FG fuel economy

[Glenn-BJ74]

Well if torque is flat from 1,600 RPM to 2,400 RPM, then cruising at 2,400 RPM chews up way more diesel for no added torque gain. Fuel consumption is closely related to engine speed.

What I am suggesting is to select tire diameter and diff ratios to allow the truck to cruise comfortably at where the engine operates most efficiently (uses the least fuel for max torque output). This will vary truck-to-truck somewhat, since it depends on an individual's trucks rolling resistance (weight) and aerodynamic drag (wind resistance) and the average grade (flatness).

 

[Amesz00]

What RPM you guys turning??

The old FG649 trucks (like mine) turn about 2900-3k rpm @ 100km/h. the newer FG84 turns around 2600 (IIRC). I run 38.5" michelins on my truck, which bring it back to 2500, which is 22% overgeared.
You could not possibly run any taller gearing/bigger tyres than what i have without changing; a) The gearbox, because the ratios are too far apart on a stock truck, they are only just bearable with the 38s.
And b) engine power/torque. Fuso's are not known for thier brilliant performance, this becomes exponentially worse with taller gears/bigger tyres.

 

[PKDreamers]

What RPM you guys turning??[/QUOTE]

Our fg649 crew cab 2003 2700 rpm at 100km/h with 285/70R19.5 tyres on it.
Avg 17 lts per 100km.

 

[Glenn-BJ74]

These trucks seem to be primarily built for construction/landscaping/utility uses rather than efficient highway cruising, and are geared low (axle ratios 5.7:1 ?). That is good for low speed, heavy load applications, but it also leads to excessive RPM for moderate load applications, say relatively flat highway cruising.
It appears the truck needs an overdrive for overlanding applications to get the highway RPMS down (say to 1,800 RPM) at the lower end of the torque curve to help fuel consumption.
Larger diameter tires are really a second best approach to achieve higher highway gearing, because they add to rolling resistance, slow acceleration and add to unsprung mass.
The low diff ratios are great off the line and off-road, but have a large fuel consumption penalty for moderate load highway cruising, where I bet these rigs spend 90 % of their time.

 

[Amesz00]

These trucks seem to be primarily built for construction/landscaping/utility uses rather than efficient highway cruising

yes. also explains small wheels and lack of power in standard form.

axle ratios 5.7:1 ?

affirmative, on the FG649 trucks. new trucks have 5.25, with a bigger motor and lower redline (although max useable rpm of around 3k is roughly the same anyway)

It appears the truck needs an overdrive for overlanding applications to get the highway RPMS down (say to 1,800 RPM) at the lower end of the torque curve to help fuel consumption.

They come standard with an overdrive of 0.75 (or so). like i mentioned in my last post, to get any more than 20-odd % overgearing would require substantial modification, because the engines simply dont have the outright torque to pull low rpms at high speed

Larger diameter tires are really a second best approach to achieve higher highway gearing, because they add to rolling resistance, slow acceleration and add to unsprung mass.

Yes and no. dont forget, these are still offroad trucks, the small (7.50R16) tyres they come with are as useless as mudflaps on a speedboat at anything, going to larger dia wheels helps not only with cruising speed/rpm, but helps enormously with offroad ground clearance and traction.

 

[Glenn-BJ74]

Sounds to me like engine is too small, if you have to run at the high RPM part of the torque curve, which burns a lot of fuel (2,600 RPM vs 1,800 RPM.) Have you tried bigger exhaust and increasing turbo boost?

 

[justduck]

I think that it's more a matter of small injectors, low boost and mild tuning. With mild mods my '95 5.9L Cummins puts about 300 HP to the wheels while pumping 34 lbs of boost, and it's pretty stone age design compared to the 4 valve Mitsu motor. I'm sure with the right ECU, injectors and turbo it would put out much more power. Not sure how the trans and clutch would like it though.

 

[westyss]

just out of curiosity, what would a 5 ton ford or dodge or other make get for fuel consumption? What do some folk on this site with a camper on their truck get for mileage, I know my brother in law with his f350 , when towing his fifth wheel gets abysmal mileage, s how are oth3er units doing??

 

[justduck]

My Dodge Cummins, standard cab with a utility box and a NCO Alaskan weighs 10k pounds with 90 gal of fuel. Cruising at 65 to 70 mph I get about 14 mpg. I'm sure there will be times in the Fuso that I'll be wishing that it was Cummins powered.

 

[engineer]

My Dodge Cummins, standard cab with a utility box and a NCO Alaskan weighs 10k pounds with 90 gal of fuel. Cruising at 65 to 70 mph I get about 14 mpg. I'm sure there will be times in the Fuso that I'll be wishing that it was Cummins powered.

So why bother getting a Fuso, stay with Cummins or what ever.....

 

[westyss]

so, 10,000lb's, is that truck rated for that?? My last trip, 6000+ miles, and I got 16.7 mpg imp. at an average speed of around 62 mph, the weight only affects hill climbs so its not really an issue other than thats why I bought the fuso, I could of continued to totally overload my westfalia and get 25 mpg I guess, so anyone else with some precise mpg numbers from some 3-5 ton available load trucks that are loaded to around 10,000 lb's? Starting to get really curios. Do these F550, topkicks etc get over 15 mpg?? And not some tank to tank mpg or the manufacturer's computer stats, real good calculations, I took my total km's for my trip using two gps's and devided by all the fuel I used for an 8,250 km trip. So far I think I am way better off with my fuso, besides I can pull into a camp spot late at night and no one hears me, try that with a cummins.:victory:

 

[justduck]

so, 10,000lb's, is that truck rated for that??

No, 8800 lbs. I have air bags in the rear plus a fat anti rollbar. It's been a great truck and handles the Alaskan well, but we want to be on the road more and have a little more space and easier setup. Also the top half of the Alaskan has serious dry rot and needs to be rebuilt. Therefore I'm building 13.5' camper on the Fuso.

 

[westyss]

mpg

found a Car & Driver report on the topkick 4500, they stated book mpg's as 8 but they reported getting 9mpg. The ford f450 was showing the same but some people state huge numbers, like 18 city, 22 hwy I really doubt that. Following my bro inlaw while he was towing his fifth wheel in a f350 diesel he got abysmal mpg's, we filled up at the same place, and around the same amount and he was looking for a fill station while I was still around half tank. And he paid double for his truck. So what does it mean? Well I guess the mpg's for fuso are really a little above average, those other trucks have way more power but thats what costs, if you wanna tow huge loads or haul stuff at 70-80mph get a ford, if you want to cruise and smell the roses get a fuso.
To each his own, and that is what every one is doing, setting up a rig for their own needs, and uses.

 

[mog]

Bring thread back to life

On a 1350+ miles from Colorado to Northern California/Baja Oregon, I averaged 11.5 mpg overall on the trip. Mileage was 12.6 mpg when the terrain was general flat (although at higher elevations). Average overall speed was 54 mph. The highway speed range was from 50 mpg (about 20%), to 65 mph {GPS confirmed} (about 10%).
But I had head winds most of the way and the truck has an 8-foot high ‘box'. So a frontal area 64.6 sq-ft. (body only, no undercarriage drag factor) with an estimated drag coefficient of 0.7 (Cd). Of course with this much drag, speed is the driving (pun intended) factor. At 50 mph it takes about 37.7 hp to overcome its aerodynamic drag, yet at 65 mph it takes 82.9 hp. So a 30% increase in speed takes 120% more hp (and related fuel). Truck weighed 8990 lbs.

My plans include lowering the height of the box by 18 inches (12 inch ‘chop', 6” drop on frame), which will reduce the frontal area by 18%. Adding aerodynamic improvements with cab roof diverter, and box side diverters, which should improve drag coefficient by 22% to 30%. And driving slower, the real winner to save fuel and smell the roses.

D'oh I gave you its drag coefficent and then forgot to say what type vehicle- 2002 Fuso FG 50K miles (used by a little old lady to delivery furniture in a Colorado mountain town),

 

[westyss]

Is that an FG or a Mog your driving?