Jim_H

Jason,
Thanks for asking. I have read 85% is the max you want to run. Enquiring minds want to know.

Imo000

As far as I know, anything over 80% is too much. After 80% the injectors will pretty much stay open all the time. There will not be enough time for them to close between pulses. This can cause the injector to over heat and short out. It can get very dangerous in no time.

I hope this helps!

Jim_H

That is what I have read a couple of times recently. Hmmm, is there a problem waiting to happen here?

Tony

Honestly, i don't know either. Wasn't in the manual . Thats why i post this stuff. There are people out there that know a he!! of a lot more about this than i do. I put the injectors in to help cure an overly rich idle. Wouldn't take too long to swap them back, but im not pulling the manifold out again. I never had my data logging up to the capability i have it at now so i never logged any 30# duty cycle. I just know that i was pretty rich under all conditions.

Questions i have are

1) in a NA 928 motor under WOT do the 19# injectors see 100%. In other words, is it a function of the WOT switch to tell the "brains" to max out the injectors under WOT?? I think it does...as the O2 sensor is out of the loop. How else is it going to get any feed back on mixture. Maybe the factory says under WOT and a KNOWN FUEL PRESSURE (57psi) that injectors fully open will provide X mixture setting (AFR) under a majority of operating conditions.

Perhaps the LH maps tell the injectors go to 80% for WOT applications and thus that is there MAX? Anyone know or can prove it by having it logged?? Nope.
I wish i had this logging capability before i did all my mods. Perhaps i can hook it up to a local 87 NA car.....uh...Bill

2)Honestly id like to see a similar duty logging of other 928s on there injector sizezs. Cough it up folks. Simple to do...1 wire from the injector connector to the Aux box and your done...press record...go run WOT for 1/2 a mile through the gears.


Still cant get the video up yet, sorry.

Chris Lockhart

Tony, have you done any data logging on just your typical "run to the store for a gallon of milk" type driving??? And if so, what is the duty cycle of the injectors under that type of operation???

Bill Ball

So, if I drive wide open throttle for mile after mile in my stock 89 S4, where are my injectors in terms of the duty cycle?

Jim_H

I couldn't remember what injectors you were running Tony. The EMS book I am reading currently talks about the exact problem you are having, rich idle with big injectors. They specifically discuss the Bosch pintle injectors but not in enough detail other than to warn against 85% dc and the problem of idling with the bigger injectors. I know I wouldn't be able to get through DEQ in OR with the #30 injectors.

From my book

Fuel injector expert Russ Collins says injectors can begin to fibrillate at more than 80%dc causing fuel delivery to become nonlinear in fuel delivery and causing lean out problems.

There is a long equation on how to compute injector requirements that I could do if anyone is interested.

Jim_H

It won't matter, you'll probably be in jail

Bill Ball

Thanks to a bunch of car nuts who convinced the state of Nevada to let us do this legally a few times a year, I have avoided jail.

FlyingDog

Tony, maybe the over rich was due to the one bad 30# injector you found when you were having your no 4-cylinder running problem.

GoRideSno

In this case installing larger injectors won't keep the duty cycle from maxing. It will still max after x amount of air is passing through the MAF even with larger injectors. If they are sized better the ratio will actually get fatter instead of leaner if you have the proper fuel pressure.

Hey guys, Tony's charts are very interesting but probably not that useful for those of you that are running the setup that I recomend. IIRC Tony is running 24# injectors and the lowest he could get his fuel pressure at idle was 40psi. The 85-86 map is different from the 87+ map too.


Andy K

Jim_H

Injector Flow Rate Calculations

Flow Rate = (HP x BSFC) divided (#injectors x max cycle)

Flow Rate is in pounds per hour of gasoline (at rated or specified pressure)
HP is projected flywheel hp of the engine
BSFC is brake-specific fuel consumption in pounds per hp hour. (Normally this is .4 to .6 at full throttle. Assume .55 for turbo engines and .45 for na)
#injectors is the number of injectors
Maxcycle is the maximum duty cycle of the injector. (Above 80 percent injectors begin to fibrillate or overheat causing them to overheat or even fail completely)

EXAMPLE: 5.7 liter v-8
Flow = (240 hp x 0.65 BSFC) div ( 8 cyl x 0.8)
Flow = 24.37lb/hr injectors required

Bill Ball

I really intended that question to be real. I drive my NA car WOT for quite a while during ORR with no ill-effects. It would be worthwhile to know where I am in the duty cycle and if this is a real problem. George Suennen has run his SC'd 90 S4 in ORR in excess of 170 for miles with no ill effects. I will be putting an SC in soon and will be doing the same. It looks like Tony is hitting 100% during a good portion of a WOT 1/4 mile. We are WOT for the first mile or so getting up to speed, then in more of a cruise mode except for a few miles here and there at WOT.

Tony

You dont know what my typical run to the store is like do you Chris

Seriously though, they dont even come close to these levels in "normal" driving.

I think the key is finiding out what the injectors are being told to do at WOT no matter what there size..and HOW they are being told

Tony

I think Andy is correct here as i sit and look at this for a while. Look at my chart. Why do they max out on the way up to the 1-2 shift and 2-3 shift...but they SLOWLY increase in duty after 3rd gear is engaged. The air flow through the MAF, due to the RPM of the engine hasnt increase to the point that will max them out yet.

Trust me, my foot was to the floor so it in hindsight it isnt the WOT switch alone that would send them to 100% duty.




I just go the logworks video to load, its of the run above.
i assumeright click save as??
http://members.rennlist.com/v1uhoh/Q...-05-LWdata.mpg

The other files are too large and i keep getting the "time out message" each time