I think that means it's time for new injectors!


http://www.turbosaturns.net/articles...orsepower.html

 

What DataMaster is saying is that the calculated pulse width is longer than the time available for 2 revs of the crankshaft. But the injector can only "try" and be open 100% of the time, never in excess of that.

Actually, it can't even be open 100% of the time, since it takes time for the injector to open and close and that is time not available for spraying full flow. That's one of the reasons you don't want to exceed 80-85% duty cycle. Once you try and open and close the injector that often/fast, it becomes unstable, reducing the fuel flow compared to its rated value, and possibly detroying the spray pattern. High duty cycle also overheats the injector.... after all, its just a big solenoid.

BUT!!! DataMaster produces some screwy results.... I have seen data logs from relatively stock engines that show 100+% DC on the stock injectors. It isn't possible. I think there is something in DM we don't understand, or there is a bug. I've recommended to many people that they go back to TTS and ask them to explain these seemingly irrational results, but as far as I know, no one has ever bothered to go back to TTS and ask the question.

The Hypertech "scan" cartridge suffered from the same sort of problems... it would indicate pulse widths that were 2X the actual pulse width the PCM was calculating.

 

Check out this chart, should be pretty helpful.

Keep in mind there are THREE DIFFERENT TABS at the BOTTOM of the page, There's 3 different charts in this file.


http://paradox.shacknet.nu/dave88lx/.../injectors.htm

Starting at tab 3, looking at that chart, if I want to maintain 80% injector duty cycle, and wnat to crank out 550 HP at the flywheel, and estimate BSFC to be .45, then I need 38.67 lbs of fuel per hour.

Going to tab 1, I can run an SVO 36# injector at 46PSI and get 39 lbs of fuel/hour.

Or, I can get an injector that's got it's rating taken at the 43.5 PSI (In the Chevy column), and run that 36# injector at 51 PSI and get 39 lbs of fuel/hour.


Seems it could turn pretty useful, no?



Let me know if you don't understand something.

 

Dave,
Your chart seems to be right on the money (nice work BTW). I wish I could post something like that with my Omniform.

On my chart, I input the injector size, base HP, base fuel pump output (Walbro GSS307), DC, # cylinders, and BSFC. The chart calculates the following:
Injector flow (#/HR) at 43.5, 50, 55, and 60 PSI.
Fuel pump output for the GSS340 in GPH and LPH at 12 volts as well as 13.5V.
HP produced with blower.
Fuel pump output required for injector size & HP.

To compare mine with yours, I looked at the 600HP results on yours.

(All calcs @ 80% DC)

I put in 38# @ .40 BSFC and got 608 HP.

I put in 42# @ .45 and got 597 HP.

I put in 47# @ .50 and got 602 HP.

The difference from 600 is since I can't put fractional settings like 37.50 in mine (rounded to 38).

Here is the calculated fuel needed (liters/hr) for the 600 HP motor:
38#: 153
42#: 169
47#: 190

A Walbro high pressure 255 LPH GSS340 pump would easily handle this load.

When I factor in the higher BSFC (.55) for a blower motor, the HP numbers change quite a bit:

38#: 442
42#: 489
47#: 547

The amount of fuel flow required remains the same.

To make 600 HP at this BSFC, I need at least 52# injectors, which will need 210 LPH @ 43.5 PSI. My numbers with 55# injectors are as follows:
HP w/ Procharger @ 8PSI: 628
55# @ 80% DC, 8 cylinders, .55 BSFC=640 HP, which needs 222 LPH @ 43.5 PSI, which is at the upper limit of the GSS340 at 12V (will probably need more voltage, i.e. 13.5 Racetronix setup).

Based on your program, it looks like 42# injectors would be your best choice ($/performance) all the way around. When I was looking on Ebay, it looks like they were going for $280 or so for 8 + shipping.

EDIT: BTW, I'm also using this chart to calculate a Chevy 6 cylinder motor I'm converting to fuel injection from carburetion. It needs four injectors rated at least 19#, so I think I will be able to recycle 4 of my LT1 injectors.

 

I'm now trying ot decide between the Bosch/SVO and the Lucas injectors. I was going to add a set of Racetronix (Lucas) injectors to my Thunder Racing order, but they don't have any. Combo Motorsports has Lucas 42#'s for $319, I'll probably just get them from them, I need their timing chain anyways...

Any thouhts on Bosch/SVO (pintle) vs. Lucas (disc) injectors?

 

I just saw something posted on here and wanted to correct it . According to my knowledge in selling Bosch injectors , their injectors are rated at 42.5 psi .

Thanks ,
Mike
www.neweraperformanceparts.com
sales@neweraperformanceparts.com

 

I can't remember back to where I got your name from to say that...but I just looked at your site...

You've got them listed as 42.5 not 43.5

 

Oops , typo . Thanks !

Mike
www.neweraperformanceparts.com