Max output from injectors

[Lambolica]

There was a thread on the old forums or early in these forums that I can't find that was dicussing the theoretical max output of an engine based on injector size.

I wish to bring this up again as I believe that from the results as I recall them have been proven wrong.

What the issue is I'm trying to get to is what is the maxinum output the a 6 cyl engine (turbo) that is running 315 injectors. (1G for arguments sake)

Cheers
Simon

[Draven]

for 6 cyl engines as a REALLY rough guide, cc of an individual injector = max BHP supplied

[Lambolica]

Yeah thats what i was working on (assuming that is crank hp)

that is what I believe to be a guide, but seems to be off the mark by 50 odd cc

[MWP]

Anyone know the formula for fuel usage from HP assuming 100% VE?
It should be pretty simple, but i cant find it anywhere and cant be bothered working it out.
Its whats needed for your question.

[Mr Ed]

Wouldnt rail pressure significantly effect how much you can get out of any particular size of injector though?

[Cruiser97_80]

Wouldnt rail pressure significantly effect how much you can get out of any particular size of injector though?

I would tend to agree with that as fuel should flow more at a higher pressure through the same injector.

[30psi 4agte]

Yeah you will find that fuel pressure plays a big part in the flow of an injector.

Most injectors will actually state what the flow at what pressure. IE from memory the injectors i use at the moment flow 870 cc @ 35psi but i run 55 psi pressure so it work out that they flow 950 cc at this pressure.



There are injector calculators out there on the net that work this out for you so i dont know a formula as such.

http://www.csgnetwork.com/fiflowcalc.html

[SIKTOY]

SIMON
Rod's car has put a bee in your bonnet hasn't it

[Billzilla]

You need 5cc per 1hp.
So for a six with 500cc injectors, you can make about 600hp safely.

[Lambolica]

SIMON
Rod's car has put a bee in your bonnet hasn't it

Yes it has, I was lead to believe that the max you can get out of a stock engine/ECU was in the area of 175rwkw.

Billzilla's information points to closer to 200rwkw.

Cheers
Simon

[Mr Ed]

I know a bloke who got 350rwkw out a 1JZ with stock injectors and just a Mine's chipped ECU (this was in an auto mind you!!!). Was obviously kinda touch'n'go but it just goes to show that these rough guides to max power based on injector sizes, are just that.

[thechuckster]

a few resources the MSEFI crowd (self included) use for injector info:

To determine how big your injector's flow rating should be, multiply estimated horsepower (HP) of your engine by the brake specific fuel consumption (BSFC)* and divide by the number of injectors and the desired duty cycle and you will get a rough estimate of injector size:

InjectorSize = (HorsePower * BSFC) / (#Injectors * DutyCycle)

for example, a 135 horsepower gasoline fueled 4 cylinder engine with 2 throttle body injectors and 0.55 brake specific fuel consumption gives:

(135 HP * 0.55 lb/hr/HP) / (2*.85) = ~ 43.7 lb/hr

*BSFC is the amount of fuel your engine uses to make 1 horsepower for one hour. It is usually between 0.42 and 0.58 at wide open throttle. Normally aspirated engines with efficient combustion processes are at the lower end of the BSFC scale [~0.45], supercharged engines tend to be towards the higher end [~0.55].

conversion factor for flow rate: 1 lb/hr ~ 10.5 cc/min

If you want to see how much more your injectors will flow with a change in fuel rail pressure:
new flow rate = old flow rate × SQRT[new pressure÷old pressure])

There's also an easy-to-use table (also at the link below) that lets you select injectors based on your engines HP and the number of injectors you intend to use:


All from http://www.megamanual.com/v22manual/minj.htm#size

cheers,
Charles.

[brett_celicacoupe]

Anyone know the formula for fuel usage from HP assuming 100% VE?
It should be pretty simple, but i cant find it anywhere and cant be bothered working it out.
Its whats needed for your question.

thats probly less accurate.


fuel energy is converted to many sources in an engine. and all engines have a different break up of where the energy goes. mainly heat, sound and kinetic.


unless you consider BSFC and the target AFR for an engine, expect to be out by up to 20%


the garret website has some basic formulas but they are more so related to air flows rather then fuel flows

[brett_celicacoupe]

using the calculator on this website,

http://www.injector.com/injectorselection.php

using 315cc injectors, times 6 for a 1G and BSFC of 0.5,

it says max HP = 288

rods 1G claims 190kw = 255rwhp

thats a drivetrain loss of 11%