std injector max flow

[sambb]

Just wondering does anyone know the cc/min @ 100% duty cycle for our stock injectors.

I'm working out fuel flow rates at max torque so that I can check that I've correctly sized my water injection nozzle for stage 2.

Back story is that with a stage 2 tune, peak flow is 26.52ms at 3120rpm. A maximum injector time formula at that rpm gives me 38.46ms. You then divide these two numbers which gives you your duty cycle %. Mine comes out at 70% duty cycle at max load. That sounded low to me - anyone know if that sounds like its in the ball park for a stock injector in a stage 2 tune?

So if anyone can help me with the cc/min flow of our fuel injectors @ 100% duty cycle, then I'll be able to work out how much fuel is flowing at peak load eg 70% of cc/min max. From that i'll be able to check whether my water nozzle is in the 10-15% water:fuel ratio that is considered ideal for water injection.

thanks
sam

[seangti]

I believe stock injectors are 330cc. Though there's a few others who can say with greater confidence. I've read that you wouldn't want to push injectors much beyond 80% duty cycle.

On my silver polo, stage one tune. Just checking my logs shows they peaked at 4700rpm at ~19ms and lower to around the 17ms at 6000rpm. Not sure what duty cycle that relates to.

Louis had some new 440's, may be worth hitting him up if you're seeking some.

[h100vw]

I believe stock injectors are 330cc. Though there's a few others who can say with greater confidence. I've read that you wouldn't want to push injectors much beyond 80% duty cycle.

On my silver polo, stage one tune. Just checking my logs shows they peaked at 4700rpm at ~19ms and lower to around the 17ms at 6000rpm. Not sure what duty cycle that relates to.

Louis had some new 440's, may be worth hitting him up if you're seeking some.

Std injectors are 315cc at 3 BAR.

They'll run up to 240 odd hp before falling short. Although not a good move to run them at 100%. There's plenty of ceiling left in these for most applications with a K03s.

[louis19]

I believe stock injectors are 330cc. Though there's a few others who can say with greater confidence. I've read that you wouldn't want to push injectors much beyond 80% duty cycle.

On my silver polo, stage one tune. Just checking my logs shows they peaked at 4700rpm at ~19ms and lower to around the 17ms at 6000rpm. Not sure what duty cycle that relates to.

Louis had some new 440's, may be worth hitting him up if you're seeking some.

Actually sold them not long ago Sean, but I think Gav was looking to move on his 440s that he ran before our 550s?

[sambb]

So Gav when they rate them at 315cc/min, that's at 100% duty cycle yeah?

[seangti]

Not sure if you've come across Julian Edgar's articles - AutoSpeed - Injector Flows

[h100vw]

So Gav when they rate them at 315cc/min, that's at 100% duty cycle yeah?

The maths in Sean's article hints that the stock injectors would be flat out at 252hp. They can make 63hp each. You're not going to see that with the std turbo. S3 injectors would be a better upgrade than 440s. The 440s don't have the best spray pattern for smooth idle and low speed running

[sambb]

I'll check out that article Sean - thanks. No not looking to upgrade, just trying to work out what duty cycle I'm at at the different inj time ms figures that I can read out of a VCDS log, and then I can work out what is the right amount of water to be injecting with it. I'll have a read. thanks

[sambb]

Alright first I have to work out maximum possible injection time available. First I looked at peak engine load which is between 2900-3750rpm (usually around the 3350rpm mark). The highest injector time of 26.52 ms was at 3120rpm in vcds logs.

1. max possible inj time available at that rpm = 60/(rpm/2) x 1000 ms = 60/(3120/2) X1000 = 38.46 ms.

2. duty cycle % = 26.52ms/38.46ms X 100 this gives 68.95% - i'll call it 70% for easiness!

3. actual fuel flow at his rpm/load point = 70% x 315cc this gives approx. 220cc/min of actual fuel flow

4 ideal water injection amount is usually taken as 10-15% of fuel flow at the load point you are interested in. A fuel injector monitored water injection system would try to always keep this ratio. All I can do is switch on for the highest load point and then hope I'm not bogging it as duty cycle falls away at higher rpm. so:

15% x 220cc = 33 cc/min max size water nozzle
10% x 220cc = 22 cc/min minimum size water nozzle

My aquamist 0.4mm "A" nozzle is 50cc/min @ 85psi (judging by their graphs) which looks to be too much water. Problem is its the smallest one I can find across all the brands. Also I don't really trust that first max inj time equation. It makes me arrive at 70% injector duty cycle at full load which seems low to me and might be understating how much fuel i'm flowing at that load point. Do any of you nefmoto/me7logger guys get duty cycle figures in your logs and could maybe discount/confirm this?

Anyway. From vcds I think that if I want the engine to be digesting water at peak load, I need to be spraying at about .85 bar. But then I may be spraying too much water as injector duty cycle falls away in the upper rpm band. Its working in the sense that it kills off timing pull and has decreased inlet temps but whether its robbing the engine of power (taking away too much cylinder pressure) well all I can really do is log and see if the maf readings deviate between water on or off.

[sambb]

woops no that's not right. I'm not direct port, I have one water nozzle feeding 4 cylinders not one. So it should be 70% of 1260 = 882cc/min of total fuel. My water then needs to be between 88-132 cc/min of water to be in the 10-15% at peak load. I actually have a second nozzle of the same size. If I run them together that will give me 100cc/min. But it still might be that it'd be too much water for up high so i'll have to check a few things.
I just wish I new for certain that it is only ever pumping a max of 70% duty cycle at full load. The last tune was sucking in 190g/s which equates estimate wise to 240Hp which is getting close to the theoretical max of the injectors going by that link. That's why 70% duty cycle at peak engine load on stage 2 sounds wrong to me from the calcs.
I'm going to look carefully at the logs. It seems counter intuitive but it may be that I'm not getting timing pull starting at peak load which is a bit of an assumption really. If it comes later due to excessive timing or leaning fuel when duty cycle is lower then what I'm spraying now might be perfect. Just wish nozzles weren't $40 bucks delivered so I could try a few.

[SuperChimps]

I have only the barest of understanding of this stuff.. But for curiosities sake i plugged your initial numbers into my calculator and got 35.82ms instead of 38.5. Not a big difference but brings the idc up slightly to 70-71%

[sambb]

yeah - what a dumbass. I did crunch all that at the end of a very long nightshift. Thanks buddy.
edit: I'd carried some numbers over from different parts of the thread and got them confused. ie working out at what load/rpm I should trigger boost and what has the biggest injector time got my head twited. Should all be fixed up now after editing the calc post.

[SuperChimps]

No worries. Easy enough to make little transcription errors like that when your writing stuff down.