Alright I'm trying to better understand the adjustments that need to be made to the inj cranking time when modifying the primary injectors.

Some time back I switched out my stock 550cc primary injectors for 850cc injectors. The car would start up fairly well after the swap, but not as quickly as it once did with the stock primaries.

I left my water correction factors on the Power FC as is. I also listed what I believe are the "stock" cranking inj times.

80C - 1.000 / 1.000 - 12msec
50C - 1.078 / 1.016 - 17.3msec
30C - 1.297 / 1.219 - 32msec
10C - 1.578 / 1.500 - 59msec
-10C - 2.016 / 1.875 - 87.2msec
-30C - 2.813 / 2.578 - 104.2msec

I then took the stock injector flow rate and multiplied it by the stock injector cranking time. This value was then set equal to my new injector flow rate, multiplied by an unknown cranking injector time.

550cc/min * 1min/60sec * .012sec = 850cc/min * 1min/60sec * x

Solve for x and that should be my new injector cranking time for 80C. Putting this equation in a spreadsheet I then solved for the remaining cranking inj times for each given temperature.

I then took my new cranking injector times and added 35% back. I assumed that this would need to be adjusted due to the reduced inj pulse factor, which in my case is approx 65% with the 850cc primary injectors

My new cranking times became 11msec, 15msec, 28msec, 52msec, 76msec, and 91msec.

Is this correct or am I misunderstanding how the inj pulse correction factor influences the cranking inj times?

I should also add that my FD does start much quicker with my new cranking inj times, but I would still like to understand if the adjustments made make logical sense.

 

Sorry i can't answer your question but i have one for you since you did the 850 primaries swap. What else did you change when you installed the injectors? You put 65% in the front primary and the rear primary, that's it?

 

https://www.rx7club.com/showthread.p...=850+primaries

Check out page 26 in the Power FC Instruction Manual

Check out your PM as well

 

i too noticied my car started up a couple cranks longer with the 850s.

if it works, it works. pretty interesting

 

Are your water correction and cranking inj times still:

80C - 1.000 / 1.000 - 12msec
50C - 1.078 / 1.016 - 17.3msec
30C - 1.297 / 1.219 - 32msec
10C - 1.578 / 1.500 - 59msec
-10C - 2.016 / 1.875 - 87.2msec
-30C - 2.813 / 2.578 - 104.2msec

 

the same except that my 30C is 1.391/1.219