Fuel Injector Question
 

We get two different messages on injector duty cycle. Some say no more than 80% and some say go to 99% and the management system should adjust in the pulswidth. I know there has to be some real knowledge out here. What do yall think?

Re: Fuel Injector Question
 

if you're consistently over 80% you probably should step up one size in injectors.

Re: Fuel Injector Question
 

I'm not an injector guy, but I'm a fuel pump guy and I hear mid 70's to mid 80's is good....90's are bad as you're getting close to locking the injector. Another item that can occur is your injectors go high due to lack of fuel volume in the system, this is normally seen in boosted applications although I believe can occur in N/A apps as well.

There are some pretty good "injector" guys out there.......Precision, Injector Dynamics, Kinsler and some pretty good tuners as well (who also know injectors....Hyperaktive, PTP, Shane T, Travis Quillen, Young's Performance out of Alabama, Jeff Taylor......good luck

Re: Fuel Injector Question
 

I wouldn't go past 80-85% duty cycle. You run the risk of the injector not being able to open and close quickly enough which can cause an injector to "hang". This could lean out the mixture.

You can compensate this with more fuel pressure, and even run past 100%, however that is a bandaid. If you are in the 80-85% range, I would get bigger injectors.

Injector Dynamics are some really nice injectors that are high impedance.

Re: Fuel Injector Question
 

I got a question about "duty cycle".
This is in the lower rpm ranges just after launch. 2 different tracks duty cycle is the same for a given rpm IE 3500, 3700, 4000, etc. Ambient temp is 20 degrees (Celsius) different
O2 sensor readings are way different? On the cooler day the O2 shows it is much richer.
Should that be the be the other way around?

Re: Fuel Injector Question
 

Art,
Read your PM and call me!

Re: Fuel Injector Question
 

For drag racing a N/A combination the 80% rule seems to be a bit of a myth. I think that 99% is extreme too. (You do need a little room to work!) I would much rather run a smaller injector at high pressure than what the manufacturers call the "correct" injector at the recommended pressure. We can talk about this over a beer one night.

Re: Fuel Injector Question
 

There is possibly something in running a smaller injector at a higher pressure, I would think.

Re: Fuel Injector Question
 

There absolutely is.

Re: Fuel Injector Question
 

I run over 100psi of fuel pressure with 2 sets of 200lb injectors per cylinder. :)

Re: Fuel Injector Question
 

So that's what it takes to make half an engine run like a whole engine! Your car is very impressive

Re: Fuel Injector Question
 

Haha, yup. :) 10hp per cubic inch gets thirsty.

Thanks man!

Re: Fuel Injector Question
 

I run 24lb injectors at about 75-80% duty cycle. They were 95% before I raised my fuel pressure from roughly 43 to 48psi and eventually 50psi. I swear I actually slowed down at 50psi unless something else is going on. Is there a way to figure out what pressure the injector "sprays" most efficiently and atomizes best? I would like to send all my injectors to someone for cleaning, testing, and maybe tell me hey the injector sprays good up to 50psi and then at 55 it starts to shoot sideways or something.. Any recommendations on who does that sort of stuff? Thanks.

Re: Fuel Injector Question
 

Bobby, I found power by raising the fuel pressure with smaller injectors. For a race car, the 80% deal is internet lore. Many Stockers I know run their's over 90% all the time. They don't hang open. You need to change the injector flow rate in your tuning to reflect the new flow rate. Injectors are rated at 43.5 psi. For example, my 36lb FAST injectors flow 42lbs at 60 psi. That is the injector size entered in my tuning.

Re: Fuel Injector Question
 

Yep I have all that programmed in the system 25.73 @ 50psi but I was going faster at 24.9 @ 48psi. I don't know if the stock rails will handle 60psi if I went to a small injector. But who was the ad in the national dragster of an injector tester/cleaner/rebuilder? Was it Mr. Injector?

Re: Fuel Injector Question
 

Could be Doctor Injector. www.docinjector.com He's up here in Washington state.