Winter fuel economy/power

NoDOHC · \r\n \r\n \r\n 11-26-2008, 12:26 AM\r\n \r\n \r\n

Have any of you noticed that Stock ECU RX7s make no power when it is cold and they also get terrible mileage? I try to log my mileage on every tank and have the following data for your curiosity.

86 GXL 5-speed (0.69 OD out of 88 GXL) 12 degrees BTDC idle timing:
Temp (F) City Mileage (MPG) Hwy Mileage (MPG)
90+ 25-28 29-31
60-80 24-26 28-29
50-60 23 (Average) 25 (Average) *Largest sample size
40-50 18-21 24-26
30-40 16-18 21-23
10-30 15-18 19-22

Using a G-tech for power comparison (numbers may not be accurate horsepower, but are comparable) I found the following:

Temp (F) WHP (G-tech)
80 121
60 130
50 134
40 120
30 108
10 92

I installed a new transmission and a Haltech E6X and after tuning (during which I had some horrible mileage tanks) I acquired the following mileage chart.

86 GXL 5-speed (0.72 OD out of 86 GXL) Haltech E6X, Racing beat headers into custom exhaust, 16:1 AFR cruising, 50 degrees BTDC timing at cruising loads and speeds:
Temp (F) City Mileage (MPG) Hwy Mileage (MPG)
90+ 29-31 36 *one tank only at this temp
60-80 28-29 31-35
50-60 28 (Average) 31-34
40-50 24-27 30-31
30-40 25-27 28-31
20-30 23-26 25-27

Using a G-tech for power comparison (numbers may not be accurate horsepower, but are comparable) I found the following:

Temp (F) WHP (G-tech)
80 143
60 155
50 160
40 162
30 165

Now I have the misfortune of driving my '91 in the winter and have collected the following data.

91 Coupe, Automatic Transmission (0.72 OD), Idle timing 17 degrees BTDC:
Temp (F) City Mileage (MPG) Hwy Mileage (MPG)
90+ 20-22 25-27
60-80 19-20 25-26
50-60 19 (Average) 23 (Average)
40-50 18-20 21-24
30-40 16-17 19-20
10-30 14-15 *Not yet tested

Using a G-tech for power comparison (numbers may not be accurate horsepower, but are comparable) I found the following:

Temp (F) WHP (G-tech)
70 110
60 112
50 108
40 102
30 98
20 94

My biggest reason for the numbers is to show the trend.

Cooler temperatures hurt mileage and power for stock ECU, but hurt mileage less and helped power for Haltech running a constant 16:1 AFR (cruising) and 13.2:1 AFR under WOT (except for above 6,000 RPM, where the primaries maxed out).

Does this mean that the stock ECU has terrible cold weather maps?

Comments/Data are very welcome

\r\n \r\n \r\n 11-21-2008, 10:55 PM\r\n \r\n \r\n	\r\n \r\n #2\r\n \r\n
\r\n\r\n \r\n \r\n jimieatgirl\r\n \r\n \r\n\r\n \r\n\r\n \r\n \r\n\r\n \r\n \r\n \r\n __________________ \r\n \r\nMy Rx-7 Vids \r\n \r\n \r\n \r\n\r\n \r\n\r\n \r\n\r\n
\r\n \r\n\r\n\r\n \r\n \r\n \r\n \r\n \r\n	\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n