long term experiment with gears for fuel mileage
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Joined: Jun 2001
Posts: 391
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From: Eh?
Car: 1988 Monte Carlo SS
Engine: 5.7L TPI
Transmission: T5
Axle/Gears: 3.73
long term experiment with gears for fuel mileage
I've been keeping notes on my fuel mileage for the past two summers. I've come to the conclusion that just because you add an overdrive gear, doesn't mean you will gain in the fuel mileage department.
I swapped from a 3.73 axle ratio to a 2.73 ratio for 1.5 summers. With my T5, this allowed me to drive the car as if I had either axle ratio (loose approximation).
3.73 * 0.75 (5th) = 2.7975
2.73 * 1.00 (4th) = 2.73
2.73 * 0.75 (5th) = 2.0475
The bottom line is I'm up about ~1 mpg with the 2.73s and 5th gear compared to 2.73s and 4th gear. My average mpg is up about 1 mpg between this summer compared to last summer (this is either due to my new engine loosening up a bit or my tuning experience getting better with time).
To gain any benefit from the extra gear, I think the engine needs a camshaft change to something closer to an LG4/L03 grind (which I'm not going to do).
Anyhow, just a curiosity is all. Anyone else experience this kind of thing? My average fuel consumption is 20-21mpg. I was hoping I could get it in the 25 range with the gear change, but I guess I need to look elsewhere.
I swapped from a 3.73 axle ratio to a 2.73 ratio for 1.5 summers. With my T5, this allowed me to drive the car as if I had either axle ratio (loose approximation).
3.73 * 0.75 (5th) = 2.7975
2.73 * 1.00 (4th) = 2.73
2.73 * 0.75 (5th) = 2.0475
The bottom line is I'm up about ~1 mpg with the 2.73s and 5th gear compared to 2.73s and 4th gear. My average mpg is up about 1 mpg between this summer compared to last summer (this is either due to my new engine loosening up a bit or my tuning experience getting better with time).
To gain any benefit from the extra gear, I think the engine needs a camshaft change to something closer to an LG4/L03 grind (which I'm not going to do).
Anyhow, just a curiosity is all. Anyone else experience this kind of thing? My average fuel consumption is 20-21mpg. I was hoping I could get it in the 25 range with the gear change, but I guess I need to look elsewhere.
Joined: Jan 2005
Posts: 10,407
Likes: 492
From: Hurst, Texas
Car: 1983 G20 Chevy
Engine: 305 TPI
Transmission: 4L60
Axle/Gears: 14 bolt with 3.07 gears
I've been keeping notes on my fuel mileage for the past two summers. I've come to the conclusion that just because you add an overdrive gear, doesn't mean you will gain in the fuel mileage department.
I swapped from a 3.73 axle ratio to a 2.73 ratio for 1.5 summers. With my T5, this allowed me to drive the car as if I had either axle ratio (loose approximation).
3.73 * 0.75 (5th) = 2.7975
2.73 * 1.00 (4th) = 2.73
2.73 * 0.75 (5th) = 2.0475
The bottom line is I'm up about ~1 mpg with the 2.73s and 5th gear compared to 2.73s and 4th gear. My average mpg is up about 1 mpg between this summer compared to last summer (this is either due to my new engine loosening up a bit or my tuning experience getting better with time).
To gain any benefit from the extra gear, I think the engine needs a camshaft change to something closer to an LG4/L03 grind (which I'm not going to do).
Anyhow, just a curiosity is all. Anyone else experience this kind of thing? My average fuel consumption is 20-21mpg. I was hoping I could get it in the 25 range with the gear change, but I guess I need to look elsewhere.
I swapped from a 3.73 axle ratio to a 2.73 ratio for 1.5 summers. With my T5, this allowed me to drive the car as if I had either axle ratio (loose approximation).
3.73 * 0.75 (5th) = 2.7975
2.73 * 1.00 (4th) = 2.73
2.73 * 0.75 (5th) = 2.0475
The bottom line is I'm up about ~1 mpg with the 2.73s and 5th gear compared to 2.73s and 4th gear. My average mpg is up about 1 mpg between this summer compared to last summer (this is either due to my new engine loosening up a bit or my tuning experience getting better with time).
To gain any benefit from the extra gear, I think the engine needs a camshaft change to something closer to an LG4/L03 grind (which I'm not going to do).
Anyhow, just a curiosity is all. Anyone else experience this kind of thing? My average fuel consumption is 20-21mpg. I was hoping I could get it in the 25 range with the gear change, but I guess I need to look elsewhere.
Good findings, I am back to my 3.08s and a stock 1,800 rpm converter with my 700r4 in my G20. I AM running the Peanut Roller cam in mine. Fuel mileage is up about 3 MPG and power in the normal driving ranges feels about the same as before when I was over-cammed and had 3.73s.
Thread Starter
Member
Joined: Jun 2001
Posts: 391
Likes: 0
From: Eh?
Car: 1988 Monte Carlo SS
Engine: 5.7L TPI
Transmission: T5
Axle/Gears: 3.73
If I still had the automatic, I'd probably keep the 2.73s and go for the peanut cam. With a manual trans, the long gear is getting old when driving in the city limits from a stop light.
How over cammed where you before? I'm running an Edelbrock Performer cam (2101?) at the moment.
How over cammed where you before? I'm running an Edelbrock Performer cam (2101?) at the moment.
Senior Member
Joined: Jul 2006
Posts: 609
Likes: 0
From: Oslo, Norway
Engine: '85 Monte SS L69 305
Transmission: TH 200-4R
Axle/Gears: 3.23
I experienced the same with the Monte L69 & 200-4R residing in my wagon..
I had to change out the 2.93 rearend, and the one that happened to replace it used 2.73 gears.. The car became a dog to drive and the motor was clearly unhappy about being lugged like that, and my MPG's dropped a lot. Soon I swapped the rearend for one with 3.23 gears, the engine was happier, I was happier, & my MPG's improved over the 2.93 gears (was up to 23mpg at one time, usually it's around 17).
Everything in a car needs to be tuned to suit the conditions where it spends most of it's operating time in order to get optimum performance (& MPG). So yes, not too high, and not too low.
I had to change out the 2.93 rearend, and the one that happened to replace it used 2.73 gears.. The car became a dog to drive and the motor was clearly unhappy about being lugged like that, and my MPG's dropped a lot. Soon I swapped the rearend for one with 3.23 gears, the engine was happier, I was happier, & my MPG's improved over the 2.93 gears (was up to 23mpg at one time, usually it's around 17).
Everything in a car needs to be tuned to suit the conditions where it spends most of it's operating time in order to get optimum performance (& MPG). So yes, not too high, and not too low.
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