Ken and Ed Anderson.

Your info and advice is well recieved and timely for me - I didn't know what to use, now at least I can talk with some knowledge to suppliers.

One small question if I may - what is the fuel rail pressure usually?

Thanks again!

George ( down under)

 

Hi Jerry and George,

The debate over the optimal injector size has been going on for years.  I personally plan to use 400cc/38 lb or 440cc/42 lb Ford injectors.  According to http://www.maxcooper.com/rx7/how-to/fuel_system/calcs.html 38 lb injectors at 80% duty cycle / 43 lb / .5 BSFC pressure are good for 242 HP.  The 440cc/42 lb injecors are good for 267 HP. 

 

Also check out RC Engineering which is the most accepted expert that I know of (http://www.rceng.com/technical.htm#WORKSHEET).  Using the same assumptions the 38 lb injectors are good for 242 HP and the 42 lb injectors are also good for 267 HP.  Looks like these guys are using the same formulas - good to see consistency from 2 different sources.

 

Lastly, note that injectors should not be run continuously over 80% duty cycle or they will overheat and fail.  A smaller is better when it comes to idle control.  DO NOT forget this part of the equation.  Lastly, at cruise altitudes the injector cycle rate decreases as the HP requirement decreases so at 8000 ft the duty cycle of the injectors will only be 60 % which is very safe for sustained operation.  Call me if you want to discuss this.  Go play with the calculators posted above (which George has already done).   

Ken Powell
Bryant, Arkansas
501-847-4721