuel pump and a walboro 255, and then tuned it and compared the final results. that thread can be found here:
https://www.evolutionm.net/forums/sh...=stock+walboro


a few of you asked how a evo9 pump compared, and i finally got those results as well.

the car was a evo 9 with TBE exhaust and a HKS RS intake. nothing else.

the first step was to get the baseline to see the improvements the MBC and fuel pump, and then tune would make. from there, the forge UNOS MBC was installed, and dialed in to 22.5psi, with another data run taken. last, the walboro 255 pump was installed and another data set taken. and then tuned to get the complete results of each individual parts effect on the car and more particularly the fuel system.

to start, i compared the boost levels i ran for all three runs. it was important that the forge MBC runs were all consistant, and they were. the plot may look like they don't line up right, and that is only because the X axis is time, not RPM. just like last time, right now i'm not logging RPM with boost and a/f directly.



once the boost was set, i compared the Injector duty cycles for the 4 different runs.



these results coupled with the A/F ratios:


the results show that the stock 9 fuel pump with basic bolt on mods is capable maintaining the fuel pressure necessary to not run lean at higher RPMs. the walboro only very slightly reduced the duty cycles, and even that was only above 6000 rpm. with the stock tune and an HKS RS intake, the car was running pretty lean at the peak torque area (3-4500 rpm). after tuning though it was brought down to a safer level.

so from my observations, if you have a 9 and are only looking to the most basic mods (TBE, intake, MBC), then the stock fuel pump IS sufficient to handle the fuel flow demands. i haven't had the opportunity to test further then that yet with a stock fuel pump. my assumption is that the walboro will outflow the stock pump once more demands are made, for instance cams, and other bolt on mods.

again, this is nothing new by any means, but for those who like to see some hard evidence, here it is.

 

nice write up...finally some actual data...either way for me the 75 bucks a fuel pump costs its worth installing...

 

Thanks for the write-up. Very good information.

I recently got an EVO 9, but have worked on EVO's before (briefly) and one thing that we found out is in relation to the fuel rail. Even if you have a 255lph walbro it’s very wise to change the fuel rail to something like the Sard fuel rail were you will use both ends of the fuel rail to feed fuel and the middle port for a fuel return line, to stabilize fuel delivery / distribution.

Overall, I don’t have that much experience with but would love to hear from someone that had the same issue or could shade some light on the issue.

 

This is the exact argument that I had with you on the previous post. You now state stock pump maintained fuel pressure and that the addition of the Walbro reduced duty cycle. How is this possible if the fuel pressure didn't change between the two pumps as you previously argued? If the duty cycle is having to be reduced to maintain AFR's then the pump has increased the baseline fuel pressure causing increased fuel supply.

 

alright, you again. this is a different comparison. a stock evo 9 pump and the previous post was an evo 8 pump, THEY ARE NOT THE SAME PUMP. if you look at the results, you will see clearly that the duty cycles are not reduced by hardly anything at all. the maybe 5% they are reduced can and is most likely attributed to the tune running the car slightly leaner above 6k rpm. i stated very clearly that the stock 9 pump DOES provide suffient flow for the demands of the car. shall i qoute it for you?

these two tests show that the evo 8 pump does not flow enough fuel for even basic mods. thats why fuel pressure drops, and A/F ratios go lean. the 9 pump flows a bit more, and therefor fuel pressures do not drop off with basic mods, the car does NOT go lean with the stock pump (as seen in the data), and therefor the flow rate is great enough. the walboro in both cases flows enough fuel to keep fuel pressures where they need to be.



i may have to explain to you how a fuel system works before you make any more comments (i'm making my case to everyone else. i really don't care about explaining it to you, other then letting everyone else know your wrong. if you're right, post up some evidence...)

lets begin:



in the diagram you can see the fuel system. tank, pump, high side, rail, injectors, regulator, low side.

the way a regulator works is to stop the fuel flow past it until pressures are high enough to open the valve. the way that works is, the valve is normally closed. it is held shut by a diaphragm and spring. the diaphragm has an area (we'll just say 2 square inches). and the spring has a spring force (we'll say 50 lb/in). it also has a preload, which is the distance the spring is compressed from its nominal length. the preload is what an adjustable FPR adjusts. the last thing we need to know is that the pump doesn't generate pressure, it generates flow rate (you know this). the pressure after the pump is determined by the restrictions in the lines. no restrictions means 0 psi. more restrictions, means high psi, assuming the pump can 1. operate at high pressures, and 2. maintain the flow rate required to run at the pressures.

for starters, we know that all the pumps can operate at the pressures we will see. that leaves only #2 to be the issue.

now i said that the valve in the regulator was normally closed which is true. it requires fuel pressure to open this valve, and that is determined by two things... the spring force (with amount of preload), and the pressure differential across the diaphragm. lets say the car is not running, therefor the manifold pressure is at atmospheric pressure (0psi gauge). now, if we have 25psig in the rail, 25 lb/in^2 over an area of 2 in^2 means 50lbf across the diaphragm. and we know the spring has a spring force of 50 lb/in, which means 25psi in the rail will open the valve up an inch. in reality the valve doesn't open an inch, and it might have a smaller area or a higher spring rate. also, lets say we have 1 inch of preload in the spring, that means it requires at least 50lbs of force before the valve will even begin to open. and sense the diaphragm area is 2 inches, it requires 25psi in the rail before the valve opens at all.

if you understand fluid dynamics at all, you would know the bigger the orifice area, the more fluid can flow through it. that means, if the valve is only open .01", then only a tiny amount of fuel will pass through it, while if it opens up to 1", then a bunch of fuel can flow through it. therefore if a little bit of fuel is flowing, it can flow through a small orifice without much restriction. more fuel, requires a bigger orifice to achieve the same pressures.

now, lets say when we turn the pump on, we see that 25 psi in the rail, and the pump is flowing 35 lb/min of fuel. now even though the car is off (25psi pressure differential across the diaphragm), we still turn on one fuel injector which in this case can flow 10 lb/min when we leave it on. so now we only have 25lb/min flowing through the return line, because 10lb/min is flowing through the 1 open injector. once we opened up that injector, there is less of a restriction on the system, less fuel flows through the regulator, but the valve is still open because the flow rate is sufficient to apply pressure on the diaphragm.

now we turn on another injector, so now only 15 lb/min is flowing through the regulator.

and another injector means only 5lb/min, and another injector, so that all 4 injectors are wide open. sense the pump can only push 35lb/min, and we have 4, 10lb/min injectors wide open, that means nothing is going through the regulator. there is not sufficient flow to even have any fuel reach the diaphragm with any amount of pressure. so basically what we have done is opened up so much flow rate before the regulator that the pressure will drop (if the valve is shut, that means the pressure is below what it should be.

that is the exact situation that is happening in the case of the evo 8 fuel pump. it cannot flow enough fuel to run all the injectors and push the diaphragm to open the valve. the evo 9 pump is sufficient.

any questions?

 

Will Putting in a 255 Fuel pump make my Base Fule Pressure higher?

 

I would think you would need an adjustable fuel pressure regulator for that.

 

I suggest walbro fuel pumps in all evos running modified boost levels

This goes for 8 and IX evos

Al

 

Very likely yes. Back pressure regulators do not behave ideally and increased flow rate will often lead to a rise in pressure.

 

I'm not sure I get this comparison. What kind of tuning did you do the the car before and after installing the Walboro?

 

 

Kevin 0
Me +1

I win

 

nice

 

none. it was a direct swap. stock tune on stock pump, then stock tune on walboro. then i tuned it after taking data from the direct swap, and still didn't see much of a difference on the 9. the 8 made a big difference though.

 

only in the case if the regulator is choking the system. which would be when you add a much larger pump (or two pumps)... but if your going to do that, you should do it right and add bigger return lines, and a bigger regulator.