Krem

Ok,
so this has most likely already been covered, and yes i did search but couldn’t come up with anything that i felt i could use.
And also please forgive my “newbiiness” on the topic

why dont people tend to run higher than 43.5psi bas pressures on rotaries?
i see it on other engines but rarely on rotors.

The reason I’m asking is that i have 4 x ID1300 and plan on using them at 48-50psi base pressure to get the fuel i need for 550rwhp, doesn’t the higher pressure means better fuel atomisation and more flow from the injector, essentially turning my 1300cc injector into say a 1500cc injector.

I understand that higher pressure means more fuel pump capacity and more heat from the pump itself, but running 2 pumps inside my tank will cover this issue,

will running higher pressure affect the duty cycle of the injector?

What are the down sides of all this and are the upsides worth it?

thanks for the help.

krem

Howard Coleman

iTrader: (6)

there is nothing wrong with running a higher base fuel pressure as long as you have the fuel pump deliverability at the the higher pressure.

fuel deliverability changes with the square root of the increase in pressure.

from 43.5 to 48 is a 10.34% increase in pressure. the Sq R of 10.34 is 3.22

1300 X 1.0322 = 1432 CC/Min

from 43.5 to 50 is 14.94%... Sq R is 3.87

1300 X 1.0387 = 1350 CC/Min

550 rw rotary hp requires 6381 Gross injector capacity

at 50 psi rail pressure you have 5400

5400/6381 = .85

550 X .85 = 467 max hp at 50 static rail pressure

6381 for 550 is premised on:

max 85% duty cycle
20% slippage due to lag
need to tune down to AFR 10.0 (while conservative, line loss etc make this a good number)

i recommend a single Walbro 90000274 (this PN includes install kit)... dirt cheap OE build quality and will deliver enough fuel at 30 psi for 600 rotary rwhp when hardwired and running at 13.5 V.

a really nice hardware combo for 550/600 is a Ground Zero LIM with four secondary injectors to compliment the two primaries.

R_PROWESS

iTrader: (3)

There is nothing wrong with doing this. I have four ID1050x injectors and run a base pressure at 80psi. The injectors are good for 100+psi base pressure if i remember right (data sheets on their site). Having a belt driven pump I'm able to do this.. if I feel the need for the extra flow.. rather than upgrade the injectors to a larger size. With this said, the deadtimes and small pulsewidth characteristics of the injectors do change when doing this so you'll need to use their flow calculator to set these values at any given psi. (they have an excel spreadsheet if you dig deep enough)

Howard Coleman

iTrader: (6)

80 static fuel pressure delivers 9.2% more fuel than 43.5

EDIT: this is WRONG... the correct output is 80/43.5 = 1.839
solve for square root of 1.839 = 1.356.

1050 X 4 = 4200 X 1.356 = 5695 CC/Min

5695 X 85% duty = 4840 CC/Min

next deduct is lag which varies based on injector, battery V and PRESSURE.

running EV14s and making power i find lag is approx 20% of the ontime.

using Injector Dynamics 1050 data:

lag at 43.5 base fuel and 13 V is 1.115 mill seconds

lag at 80 base is 1.410

at 80 base lag is up 26.5% V 43.5 and it is a deduct.

at 80 psi static you gain 35.6% flow

because lag increases with pressure, this deduct increases 26%.

assume 43.5 lag at 20%, add 26% additional and lag ends up at 25.2%

net (of lag and 85% max duty cycle) fuel delivery rises from 2856 CC/Min to 3620

higher rail pressure does significantly move you out and downward on the fuel flow decline curve on the pump.

looking at one of the highest flowing intank electric pumps, the Walbro 90000267:

at 30 psi boost w 43.5 static you look at the pump flow graph at 73.5 psi and find just over 90 gallons per hour (5678 cc/min)

at 30 psi boost w 80 static you look at the fuel pump flow graph at 110 psi and find about 35 (2208 cc/min)

it is clear if you are going to run significantly higher rail pressure that the flow decline curve V pressure would be a central consideration.

thanks keithrulz for catching my error.

R_PROWESS

iTrader: (3)

I'm not calling you a liar but your math doesn't add up. Id1050x flow 1065cc at standard base pressure and 1420 at 80psi, this is more like 33 percent increase in flow on the curve according to their data. Also the deadtime of the id1050x is more closer to 1.0 at 80psi.. not sure where you're getting your stats but I'm looking directly at ID's website.

Krem

Thanks for the input guys, i appreciate the time it takes.

so I’m just getting my figures off max coopers calculator online, and according to that i will have the fuel for the 550rwhp.
ive also looked up the ID website for the flow of the ID1300 and i cant remember the exact figure but its way more that what Mr Coleman has stated, although like i said, i do really appreciate the time it takes for people to respond and answer questions that ppl like me ask.

the fuel pump i have is 90000267, which at my base of say 48psi and 25 psi of boost and allowing for around 15% drop has the capacity for my goals, bearing in mind I’m more than happy with anything from 480-520rwhp, but i have the compressor flow for more hence why i said more if i choose, but running pump fuel, I’d be happy with the lesser.

so Keith, what’s your setup and power level at 80psi base pressure??

cheers, Krem

Krem

Another thing, if some one could clear this up for me (and if i can explain it properly)

so if I’m running a base pressure of say 50psi and ID says my injector will flow 1440cc at that pressure, and i run 25 psi boost and my reg is 1:1, that puts my pressure at 75psi and ID states my injector will flow 1770cc, so x4 at full boost i have 7080cc of fuel.

so at idle i have enough fuel for say (example as i have no idea how to do calculations like the above posts) 400rwhp, but under full boost of 25psi (with base of 50psi) i have enough fuel say 650rwhp,

I’m never gonna make hp at idle, only under boost which flow from injector will rise with the rising rate reg, so why do ppl always look at the flow of an injector at the base pressure and not at the boosted pressure flow when sizing their injectors, as you never need that size injector for off boost driving??

hope that makes sense (it does in my head but yet again, im not real smart, lol)

krem

R_PROWESS

iTrader: (3)

Yes, if your fuel pressure is 50 psi at atmospheric pressure, then you hit the skinny pedal and raise your intake pressure to 25psi -at a 1:1 rate- this brings the fuel pressure up to 75 psi, BUT you're no longer injecting into the same atmospheric pipe, it now has 25psi trying to force the fuel to stay in the injector. The injector is now working against pressure, but it also has an equivalent increase in pressure to help it overcome. The flow capabilities stay the same and this is the 1:1 rate of change. and this is the value the ECU bases its calculations off of because if your regulator is working properly it is a constant value regardless of how much boost/vac you run. (the offsets and latency at X base pressure)

As for my setup I have never had it on a dyno but im guessing 450-500 wheel. All i know is 3rd gear.. I sometimes get traction on my 285/30/18 Advan Neovas.
Non turbo rotors, large street port, 93 octane, methanol 30% water 70% by volume injected pre turbo. right now I'm running 18lbs I would have to look at my data logs to see what my duty cycles are

peejay

No. Your fuel pressure is still 50psi. There is 75psi in the rail but there is also 25psi of air pressure pushing on the other side. This is why manifold referenced regulators are used in the first place.

If you had a fixed 35psi base pressure regulator and could get 40 pounds of boost, you'd actually pump air into the fuel rail.

Krem

Ok thanks guys, really appreciate it, it clears it up for me in a way i can understand.

krem

Krem

Just one last question,
what is a “average” % pressure drop in a fuel system, i know it relies on line size, etc, but if i allow 15% should that be in the ball park??

cheers, krem