Just got 14.3 last tank, all time record for city. I am giddy!!!

 

With only 2700 miles on the clock and a 6 mile one-way stop and go commute with no highway miles, I get 14 mpg.

 

I don't know for sure if I reset the trip odo the last time I filled up, but I usually do...But as most of you all know, I have had my PCM reflashed with a performance program recently (experimental) and anyway, I filled up last night at about a 1/4 tank down and I had 140 miles on that tank and it took 6.2 gallons to fill up again...If you don't feel like doing the math right now..that figures to about 22.5 MPG..Before I throw a party..I'll do this again under the same driving conditions and see what I get next time.

 

[sm=interesting.gif]

 

Just completed a road trip from LA to Sonoma back down through Big Sur. I got 16.9MPG going 70 and Santa Barbara traffic. Probably translates close to 19-20 at 55-60. Can't complain. I passed a very slick Unimog camper and he was lucky to be going 50, cool truck though.

 

I average a bit over 16mpg...... some city, mostly highway..... have not checked recently though, only first 3 or 4 months when I bought the car. If I was averaging 13 like you I would sold the gas hog a long time ago something wrong with it for sure

 

Mileage isn't necessarily better with cruise control. I can beat the cruise control every time. Example: you come to a hill. Cruise tries to maintain constant speed. With auto trans, it may downshift, and now your mileage is in the tank. With manual, it may put in so much throttle, it gets into power enrichment, and again your mileage hosed.

If you can maintain steady level speed with manual throttle, and compensate appropriately for hills, you can beat the cruise control.

Also there was some mention about fuel octane. Unless the engine is retarding spark advancement due to pinging, you won't get any benefit from a higher octane fuel. Premium fuel doesn't necessarily have higher octane than regular, and will have less if the octane was obtained with additional oxygenate. The EPA did a study, and they found a variation of -4% to +2.2% energy content of gasolines from normal. Only problem, you can tell when buying gasoline which one is going to have the higher energy content.

I get fantastic economy with my cars. I keep the tires inflated to the recommended pressures. I don't carry anything I don't need to. I use the brakes as little as possible. Most importantly, accelerate the car at moderate throttle (not floored), shifting to the next highest gear at LOW RPM (easiest with a manual trans). The key is driving in the highest gear possible.

If you want to see how much gear ratio affects mileage, go down the freeway in the car with a mileage gauge at a steady 70 mph. Note the MPG reading, and then drop it down a gear. In my cars, I'll lose 2 or 3 miles per gallon per gear! Two gears, and I'm down 5 or 6 MPG. That's a lot!

Michael

 

Wish I could edit these posts...

Anyway, it should read you CANNOT tell the energy content of the fuel when puchasing.

Michael

 

RPM doesn't have as much of an impact on fuel economy as you may think. It all depends on the load placed on the engine. This will affect how much manifold pressure, or vacuum, is going into each cylinder on the intake stroke, (modulated by the throttle butterfly). A high RPM setting with low manifold pressure (high vacuum) can result in better economy then a low RPM and high manifold (low vacuum) pressure. As an exaggerated example, think of driving around at 15 MPH in high gear and trying to accelerate. You get low RPM and high manifold pressure (low vacuum). On the other hand, think of cruising around at a steady 60 MPH in high gear. You now have high RPM and low manifold pressure (high vacuum). Aside from possible damage to the engine in the first part of the example, it is obviously more economical to operated in the relm of the second half of the example. The other end of the spectrum has us cruising around in low gear at a relatively high speed with the engine screaming with RPM. Now you have high RPM and a relatively low manifiold pressure (high vacuum), but you now have more RPM then the engine needs and it is wasting fuel.
The PCM monitors manifold pressure via the MAP sensor, and it monitors RPM usually off of the flywheel. Once the RPM starts to change (the degree of change is dependant on the programming of the PCM) the PCM opens the throttle valve to allow more air (higher manifold pressure/lower vacuum) and fuel into the engine to overcome the greater load. Once the throttle is opened all the way and the load continues to get bigger, or the load is added faster than the throttle can compensate for, the PCM tells the trans to downshift. It if is a manual trans, then the operator must make that decision. The PCM can detect these changes quicker then you can, and modulate the fuel/air mixture more precisely then you can.

Rememer that POWER= PLAN (Pressure in the cylinder, Length of stroke, surface Area of the piston, and the Number of times per unit of time measure) For any given RPM and load setting, the engine has a specific fuel consumption. Sometimes the most economical setting can be a high RPM setting, and sometimes it can be a low RPM setting.

Your idea of trying to maintail the same speed in hilly terrain is exactly what the PCM is trying to do. You just have the ability to see the increase in grade ahead of time and can add more throttle (manifold pressure) before the load increases. But, you dont know precicely if you added too much or not enough from the optium setting until you are on the hill and modulating the throttle. Both systems will allow you to coast down one hill and up the other, thus reducing the power requirement to climb.

As for the octane rating, you are partially correct. The different grades of fuel do have a different octate rating. That is the primary distinction between them. The higher the octane, the more resistant the fuel is to detonation. Detonation occurs from preignition or hot spots in the engine that cause the fuel to explode rather than burn smoothly. These explosions can be detrimental to the engine, and to fuel economy. High compression engines, and high performance driving require higher octane. Daily driving typically will not require a higher octane, unless the engine is designed for it (higher compression). You are correct about the energy content of the fuel, but that has nothing to do with octane. Bear in mind, those differences are within the allowable specifications set forth by the EPA and are considered to be acceptable.

 

Michael you are 100% right about cruise being hard on MPG. I just did 333.3 miles on hwy @75-80MPH and got 16.4MPG. Not bad considering the aerodynamics of the H3 nose and windshield.

Happy 4th to all!!