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Old 11-18-2002, 01:56 PM   #1
SonicWRX
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Surgeline Tuned

Default Injector Pulse Width to Injector Duty Cycle

Is there a conversion? With my nearly stock WRX, I see 2.30 ms at idle and a steady 20.73 ms at WOT in 2nd gear. There is talk in other threads about the high IDCs that even mildly modified cars can attain and I'm wondering where I baseline before I start raising boost.

Thanks!

Mitch
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Old 11-18-2002, 04:07 PM   #2
n2xlr8n
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Default Re: Injector Pulse Width to Injector Duty Cycle

Quote:
Originally posted by SonicWRX
Is there a conversion? With my nearly stock WRX, I see 2.30 ms at idle and a steady 20.73 ms at WOT in 2nd gear. There is talk in other threads about the high IDCs that even mildly modified cars can attain and I'm wondering where I baseline before I start raising boost.

Thanks!

Mitch
There are a number of means, but here's what I've used:

Maximum permissible pulse width:
M * 60,000
-----------
rpm
where M= inj duty cycle, and rpm = max rpm / 2 (for seq. firing injection)

The rule of thumb I've read is never exceed 16msec (that means you're either running the injectors too hot, or your test equip. is wrong )

To calculate (approx) fuel flow per cylinder on petroleum:

HP * K
-------
C
where HP is max hp, K= 4.6 for n/a, 5.6 for blown/turbo, C= number of cylinders So, for ex. if you wanted 400hp from our engine, the above ans. would be 560cc per cylinder (100% duty cycle)

What size injector (cc) based on prev formula:
TF * 100
---------
N * M
where TF = theorical flow, N= number of inj per cyl, M injector duty cycle. Again using the previous data, the answer (assuming a max duty cuycle of 80%) is 448cc.

HTH
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Old 11-19-2002, 08:54 AM   #3
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Old 11-19-2002, 09:36 AM   #4
SonicWRX
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Default

Great thread. Thanks Adam. Makes me doubt what my Techtom is reporting. I am definitely getting consistent injector pulse width readings of over 20ms which in a nearly stock condition as I am makes no sense.

Mitch
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