Diesel Rover

I've got a 1993 5.9 CTD an A518 swapped into an old Land-Rover pickup. I've got great big tires on it right now and the rear axle ratio is about 4.56. It runs down the highway at about 700F, 3 lbs of boost, and about 2000 rpms (no tach). I am getting less than stellar mileage. I am thinking of regearing to 4.10s (which would be equivalent to a stock 1st gen with a 3.07 ratio and an auto) but I am worried that it might be too low. The truck is very light and moves along like a scalded cat, but I would like to get better MPG numbers out of her. I have yet to do any kind of tweaks to the engine, but it has full 4inch exhaust and a Banks intercooler. Does 1500-1600 rpms sound too low for the highway? based on my math it would mean that the truck would top out at about 60 mph in 3rd (which is great if I am towing heavy) and would cruise along nicely in OD. Just looking for some feedback. Thanks!

krazykarl454

what do you concider great big tires? i plan on running 38s and 4.56s in my chevy swap and in OD at 70MPH the engines goin to be turning like 2300. which is abit high

PapeCAT

that sounds like a great cruising RPM. our Torque peak is around 1700 RPM. Lower rpm even won't hurt.
3.07 with OD 5sp and GV overdrive =

Diesel Rover

I am running 39s. Based on what iam seeing 2300 is going ot be very high for you. I think it would just love 1600 RPMs at cruise.

dozer12216

Since unit is very light(by your description) don't see why 3.55 -3.91 would be acceptable if avaliable. Find out where you are now and figure to where you want to be and the gear ratio to accomplish. I figure you do little or no heavy towing with rig. Something light would be O'K would assume.

MoparMarv

Normal hwy speeds of 55-80mph with my 3.07's gets me 1400-2000rpms in
5th. No problems here. keeping that engine below 2000rpms really helps the MPG IMO.

mhuppertz

If you have a dual range transfer case and manual hubs, you can put 3.08's in there and still have low range if you need it.

haloman

What kinda mileage are you seeing?

Diesel Rover

Thanks guys, I cannot get gears higher than 4.10 for these axles so I am a bit limited. The truck is very light, probably 4500 lbs - 4800 lbs on the road. The body is all aircraft aluminum and it originally had a small 4 cylinder. I did put a lot of steel into the frame to beef it up but it is still pretty lightweight.

I was just worried that the slip in the stock torque converter would eventually get to the point where the gears would not have the same effect. The higher the gears, the higher the load on the torque, the higher the percentage of slip for any given speed. I do think that the 4.10s will actually work out pretty well.

Right now I am getting about 16 mpg but there is still some work to be done to optimize things. The timing is most likely way off (I have the tool to reset it to 1.6mm, it's just been too cold to do it!!) and the pump needs some tweaks. I bought a set of 37" BFG ATs which will have a much lower rolling resistance than my current tires (325/85R16 Michelin XMLs). Would retarded timing have a big effect on mileage, as in 3-4 mpg?

haloman

Ok What you should look at:

Building the tranny for your power goals.
Check the timing.
Check all fluids and tire pressures

Then worry about changing gears.
Timing would make a difference in mileage.

16mpg is not bad for those big tires tho. I think you could squeeze 18-19 out of it with 37's.

krazykarl454

hey man what do you think of those xml's i was thinkin of running them? they messure up to 39's? thats cool thats what i would really like to have. are u lookin to sell those by any chance?

Diesel Rover

The XMLs are OK tires, not as good as a bogger or a TSL in the rough stuff, but they run nice on the road. They seem to have a very high rolling resistance though and thye are no good in the snow. Very tough though. I think my new BFGs will be better for all around use, the XMLs I am keeping for off-road. They measure 38 on my 7" wide wheels, which are too narrow for these tires. NJ is a little far, I am in Ontario but I know a guy who sells them, www.armytires.com, he's good and his prices are OK.

MunK

I like mine.

I have run a set for 65K miles now on our Crew Cab. They work adequately in most terrain. They are exceptionally good driving tires on the hyw.

I cut and grooved mine for wet weather/snow performance. This also made a dramatic difference in how they worked in Moab on the slickrock as well.

I really have no complaints... typical Michelin durability, great wear, decent manners on and off road, and if you can live with the weight a decent choice for a "do everything" tire.

NoRM