pulse widths w/ 24 or 30 lb injectors w/AFR 165's

Discussion in 'Fox 5.0 Mustang Tech' started by rockin_rick, Dec 14, 2003.

  1. I am building a 100% street car with a AFR165, FTI, Performer, long tube setup and have been back and forth on which injector is better - 24 or 30?

    Has anyone logged the pulse widths with a tweecer to determine if the 24's are undersized and pushing the duty cycle over 80-85%? (I've also heard that the tweecer doesn't log the pulse widths or duty cycle correctly and the value logged needs to processed with an adjustment value.) At what fuel pressure is this at?

    I'd like to stick with the 24's, if possible, to help with idle quality, but don't want to push them too hard at WOT, either. I'm sure the 30's won't lean out at WOT or have their duty cycle too high, but having the 30's causes the pulse width to get smaller at idle (and consequentially the poor atomization of fuel), possibly contributing to poor idle.

    I know a lot of people run with 24's and it's entirely possible that they're not running lean because of them, but they could be pushing the duty cycle to 95-100% which reduces the injector's life. This would be difficult to determine without actually knowing the pulse widths that the ECU is commanding.

    Of course, if any of what I said is wrong, please point it out.

  2. I ran 30s with my AFR 165s and a Crane 2031 cam for a while, but they were horribly rich at idle, and I just couldn't lean out the fuel pressure enough so that the car would idle correctly. I purchased 24s and installed a Pro-M MAF Tuner system. The car ran better immediately, but when I turned the fuel pressure up to the 42-46 psi. range, it got really rich at idle and surged a lot. So, to cure that, I fooled the ECU by adjusting the MAF voltage at idle with the MAF Tuner. I guess it worked, because I'm running extremely well at idle now, and running nearly 13:1 or so based on my "guestimates" from my A/F meter at WOT. I know the 30s were good because I sold them to a guy with a 383 vette, and his car picked up 3 1/10s over his previous 24s...

    I don't think you want 30s with the 165s unless you're going to be running a really radical cam. They were wayyyy too much for me. I think you'll get much better fuel atomization with the 24s at a higher pressure, than running the 30s at a much lower pressure...

    I have never logged the pulse width of the 30s vs. 24s because I have no way of doing that... I hope I helped some...
  3. Rick,

    I have a 306 NA with 24# inj and C&L 73mm MAF with Edelbrock Performer intake and heads, Crane 2030 cam. The highest injector duty cycle I have datalogged with Tweecer RT is 16.571ms at 5720 RPM or 79% unadjusted. I think the PW is about 30% high, so that gives 55.3% duty cycle, so it looks like 24's should work fine.