As many of you know we just recently purchased Shawna a new to her Evo 8. With the intentions of using the car to do some testing and for her to daily drive it was a win win situation. Well the other day we had some time to toss it on the dyno to get her up and running right and develop a new intake for the stock turbo. I know a lot of companies already make them but we wanted our own and testing is kinda the fun part of this job. Enough about the intake.

While we had the car on the dyno we decided to change the fuel pump because the old one was just that, Old. While we did that we decided to do a test that would show just what happens when you change these with out a tune and this is what we came up with.

Solid lines are with new walbro 255 pump
Dotted lines are with stock pump.




This car was dialed in as far as fuel goes before the test started and nothing was touched between pulls but the pump itself.

It's hard to argue against cold hard numbers! Looks like the stock pump shows a pretty significant pressure drop at the rail that was accounted for in the tune compared to the Walbro.

I suspect if you plotted AFR you will see the Walbro setup running richer. If you increase the pump flow and maintain the restriction based on the stock regulator you will have higher fuel pressure.

I don't get it - what are you telling us? That it's bad to do a fuel pump w/o a tune? Or just general results?

I'd like to see a graph of a before and after tune when doing JUST a Walboro 255.

im guessing general information. every mod done without a tune can potentially do more harm than good.

looks like he is saying you will lose power by not tuning after installing a better fuel pump.




if you tune before installing a pump and then add a pump, the effect of the new pump would be nil if the afr are the same.

I had been told that an upgraded pump would not affect a tune since the effective pressure at the injectors is controlled by the Fuel Pressure Regulator. If that goes unchanged how do you account for the change in HP or is it just BS about the Fuel pressure regulator?

WADAD

wow good info to know for sure, i was going to upgrade my fuel pump and not tune for a good while to come.

simple math.
with the stock it goes lean which as we know can rob power and/or lead to det ignition pulls etc.
with the walbro the correct afr is maintained and power is made

I don't think one of us is looking at that graph correctly. What I'm seeing is a loss in power from the Walbro w/o a tune due to richer AFR.

I've heard both theories, but this seems to confirm the need for a retune after adding the Walbro. My tuner said I'd need to retune also, so I've been following his advice and waiting to install my pump until I get the new injectors in also.

The pressure will not stay the same just because you have s tock regulator.

Lets say you have a fuel pump that is 10 times more powerful than a Walbro, install it in your EVO, the base pressure will be much higher. The spring resistance and pressure shown is in relation with pressure delivered by the fuel pump.

When at idle they may both show the same pressure, but when the injectors open prssure drops dramatically (just like opening a faucet), here is when a Walbro shines, it delivers the pressure consistently all the way to redline.

The stock fuel pump overheats and will not maintain the required pressure when the injectors demand fuel at higher rpms, the fuel pump maxes out creating a lean situation, robbing the engine power.

starting at far left;
Top lines are AFR
Second lines boost.
Third lines Torque.
Forth lines Horse Power.

I did not pay attention to the graph so thanks for pointing this out. AFR are consistently richer across the board with the new Walbro, which would explain the decrease in power. If you want to install the Walbro and not seek a retune you need to get a fuel pressure gauge and record the baseline fuel pressure (with vacuum line removed). Once you install the new Walbro you should install an adjustable fuel pressure regulator and adjust to match the factory setting. For those who have a fuel pressure gauge you should see an increase in fuel pressure when going from stock to Walbro.

Interesting info.

So is a 255 a necessity for a basic "TBE+ intake" tune?

is correct. if you just slap a larger pump in and expect pressures and numbers to stay the same, youre wrong.

i always thought this was common knowledge? if you plan on putting in a larger pump without a tune, you will need an adjustable pressure regulator of some sort.

i CAN be incorrect about this, but i believe the stock pressure regulator can only help an aftermarket pump by not letting the pressure get too low so it doesnt run lean. it cant compensate for the pump trying to run a higher pressure, which seems to be the case with these numbers.