5th gear - less MPG?

[NoDOHC]

Awesome discussion! I did some research on instantaneous fuel economy when the '86 was still N/A and I had the Haltech in it.

With some quick math, I discovered that instantaneous fuel enconomy in MPG can be computed easily with the injector energized time (assuming operation below staging setpoint. Please bear with the numbers as I was running 50 degree BTDC timing and 16:1 AFR.


5th gear, MPG = 110/injector on time in ms.
4th gear, MPG = 80/injector on time in ms.
3rd gear, MPG = 58/injector on time in ms.
2nd gear, MPG = 39/injector on time in ms.
1st gear, MPG = 23/injector on time in ms.

At various continuous speeds in 5th gear I had:
23 mph: 31 mpg
46 mph: 28 mpg
55 mph: 32 mpg
61 mph: 36 mpg
66 mph: 32 mpg
71 mph: 36 mpg
75 mph: 38 mpg

These numbers were extracted from the Haltech data log and entered into a spreadsheet to compute the instantaneous mpg. I tried to pick spots where the throttle position was constant (level patches of road).

In fourth gear I had:
20 mph: 24 mpg
30 mph: 28 mpg
35 mph: 30 mpg
40 mph: 32 mpg
50 mph: 26 mpg
55 mph: 24 mpg
60 mph: 21 mpg

So what I can conclude is that you are actually better off in fourth gear up to 50ish mph

(The relative engine efficiency should not have changed between a stock ECU and the Haltech, even if the efficiency is better overall).

edit: If I entered data above 75 mph, it might indicate that I was speeding, which of course I wasn't.