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Author Topic: Duty Cycle, what value means bigger Injectors?  (Read 497 times)


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Duty Cycle, what value means bigger Injectors?
« on: June 09, 2001, 10:10:20 PM »
Registered User
(4/17/01 1:24:35 pm)
Reply  Duty Cycle, what value means bigger Injectors?
 My GTR Vspec has an Apexi Power FC and after tuning it over the weekend I notices some high Duty Cycle readings from my handset. I reached a peak of 87%. At what point do I need to increase my injector size? Being a V-Spec I assume it has the 440cc injectors. I have heard of values around 80% & 90% is the mark to replace, and I think IM there. Please let me know what you think.
What do I have dome to my car?
Nismo Headers & 3.25" exhaust, 3" high flow cat.
Apexi Power FC,
Standard air box & filter, except I have removed the plastic stopper for the second air feed that goes into the Front Left Guard.
Turbo Smart Bleed valve set to about 12 pound.
Cold water spray on standard intercooler.
Platinum Plugs.
Rev limited set to 8250RPM.
I tuned the apexi by mapping the fuel curves to 12.5 air/fuel mix for all load/rev settings, and I played with the timing setting to keep my Knock sensor below 15. Inlet air temp never got above 48 Deg.
If anyone has something else I should look at & try please let me know.

Melbourne Ozzy Admin
(4/17/01 2:38:28 pm)
Reply  injector duty cycle
 Well unless your planning on doing more mods like new turbos or something like that 85-90% is ok i think.
Its nice to have some head room like 20-30% but not really required if your car doesn't run over about 95%

Now my car is another story, i have to keep the boost down so i only run 99% duty cycle !!! Thats living on the edge but it still runs a little rich at full boost so its ok.


Registered User
(4/17/01 6:06:52 pm)
Reply  Re: Duty Cycle, what value means bigger Injectors?
 I guess that once you hit 100% duty that is the most fuel you can get into the pistons. So I guess that once you hit the roof you can only lean out from there and hence the possible danger. I have turned my fuel map to I never lean out, I guess the magical number I am looking for is 100%. On my Apexi my fuel map is maxed out at L20 & N20, i.e. full load at 10000RPM, for some reason I don't think I will ever get there.