Fuel Injector Duty Cycle Vs Rwkw?

[benl1981]

Just wondering if anyone has had practical experience with injectors and rwkw.

Can you use a linear relationship to determine the approx duty cycle as you raise the boost and make more power.

e.g. If you are seeing 70% inj duty ~ 170rwkw

If linear then at 90% inj duty should be ~ 218rwkw (based on quick calc)

And I guess 90% is about the most you want to push it..

Question: I'm going to keep my stock injectors so would I be safer to

1. Just tune till these get close to 90% and live with that (Would that be around the 220rwkw..).

Or

2. Would I be best to increase the Fuel pressure slightly so that the inj duty max 85%?

I really want to get about 220rwkw which will be about a 27% increase in power. I realise I should renew some of the hose to do this..

P.s. I'm going to be putting in a gtr pump to ensure the pump isn't limiting things..

The R34 in HPI got to 90% @225rwkw

http://www.whiteline.com.au/default.asp?page=/reviews02.htm

Edited February 27, 2007 by benl1981

[paulr33]

you should be able to do 220rwk on stock injectors

just get a fuel pressure reg (nismo one) and it will be fine

[Guilt-Toy]

there is no way you can get a relationship between injector duty and rwkw. thats just silly. every car is different. different pump conditions different fuel line different engine condition / turbo condition / intercooler setup / head setup and the list goes on.

run the fuel pressure at 46psi and use the injector duty up to around 95% absolute maximum which should see between 210rwkw to 230rwkw

[benl1981]

Its on the same car though...so I thought you may be able to compare..

Provided the fuel pump etc can hold the pressure.

Yeah - Ill probably get a Nismo FPR and set it about 8 or 10psi above stock pressure. Does anyone know what stock fuel filters are rated at? I.e. how many psi ..because 46psi + 15psi (for boost) = 61psi max fuel pressure

See how we go.

Cheers

[MANWHORE]

no. Definitely not.

More fuel does not equal more power in a linear relationship. A 500 kw car does not use 2 x the fuel as a 250 rwkw car. It uses a shitload more.

By oging up 10% duty cycle, you might go up <5% power? (just an example)

[MANWHORE]

PS: if you have a look at the construction of the fuel filter, they're very strong and solid. Imo as strong as the fuel line. something else would pop by the time the filter does.

Edited February 27, 2007 by MANWHORE

[Omurru]

So really what everyone is saying is you dun want to see this....oh 11psi and yes it's tuned

p.s. new fuel system is on it way

[GTshortie]

100% injector duty eek!!!.. hope you got the $$$ ready for a engine rebuild.

[Adriano]

Im sorry, i would have to disagree with most of you, injector size is definately proportional to horsepower assuming the same AFR and duty cycle. A ported head or bigger turbo will make more horsepower and require bigger injectors. A car making 500rwkw will need double the fuel(approximately) than that of a 250rwkw car. There is a simple calculation of what duty cycle and fuel pressure will support a given hp with a certain set of injectors, i just cant remember where the formula is.

[Omurru]

100% injector duty eek!!!.. hope you got the $$$ ready for a engine rebuild.

lol it's the first time I found the magical 100% I was told there's only 2 or 3 places in the mapping where it reaches it. normally it don't go above 90% but i do drive it fairly suttly at the moment, but these things happen when your showing of to someone

Anyway to clear it all up a little better, a better way of working out how much power your injectors will support isn't to look at the duty cycle so much but to look at the actual ability of the injectors to supply fuel. Generally it is more widley accepted with a 2.5-3L ish 6 that for ever 1cc of injectorage you'll get 1hp at the crank, so if your running 600cc injectors they'll safely support 600hp at the engine. If you relate this to my pic above for example, 440cc GTR injectors are supporting 415HP at the wheels but on very high injector duty which is bad. As I always say if you want more power, dun be a tightass just get bigger injectors they ain't expensive....

[Sydneykid]

Don't forget the affect of acceleration enrichment.

cheers

[Adriano]

Exactly, so 370cc injectors at standard fuel pressure have the ability to make 370hp(its actually a bit less)so 360hp, which equates to about 220-230rwkw safely, as has been proved a number of times. Hope that answers a the question.

[MBS206]

Most places I've spoken to, and sized up, have managed to work out the correct inj size, and they don't like to run over 80% DC at all!

They leave 20% for spiking etc, and for other necesities, and since using up to 80%, it makes it easier to tune (Rather then a car that only uses say 40%)

[rob82]

HP is almost directly proportional to fuel consumption (BSFC - Brake specific fuel consumption) in spark ignition engines if the same AFR is to be used. What you've got to remeber is that dynamic flow rates and static flow rates from injector to injector are quite different. Most Japanese injectors are expotential flow - meaning their flow rates with low duty clcyes may be far less than their flow rates at high DC ie its not linear.

Aslo accelleration enrichment in 90% of cases wont effect peak DC as once full thorttle is seen there is no more correction.

[mickr33]

Don't forget the affect of acceleration enrichment.

cheers

This is the case with my car. If i dont let it warm up it will hit 100%. But after this

it only ever see's no more than 90% duty cycle. The car is a R33 GTST using the

stock injectors with a nismo FPR and is making 260RWKW. It's not a happy dyno

as i first thought because the car was run on there dyno when it was 160kw and

was run on two different dyno's in the space of 3 months and between all three

it varied 1kw.

[rob82]

This is the case with my car. If i dont let it warm up it will hit 100%. But after this

it only ever see's no more than 90% duty cycle. The car is a R33 GTST using the

stock injectors with a nismo FPR and is making 260RWKW. It's not a happy dyno

as i first thought because the car was run on there dyno when it was 160kw and

was run on two different dyno's in the space of 3 months and between all three

it varied 1kw.

Thats coolant correction not acceleration enrichment.

[Cubes]

lol it's the first time I found the magical 100% I was told there's only 2 or 3 places in the mapping where it reaches it. normally it don't go above 90% but i do drive it fairly suttly at the moment, but these things happen when your showing of to someone

When I was running stock injectors once it hit 100% it stayed there and fuel requirements only increased as rpm did so even if it wasn't making more power. Mine hit 100% duty at around 5200rpm at WOT from memory.

[mickr33]

Thats coolant correction not acceleration enrichment.

Please explain your theory in detail?

[Abo Bob]

ECU puts more fuel in when cold because the cylinders are cold. What happens is some of the fuel when sprayed in, condenses on the inside of the chamber leaving less available for burning. The ecu knows about this so puts more fuel in when the engine is cold to compensate. It assumes cylinder temps based on water temps.

It's just trying to keep the AFR's where they normally are when the engine is wamed up.

Also has anyone watched a dyno run when the injectors hit 100%? It actually goes rich. I'm told this is because they have given up all pretense at opening and closing and just stay open all the time. This means that much more fuel is put in at 100% compared to 99% than is put in aat 99% compared to 98%.

[rob82]

Also has anyone watched a dyno run when the injectors hit 100%? It actually goes rich. I'm told this is because they have given up all pretense at opening and closing and just stay open all the time. This means that much more fuel is put in at 100% compared to 99% than is put in aat 99% compared to 98%.

Never seen that before. Most injectors flow about the same between around 97-100% Duty cycle. Usually you can tell your out of injectors as the AFR will enlean linerarly at 45deg angle.