MPG run, part deux

[thered56]

Higher elevation will give you noticably better results, due to (1) lower air resistance and (2) less fuel used, since the computer mixes the available (less) air with less gas, so you maintain a mixture not too lean or rich.

Higher elevation may be better, but I doubt it makes up for the extra fuel used to make the climb up the mountain. That's how it seems to
me at least. Elevation where I live is pretty much sea level btw. I'm gonna try it though, it's gonna be 400-450 miles of mixed driving, most of it being highway (60 miles/day), varying mostly between 70 and 80 km/hour (80km/hour=50mph). I'm shooting for 55mpg. At any rate, it'll be a stretch from my last tank, which I recorded my worst mpg of 38.9...haha...not bad considering a fair bit of it was averaging 50mph on gravel spending most of my time in 3rd with my foot down! lol

[TominMO]

i do recomend the better coil, but i DO NOT recomend you over gapping the plugs as it puts more stress on the coil and can hasten it's demise. swap out the coil, properly gap the plugs, and if you can, index them to have the gap face the exhaust valve in the chamber. also, prop open your rear windows (weather permiting), i've recorded better milage at highway speeds with them open as opposed to closed (this requires the driver or passenger window to be open 2.5-3" to equalize cabin pressure if traveling at 60+ mph)

A 45,000-volt coil will handle the larger gap. That's the point of buying it; not just a stronger spark but a larger one too. When I do this kinda stuff, I keep the original coil in the car along with tools to change it back, so I'm not worried.

I will try to index the plug as you said; glad you reminded me.

Really? Better mileage with the rear windows open? I will definitely have to try that.

Another issue that I didn't mention is summer gas vs. winter gas; winter gas cuts mileage by about 10% in my experience, so I will try to get it all done before fall. Then I will do one last run with winter gas and every trick I can come up with at, 55 MPH, for comparison.

[FestYboy]

i do recomend the better coil, but i DO NOT recomend you over gapping the plugs as it puts more stress on the coil and can hasten it's demise. swap out the coil, properly gap the plugs, and if you can, index them to have the gap face the exhaust valve in the chamber. also, prop open your rear windows (weather permiting), i've recorded better milage at highway speeds with them open as opposed to closed (this requires the driver or passenger window to be open 2.5-3" to equalize cabin pressure if traveling at 60+ mph)

[TominMO]

Ooooo I really wanna try and beat that...heheh...it's hard for me to do when I've gotta go over a mountain every day for work though. Best I've done so far is 57.7 mpg. That was on tires that were very worn (on my way to get new ones from 'hotrodin4me'), windows down, stereo on, goin up a mountain (Malahat). But I really wanna try for better. You give me a number to shoot for. Good figure btw well done. I think a full tank would give more accuracy though too.

Higher elevation will give you noticably better results, due to (1) lower air resistance and (2) less fuel used, since the computer mixes the available (less) air with less gas, so you maintain a mixture not too lean or rich.

There's little practical opportunity to do a full tank without going on the highway, where you are almost forced to be doing something like the prevailing speed to make it safer for everyone. You would need some type of closed course, or a long little-used back road, to try this at lower speeds. I want to try one run at 35 MPH/4th gear, early Sunday morning on a farm road, then stick with runs at 55 with different variables: ignition timing, high-volt coil/increased plug gap, any other suggestions you all might have. Naturally I will use the same car for every test.

[Amos]

Lol, I was doing 75MPH with what must've been a 50 or 60 MPH head-wind...

I got 110 miles to a tank, it was brutal.

[thered56]

Ooooo I really wanna try and beat that...heheh...it's hard for me to do when I've gotta go over a mountain every day for work though. Best I've done so far is 57.7 mpg. That was on tires that were very worn (on my way to get new ones from 'hotrodin4me'), windows down, stereo on, goin up a mountain (Malahat). But I really wanna try for better. You give me a number to shoot for. Good figure btw well done. I think a full tank would give more accuracy though too.

[ejp2fast]

nice run! will be interested in seeing what the plug gap will do.....

keep it up!

[bhazard]

Probably 5th gear at the lowest rpm possible, 1000-1500 rpm. Then again you cant get miles per gallon without miles...

[TominMO]

Be curious to see how that turns out as well. Seems to me I either read, or heard, that 45 mph is pretty much the optimal speed for mpgs. Above, and below that they tend to be worse. Higher I understand, but lower I'm guessing is all about air flow. I believe that is why EPA fuel economy tests are done at 45.

I believe the optimal MPG speed would be in first gear; virtually no airflow at all to worry about. Then it's a matter of finding at what RPM the engine is most efficient.

Or, if you're driving 30 MPH with a 30 MPH tailwind, it's virtually like driving in a vacuum! I remember once I was driving my Acura Integra, 1.8L. Set it on cruise at 55, no A/C, basically flat highway. Had a tailwind I estimate to be 20-25 MPH. After 200 miles, I had gotten 45 MPG! I was tapping the gas gauge while driving, because it just wasn't moving anywhere near as much as I was used to.

[batstiva]

Be curious to see how that turns out as well. Seems to me I either read, or heard, that 45 mph is pretty much the optimal speed for mpgs. Above, and below that they tend to be worse. Higher I understand, but lower I'm guessing is all about air flow. I believe that is why EPA fuel economy tests are done at 45.

Edit. Post number 2000. Woot!! :headbang: :headbang:

[TominMO]

I think your best bet is going to be the way you did it this last time. Cram as much gas as you can into it, drive it for however many miles you decide to go, refill it all the way, and calculate from there. I think trying to guess how much is in there, and then try to put that exact amount back in is going to be pretty much impossible. Unless you run it dry, put x amount of gallons in it, and then run it dry again. Still, without using any hypermiler tricks, what you ended up with is pretty impressive.

Yeah, this methodology seems best. Speaking of hypermiling, on Mythbusters they showed that drafting a semi improves MPG by 20% or more. And you don't have to be tailgating, either. You can keep a safe enough distance so that if he brakes, you can brake in time. It will take a semi a lot longer to brake, too.

Another trick on the highway is to just go a little slower than the surrounding traffic; doesn't have to be a lot slower. Them passing you will "pull you along". The heavier the traffic, the better it works.

One future run, I will try to go 1800 RPM in fourth gear; that's probably about 35-40 MPH, I'll check. On this 45 MPH run I just did, I was doing 1800 RPM in fifth gear. So same RPM but lower air friction; should be interesting. This would be a normal city-street speed. I won't do this on a highway, naturally! Probably a long country road with few or no stops.

[batstiva]

I think your best bet is going to be the way you did it this last time. Cram as much gas as you can into it, drive it for however many miles you decide to go, refill it all the way, and calculate from there. I think trying to guess how much is in there, and then try to put that exact amount back in is going to be pretty much impossible. Unless you run it dry, put x amount of gallons in it, and then run it dry again. Still, without using any hypermiler tricks, what you ended up with is pretty impressive.

[TominMO]

I should also point out that during my first mileage run I was not quite as careful in the two fillups, to make sure they were exactly the same. I may have filled it the first time to a little less than the second time. Even a .1 gallon difference would have made a difference of 3 MPG, so possibly I was actually getting as high as 54 MPG. But I'll never know for sure unless I run it again--which I might do.

[TominMO]

^^ I think in a way, you're both right. I see no real reason why driving more miles, under the same conditions, at the same speed would render different results. But I also think that actually going 200-300 mile would be more like a real world test. I still see no reason why the result should/would be that much different. Course, I also think I might want to shoot myself if I had to drive 45 mph for the 5 or 6 hours it would take to cover that much ground.

I agree, a longer test would seem more definitive. But practically speaking, it was quite hard to go that slow for that long--only 75 miles--on a highway. The main problem was the psychological pressure, when everyone else was driving so fast. I didn't want to be hassling people, or creating a potentially dangerous situation. Quite a number of times I thought about aborting, but hung in there because I said I would do it, and I hate not keeping my word if at all possible.

On a closed course like a racetrack or a very long country road with no stop signs, this would not exist. Plus it was somewhat boring, though on the other hand I did like the relaxation of going so slow; almost meditative.

[batstiva]

^^ I think in a way, you're both right. I see no real reason why driving more miles, under the same conditions, at the same speed would render different results. But I also think that actually going 200-300 mile would be more like a real world test. I still see no reason why the result should/would be that much different. Course, I also think I might want to shoot myself if I had to drive 45 mph for the 5 or 6 hours it would take to cover that much ground.