View Full Version : injector sizing

08-27-2005, 09:54 PM
What determines how big you should go with injector size? I currently have TA49 turbo,THDP and 42 lb 009 injectors.

08-28-2005, 11:09 AM
The basic formula is:

Usually you want to use 80% duty cycle rating ...

(HP x BSFC)/(#cyl x .80) = lbs/hr

SO, say with a TA49, let's say you are making 400 HP (just for round numbers)...

400 x 0.55/6 x .80 = 45.83 lbs/hr

009s can support that with a tad more fuel pressure to up the flow rate.

BTW, an the change in an injector flow rate is roughly expressed as:

sqrt( old pressure/new pressure) x rated flow rate = new flow rate

An example:

sqrt (43.5 psi/48 psi) x 42.5 lb/hr = 45.69 lb/hr

08-28-2005, 11:41 AM
What is BSFC @ .55?Also would a higher stall speed convertor allow the motor to produce more power by operating in a more optimum RPM range?It feels like I'm around 325-hp.

08-29-2005, 10:30 AM
BSFC is base specific fuel consumption and has to do with the effiiciency of the engine in converting fuel to energy. It's basically how much fuel (mass) does the engine take to make a certain amount of horsepower.

Usually a turbocharged 4 stroke motor is somewhere between 0.57 and 0.50. Seems from just "rule of thumb", 0.55 seems to work prety well with most of our motors. Basically, the smaller the number, the more efficient.

A torque converter can help with launches and keeping the motor in the peak torque range. A slightly higher stall converter with that turbo may help the launch slightly, but isn't strictly necessary. I'd start looking to see if the chip is calibrated properly and maybe not too rich.

08-29-2005, 11:25 AM
nice post Ken, is that in the GNttype archives? if not it should be

08-29-2005, 11:56 AM
:idea: Thanks! Basically, it's something I've learned while working with calibration stuff here at MotoTron and spec'ing out some of the design parameters.

It's archived here, at least ...

08-31-2005, 08:10 PM
i found an injector calculator after reading Ken's post.
hope this helps somebody