Fuel regulator vs. Injectors ...

Alrighty ... here is what I'm considering ...

Fuel system upgrades for the Evo generally consist of the Walboro 255 and bigger injectors. Many people don't think about the FPR. Here is my thinking ...

Adding the Walboro can possibly overrun the stock regulator at high boost levels. The stock regulator operates at 43.5 psi (out of boost) as I understand. This 43.5 psi increases at a 1:1 ratio with boost. With the Walboro, that static pressure is increased to ~52 psi (as I understand) due to the increased flow form the pump.

Now, consider the stock regulator at ~52 psi under 22 psi boost ... that puts the fuel at ~74 psi, which is likely beyond it's capabilities (which I assume to be around 70 psi). When the stock FPR is overrun, the pressure no longer rises with the boost and the FPR becomes a bottleneck in the system.

On my car, I run ~26 psi at the low end of the rev band. That would put a stock FPR w/ Walboro at ~78 psi which is likely a bit outside of what the regulator can handle.

So, my thought is ... why not just upgrade the pump and FPR rather than injectors at the start? If you upgrade in that order, the bottleneck would be the injectors which are likely far from being maxed out with only the pressure increase.

Now, I know that a simply injector upgrade is only a little more expensive than the FPR upgrade and gives a larger overall increase of available fuel, but upgrading the FPR first should make for a much more reliable fuel system.

Thoughts?

I havent heard of too much of the bottle neck thing. I had a gauge on my rail (when the car ran, hahaha) and I cant remember the exact psi at idle, but it wasnt 50psi, I wanna say it hovered about 35-43. I agree that the regulater needs to be replaced when doing a pump (but im lazy and havent done it yet)

Good plan of attack.

IMHO you should still check your injectors duty cycle after the pump & FPR install just to give you an idea of where / how close you are to maxing them out though.

Well, just the pump will drop the IDC% by 12% to 14%. The FPR should add another 5% or so on top depending on the baseline setting.

I hit around 94% up top now with 19 psi and a ~11.2:1 mix. So, I would be roughly around 77% IDC max with the pump and FPR.

I plan to eventually upgrade to the Forge wastegate actuator, so that would bump up the boost up top a little and I would need that extra IDC%.

I would never exced 85-90% duty cycle

And that's exactly why I'm looking to upgrade ...

Actually, the IDC calculation I'm using isn't exactly right. 100% calculated isn't technically 100% of IDC. around 112% calculated is really 100% IDC. So, my 94% is really around 88% or so IDC.