Injector Theory

JonathanN

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Ok, I'm not near as well-versed as some of y'all are, but I think it'd be cool to share what we know. I'm also going to state the all that's below is assuming we have adequate air as well as oil. Here goes!

I've got stock sticks and I've been running tunes. I've noticed that obviously, more fuel has equated to more smoke and higher egt's... to get more fuel requires increasing the PW (pulse width). This also increases CP's (cylinder pressures) too. But, I know that guys who swapped out for AC's (stage 1's) noticed more power, lower egt's, and better mileage. The egt's are lower and the mileage is better because the larger amount of fuel is delivered in a shorter amount of time than with stock sticks. Egt's can still get high as well as cylinder pressures and the amount of smoke, but only when the PW starts getting higher than what was typically allowed in stock tuning with the stock sticks... 2.5 milliseconds I think? Throw nozzles into the mix and now we're capable of emptying the injector faster... we're not necessarily flowing more fuel either. I have been told that ideally an injector should empty in 2.5 to 3 milliseconds... sound right?

So here's what I'm more curious about more than anything... the egt's and CP's increase not necessarily because we put more fuel in, but because the PW was drawn out to the point where the injection of fuel is occurring farther before and/or beyond that ideal point/time needed to burn it all off efficiently causing incomplete combustion which results in higher egt's and CP's as well as more smoke, right? Stock sticks (AB's, AD's, and AC's w/stock nozzles) take longer to fully empty than is really desired, that's what the nozzles help with... to allow the injector to empty sooner, right? It also helps with more complete combustion so we get a few more horses there as well as less smoke, right?

So here's my thinking in regards to what I have in mind for my truck in the future. My motor is by no means done (323K), but it does need to be treated a bit nicer than a motor with 100K on it. I like my tunes, they make a big difference and if I had enough oil, my tunes would be even better! But I also have much higher EGT's, it smokes more, and I know my CP's are alot higher too. I could go and put nozzles on my AB's... that would bring my EGT's down as well as my CP's, and I'd also get a few more horses and less smoke because combustion is more complete but it wouldn't be much of a power gain. Plus, my injectors are pretty old. So how about some AC's (stage-1's)? They flow more fuel, are more efficient since they're single shots (does that affect EGT's any? Have to wonder), have less smoke to the power, and also are more oil-friendly. I can get more power out of them and the EGT's and CP's will stay nice and low until the PW goes above typical stock PW's. Once the PW starts getting longer, the EGT's and the CP's start to get hairy and it'll smoke more. This is why I'd like to have AC's with nozzles (stage-2's). They'd empty faster and I would assume would lower EGT's and CP's... I'd also get more power because of the more complete combustion and less smoke. This would put me in the 425HP range and would in my mind make for a pretty reliable truck... EGT's stay down as well as CP's and PW. Power would be up and so would the mileage.

So there's how I understand it... add to or correct me. I'm a firm believer in learning something new every day.
 
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more fuel = higher EGT's... black smoke= un bunt fuel,, bigger sticks or nozzles will make for even higher temps and even more black smoke unless they are de tuned, witch could = less power..
you need more air...the GTP38R alone dropped my EGT's 200* and I got far less black smoke with more lower end power...I then added stage 2 injectors and got more top end power and no smoke and i really need to work her hard to hit 1200* when i start to run my 315/200 ill need to step up to a bigger turbo to get full use of them...
 
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Chvyrkr

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You don't get higher CP out of longer PW unless you're increasing timing proportionately.

Higher EGT's, definately.
 

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