Fuel Pressure Regulator: 1:1 or Rising rate?

Make it quick...and reliable
Post Reply
Turbo125
Member
Posts: 21
Joined: Wed Jan 20, 2021 1:14 pm

Fuel Pressure Regulator: 1:1 or Rising rate?

Post by Turbo125 »

Hello everybody,

Just a question as I am looking at a suitable FPR.

Rising rate or 1:1?
I understand with a rising rate FPR while the fueling is enriched, the idling stays leaner and hence "cleaner"

Any thoughts?

http://www.officinamalpassi.it/en/

1:1
http://www.officinamalpassi.it/en/injec ... ndard.html

Rising rate
http://www.officinamalpassi.it/en/injec ... -rate.html
longfiredragon
Supporter
Posts: 2203
Joined: Thu Mar 27, 2008 2:13 pm
Location: cocoa florida USA

Re: Fuel Pressure Regulator: 1:1 or Rising rate?

Post by longfiredragon »

You can do a search on here and see what types people have used. I have done some research on this and the general thought out there is the FPRs out there that use japanese diaphragms seem to be the best and hold up the longest.

Currently I am running a VMS SARAD style using a japanese diaphragm. VMS swears by the japanese diaphragms.
People have also used genuine SARAD from Japan, and Turbo smart with good success.

Oh, yes it needs to have a 1 to 1 rise rate.

Happy searching.
User avatar
Charlie @ Evergreen
Intercooler
Posts: 6824
Joined: Sun Nov 17, 2013 12:20 am
Location: Ocala, Florida USA

Re: Fuel Pressure Regulator: 1:1 or Rising rate?

Post by Charlie @ Evergreen »

For clarity if your fuel pressure is 40 lbs at idle when you go into boost the FP will rise 1 lb for each pound of boost ie if your at 5 lbs boost your fuel pressure should be 45 lbs. or 15 lbs of boost your fuel pressure should be 55 lbs FP giving you enrichment during boost mode. :thumbup
84' ZX750 Turbo 85'ZX750 Turbo
User avatar
Lorcan
Intercooler
Posts: 14354
Joined: Mon Jan 08, 2001 10:35 pm
Location: Norfolk, UK

Re: Fuel Pressure Regulator: 1:1 or Rising rate?

Post by Lorcan »

There is some merit in rising rate regulators but they are a band aid, in my opinion, not a substitute for proper tuning via injector duty. Here's why.

As Charlie says, standard 1:1 pressure regulators have a pre-set base pressure, known as the "static" pressure. On the 750 turbo this is 36psi. When running, fuel pressure in the system won't drop below this. As inlet vacuum becomes boost, the fuel pressure will rise due to boost pressure acting on the internal spring and diaphragm to limit fuel flow back to the tank, thus increasing pressure in the system. So 5psi boost increases fuel pressure to 41psi, 7psi boost makes fuel pressure 44psi and so on.

THIS DOES NOT PROVIDE ANY FUEL ENRICHMENT.

All this mechanism is doing is maintaining the delta (difference) in fuel pressure at the injector nozzle. When you have 5psi boost this air pressure is literally trying to blow fuel the wrong way back through the injector. To maintain fuel flow, fuel pressure has to be increased by the same amount. This maintains the delta at 36psi. Fuel enrichment is handled by the ECU opening the injectors for a longer time period as boost increases, not by fuel pressure increase. At 10psi boost you will have 46psi fuel pressure but the injectors are only "seeing" 36psi as they have 10psi of air pressure in the inlet.

Now, our bikes are mapped to at least 15psi, maybe more, but when you get to higher boost levels they are definitely not mapped for this. The best way to adjust the mapping is with a Powercommander or an aftermarket ECU, but if you don't have one of those a little extra fuel can be added using a rising rate regulator working against them.

NB in the car world sometimes even a 1:1 regulator is described as "rising rate". It is not.

True rising rate regulators can be 1.5:1, 2:1 or even 3:1 or more and will increase fuel pressure above static by that amount. So a 2:1 would make 46psi at 5psi boost (2 x 5psi + 36psi = 46psi). This will provide SOME fuel enrichment, but (and it's a big but) it gives diminishing returns to fuel flow.

The reason for this is that to double the flow through a hole or pipe you need to SQUARE the pressure not double it. So to double the fuel flow in a 36psi static system would need 36 x 36 = 1,296 psi :rofl: . Needless to say, your fuel pump cannot deliver this. Bear in mind that as you increase fuel pressure from an electric pump operating at a constant speed the fuel flow goes DOWN, not up. Really you would want to check that the pump can deliver the fuel flow you require to keep the injectors supplied at the elevated pressure you are asking for. It's like putting your finger over the end of a garden hose. The pressure of the water coming out goes up but flow actually goes down.

Bottom line, you will get some actual fuel enrichment from a rising rate regulator but not enough at higher boost levels to compensate for the extra fuel flow required. This can only be achieved by opening the injectors for longer and, ultimately, using larger injectors. Worth a tinker, maybe, if you want to run 15psi or so (50% more boost than stock) but not beyond that IMO.
First to 200mph (2006) and still the fastest (211mph)
Quickest turbo-only 8.69 @ 162mph
User avatar
Charlie @ Evergreen
Intercooler
Posts: 6824
Joined: Sun Nov 17, 2013 12:20 am
Location: Ocala, Florida USA

Re: Fuel Pressure Regulator: 1:1 or Rising rate?

Post by Charlie @ Evergreen »

There's the man who knows how to really explain details!

Good detailed info to maintain the injector flow in boost.

Like to use, for old school,
the 300cc NAPA injectors for 15lbs turbo setups upgraded billet turbo. Actually kept my personal bike FP almost at factory, 38 lbs. Did one stock engine, setup with stock FPR and the billet turbo with 300s tuned to 15 lbs/TPS re set in Race Mode ran beautifully and tuned. :thumbup
84' ZX750 Turbo 85'ZX750 Turbo
User avatar
Lorcan
Intercooler
Posts: 14354
Joined: Mon Jan 08, 2001 10:35 pm
Location: Norfolk, UK

Re: Fuel Pressure Regulator: 1:1 or Rising rate?

Post by Lorcan »

Sometimes I try to explain to people how the air clutch works on Storm, but when their eyes glaze over I stop :mrgreen:

I ran my 200mph bike at stock fuel pressure, 36psi, using the stock non-adjustable regulator. All the tuning was done by injector size and duration though the PC.
First to 200mph (2006) and still the fastest (211mph)
Quickest turbo-only 8.69 @ 162mph
Turbo125
Member
Posts: 21
Joined: Wed Jan 20, 2021 1:14 pm

Re: Fuel Pressure Regulator: 1:1 or Rising rate?

Post by Turbo125 »

Exellent answers. Thank you
Post Reply