The single most important improvement to FE you can ever do. FREE.

[cfg83]

skewbe -

Originally Posted by skewbe

Yah, on some cars (i.e. mine, apples if you like) the scangauge reports base fuel consumption during overrun/EOC in gear, even there isn't any, which is not a big deal IMHO.

CO reported zero fuel used at the end of his first test leg so I assume his doesn't do that.

Just a thought, A carbureted car very likely would still spew fuel into the engine when coasting with in-gear coasting with the ignition off , and make a nice backfire when you turned it back on

In my second ill-fated Karmann-Ghia (the one I don't like to talk about), the engine was so bad that when I floored it, the 4 CONICAL shaped exhaust tips on my muffler would make a righteous explosion from unburned gas. Looked great at night, just like the 4th of July.

I keep looking for that muffler in the Hot VWs mag, but I can't find it. Must have gone out of business. Best sounding VW muffler EVER!

CarloSW2

[VetteOwner]

Originally Posted by skewbe

Yah, on some cars (i.e. mine, apples if you like) the scangauge reports base fuel consumption during overrun/EOC in gear, even there isn't any, which is not a big deal IMHO.

CO reported zero fuel used at the end of his first test leg so I assume his doesn't do that.

Just a thought, A carbureted car very likely would still spew fuel into the engine when coasting with in-gear coasting with the ignition off , and make a nice backfire when you turned it back on

yup it will, especially if you have a mechanical fuel pump (like my vette) since its run off the distributor, if th eengine is turning the fuel will spray, flood the engine possibly hydrolock

[CO ZX2]

Bump.

With all the new influx of people to GasSavers, thought I'd bring this back to the top.

[basjoos]

Your test results agree with my driving style. I coast the downhills with the engine off and only use engine braking on steep downgrades where my speed would rapidly get too high or where there is no straight runout area at the bottom.

An extension of these tests would be to test the uphills. Do you get better FE if you accelerate on the flat at the bottom of the hill to build your speed up before reaching the bottom of the hill so you can get further up the hill before having to drop into a lower gear, or is it better to maintain the lower aero drag of your normal cruising speed and accept having to drop into a higher fuel consuming lower gear earlier on the uphill?

[DRW]

Originally Posted by basjoos

An extension of these tests would be to test the uphills. Do you get better FE if you accelerate on the flat at the bottom of the hill to build your speed up before reaching the bottom of the hill so you can get further up the hill before having to drop into a lower gear, or is it better to maintain the lower aero drag of your normal cruising speed and accept having to drop into a higher fuel consuming lower gear earlier on the uphill?

I like to look at what the fuel is used for. When you drive fast a larger portion of fuel usage is used to overcome aero drag, which you'll never get back. When you climb a hill the fuel is being used to create potential energy (mass of car raised up to a height) which you have a chance to recoup when you coast down the hill. Hopefully you won't have to brake on the downhill and waste the fuel. I don't think it's bad to have to downshift on a climb. To me this means you're still converting fuel into potential energy as quickly as the car is capable of. Just make sure you don't go into open loop or rev the engine higher than needed.

[CO ZX2]

Originally Posted by basjoos

Your test results agree with my driving style. I coast the downhills with the engine off and only use engine braking on steep downgrades where my speed would rapidly get too high or where there is no straight runout area at the bottom.

An extension of these tests would be to test the uphills. Do you get better FE if you accelerate on the flat at the bottom of the hill to build your speed up before reaching the bottom of the hill so you can get further up the hill before having to drop into a lower gear, or is it better to maintain the lower aero drag of your normal cruising speed and accept having to drop into a higher fuel consuming lower gear earlier on the uphill?

Sorry, I first thought your reply was directed to someone else.

I have done no official tests on uphills but have been driving in the manner you describe by accelerating before and quite often during uphill climbs. I almost always do this on hills not too long, i.e., that I can see the crest. I am sure I have improved my uphill FE with these methods.

Longer climbs I get questionable payback for increased approaching speed. But during long climbs I will accelerate if my instant MPG drops below 30 MPG. When my SG II drops into the 20-30 MPG range, extra throttle does not lower the MPG reading substantially(when it's that low, how much lower can it get?). Quite often I can level off after acceleration to a higher speed and see much improved MPG readings for a time. I downshift only when absolutely necessary and when I do I will accelerate immediately to gain enough momentum to get back in 5th gear as soon as possible.

If you drive this way, I would like to hear your assessments.

[skewbe]

Originally Posted by CO ZX2

... I downshift only when absolutely necessary and when I do I will accelerate immediately to gain enough momentum to get back in 5th gear as soon as possible...

Do you drop to the next lowest gear, or an even lower gear so you can accellerate better?

[CO ZX2]

Originally Posted by skewbe

Do you drop to the next lowest gear, or an even lower gear so you can accellerate better?

I always drop into the next lowest gear. I don't very often go lower than 4th. In the past, if I let my car pull way down 5th, it was also too slow for 4th to pull strong. Then I would use 3rd to bring it back up. I do not skip shifts often.

Keep in mind that I have a 130 HP 2.0 liter engine. But it may not be as different as it seems. At my 10,000 ft. altitude, I may be losing 35% of HP and torque. Actual barometer readings here are in the 21-23 in. Hg area, vs 29-31 in. Hg at altitudes of 0-2000 ft. What this means is that I have about one third less atmospheric pressure pushing air into the engine. Like a supercharger in reverse.

[cfg83]

CO ZX2 -

Originally Posted by CO ZX2

I always drop into the next lowest gear. I don't very often go lower than 4th. In the past, if I let my car pull way down 5th, it was also too slow for 4th to pull strong. Then I would use 3rd to bring it back up. I do not skip shifts often.

Keep in mind that I have a 130 HP 2.0 liter engine. But it may not be as different as it seems. At my 10,000 ft. altitude, I may be losing 35% of HP and torque. Actual barometer readings here are in the 21-23 in. Hg area, vs 29-31 in. Hg at altitudes of 0-2000 ft. What this means is that I have about one third less atmospheric pressure pushing air into the engine. Like a supercharger in reverse.

Is there a way you can measure your "effective HP" at your altitude? I was using a tangential "Colorado Rockies" metaphor where, in Denver, a baseball can travel 10% farther in the thin air of Coors Field, 5280 feet above sea level.

Ok, maybe I can answer my own question. I just googled "engine horsepower elevation" and got these results :

Engine Tuner's Calculator
http://wahiduddin.net/calc/calc_hp_dp.htm

Using this in conjunction with weather.com, I got current "relative horsepower" assumptions for Denver to be 83% of rated HP, a 17% reverse supercharger in Denver.

Density Altitude Calculator - selectable units
http://wahiduddin.net/calc/calc_da_em.htm

CarloSW2

[basjoos]

Originally Posted by CO ZX2

Sorry, I first thought your reply was directed to someone else.

I have done no official tests on uphills but have been driving in the manner you describe by accelerating before and quite often during uphill climbs. I almost always do this on hills not too long, i.e., that I can see the crest. I am sure I have improved my uphill FE with these methods.

Longer climbs I get questionable payback for increased approaching speed. But during long climbs I will accelerate if my instant MPG drops below 30 MPG. When my SG II drops into the 20-30 MPG range, extra throttle does not lower the MPG reading substantially(when it's that low, how much lower can it get?). Quite often I can level off after acceleration to a higher speed and see much improved MPG readings for a time. I downshift only when absolutely necessary and when I do I will accelerate immediately to gain enough momentum to get back in 5th gear as soon as possible.

If you drive this way, I would like to hear your assessments.

My main hill is a 1000 foot climb up to the North Carolina state line. The 1st part of it is a steep 3rd gear climb for about half of the elevation increase, then a stop sign before getting onto US25, which is more gradual 4th gear climb. I used to maintain cruising speed (40mph) to the base of the hill, then go to 80% throttle and drop into the lower gears as my speed dropped off during the climb, coasting to the stop, then 80% throttle accelleration up to 4th gear on US25, then using the minimum throttle needed to maintain 40mph for the rest of the climb. But for the last few tanks I have been accelerating up to 55mph at the base of the hill then going to full throttle and dropping gears as my speed dropped off in the climb. So I am spending about half the time in 3rd than I used to. The rest of the climb is the same as before. Tank mileage seems to have improved by 1 to 2 mpg since I made this change. When Yoshi cranks up production of the MPG SuperMID, I'm planning to get one so I can get faster and more specific feedback on changes in my driving technique.