good gas milage when fast???

i know this sounds crazy and alot of people are going to say im full of crap but i did an experiment



20 dollars in gas for each week in a 2 week period

1st week going 50 mph

2nd week going 70 mph (shh)

and the 2nd weeks gas lasted longer

1st gear up to 45 mph 2nd gear up to 70 mph and 3rd gear to when ever it stops (havent gone over 120 lol)

your opinion on whats going on here???

i would think that it would suck down less gas going 50 then 70 mph

 

Depends on a lot of factors, gear ratio, road conditions, etc... But your engine runs at different efficiencies at different rpms. This is why you see an arc or curve on a dyno chart. Whatever speed your engine was turning at 70 mph is apparently more efficient than what it's taching at 50.

 

lol thanks now i dont feel as bad going 70 mph

 

lol maybe its because you had some of week 1s gas left in the tank before you started counting for week 2

 

You may be getting better mileage at 70, but the speeding ticket will offset any savings.

 

I run 75+ every day back and forth to work in my '72, 66 miles a day total all highway driving, plus the 4 or 5 city miles I may put on it at lunch break if I don't like what the cafeteria is serving that day. No doubt in my mind it gets better mileage at 70 mph then it does at like 40.. I have a vacuum gauge that I drive by. It stays constantly right in the green zone at 70-75 mph. If I'm driving like 40 or 50, it often dips down into the red on small hills and stuff. The speed limit is 70, and I usually just run along with traffic, which is usually like 75-80 mph.

 

thats why i live in hte country were we have no speed limits LOL (dead serious... no speed limits for miles)

 

You might want to check into that before you get a ticket. I live in Wyoming (more antelope then people) so I am in the middle of no where and we still have speed limits. If I remember right, Montana just went to speed limilts (no where roads) a few years ago, they had it on the national news about it being the last place with no speed limits.

 

:16suspect ill check into that

 

Justin, Justin . . . there are speed limits for zones that you have to obey regardless of whether or not there is a sign. For example, residential areas are 25 mph unless posted otherwise; business areas are 20 mph, unless posted otherwise. Sort of like there is not a stop sign at the end of every driveway or every gas station, but you still are required to stop--yes you can and will get a ticket if you don't stop. Another example, yellow lights -vs-red lights. Both require you to stop! Though if you are at the point of no return on a yellow you would/could not stop in time to stop properly and safely--still a yellow does NOT mean speed up to make it, as you are to prepare to stop instead. So stop pushing it before you get a ticket and make it so you can't drive for a long time.
Hope this helps and good luck!

 

asked the sheriff today and he said around 65 is a good speed (he did not say that was the speed limit but thats the closest i could get to an answer

 

Don't forget these were econo-boxes when designed in 1968 or whatever... and the speed limit was... like... 70MPH.

Carbed cars run like pigs at low idle but most efficiently fuel ~ power at 2000-3000 rpm I think. B.C. has an "air care" testing system and old cars like my Comet are allowed excessive hydrocarbons at idle... but for the "highway test" my old beater runs exceptionally clean (twice as good as my 93' Chevy Astro which - incidentally - failed the emmisions test).

I used to have a Buick GS-455 (ram air 4 bbl Quadrajet with small primaries and massive secondaries) and my dad drove it from Vancouver to Calgary once... at the Canadian 55MPH speed limit with 2.70 gears... he swears it got 25MPG on the highway most of the time - the car was basically idling the whole way and didn't slow down on gradual inclines.

But when I drove it in the city it was more like 10MPG. When I was 'having fun' it was more like 5MPG.

Of course... the scientific method stipulates that you would need to do each test 3 times to verify the results... heh heh. That would be your excuse for doing 70 quite a bit more...

 

I have seen this several times with my buddies and I that built up their cars in H.S.. A mild cam, the right 4 barrel carb, duel exhaust and the right gears and you have a good recipe for reasonable gas mileage. You want your car to pull RPM's that are just above idle at cruising speeds and you should get optimum gas mileage. But if you drop in some 4:11's in the rear and you are in the 4 barrels doing 55, you will get crap mileage.

 

For the best gas mileage be sure to use a vacuum advance on the distributor.
The vacuum advance doesn't count when figuring your total "under power" advance because it goes away under power but it adds a lot of timing under part throttle cruise. I get somewhenre around 21 (20 -22) mpg with a stock 302 in a '73 Mav 2door. If I added some compression and tuned the timing (future projects) I know I can get close to 25 mpg with it.

 

I've noticed that vacuum advance is an option on new aftermarket distributors... I always thought it was NEEDED for a given engine. Does the vacuum actually retard timing under light load then "let it go" for hard acceleration?

If weights and springs can change the mechanical curve... is there any way to "vary" vacuum advance?