Is there a duty cycle gauge?

**ericwilloughby** · 10-19-2006, 04:54 AM

Is there a gauge that displays injector duty cycle?
How much is HP Tuners now??

**93lt1vette** · 10-20-2006, 06:01 PM

thats a damn good question
Its definantly posible since the MPG gage on the corvettes just compares speed with injector pulse width

**jimmyblue** · 10-21-2006, 09:56 PM

As a practical matter, the voltage across the
injector as displayed by a slow reading voltage
meter is your duty cycle (referred to the ignition
voltage, though). If you got yourself an old low
current panel meter with a 0-1 (10, 100, 1000)
linear scale and a variable resistor adjusted
such that you barely pegged it when run from
running IGN to ground, then attach this across
any injector and it will be reading duty cycle
directly.

hptuners.com web site has all the pricing info
for whatever options suit you.

**ericwilloughby** · 10-22-2006, 07:51 PM

http://www.speedspecialty.com/store/...oduct=tazzoefi

Duty cycle percent, %85 & %95 lights, O2 voltage. I found another, I think it read DC & boost. $100

I like it but I think I'll buy the Predator & try reading it off that.

**ericwilloughby** · 11-05-2006, 06:55 PM

Shit. I bought the Predator and like it. It monitors all kinds of good and useless crap, but there is no duty cycle. Only pulse width. How do you convert PW and RPM into duty cycle?

I'm having a major problem with the math on this because I don't know if %100 duty cycle means the injector never turns off, stays on through all 4 cycles, or if it means the injector stays on through the entire intake stroke only???

I'm starting to think it means something completely different because this is a stock 05 GTO and the pulse width stays 19 ms from 4,000-6,500. Since the intake stroke at 6500 only takes 18 ms to occur

at 6,500 RPM.
Only half the revolutions contain intake strokes. 3250 strokes per min.
\ by 60 to get strokes\sec.
54.16 strokes per sec.
1\x, or invert it to get from strokes\sec to sec\stroke.
018 sec per intake stroke = 18 ms

Either the factory setup is at %100 at 6,500 and almost %200 at 4,000 or I just don't understand what a duty cycle is. Someone explain it and why this math is wrong?

**Doc99SS** · 11-19-2006, 04:41 PM

I calculate my DC by data logging with AutoTap and dumping the log into an excel spread sheet. 120 / eng.RPM is the time for the crank to make 2 revs. Since an injector fires once per 2 turns of the crank, you can then simply divide the PW of the injector by the result of 120/RPM and you have your DC.

This can easily be done with AutoTap and Excel, but is not actively displayed as you drive, its done after you have tken a test drive.

**ericwilloughby** · 11-20-2006, 01:12 PM

Okay, I figured all the duty cycle and injector stuff out. There is a problem with figuring the DC. If you, my, readings are off by only 2ms on the pulse width, that is 10% at 6,000rpm. I think this is happening to my Predator. As I go over 6,000 the pulse width starts getting shorter. I think this is because the max PW at 6500 is 18.5 and my Predator is logging 17+ over 5,000. I think the #'s from the log are off by just a bit and I am actually at %100. I guess that is why people say when you go over %85 you are done....The smallest amount of error can make up the last %15.

**Doc99SS** · 11-20-2006, 02:45 PM

Eric, It all depends on the speed of the data logger. In order to get data that corresponds more to one instant in time, you want to log the minimum number of engine parameters. For the most accurate DC, only log engine RPM and PW.