MSefi.com read only forum (Jan.15,2018)

Howdy,
I have searched and heard differing opinions. I just bought a Rising Rate FPR for my 1.8 16v turbo app in my VW Rabbit. I will be running MS1 v2.2 board and 55lb injectors. I have heard that the Rising Rate FPR is a waste and I have also heard that it's the smart way to go. MS will adjust the fuel curve with a stock 3 bar FPR... but will MS work the same with the Rising rate FPR? Would there be any advantage to having a RRFPR?

Cheers.

Pic of the bunny for clicks:

FPR (1:1 ratio) is to combat the pressure against the injector. While MS can compensate to a point -- you would need to jack up fuel psi to you expected boost to get the rated injector flow.

Would that be an endorsement for a Rising Rate FPR then?

Any other opinions and or facts yall?

Fact #1: Injector flow varies with manifold pressure or vacuum, example from a 97 Corvette:



Notice the flow rates get bigger as vacuum increases, meaning the injector pulse width is going to decrease (larger injector constant = smaller injPw)

Fact#2: With 1 bar of positive boost (2bar abs.), the injector size will have virtually shrunk. You will not get the rated flow (injectors are rated at atmospheric pressure) which could be problematic if your sitting on the borderline of what they can support. Since they are effectively a smaller injector when the manifold is pressurized, you may run 100% (static) duty cycle.

Fact #3: You may have large enough injectors that your duty cycle will be high, but not over 80-85%.

Can you dig it?

I can dig it. I will be using a 3.5 or 4 bar fpr. Not the rising rate one. I just need a wideband now

I disconnected my RRFPR and jacked up my fuel pressure to compensate for boost pressures. It didn't work out the way I had hoped, so I'm re-attaching the line to my RRFPR to compensate for boost pressure. Here's my 2c from this experience: Get a RRFPR and try it. You can always dis-connect the line from the manifold to the RRFPR and use it like a regular FPR, but you cannot go the other way around.
Good luck.

A rising rate reg is used when adding a turbo to a non turbo car cheaply. It makes the mixture richer as the pressure increases, adding some safety against detonation.
Injectors don't flow less just because you boost The flow on an injector is proportional to the pressure differential, between the fuel line and the manifold. If you have for example 2 psi boost and your fuel reg increases the fuel pressure by 2psi, it did not shrink in size at all. So no a rising rate reg is not necessary with MS but a 1:1 reg certainly is.

Thanks yall!