F-134 mpg

New Guy on the Block... doing my 1st restoration on a CJ-5 with an F-134 motor. Motor is a fresh rebuild, .040 pistons, carter YF, 427 gears and a Warn O.D. I'm thinking of switching to 488 or 538 gearing as I do not have enough "motor" to use the OD. Plan on using this for light 4-wheel trips and don't want to tow it to and from. Any thoughts or opinions ??? Also what kind of gas millage should I expect to get? Thanks in advance for any help.
The Irishman

 

best my f-134 ever got was 16mpg 5.38axle 60mph with a tailwind.
got an overdrive later but mpg didn't change, it just lugged instead of rev as high.
mine has 32" diameter 8.25" tread Trans Trac LT, at 45psi

 

Thanks for the replies, Tires are 7.00/ 16 military ND T's on stock rims. Right now speedometer is off, think the drive gear is for a 538 gear set-up, its a 15 tooth. At 30 MPH I am actually doing about 40. don't think I'm getting 16mpg though.

 

Your gas mileage should go up as the newness wears off of the engine.

 

Thanks for info! Any thoughts on 538 verses 488 gearing ???

 

With the OD, I'd say 5.38 all the way with the little 4-banger.

 

Let's put it this way.

I have the 5.38 gears in my '60.

50 mph is 3200 rpm on the tach on the steering column.

with the 4.27 you will probably be around 2920 on the tach at 50. With out the overdrive. T-90 3spd.

With the overdrive in there, you may drop down to 2200. That will increase your gas mileage.

And you can always run up to 45 or 50 in the 1:1 final drive mode, then shift into overdrive.

I don't have the overdrive. If I can locate a set of axles running 4.09 gears or 4.27 gears I would switch them out, just to improve the gas mileage.

The wheeling I do out here in the desert can be done just as well with the numerically lower gears.

 

According to Willys Motors Inc. Warn O.D. is recommended equipment for 5.38 and 4.88 to 1 axle ratios only.
If you plan on driving grades the F-134 HP is marginal at hiway speeds.
Hurricane powered CJ used on hiway the 5.38 final drive plus O.D. turning 6.50 or 7.00 x 16 tires is as good as it gets.

 

Thanks for the input Guys. Side note, when I push the little motor up to 3 grand and shift into O.D. I drop to 2100-2200 rpm but can't hold it even on the flats. To much wind resistance I guess. She gradually drifts down to 2000 rpm and lugs! Guess I'll start saving for a set of 538's .

 

Good Plan. Of course you could always throw a Dauntless at it =P

 

If I were in your shoes, I'd look for some 5.38 axles. The original axles on CJs are considered throw-aways by the Pirate crowd, and you should be able to find some complete. This will be much less expensive than replacing the gears in your existing axles, and save you the time and effort of changing gears. Axle gear setup is likely the most challenging mechanical task on one of these vehicles.

An alternative would be to try and get a little more power out of the F134. There are a lot of old threads about this, and at least one recently. http://www.earlycj5.com/forums/showthread.php?93899-need-a-little-more-power-out-of-a-134-F-head

A modern 4-cylinder is another option, along with the popular V6s.

 

Regardless of what axles you choose, based in Long Beach, you have to take a freeway to get to most wheeling sites in Southern California. I've driven my F-134 4.27 OD powered 64 CJ5 on the freeway and it's not fun. Not that it can't go 60-65 on the flats (I have to pull it out of OD anytime the road goes past level, like an overpass), but everyone else is doing 70-80, and I never felt very safe. You have to stay in the right hand lane, and that's always the crappy one that the 18 wheelers beat up so it's not a comfortable ride. I'd vote for 5.38s, but not for the freeway ride, but for lower gearing once you get there. I'd seriously consider towing the jeep to where you want to go ( my 2 cents).

I rebuilt my jeep in Cypress, and drove it up to the Big Bear area where it lives. I did it early on a Saturday morning when there wasn't much traffic. It's not too bad when you don't have crazy people tailgating you, but I was pretty tired by the time I got there. Imagine driving that 80 miles, wheeling all day, and driving back? I'm tired just thinking of it.

Eric

 

I'm not a high HP kinda guy. I get by with a stock built Hurricane engine.
My one and only daily driver is a stock standard 1962 3B as is noted below.
I live near and often drive the Mo. Ozarks.
5.38 with O.D. is as good as it gets for the Hurricane.
I don't baby the Hurricane. I run it hard with decent results. About 80K between rebuilds.

I run up to 65 mph anytime and anywhere on the Interstate excepting the steepest grades.
On long steep interstate climbs the Hurricane sometimes runs low on HP forcing me down to 50 MPH.
This is generally hilly country and not severe mountain grades.
I do run severe mountain grades in the NW Arkansas Ozarks but those roads are mostly remote secondary hiways.
(two lane blacktop)
Also very strong head winds are all that the Hurricane can tolerate with 5.38 in O.D.

 

To be honest the difference between 4.27 Direct and 5.38 O/D is minimal. the only loss is getting started off the line in town.
5.38 lugging at in O/D is worst (13 mpg) than 5.38 at 3600rpm direct (16mpg) and that is 60mph with my tires and at the time old f-134
If city or highway is a concern, I might look into friends with trucks to flat tow and act as spotters on the trail before a regear.
we flat towed mine behind an 02 silverado from iowa and still got 18mpg. and you don't have to worry about breakdowns

 

My '65 with 4.27s and O.D. will go an indicated 70+ on the flat with standard size tires. It's got 23,000 orig. miles so feels tight and reasonably safe. Inclines are another story however.

 

Back to mpg, not exactly apples to apples, but here's a link from vernco that shows the flathead engine's mpg for a 48 CJ2A:



http://www.vernco.com/Fuel/id648.htm
http://www.vernco.com/Fuel/

 

Joseph,
The actual difference is 4.27 vs 4.04 final drive ratio.
Also early CJ's with 4.27 final drive always had the lower geared T90C.
The "TAKE OFF" reduction (overall reduction for street use) is 15.04 / 1 (2.798 x 5.375) for pre 1963 and 14.27 / 1 (3.339 x 4.272) for post 1962 CJ's with Hurricane.
The main concern is that the OD acts as a gear splitter allowing one to better utilize the optimum Hurricane RPM range.
For the road I typically shift the OD equipped Jeep using 5 out of the 6 possible foreward gears.

 

Thanks , Eric. This graph answers a lot of questions. Guess I'm leaning towards using the 5:38s. Going to stay as stock as possible but still be able to drive it down the road. Which bring's up another question, I have the stock 16" rims. They are 4.5" wide correct??? Besides NDT's what if any are my tire choices?