5x Racing Mazda RX-8 Project MPG
Project Details:
Overview and Goals:
When the time came to replace Brittany's daily driver 2000 Mustang GT, as Mazda racers we were naturally drawn to the Mazda RX-8 for it's looks, handling, usefulness, and super cool rotary engine. While we knew the rotary powered RX-8 did not get Mazda 3 gas mileage, we were still surprised to find out that the rotary got around the same miles out of a tank as a the V-8 Mustang GT it replaced. This is quite acceptable being a sportscar, as you sacrifice fuel mileage for power, ride quality for superior handling, creature comforts for weight savings, etc... In other words, we knew what we were getting into when we bought the car.
After the first tank of gas came and went, and the next, and the next, with about 275 miles squeezed out each tank (20.5 mpg), it left me thinking that there had to be some way to get better gas mileage and at the same time not sacrificing power, but GAIN power. There are several ways to save mpg's, but some will reduce performance, such as reducing gear ratios and unspirited driving. We want to preserve the spirit of the Mazda RX-8, and at the same time see if we can increase power output while getting better gas mileage.
What we will be doing with Project MPG is performing simple modifications at every oil change and logging the gas mileage to see if what we did had any effect on mpg's. The modifications will be simple at first, such as: using different engine oils, installing a Green High performance air filter, using different spark plugs, upgrading the spark plug wires, replacing the transmission and rear end oil with lighter weight equivalents, etc...
Follow along with our project and hopefully it will help you get better gas mileage out of your RX-8, or any car for that matter. I hate to think that many RX-8's get traded in shortly after being purchased because people expect the car to get 30 mpg, perhaps because it is "Japanese", "has a 1.3L engine", or is a "lightweight sportscar" and forget the fact that it has a rotary engine that consumes more fuel than a piston engine. We will be adding information to this page continuously, so check back ofter for updates and planned modifications.
Current Data
Subject: 2007 Mazda RX-8 GT 1.3L Rotary/Manual Transmission/Factory Fuel Economy: 16 mpg city - 22 mpg hwy
- Calculating Data
To begin, we calculate our gas mileage by resetting our Trip Odometer at every complete fuel tank fillup. After driving until our low fuel light comes on, we then do another complete fuel fillup and calculate the mileage of the tank by dividing our total tank mileage from the Trip Odometer by the amount of gallons used in the fillup. For example: 300 miles to a tank on the trip odometer, 14 gallons used in the fillup would be: 300/14= 21.42 mpg - Average MPG: 20.48
- Highest MPG from one tank: 21.75
- Lowest MPG from one tank: 19.9
- Mods Performed: Castrol GTX 5w20 oil
ScanGaugeII Installed- Average MPG: 21.05
- Highest MPG from one tank: 21.9
- Lowest MPG from one tank: 20.5
- Mods Performed: ScanGaugeII Fuel Mileage Gauge
- Previous Mods: Castrol GTX 5x20 oil
- Gains/Benefits: Gained 0.57 MPG
- Thoughts: While it did not yield huge MPG gains, the ScanGaugeII really shows you what your car is doing as far as MPG consumption goes. It really does make you easier on the throttle as you watch your MPG go all the way down to 6-7 mpg when the throttle is pushed even the slightest amount. I can see the ScanGaugeII working well in the long run as it trains you how to drive, there are a lot of habits that hinder your fuel economy. I did try the "in gear coasting" method discussed on rx8 forums as a method to save fuel and I can say that it does not work. Coasting in neutral saves more gas than keeping engine rpm's high while coasting in gear. After getting the ScanGaugeII dialed in, we found that you must disable the open loop/closed loop function to get accurate readings on the RX-8. Any speed over 77 mph or coasting puts the injectors in open loop mode and the ScanGauge does not measure mpg's accurately in open loop operation. Overall the ScanGaugeII is sweet, and I would recommend it to anyone that is looking for increased fuel economy or an all in one tool to keep an eye on your engine vitals and to use as a scan tool.
With the addition of a ScanGaugeII Ultra Compact 3-In-1 Automotive Computer from Project Sponsor Linear Logic (manufacturer of the ScanGauge II), we were able to monitor our fuel milage in real time as we drove. In addition to being able to monitor our fuel mileage in real time, the ScanGauge II also provides a ton of useful information about what your car is doing, as it reads info directly from the vehicles ECU. So, now that we have a ScanGauge II we can accurately monitor and double check our fuel mileage efficiency to back up our data and provide us with some insight on what is helping, or hindering our fuel mileage.
Our current findings:
The type of driving we do is a good estimate of average driving conditions. The car is daily driven by Brittany 4 out of the 5 day work week, and driven by John (who is a racecar driver) at least 2 or 3 days out of the week. Brittany drives conservatively, John drives more aggressive, so a good performance balance is achieved by sharing driving duties. The car is shifted normally during long highway stints, and more aggressively during stop and go city driving.
During our first 3000 miles of the project, we saw:
Modifications
- The strict useage of Castrol GTX 5w20 non-synthetic oil.
ScanGauge II 3-in-1 Automotive Computer (special thanks to project sponsor Linear Logics) added to monitor fuel efficiency during the project duration
Sponsors
Linear Logics: Manufacturer of the ScanGauge II 3-in-1 Automotive Computer
