Full Version: Must read. For those track event days
nice info spy!
Very good info Spyguy.
I have seen this info on fuel pumps before. The part I remember and question is that they recommend a BSFC factor of .65 to .68 for forced induction engines. This makes their example which useses a BSFC of .625 confusing to me. Does anyone know where the .625 BSFC came from? Is it a more agressive, on the edge calculation or just a mistake?
Interestingly working backwards with these equations you'll find that a 255lph pump is adequate for up to 595HP using the .65 BSFC and 621HP using their .625 BSFC. (I figured both of those using a 1.25 safety margin.)
This also means that the 190lph pump would be good for 445HP @ .65BSFC or 463HP @ .625BSFC using the same safety margin. This is quite a lot higher rating than I expected out of the 190, considering I felt I was running lean with it on my 300HP 14b Talon.
Aren't there some other factors like RPM and fuel pressure to take into consideration? I'm just thinking out loud to keep this kind of discussion rolling before I read some more.
I have seen this info on fuel pumps before. The part I remember and question is that they recommend a BSFC factor of .65 to .68 for forced induction engines. This makes their example which useses a BSFC of .625 confusing to me. Does anyone know where the .625 BSFC came from? Is it a more agressive, on the edge calculation or just a mistake?
Interestingly working backwards with these equations you'll find that a 255lph pump is adequate for up to 595HP using the .65 BSFC and 621HP using their .625 BSFC. (I figured both of those using a 1.25 safety margin.)
This also means that the 190lph pump would be good for 445HP @ .65BSFC or 463HP @ .625BSFC using the same safety margin. This is quite a lot higher rating than I expected out of the 190, considering I felt I was running lean with it on my 300HP 14b Talon.
Aren't there some other factors like RPM and fuel pressure to take into consideration? I'm just thinking out loud to keep this kind of discussion rolling before I read some more.
I don't know for sure, but I'm assuming since they are talking "moderate boost" (whatever that means) in that example they chose a lower BSFC. I've read about this stuff before in another article and they used a higher BSFC for larger turbos and higher boost pressures. Makes sense, more airflow = more fuel consumption.
I think if you gave the 190 less restriction in the fuel line it could cover that kind of horsepower. Less restriction like 6 -an fuel lines and a high flow filter. I think the stevetek guys were supporting 660 injectors with the stock fuel pump using the larger fuel lines.
Fuel pressure and RPM definitely have to be taken into consideration. I'm surprised AEM left this factor relatively untouched. A higher fuel pressure will raise the effective flow rate of the injector. The equation for finding the effective flow rate for an injector when changing the base pressure is:
New Inj. FR = Old Inj. FR*(sqrt(New FP/Old FP))
For example, New Inj. FR = 450*(sqrt(45/37)) = 496 cc/min
The RPM factor comes in especially when considering the inj. effective dead time. The true value for this is calculated using many factors like battery voltage, fuel pressure, injector size, etc. The injectors dead time increases with fuel pressure and injector size, and decreases with battery voltage. If the time it takes for a piston to reach the intake stroke after the previous intake stroke becomes less than the injectors dead time, then the injector will be constantly open and there is no control over how much fuel is entering the combustion chamber. Ironically, the way to fix this, increase base fuel pressure or increase injector size and tune for either, also increases the dead time, but it helps more than it hurts.
I think if you gave the 190 less restriction in the fuel line it could cover that kind of horsepower. Less restriction like 6 -an fuel lines and a high flow filter. I think the stevetek guys were supporting 660 injectors with the stock fuel pump using the larger fuel lines.
Fuel pressure and RPM definitely have to be taken into consideration. I'm surprised AEM left this factor relatively untouched. A higher fuel pressure will raise the effective flow rate of the injector. The equation for finding the effective flow rate for an injector when changing the base pressure is:
New Inj. FR = Old Inj. FR*(sqrt(New FP/Old FP))
For example, New Inj. FR = 450*(sqrt(45/37)) = 496 cc/min
The RPM factor comes in especially when considering the inj. effective dead time. The true value for this is calculated using many factors like battery voltage, fuel pressure, injector size, etc. The injectors dead time increases with fuel pressure and injector size, and decreases with battery voltage. If the time it takes for a piston to reach the intake stroke after the previous intake stroke becomes less than the injectors dead time, then the injector will be constantly open and there is no control over how much fuel is entering the combustion chamber. Ironically, the way to fix this, increase base fuel pressure or increase injector size and tune for either, also increases the dead time, but it helps more than it hurts.
QUOTE (awd4kicks @ Jul 21 2005, 10:59 PM)
This is quite a lot higher rating than I expected out of the 190, considering I felt I was running lean with it on my 300HP 14b Talon.
Your stock injectors were the limiting factor there. I burned up several 450's from running them static (100% open) at WOT for extended periods of time. The 850's have proven much better.
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