Speedtoys

I have a basic close-enough map to work with on my supercharger setup, and from there..here is my question.

I have Bosch 0-280-150-803 injectors, with an opening time of ~1.15ms

They are shown to flow 39.11lb/hr at 3bar, 43.5psi.

We sit at idle, vacuum line on, at about 3.8bar, 55psi.

Im seeing that at 55psi, that is now about 43.9psi


Im planning to tell the ST these are 44psi injectors@1.15ms opening time and start logging.


Any errors in these assumptions?

Thanks!!

Hilton

You could find out what cc/min they flow compared to the stock injectors at the same pressure. Then use the % variation to calculate a "custom" ST injector size based on the stock ones being the 19lb setting.

That way it removes any question of "what PSI is it based on" and just models it against the stock S4 19Lb injector setting in the ST software.

Of course, that creates the challenge of finding a site with reliable injector data

http://www.usrallyteam.com/content/p...ector_data.xls

Hmm. just found Witchunter have their own flow measurements for a lot: http://witchhunter.com/injectordata1.php. Interestingly it says my "19lb" design III flow 8% more than our stock ones, which is more than the other source I used - however, they may not be compensating for variation in opening time.

edit: based on browsing a few of witchhunter's injector flow figures, I'm pretty sure they're not compensating for opening time (i.e. they're just using their cleaning rig to measure flow at its standard pulse rate and then scaling the fluid captured into a cc/min figure). So a faster injector will appear to flow more for a given pulse time; however, as the duty cycle raises, it will tend towards the actual flowrate of the injector as opening time becomes a smaller proportion of the total pulse time.

Hilton

Hmm.. just looked up your injectors in the spreadsheet linked..

They flow 409ml/min compared to 216l/min for the stock "19lb" ones. That seems to be a ST setting of 36lb?

(stock injectors apparently flow 151g/min at 43.5psi (3bar), which is 19.97lb/hr. yours are 286g/min which is 37.8lb/hr).

by weight:
37.8/19.97 * 19 = 36lb/hr in the ST settings

FredR

Jeff,

I am not entirely sure what is going on here but let's assume for purposes of discussion you have a custom sharktuned map for the previous injectors you were using- be they stock of whatever.

You have now fitted injectors of a different capacity and need to adjust the injector rating to get back to the LH map tune you had previously.

The injectors have a nominal rating based on a certain fuel rail pressure and thus our stock injectors are rated to deliver 19lb of fuel per hour [per injector] at rthe rated fuel pressure. Thus you need to adjust the injector rating setting to whatever the rated pressure is to get back to where you were.

ST2 has a number of stock rating but it also has the custom rating feature where you can select and rating you want. Thus if your last injectors were stock 19lb units [I have a feeling they were not] you simply dial in the new rating- in this case Hilton suggests they are nominal 36lb units -so you dial in 36lb. You then run the motor and see where your AFR's are - if they are same as with the old injectors you know you [probably] have the correct rating.

On my motor, I wanted to fit a new set of design 2 injectors with the 4 hole spray pattenr [did not like the idea of plastic bodies design 3's under the hood]. The set I was sold were allegedly 30 lb injectors- so in my mind they could be tuned for my stock motor and also be suitable for a future project should I decide to "force feed" like you do. After I fitted them I dialled in 30lb's but saw everything was running lean. I then reasoned that relative to the [lean] AFR's I was seeing I needed to correct the rating to 28 pounds. This is a custom number, I dialled it in and hey presto I was more or less to back to where I was.

I suspect you are aware of all the above- but just in case. If you have doubts as to what to dial in, start with a smaller than actual rating number and work upwards- assuming your motor is warmish, you will see the AFR at tickover is proportionately out [rich] and can work on increasing the number until it settles at the correct AFR for tickover. All things being equal that will be the correct setting for your injectors.

Similarly, remember that the optimal AFR for a stable tickover is about 14:1 [CO= 0.5%].

Beyond that, as I discovered with my injectors, differnt injectors have a range of different characteristics that need to be accomodated. My motor has a characteristic that when it is cold [for this part of the world] it stumbles and sometimes cuts out. I believe I need to adjust the warm up enrichment settings due to the different injector characteristics- have not been bothered to mess around with it yet.

Hope that above helps some.

Regards

Fred

John Speake

Bear in mind that flow rate is the square root of the pressure change..... so for a doubling of fuel pressure the rate will increase 1.4 times.

SeanR

Watching with great interest.

jcorenman

Short answer: I think you are over-analyzing this. As mentioned, complete specs are hard (impossible?) to find. The only "spec" that is always available is a nominal flow rate at some pressure, usually 3.0 bar psid.

If you change injectors you are going to need to remap fuel, either because the injector-size and open-time parameters are not quite right for the new injectors, or weren't quite right when you tuned the old ones.

But fuel tuning is not difficult. Just start with the best numbers you have, do some quick tuning, modify the settings if needed, rinse, lather, repeat.

Long answer: Static flow is simple, pulsed flow is not: There is an delay in opening, but opening itself is not a "binary" event-- it takes time for the valve to fully open. The injector will then typically flow at a higher rate for a while (in effect "catching up" a little), then slow to some steady-state flow rate. Then there is a closing delay, again not a binary event. Flow and open/close times are all pressure dependent, and opening is also voltage dependent. I also suspect that there is some temperature dependence. And in addition, in spite of best design efforts, there will always be some pressure variation in the fuel rail during the injector cycle.

The result is a complex flow curve, which most manufacturers don't characterize beyond a simple static flow-rate spec. Ford Motorsports does characterize their versions of the Bosch injectors in terms of a high (initial) and low (static) slope with a break between those slopes, all charted versus pressure, plus net latency (open-time minus close-time) which is charted versus pressure and temperature. No one else, that I have found, comes anywhere close (except maybe Injector Dynamics). Some modern ECU's (e.g. Ford) use the hi/lo slope model, others (GM) use a separate table for flow characteristics versus time.

Sharktuner uses a simple open-time (net latency) and static flow-rate model, everything else gets taken care of by the fuel maps. ST's flow-rate parameter is simply the nominal flow rate, e.g. 19# for stock injectors (which actually flow more than 19# at the 3.8 bar operating pressure).

The 0-280-150-803 injectors are nominally 40# injectors, so start with that. I don't know where the 1.15 ms came from, or if it is correct for our operating conditions (3.8 bar and 12.0 volts at the injector) but that's a good start.

Use those, and do some quick checks starting with idle and light load.

Light-load map numbers are very dependent on the open-time parameter (open time is a large fraction of the total pulse), while WOT numbers are much more dependent on the injector-size parameter.

So if your map numbers at idle and light load get towards the plus limit (adding fuel) then increase opening-time (which adds fuel), and vice-versa.

And if the WOT map numbers get towards the plus limit (adding fuel) then decrease the injector size setting (which adds fuel), and vice-versa.

And of course both opening-time and injector-size contribute to the pulse-width calculation, so changing one may require changing the other, as well as remapping-- it is all connected.

Now, all that said, it would be nice if we could just change a couple of parameters and be close on the maps. And sometimes you can: For example, going from stock 19# to Ford M9593-A302 24# injectors simply requires changing ST's injector-size to 24# and opening-time to 0.84ms, and you are very close-- those injectors are apparently very similar to the 19# in flow characteristics. But other 24# injectors will be not be.

Another data point is that going from the A302 24# to the BB302 30# injectors, there is no opening-time/injector-size setting that would get me close-- those apparently have quite different flow characteristics. And the Accel and Bosch 30# injectors also behave quite differently in spite of having the same nominal flow spec.

I hope this helps.

Speedtoys

With Colin's cams and headers, exhaust...Im not sure I could use a stock map set of numbers at idle to dial in the 'size' that way, although that is a neat way of getting there.

Hilton

Fred - the one caveat with the setting the custom injector sizes, is you need to be aware of the injector opening time, as that affects the mixture at low rpm's greatly.

As Jim notes above - it makes sense to compare AFR's up the rev range to see how the injectors flow at higher duty cycles compared to the stock ones.

I'm in the process of setting up my '89 to use as a test mule for working out injector parameters by comparing to stock injector performance.

Plan is to set the car up in a known state with stock injectors (new MAF, idle mixture adjusted to spec etc.), data log some high-load runs up a specific local steep straight hill (for repeatability), then swap injectors and tweak the injector opening time and custom size parameters to match the same idle mixture and log results. Swapping injectors is actually a pretty fast job - less than 45 mins.

This is all because the injectors in my '87 are fast opening, but with no published specs, and I'm **** enough to want to actually figure out the parameters correctly.

I tried logging knock sensor output when the injectors are pulsing (using digital o'scope) but there's too much other background noise to reliably distinguish the injector open/close events in the knock sensor output, likely due to the rubber o-rings and intake gaskets insulating the injectors from the knock sensors (I can see the injector open event pretty well, but the close is too fuzzy to be reliable)

If my plan works, I'll be doing the same process for some 32lb injectors too with the car still stock, so that when I install the bigger cams I'll already have the injector specs sorted

danglerb

Didn't see it mentioned, but injector pressure is the differential between manifold pressure and fuel rail, not just fuel rail.

jcorenman

Good point, injector pressure is always psid -- differential pressure, fuel rail to intake.

Speedtoys

Which should always be the same, because of the fpr.

And..55psi plus another 17 for vaccum, right?

FredR

Hilton,

That is the parameter I suspect in my particular case. If you have any seat of the pants suggestions I can try adjusting to much appreciate your thoughts. Unfortunately I have no idea of the range of possibilities. I was thinking of simply adding a little more fuel [pulse duration] to the warm up maps.

The problem is so minor it only seems to need about a minute to stabilise before I can drive off- when warm no problem. Of course it is never too cold here so engines warm up quite quickly [generally speaking].

Regards

Fred

Regards

Fred

FredR

Jeff,

Exciting prospect as they are, I doubt Colin's cams, headers etc would "not work" with stock maps- just that they would not be optimal. As I understand you simply want a base operating point with the correct poundage dialled in to build on in ST2. Wen you have the correct poundage dialled in, the corrections should float around the zero mark and then you are good to go ST'ing I would think.
Remember, it is only when you are maxxed out there is no where to go and with those monsters you have that is just not going to happen unless you rev to 10,000 plus for the two milliseconds the motor lasts before it grenades.

Thus for a given dialled in injector poundage, if you adjust the cruise map to get stoich and the values are mostly high negatives you will need to tell ST2 that the injectors are bigger and then it will reduce the opening time and the amount of fuel flowing accordingly [and vice versa if the corrections are mostly positive]. Remember, the adjustment range of values + or - 125, corresponds to an opening time of + or - minus 25%, or 50% of rated capacity across the full span range of adjustment- that is a big adjustment range permutation and with bigger injectors guess what?- you throw more fuel in to start with.

You will soon crack this concept if you have not done so already.

Regards

Fred

jcorenman

Correct, the FPR regulates a constant pressure relative to the intake manifold pressure.

The 3.8 bar (55 psi) spec is relative to atmospheric. So if the manifold pressure was 17" of vacuum (approx -7 psi relative to atmospheric) then the fuel rail gauge pressure would be 55-7 = 48 psi, which is about what you see on a fuel pressure gauge with the engine running. For a proper check, run the pump by jumping the relay-- the intake pressure will be atmospheric and the gauge should read 55 psi.

Cheers, Jim