Stroker guys what lb injectors are you using?
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Joined: Jul 2000
Posts: 2,735
From: Buffalo, NY
Originally posted by rskrause
No question, go for the 36#. BTW: I think Bob Kennedy has a nice price on some Siemans 42lbers he picked up if you want to check that out.
Rich Krause
No question, go for the 36#. BTW: I think Bob Kennedy has a nice price on some Siemans 42lbers he picked up if you want to check that out.
Rich Krause
I sent you mail.
Registered User
Joined: Mar 2002
Posts: 565
From: mt. holly, nc , usa
Originally posted by Injuneer
The online formulas for injector sizing are VERY conservative. They assume a brake specific fuel consumption (BSFC) of 0.50#/HR/HP. For an N/A application, that is probably too high. I have my actual engine dyno data, and I ran 0.45#/HR/HP or less on the final tune. I suspect that you might even find some well tuned engines are able to achieve even lower BSFC's... but I think that 0.45 for a weel tuned NA application is a good assumption.
For running a dry nitrous setup (300HP N2O on top of a 500HP N/A engine) I saw BSFC figures of 0.52#/HR/HP. Obviously, N2O only affects choice of injectors if you are running a dry system. Wet, you size the injectors for the N/A HP, and add the fuel for the N2O elsewhere.
Then you look at duty cycle... they recommend 80%. Each type of injector - ball (OEM RP), pintle (Bosch/SVO/Denso/etc.), disc (Lucas) - will have a slightly different duty cycle limit, and there will be a difference between high impedance and low impedance/peak & hold injectors. Maybe try 90% duty cycle.
Also... use flywheel HP to calculate fuel demand. RWHP means nothing to the calculation formulas... my losses were only 12% with an M6 and almost 20% with the A3, so you have to use flywheel HP.
Bosch/Ford/SVO/etc. injectors are GENERALLY rated at 2.7bar = 39.15psi. That compares to 3.0 bar = 43.5psi for the OEM RP's. The consequence of running the SVO's at 43.5psi is an increase in flow of 5.4%.... so the factor is 1.054X, not 1.2X.
As far as injector size, if you are on the border at 30psi, either up the fuel pressure, or go to 36's. There is really no downside with doing this. The stock PCM should be able to drive the 36's at the low, sub-1mS pulse widths required for idle.
If your injectors are too small, they obviously can cause lean out problems and loss of peak HP. I'm not convinced that these problems, caused by excessive duty cycle, will even show up in the 1 or 2 seconds that the engine actually runs at peak fuel consumption on a dyno pull. Run them for extended periods of time, and they will overheat, start to flutter, and start to wear out. Eventually, this is going to catch up with you. Why not bite the bullet and opt for "fat" sizing rather than "tight" sizing.
To actually answer your question, I run Bosch 64's at 4bar (58psi), making them 74's. And with the full shot of juice, duty cycle is about 67%. But that's with the MoTeC computer driving them. And the car idles like a kitten, at 800rpm, and will pass rolling emissions with cats.
The online formulas for injector sizing are VERY conservative. They assume a brake specific fuel consumption (BSFC) of 0.50#/HR/HP. For an N/A application, that is probably too high. I have my actual engine dyno data, and I ran 0.45#/HR/HP or less on the final tune. I suspect that you might even find some well tuned engines are able to achieve even lower BSFC's... but I think that 0.45 for a weel tuned NA application is a good assumption.
For running a dry nitrous setup (300HP N2O on top of a 500HP N/A engine) I saw BSFC figures of 0.52#/HR/HP. Obviously, N2O only affects choice of injectors if you are running a dry system. Wet, you size the injectors for the N/A HP, and add the fuel for the N2O elsewhere.
Then you look at duty cycle... they recommend 80%. Each type of injector - ball (OEM RP), pintle (Bosch/SVO/Denso/etc.), disc (Lucas) - will have a slightly different duty cycle limit, and there will be a difference between high impedance and low impedance/peak & hold injectors. Maybe try 90% duty cycle.
Also... use flywheel HP to calculate fuel demand. RWHP means nothing to the calculation formulas... my losses were only 12% with an M6 and almost 20% with the A3, so you have to use flywheel HP.
Bosch/Ford/SVO/etc. injectors are GENERALLY rated at 2.7bar = 39.15psi. That compares to 3.0 bar = 43.5psi for the OEM RP's. The consequence of running the SVO's at 43.5psi is an increase in flow of 5.4%.... so the factor is 1.054X, not 1.2X.
As far as injector size, if you are on the border at 30psi, either up the fuel pressure, or go to 36's. There is really no downside with doing this. The stock PCM should be able to drive the 36's at the low, sub-1mS pulse widths required for idle.
If your injectors are too small, they obviously can cause lean out problems and loss of peak HP. I'm not convinced that these problems, caused by excessive duty cycle, will even show up in the 1 or 2 seconds that the engine actually runs at peak fuel consumption on a dyno pull. Run them for extended periods of time, and they will overheat, start to flutter, and start to wear out. Eventually, this is going to catch up with you. Why not bite the bullet and opt for "fat" sizing rather than "tight" sizing.
To actually answer your question, I run Bosch 64's at 4bar (58psi), making them 74's. And with the full shot of juice, duty cycle is about 67%. But that's with the MoTeC computer driving them. And the car idles like a kitten, at 800rpm, and will pass rolling emissions with cats.
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