Stock fuel injectors?
10-07-2005, 04:46 AM
#2
Depends on the year. 98s had 28.x #/hr injectors, 99s and 00s had 26.4 #/hr, 01-02s had 28.6 #/hr injectors. As far as power, it all depends on how close to the edge you are willing to run. Most people (SAE, fuel injector industry types, racers, etc) will tell you that you should not run above 80% duty cycles. Here's the equation to use:
(Injector rating)(IDC)(# of cylinders)/(BSFC) = fwhp
Injector Rating is the rated fuel mass per hr @ 58psi
IDC is Injector Duty Cycle (should be < 80%)
BSFC is Brake Specific Fuel Consumption which is the fraction of fuel consumed per unit hp produced by the engine (usually .50 for NA)
Plug the #s in and you can see just how close the cars run to 80% IDC stock. That's not to say that you can't run stock injectors on a bolt on car, or even a cam. You can, you'll just be running your injectors closer to static (open 100% at WOT) which is not what they were designed to do. At high IDCs it is much more difficult for the injector to regulate the amount of fuel in the cylinder.
Another way to go is to run a higher pressure at the fuel rail. This will effectively raise the #/hr the injector will be able to deliver.
Hope this helps...
(Injector rating)(IDC)(# of cylinders)/(BSFC) = fwhp
Injector Rating is the rated fuel mass per hr @ 58psi
IDC is Injector Duty Cycle (should be < 80%)
BSFC is Brake Specific Fuel Consumption which is the fraction of fuel consumed per unit hp produced by the engine (usually .50 for NA)
Plug the #s in and you can see just how close the cars run to 80% IDC stock. That's not to say that you can't run stock injectors on a bolt on car, or even a cam. You can, you'll just be running your injectors closer to static (open 100% at WOT) which is not what they were designed to do. At high IDCs it is much more difficult for the injector to regulate the amount of fuel in the cylinder.
Another way to go is to run a higher pressure at the fuel rail. This will effectively raise the #/hr the injector will be able to deliver.
Hope this helps...
10-08-2005, 04:36 AM
#5
The pressure at the rails is due to the pump and regulator combo (ie, mechanical). There is no tuning to adjust pressure at the rails. The only parameter that can be altered through tuning is how long the injectors pulse (injector pulse width).
The equation for calculating the new #/hr rating of an injector for a given pressure is:
[sqrt(new pressure)/sqrt(old pressure)] x old #/hr = new #/hr
If you have HPTuner, it will automatically calculate this for you under the unit conversions section of the tools drop-down menu. Since we are dealing with root functions though, it will take a large increase in pressure to affect a decent gain in #/hr injector output.
At my future power levels I won't have any problems finding a suitable aftermarket injector to fit so I haven't looked into what it would take to raise the fuel pressure. Maybe some of the hardcore racers could chime in on what would need to be done...
The equation for calculating the new #/hr rating of an injector for a given pressure is:
[sqrt(new pressure)/sqrt(old pressure)] x old #/hr = new #/hr
If you have HPTuner, it will automatically calculate this for you under the unit conversions section of the tools drop-down menu. Since we are dealing with root functions though, it will take a large increase in pressure to affect a decent gain in #/hr injector output.
At my future power levels I won't have any problems finding a suitable aftermarket injector to fit so I haven't looked into what it would take to raise the fuel pressure. Maybe some of the hardcore racers could chime in on what would need to be done...
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10-10-2005, 02:25 PM
#8
In order to make 450 rwhp (~517 fwhp) with the stock injectors at 100% duty cycle you would need a BSFC of .44 (most new engines are .45-.50). Is this possible? Yes, it is. It would require a very efficient engine to achieve it though. Keep in mind that you also need to run 100% IDC to get these #s. Combine that with the fact that stock injectors are not balanced and matched from the factory and you have a recipe for going lean / rich in different cylinders at wot.
The way I see it is this - Why spend $2000 - $3000 on a good head / cam setup (or even more on a stroker motor) only to risk damaging it due to running the stock injectors beyond there safe margins?
Its very easy to change out injectors and adjust the fueling tables to make them work. So it just doesn't make sense to me to not run safe with bigger injectors.
The way I see it is this - Why spend $2000 - $3000 on a good head / cam setup (or even more on a stroker motor) only to risk damaging it due to running the stock injectors beyond there safe margins?
Its very easy to change out injectors and adjust the fueling tables to make them work. So it just doesn't make sense to me to not run safe with bigger injectors.
