Injector Sizing

[T5Hammy]

Ok, so I've been researching new injectors and the more I read the more I get confused on what size to use.

It all started when my dad (who's a mechanical engineer and has been restoring and building cars for 40 years) said he didn't think I should turn up the boost on my 98 s70 t5 because the injectors probably can't support the power I was shooting for.

As far as I know many people are running 350cc injectors at over 300bhp but according to all the calculations those injectors can support around 220hp (less than stock on a 98 s70 t5).

So what am I missing, bsfc should be around .6 for turbo applications and most people don't wanna run more than 80% duty cycle, fuel pressure is 3 bar or 43.5psi

So if:

Injector Flow Rate (cc/min) = Engine HP(1) x BSFC(2) x 10.5

Number of Injectors x Injector duty cycle(3)

240hp x .6 x 10.5

5 x .8

Then stock we should be running 378cc injectors to support stock hp. Which is obviously not the case, what am I missing?

[theForgottenone]

Your calculation seems to be correct as far I can see.

http://www.rceng.com/technical.aspx

[B_Dub]

I had the same questions regarding injector size when I did the stage 3 upgrade on my '98 V70R. I even bought some green injectors (off '00 VR) and had them cleaned, flow-tested and fitted with new o-rings in preparation for the stage 3 upgrades.

However, after talking with Lucky on the subject of injector upgrades he asked if I had seen any data supporting a need for a larger injector. He was of the opinion that with the stage 3 tune IPD provides, adding larger injectors really serves no purpose, and would have required modification to the ECU re-flash to accomodate increased flow.

So, the question of whether or not to upgrade injectors would have everything to do with the variables specific to your setup and tune.

Your specific calculation certainly seems accurate mathematically-speaking, but perhaps the variances and nuances of the particular auto manufacturer's engine specs can skew those calculations.??.

As for my personal experience, IPD's Stage 3 tune, like many off-the-shelf tunes, is quite conservative and thus if anything, I'm running rich with the stock 350cc Whites.

I'd be curious to see some hard data on this subject, myself. Maybe I'll end up keeping those greens after all!

[theForgottenone]

You can be running rich but it doesn't show what is the duty cycle for the injectors. A/F ratio is all in the tune.

[B_Dub]

You can be running rich but it doesn't show what is the duty cycle for the injectors. A/F ratio is all in the tune.

That is true. I wonder why Volvo changed from whites to greens (425cc IIRC) in MY '00 hpt applications. There is only a 20 bhp difference from '98R to '00R, yet a substanially larger injector. It makes one wonder what was so different between the 4.4 and ME7 (I believe that's the newer engine management sys in MY '00).

[T5Hammy]

However, after talking with Lucky on the subject of injector upgrades he asked if I had seen any data supporting a need for a larger injector. He was of the opinion that with the stage 3 tune IPD provides, adding larger injectors really serves no purpose, and would have required modification to the ECU re-flash to accomodate increased flow.

So, the question of whether or not to upgrade injectors would have everything to do with the variables specific to your setup and tune.

Your specific calculation certainly seems accurate mathematically-speaking, but perhaps the variances and nuances of the particular auto manufacturer's engine specs can skew those calculations.??.

this is basically what I was curious about, the calculations just don't support it but dyno results say that it is possible, at 340bhp (or around there whatever the stage 3 hits) these injectors should be so over used they are overheated or stuck open if they could even support it without running lean (highly unlikely that they could).

A big company like Ipd wouldnt be selling it without bigger injectors if that was the case and as far as I know that isn't an issue for anyone running the tune

Is it possible the flow rate is just underrated for these injectors?

However, after talking with Lucky on the subject of injector upgrades he asked if I had seen any data supporting a need for a larger injector. He was of the opinion that with the stage 3 tune IPD provides, adding larger injectors really serves no purpose, and would have required modification to the ECU re-flash to accomodate increased flow.

So, the question of whether or not to upgrade injectors would have everything to do with the variables specific to your setup and tune.

Your specific calculation certainly seems accurate mathematically-speaking, but perhaps the variances and nuances of the particular auto manufacturer's engine specs can skew those calculations.??.

this is basically what I was curious about, the calculations just don't support it but dyno results say that it is possible, at 340bhp (or around there whatever the stage 3 hits) these injectors should be so over used they are overheated or stuck open if they could even support it without running lean (highly unlikely that they could).

A big company like Ipd wouldnt be selling it without bigger injectors if that was the case and as far as I know that isn't an issue for anyone running the tune

Is it possible the flow rate is just underrated for these injectors?

[B_Dub]

Hopefully Lucky will chime in, and not to speak on his or IPD's behalf, but I tend to agree with your logic, IPD engineered and developed their stage 3 package with specific interest in engine longevity and I can't believe they didn't pay close attention to injector flow.

As for the real question at hand, at what point (hp wise) are the whites insufficient??

[ozzimark]

Which is obviously not the case, what am I missing?

You know the HP, everything else is a constant except one thing: BSFC. Most likely 0.60 is way high for the stock setup.

I have seen ~210 g/s of airflow through the MAF sensor on a stock T5, at 12.5:1 AFR, that's 16.8 g/s of fuel, or 272 cc/min assuming 0.74 g/cc density. Working backwards through the equation you quoted, that means the stock engine's BSFC is around 0.55, assuming it is actually running at 12.5:1.

Whites are typically good for at least 300hp on typical builds, I believe I've seen higher.

That is true. I wonder why Volvo changed from whites to greens (425cc IIRC) in MY '00 hpt applications. There is only a 20 bhp difference from '98R to '00R, yet a substanially larger injector. It makes one wonder what was so different between the 4.4 and ME7 (I believe that's the newer engine management sys in MY '00).

'99 switched to ME7, and the HPTs got blues and 3.8 bar fuel pressure.

[B_Dub]

I remember a thread from a while ago where someone suggested for every one bhp, you should be flowing 1cc/min, so 350cc whites would be good for 350bhp. I'm not sure how they arrived at this math. I'll dig around and see if I can't find that thread.

[Texas850Turbo]

Yep I wouldn't assume that the bsfc is .6 for these engines. Also you can't assume that the injectors don't go beyond 80% duty cycle- the ipd tune probably pushes the duty cycle fairly high. The benefit of running larger injectors at the same power level is that you get more precise injector timing since the injectors are open for less time, but the downside is you are operating further into the non-linear region of the injector at idle, which makes it hard to predict the injector characteristics. A rising rate fuel pressure regulator helps here, as you can operate in the linear region at idle but then you have more headroom at high manifold pressures. Or you can spend a long time characterizing the non-linear region of the injectors on a test bench, which is what we do in FSAE.

[T5Hammy]

Well with a bsfc of .55 and 100% duty cycle of 350cc injectors that put you around 300 hp possibilities so that makes more sense but still short of the ipd stage 3 mark.

[lookforjoe]

That is true. I wonder why Volvo changed from whites to greens (425cc IIRC) in MY '00 hpt applications. There is only a 20 bhp difference from '98R to '00R, yet a substanially larger injector. It makes one wonder what was so different between the 4.4 and ME7 (I believe that's the newer engine management sys in MY '00).

Greens flow 468cc @ Me7's 3.8bar regulated pressure.

I would tend to follow the lead of those running the kind of power you're looking for - if it's IPD tune, then use their recommendation.

People using standalone EMS or TurboTuner, looking to make 400+BHP seem to use 550 or larger injectors, but we can adjust the injector calibration.