Supertop & Gas Mileage.....

So... Here's one to ponder : Took my CJ5 for a highway ride. Very pleased that she Ran fantastic , roundtrip.
First 80 miles @ 60 MPH , west wind ~ 15 mph , with the top on & doors & windows off. Got 13 MPG


Return trip , top down , cinched & stowed. 80 miles @ 62 MPH, tail wind ~ 10 mph. Got 20 MPG ?

 

Square box, round wind?

 

Yes Sir.......6.1 Gallons , 1st leg. 4 gallons , return .

 

So you had a 15 mph headwind going and a 10 mph tail wind returning? The wind resistance (drag) is a mighty barrier... it increases like the square of the velocity. Add the headwind/tailwind to your speed, and wrt drag you had a 75 mph speed on the first leg, and a 52 mph speed returning. (75^2 - 52^2) / 75^2 = 0.52, or a 48% reduction in drag on the return trip. If your gas mileage only depended on drag, you would expect a =1/0.52 = 1.92 (92%) improvement in gas mileage, or roughly doubling. You didn't quite make that, instead making a 20/13 = 1.54x (54%) improvement - drag is a major thing in gas mileage, but not the only thing. Possible that top up or top down made the situation better or worse; with the wind effect, you cannot make any conclusion.

 

I always estimated my jeep V6 . only got 12mpg ever
so if you got 20 your way ahead

 

I think there is something to it. When I switched from hard top to soft top on my wrangler this spring I noticed it felt like it needed more throttle to maintain speed on the highway. All that fabric moving around must create some drag.

 

Same here, even all tuned up. I blame the 4.88’s and no OD.

 

Yeah, (13 + 20) / 2 = 16.5 mpg which is phenomenally great for a CJ. I would be very pleased with that. Frontal area does not change much, top up or down. I would not be surprised at a small but detectable difference depending on the top folded or not, but IMO the conditions were not well enough controlled to say anything about that from this data.

 

Always drive 62mph.

 

I got a pretty consistent 18mpg on my cross-country trip until I got close to home and put the hammer down.

 

Huh? How on earth did you come to that conclusion? Soft top or not, you are still driving a BRICK.

 

Next trip, do the drive with the windshield folded down and note the MPG.
A major part of the 'brick' is that big flat windshield, no?

Be sure to wear some nice aviator goggles.

 

I've always noticed a gain in power with the windshield folded down.

 

Correction: No top and windshield down and with or without a roll bar; e.g. run what you brung.

 

Spoken as only someone well versed in 4-cylinder Willys jeeps could