my injector duty had risen as high as 96%(well that was the 297hp dyno) but still what happens when the injector duty gets to 100%. i know they lock up either open (where they will be spraying constantly) or they will lock up closed and u will run dry. or at least thats what i was told. i dont know like lets say it does to 100 whats gonna happen. will they definatly lock up or what?



also will getting bigger injectors help b/c it ust seems like they will be able to inject more fuel on each spray. not be able to spray faster. i dont know im talking jibberish cause im tiard and rambling. ]



just looking for some more info i have pretty much learned everything i know from forums and askin questions so feel free to go crazy and explain as much as u can. fuel systems are still very hazy for me, im working on that though. https://www.nopistons.com/forums/pub...IR#>/smile.png



i dont even wanna get started with ignition phew



anyway thanks id appreciate any and all info i can get.



-Mike

what size injectors do you have now?

i got th3e stockers what is it 550cc's and 850cc's

i wanna upgrade to the 1300cc's as soon as i have the money(oh well after i get caback https://www.nopistons.com/forums/pub...)

Duty cycle is the percent of the time the injector is spraying fuel. Over 85% is not recommended for reliability reasons. If you run to 100%, besides being bad for the injectors, your engine will not be getting enough fuel. (BAD)



Upgraded (i.e. larger) injectors will flow more fuel, PROVIDED that your fuel pump can suppy it.



If you are running at 96% duty cycle, the time to upgrade your fuel system is yesterday.



If I'm wrong anywhere here, please correct me!

They won't open and close correctly at 90% and over, you'll end up getting about the same fuel as around 60-70%...

you will lean out............

the factory ecu runs 85-90% duty



mike

1988RedT2,



Curious to know what the stock duty cycle (%) is? How is that measured?

the stock ecu will run about 85-90%, you can hook it up to an oscilloscope



mike

Or get a PMS or PFC https://www.nopistons.com/forums/pub...#>/biggrin.png

I watch mine while I drive.. or should I say when I drove https://www.nopistons.com/forums/pub...O_DIR#>/11.gif

Just slap some 1300's in there and let it rip

I would also upgrade the fuel pump at this time

thx i know how much injectors run but how much am i looking at for a fuekl pump. and what should i be looking for

the walbro pump works REALLY good

Yep get the walbro pump, cheap and excellent...

Two things:



Is there such a thing as to run too low a duty cycle? Perhaps you have some gigantic injectors on a stock motor. Would there be any drawbacks besides a little rougher idle?



Is there anything else that should be taken into account when upgrading the fuel system? Injectors, Fuel pump, etc. How about fuel rail, wiring, etc.?



Thanks.



Kyle

In most applications it would be best to keep the stock primaries. This way you can have a good idle. When you really need more fuel than the 550's can supply will be in the higher rev ranges so you get the 1300 or 1600 secondaries and can reduce the duty cycle for them. This gives you small enough primary injectors that you can pass emissions at idle and large enough secondaries to get all the power you want at higher rpm.

Duty cycle = (on time/(on time + off time) x 100

Therefore 100% duty cycle means the injector is turned on all the time. Obviously the injectors cannot supply any more fuel past this point unless the fuel pressure is bumped up which is a lousy way of trying to fix the problem. As already stated big injectors are useless if the pump cannot keep up.

No offense to Dragon cause he has taught me a bit about turbo stuff and his FD makes mine look like a piece of ****, but I disagree with his statement abount injector flow decreasing at high duty cycles. I have heard this argument before, but from my experience it just doesn't happen.



Yes there are problems with having very large injectors and running very low duty cycles at idle. The resolution is dereased dramatically. i.e. a 1% change in duty cycle gives a large change in the amount of fuel being delivered, so it is harder to get a good tune at idle/cruise. Thankfully us EFI rotary owners have staged injection so we can have smallish primarys and big secondaries and get the best of both worlds.

I did 1200's with a high flow fuel pump. even at 13 PSI I'm only at 49 pct. Pretty sweet. (315.8 rwhp @ 12 psi).