Right, I thought I'd post it in here so that if anyone else wants to insert some figures for themselves, they can do.
You can work out the injector size needed to hit a certain bhp figure:
Needed Fuel flow (cc per minute) = (Maximum BHP) x (A constant (roughly 5.6 for boost, 4.6 for NA)) / (Number of Cylinders)
So for say 160bhp with boost, you'll need (160 x 5.6)/(4) = 225cc injectors
To work out the size of injectors you'll need to keep a nice duty cycle, it is as follows:
Injector Static Flow = ((theoretical flow (from above formula)) x 100) / (Number of injectors per cylinder x Desired Duty Cycle)
So sticking with the 160bhp boost example, (225 x 100) / (1 x 80) = 281cc/min
Roughly speaking, with a 160bhp target in a turbo engine, you'll need injectors around the 280cc mark to keep a nice duty cycle at the max bhp point.
These are only rough calculations, and have been taken straight from a forced induction and performance tuning book.
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On a side note, you can work out the cc increase you'd get from upping the fuel pressure.
The formula is as follows:
Revised Static Flow = (Injector Static Flow (from formula above)) x (New Fuel Pressure / Old Fuel pressure)^0.5
So for example,
vts injectors at 3Bar are known to be around 225cc@3Bar, but what if we were to increase the fuel pressure to 4Bar?
Well, 225 x (4.0 / 3.0)^0.5 = 260cc.
So by upping the fuel pressure to 4Bar, you're effectively increasing the max bhp of the injectors at a nice duty - you can only up the fuel pressure a certain amount though - I personally wouldn't go above 4Bar.
If you put the above formulas into an excel spreadsheet then you can play about with figures and try and gauge the rough size of injectors you'll be needing.
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