I've searched and read all through the posts about the advantages to switching to a bigger gear. IE- 4.30, 4.88 etc. I read all about the experts saying the lower gearing wouldn't really effect net MPG that much. And I was skeptical.
So, I went over to one of the rpm/speed calculators and input some data. I wanted to find out what gear would equal my stone stock 3.27 if left in 4th. I was surprised to see that a 4.88 final drive ratio in 5th exactly matched my current 3.27 if left in 4th. Next I devised a test card, and set about gathering some data.
I had originally planned to gather more data, but thought I would share what I found out today.
Givens -- nice day here in SW Texas. Light winds, mid 60's temp. I drive a 3 hour cruise one way home every weekend from Del Rio to San Antonio. About 160 miles. Overall, it is slightly down hill, as Del Rio is about 1000 feet above sea level and San Antonio is about 500 feet. 99 Cobra stone stock, stock tire size, no mods. Has a bra on the front. Car was lightly loaded with just me and a few gifts in the trunk. I checked air pressures before I started and evened them all 4 out at 44 psi.
I filled up and hit the highway. The first leg was 66 miles to the next big town. I set the cruise at 70 mph in 5th gear for a baseline and only had to slow down through one very small town and then come to a quick stop at the border patrol checkpoint. Then, once in the thriving metropolis of Uvalde, I stopped and filled up at 66 miles. The car burned 2.7 gallons for 24.4 mpg, and 2.4 gallons per hour fuel burn. RPM was right at 2000 RPM.
Next, I got on the same highway and continued East for San Antonio. Again, I had to slow down through some small towns, but not for long. Driving through Hondo is about the same as driving through Uvalde, so I figure it is a wash. This time I kept it in 4th, exactly replicating what the car would be like in 5th with 4.88 gears. RPM was right at 3000 RPM. The noise was not bad at all. The Khumos make far more noise. I had the stereo blasting as well. Excessive engine noise was not a problem. I stopped and filled up again at 70 miles. This time, the car burned 2.9 gallons but I did drive a touch farther. MPG is 24.1 and essentially the same 2.4 gallons per hour fuel burn.
I was expecting far worse mpg at the 3000 rpm steady cruise.
So, all those guys with the big gears are right. It really doesn't make much difference with this motor. My guess is 4.30's would barely reduce the MPG.
Of course I did not factor in a humming bird farting upwind and causing some bees to circle around and temporarily alter the magnetic field of the earth. I just tried my best to keep the car at the same 2 RPM's over a relatively flat stretch of road on the same day and see what the difference was.
Let the daggers start flying.
Dano
So, I went over to one of the rpm/speed calculators and input some data. I wanted to find out what gear would equal my stone stock 3.27 if left in 4th. I was surprised to see that a 4.88 final drive ratio in 5th exactly matched my current 3.27 if left in 4th. Next I devised a test card, and set about gathering some data.
I had originally planned to gather more data, but thought I would share what I found out today.
Givens -- nice day here in SW Texas. Light winds, mid 60's temp. I drive a 3 hour cruise one way home every weekend from Del Rio to San Antonio. About 160 miles. Overall, it is slightly down hill, as Del Rio is about 1000 feet above sea level and San Antonio is about 500 feet. 99 Cobra stone stock, stock tire size, no mods. Has a bra on the front. Car was lightly loaded with just me and a few gifts in the trunk. I checked air pressures before I started and evened them all 4 out at 44 psi.
I filled up and hit the highway. The first leg was 66 miles to the next big town. I set the cruise at 70 mph in 5th gear for a baseline and only had to slow down through one very small town and then come to a quick stop at the border patrol checkpoint. Then, once in the thriving metropolis of Uvalde, I stopped and filled up at 66 miles. The car burned 2.7 gallons for 24.4 mpg, and 2.4 gallons per hour fuel burn. RPM was right at 2000 RPM.
Next, I got on the same highway and continued East for San Antonio. Again, I had to slow down through some small towns, but not for long. Driving through Hondo is about the same as driving through Uvalde, so I figure it is a wash. This time I kept it in 4th, exactly replicating what the car would be like in 5th with 4.88 gears. RPM was right at 3000 RPM. The noise was not bad at all. The Khumos make far more noise. I had the stereo blasting as well. Excessive engine noise was not a problem. I stopped and filled up again at 70 miles. This time, the car burned 2.9 gallons but I did drive a touch farther. MPG is 24.1 and essentially the same 2.4 gallons per hour fuel burn.
I was expecting far worse mpg at the 3000 rpm steady cruise.
So, all those guys with the big gears are right. It really doesn't make much difference with this motor. My guess is 4.30's would barely reduce the MPG.
Of course I did not factor in a humming bird farting upwind and causing some bees to circle around and temporarily alter the magnetic field of the earth. I just tried my best to keep the car at the same 2 RPM's over a relatively flat stretch of road on the same day and see what the difference was.
Let the daggers start flying.
Dano
