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Old 04-20-2002, 06:39 PM   #1
annointed
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Join Date: Apr 2001
Chapter/Region: Tri-State
Location: Atlantic City, NJ
Vehicle:
FXT 11.6@118 93 oct
NSX 450 whp SC'd (93 oct)

Default 8 year old injectors run at 95% duty = bad?

Should I be concerned that I'm nearly maxing out my stock '94 WRX injectors? Although they're 8 years old, I was told the front clip only had 50k miles on it, but no one ever knows exact milage...

Anyway, we're running upwards of 95% duty on them, to put out what we believe to be ~300 hp, and I'm told this is basically maxing them out. The car will be dyno tuned in a month, but I was tempted to just go ahead and upgrade the injectors to 550+ cc now, even though I was planning to hold off on injector upgrade (ie, why spend $500+ when I don't have to yet?) until 2003. At that time I plan on upgrading internals and compressor wheel to shoot for ~400 hp.

Any thoughts/suggestions? I'm running a Supra TT fuel pump, BTW.

Thanks.
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Old 04-20-2002, 07:12 PM   #2
WRXThis
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Sounds to me like you answered your own question. Yes, it is bad, and yes you need bigger injectors.
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Old 04-20-2002, 07:38 PM   #3
mitch808
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Mark, duty cycle is not everything. Make sure to pay attention to IPW.

You can run your injectors at 110% and be fine. but if your IPW is too high, thats what people are talking about when going "static" or open.

However at your questionable mileage and performance mods, it would be a good idea to get it swapped out just for piece of mind.
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Old 04-20-2002, 07:40 PM   #4
Cosie Convert
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Can you explain the difference between IDC and IPW ? other than one is in % and the other in ms ?
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Old 04-21-2002, 04:08 AM   #5
mitch808
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Quote:
Originally posted by Cosie Convert
Can you explain the difference between IDC and IPW ? other than one is in % and the other in ms ?
The Injector Pulse Width (IPW) is the amount of time (in milliseconds) that the ECU wants the injectors to be open between compression strokes. The injector duty cycle (IDC) in percent is determined by multiplying the RPM times the IPW and dividing by 1200.


So in other words, the IPW is the number your really concerned about as IDC is derived from that.
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Old 04-21-2002, 04:11 PM   #6
john banks
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What I still don't get though is how you can have an IDC > 100 %. Physically you cannot - but I understand that different ECUs use different conventions and maybe they fix "100%" at a real 85% or whatever the injectors are rated at?

Also the duty cycle or pulse width of the electrical signal is not the same as the actual duty cycle or pulse width of the actual injector as there is a mechanical delay - they open slower than they close IIRC. Until you reach the step point when the duty cycle or pulse width underestimates the action as they stay open with a genuine 100% duty cycle and an infinite pulse width - until they fail or you back off the throttle.

If injectors do not overheat or stick open when at a true wide open condition, then how does that affect their life?

You can overdrive many components (turbos, op amps, pressure hoses, CPUs, tyres) but there is usually not a free lunch.
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