Is there an easy way to show injector duty cycle or the percentage it is in use?

Have borrowed this from another thread

If the BPW is 4.8ms and rpm is 1078rpm or 18 revolutions a second or 9 fires a second or a fire every 111ms does this put the injector duty cycle at 4.3% at idle?

Is 80% a safe maximum?

Generally where do the stock injectors run out of fuel or lose effective control?

cheers
Surly

Scotty and Surly are both correct, if you see 20ms at 6000rpm youir injector NEEDS to be replaced, 16ms at 6000rpm would be ideal for about 80% duty cycle.

Now you can have 20ms at 3000rpm with no troubles because the motor is turning half the rpm which gives it twice as much time to deliver the fuel and shut off. 

Too big of an injector will have trouble in the lower rpm with consistent fuel delivery, the best way to figure out your needs is with a fuel calculator that you can find on the net....I believe RB Racing has a good one to use.

Doc  

A rule of thumb is 1/2 pound per hour of fuel for 1 Hp or 0.063049 grams per secomd of fuel for 1 Hp. So a 100 Hp HD motor would need 100/2 (cyl)=50, 50*.5 = 25 lbs per hour of fuel per injector or 3.1525 grams per second per injector.

Also spraying fuel on a closed intake valve is a good thing. It helps cool the valve and turn the fuel into a vapor. You just do not want to get carried away with it.

Is there a rough rule of thumb for when the stock injectors run out?

Will they happily do 100/100?

cheers
Surly

Factory injectors are different sizes for different models and years. They vary from 3.91 - 4.35 grams per second. The SE injectors are 4.89. The injectors max power on the 4.35 injectors are good for about 138 Hp and the 3.91 are good for about 124. Now you need to remember this is crankshaft power not rear tire power. If you use the 80% rule that some like to then you would de-rate these numbers.