# Thread: Check it out--Fuel flow calculator

1. ## Check it out--Fuel flow calculator

Iv'e gone off the deep end trying to determine my skis hypothetical fuel flow requierments to keep a/f ratios good at idle, in midrange and on top end. Made up a fuel flow calculator to compare various fuel flow rates with various setups. Have come to the conclusion that we need an adjustable rate fuel pressure regulator where we can control the rate of rise. Instead of a 1/1 rise (fuel pressure increase vs. boost pressure increase) we need more. This way we can set the base fuel pressure low, to maintain idle and midrange, but still have the fuel we need up top. Then again, I may just be confused.

Mark

2. Originally Posted by Mark S
This way we can set the base fuel pressure low, to maintain idle and midrange, but still have the fuel we need up top. Then again, I may just be confused.

Mark
Mark, the calculator is awesome but setting the RRFPR at a lower base pressure with larger injectors will still maintain proper AFR at idle and midrange as it does not force as much fuel thru the injector.

3. Originally Posted by Mark S
Iv'e gone off the deep end trying to determine my skis hypothetical fuel flow requierments to keep a/f ratios good at idle, in midrange and on top end. Made up a fuel flow calculator to compare various fuel flow rates with various setups. Have come to the conclusion that we need an adjustable rate fuel pressure regulator where we can control the rate of rise. Instead of a 1/1 rise (fuel pressure increase vs. boost pressure increase) we need more. This way we can set the base fuel pressure low, to maintain idle and midrange, but still have the fuel we need up top. Then again, I may just be confused.

Mark
regulator than it was desined for. But there are some companies out there
that make a 2 to1 rising rate. But in the long run I think you will get your
best bet is using electronics for fine tuning. Such as a fuel control unit or Full engine manigment.

Thats my opinion!!!!!!

4. Like The R And D Powershot

5. Granted, lowering the base pressure will reduce the fuel flow at idle and in the midrange. Static injector flow (at 100% open) X duty cycle = #/hr flow through the injectors. Look at the static flow on the stock ski at idle and in midrange (44.63 at idle and 41.94 midrange). Then compare that to a rotax stage 3 with the stock regulator--a little richer. Then compare to a rotax stage 3 with the rrfpr. Still good at idle and midrange but with more fuel on top. That horsepower range is about the limit of a 1/1 regulator to maintain good idle, mids and be good on top.

Using the rotax stage 3 with ported head and cam (what I have now) and rude sc'r on the calculator, try setting the rising rate ratio at 1 (from 1.75) and set the base pressure to 55 (from 46) to be safe up top. Static flow is now 54 #/hr per injector at idle instead of a desired 48 or less, a 12.5% increase in fuel flow. Same increase in midrange too.

Then use a 1to1 on a turbo ski @ 18# boost. Plug in say 365 hp and 56# base pressure to keep a/f ratios good up top. Now you are at 62.4#/hr static flow, a 33% increase in flow.

My point being, once we get above 280-285 hp a 1/1 rising rate regulator won't do the job, hypothetricaly.

Mark

6. Originally Posted by Mark S
My point being, once we get above 280-285 hp a 1/1 rising rate regulator won't do the job, hypothetricaly.

Mark
Maybe hypothetically but these are not real world results. I'm using a 1:1 on both of my turbo skis. One of them making well over 400 HP and is running almost 100 mph
Malvin also runs the exact same 1:1 Turbosmart RRPFR on every turbo ski he sets up.

There are many variables to take into consideration. Fuel mapping on the ECU's and the mapping is different on each brand and flow rates of the fuel pump.

7. Here's some interesting charts on the flow rates of the stock fuel pumps in our skis. Testing was done by RC Engineering (the RC injector company)

8. and another wrench into the equation

If you have 15 pounds of boost and 70 pounds of fuel pressure on the gauge..... actual fuel pressure at the fuel rail/injector is 55 psi

9. Originally Posted by Green Hulk
and another wrench into the equation

If you have 15 pounds of boost and 70 pounds of fuel pressure on the gauge..... actual fuel pressure at the fuel rail/injector is 55 psi

Correct. All the formulas and flow ratings are based on this. The column "net injector" is the net pressure drop across the injector. That number is used along with the injector size to calculate fuel flow.

10. Originally Posted by Green Hulk
Here's some interesting charts on the flow rates of the stock fuel pumps in our skis. Testing was done by RC Engineering (the RC injector company)
Sweet! I absolutely couldn't resist making a graph out of that one.
Excuse me, I need to go take my meds now.