FPR's work like manual boost controllers.

They bleed of excess pressure.

So if you put in a pump that flow more, it doesn't matter. The excess is still run back to the tank via the fuel return.

So base pressure will not change.
Rising ratios will not change either.

The only benefit is that at higher RPM and boost, it will not drop pressure because it flows more and is apparently more stable.

So my question is. Why would you need a retune for this?

 

Because you will run a lot richer.

 

Becuase the walbro flows more fuel at a higher psi level than the stock pump

 

what role does the FPR play then?
Didn't someone say that the base fuel pressure was unchanged?

 

i am bumping it upto 20 psi constant i believe the stock 9 pump will be fine. stock it hits 19 will see this week. maybe i will pick one up for safety

 

Ok. Now I'm confused. I'm looking at the possibility of getting a pump for my IX SE. I plan on going with a boost controller and holding boost at 21PSI, which I heard was the correct level of boost, I think...

So, from what I gather, a fuel pump is best even though I'm only going up a couple PSI... Right?

 

No, you don't really need one, but it's a good safety mod for less than $100. Don't mess with your boost OR a fuel pump without a TBE and tune.

 

The Walbro 255 IS recommended for the IX. Yes, the IX is far better than the VIII on the stock pump, but its still not as good as the Walbro. The stock pump is often inconsistant and gets weaker when it gets hot under load.

Do you need it? Need is a strong word...... Is it a good idea? Without question. Furthermore, its only a $90 part that takes about 45-60 minutes to drop in.

 

+1 Forgot to mention that you will need to adjust the tune for the fuel pump.

 

I know it sounds like a stretch but that was my hands on experience on a different non-evo 600+bhp car. At a 1/4 tank and lower I would have hard time maintaining fuel pressure and would drop .5-.8 in A/F at WOT.

Now thats obviously not the same situation we have here, but I think it demonstrates that the pump does have to work a bit harder.

 

21psi for a IX stock pump is fine.

More importantly, make sure your tuner tunes according to the pump you are using.

 

Yes the stock pump will be fine i have been running mine at 20 to 22psi and it runs perfect. my A/F is till 10.8 to 10.0 it works fine.

 

You need to worry about injector duty cycle as well as AF ratio.

 

is this something that could be cured by rewiring, such as in the old DSM's? or possibly a kenne bell boost a pump type system.

 

No, Evos already have a factory dual stage voltage system for the pump.