Inj. Duty Cycle

[2006SS]

I have read many places you don't really want your INJ duty cycle over about 80%. I'm seeing sometimes as high as 91%. I was wondering if there something a little off in my tune or should I get bigger injectors. I consider my mods nothing big enough to justify larger injectors. I was just wondering what some you experts may think. Here's a scan I did, check out around the 31 minute mark, also heres the stock tune and well as modified.

2006 Monte Carlo SS
Yella Terra 1.8 Rockers, Comp 918 Valve Springs, Comp Chrome Moly Pushrods, Comp Titanium Retainers, HPtuned, Cold Air Inductions Intake, Resonator Delete, Magna-Flow Mufflers, ZZP Shift Kit, P&P Throttle Body, Vector LS4 Heat Reduction Kit, Hogan 3" Offroad Downpipe, Flipped Motor Mount, NGK TR-55 Spark Plugs

[BBA]

Well, with a stock TBSS I am hitting 81% duty cycle...if your duty cycle stock was like mine is, I would say larger injectors would cure your need for fuel.

[Russ K]

A lot of stock vehicles exceed 80% IDC. My car hits ~94% IDC (stock injectors 434 rwhp). The 2004 & up Pontiac Grand Prix GTP's hit over 110% @<10.0 AFR. After tuning the AFR to 11.5, the IDC comes down to 104%.

I would not install larger injectors if the IDC was <100%.

Russ Kemp

[MNR-0]

At 100% you are static. So basically you are at the mercy of your fuel pump. If the pump drops pressure or you need more fuel you will run lean. The injector solenoids are held continuously open and will heat up substantially. If that's OK with you then don't change them.

Next time after a WOT run on the dyno hold out a hand to your injectors.

At 80% you are effectively at static. You have 20ms to fire and 1.6ms to allow for injector dead time. Stockers will usually meter 1.2-1.4ms dead time, so that brings it up to 83-84%.

Now when you dive into dead time the pintle has not closed before you are jamming it open again for the next combustion cycle. Kinda like lowering a hammer to a nail but jerking it back at the last minute. Injector control can become unstable causing lean spots.

Injectors need time to cool as much as any other component. The risk is up to you.