Bad gas mileage is it normal???
It's more than fuel economy. It's also to keep the engine running w/in it's powerband and the most efficient at any given rpm. Gears alone do not "kill" fuel economy. A perfect example of this is how autos always suffer from worse gas mileage than manuals. The engine has to work harder, and sometimes for a longer period to achieve the same output as a manual.
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From: CT/NJ
It's more than fuel economy. It's also to keep the engine running w/in it's powerband and the most efficient at any given rpm. Gears alone do not "kill" fuel economy. A perfect example of this is how autos always suffer from worse gas mileage than manuals. The engine has to work harder, and sometimes for a longer period to achieve the same output as a manual.
All else being equal, a lower final drive than GM installed in the car will hurt fuel economy. Say it takes 20 horsepower to keep a Camaro moving 65 miles per hour. An LT1 can make 20 hp at 1200 rpm or 4000. There are quite a bit more frictional losses at 4000, AKA burning more fuel to go the same distance.
All else being equal, a lower final drive than GM installed in the car will hurt fuel economy. Say it takes 20 horsepower to keep a Camaro moving 65 miles per hour. An LT1 can make 20 hp at 1200 rpm or 4000. There are quite a bit more frictional losses at 4000, AKA burning more fuel to go the same distance.
If RPM is not what kills MPG's, why does GM us the first to fourth skip shift OTHER than, to improve MPG's? The RPMs when the skip shift is in action is around 1.8K RPM IIRC.
If that is the actual reason why they did that it is because the engine made enough torque to get away with it. I have no idea if it actually improved mileage or not. It was a pain in the *** and I believe was one of the first "mods" owners did before doing anything else. The stock torque curve on a LT1 is extremely flat. Try that after a cam install and see what happens to your mileage.
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Really you should drive by a vaccum gauge, not the tach. A motor is a lot happier mpg wise with the least amount of load possibe.
I have gotten 27mpg once on the highway, I average about 24-25 doing about 80 down the freeway. I usally average 18 in town.
I have gotten 27mpg once on the highway, I average about 24-25 doing about 80 down the freeway. I usally average 18 in town.
If that is the actual reason why they did that it is because the engine made enough torque to get away with it. I have no idea if it actually improved mileage or not. It was a pain in the *** and I believe was one of the first "mods" owners did before doing anything else. The stock torque curve on a LT1 is extremely flat. Try that after a cam install and see what happens to your mileage.
For me to get my best mileage, I start in 1st, shift to 2nd, then to 4th while keeping RPMs under 2K being my shift point. I also avoid being in 6th and having the revs drop under 1.5K or so. I also monitor the injector duty cycles while trying different driving styles to determine what gives the best mileage and it seems to me that lower RPMs and low load are key to MPG's assuming you dont drop too far under the curve. Just my two cents.
What you just described has far more to do with load than RPM. What you are doing is making the engine alleviate unnecessary work when accelerating because there is enough leverage for you to get from point a to point b. Besides, you are only bringing up acceleration which is when an engine is the most inefficient. If you'd like, conduct an experiment at highway speeds. Run the car in 5th for a certain distance. Note fuel mileage, then run in 6th while traveling the same MPH and see which result gives you a better fuel rating.
Last edited by SS RRR; Oct 21, 2010 at 09:19 PM.
So you think the throttle percentage would be enough to answer the question? So if I set the cruise at 70MPH (level ground) in 5th and 6th gear, and if 6th uses a smaller throttle percentage, that settles it and its the RPM's? I think I would trust injector duty cycle more, but I will do it.
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Nope, I sure didn't. Leverage only helps your fuel economy getting up to speed and climbing hills.
My other vehicle, a 454 dually needs leverage to pull 20,000 lbs up a hill. That is why GM graced it with 4.10 gears from the factory and a blazing 10 miles per gallon. My LT1 doesn't need nearly as much leverage to get 4000 pounds max going, hence the more economical 3.23 ratio and 22 mpg.
The idea is to maximize economy for a given load. That load is the drag created by wind resistance, tire rolling resistance, brake drag, and driveline friction. The only part of that equation you have changed with reduction gearing is to increase driveline friction.
If what you suppose where true, all we would have to do to get better fuel economy is downshift a gear or two. Or better yet, eliminate those wasteful overdrive gears all together and swap in a TH350 or maybe a Muncie 4 speed for the gear grinders!
My other vehicle, a 454 dually needs leverage to pull 20,000 lbs up a hill. That is why GM graced it with 4.10 gears from the factory and a blazing 10 miles per gallon. My LT1 doesn't need nearly as much leverage to get 4000 pounds max going, hence the more economical 3.23 ratio and 22 mpg.
The idea is to maximize economy for a given load. That load is the drag created by wind resistance, tire rolling resistance, brake drag, and driveline friction. The only part of that equation you have changed with reduction gearing is to increase driveline friction.
If what you suppose where true, all we would have to do to get better fuel economy is downshift a gear or two. Or better yet, eliminate those wasteful overdrive gears all together and swap in a TH350 or maybe a Muncie 4 speed for the gear grinders!
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My car when I got it got 30mpg cruising at 75mph with 3.23's and when all I did was swap out the catback to SLP LMII and 3.73's my gas mileage on the highway cruising at 75mph was 22mpg.
Is my cruise control messed up or did the SLP LMII take away all that efficiency?
Is my cruise control messed up or did the SLP LMII take away all that efficiency?
Just something to think about... Why does a Z06, rated at far more power than a stock f-body, have close to the same mpg rating? Why are auto cars most always rated for worse mileage than manuals? Why is it SUV's that have different engine options all get about the same mileage rating, or far worse than a ZR1?
To set the record straight, I do believe gears affect mileage no doubt, but not close to what people claim how going to a steeper gear will "kill" gas mileage. Fuel efficiency is far more influenced by load on the engine and how hard it has to work.
I don't trust you to get the results right, and it wouldn't change my mind anyway based on my own personal experience with the multiple amount of gear swaps I've done in my on turd in the last 14 years.
30mpg out of an auto? I knew Iowa was hilly, but it must be downhill everywhere you go.
To set the record straight, I do believe gears affect mileage no doubt, but not close to what people claim how going to a steeper gear will "kill" gas mileage. Fuel efficiency is far more influenced by load on the engine and how hard it has to work.
So you think the throttle percentage would be enough to answer the question? So if I set the cruise at 70MPH (level ground) in 5th and 6th gear, and if 6th uses a smaller throttle percentage, that settles it and its the RPM's? I think I would trust injector duty cycle more, but I will do it.
30mpg out of an auto? I knew Iowa was hilly, but it must be downhill everywhere you go.