Fuso FG vs FE frame

The Fuso FG frame rises up so the engine can be mounted higher off the ground by a few inches. This provides extra clearance for the transfer case and front drive shaft.

However, the curved frame makes it more difficult to fit a camper body onto the frame. Compare the Fuso FG 4x4 in the foreground of this photo with the straight frame of the Fuso FE in the background.



Mitsubishi Fuso of America has announced that a new 4x4 truck will be available late in 2008. It's possible that the new model will use the straight frame of the FE.

Chip Haven

Chip,

That is a great photo for showing the differences between the frames on the two models.

Step Down Frame

I'm not an engineer, but from what I can see from ours, unless Mitsubishi Fuso significantly changes the design of the transfer case and front suspension we are likely to continue to see a step down frame on the FG.

The FG's step down frame can be an advantage, depending on your design.
1. The step down section enables an easy frame extension. Grind off the rivets that connect it to the straight frame section, fabricate and install the extension, put in proper grade bolts, get a lengthened intermediate section drive shaft, have a muffler shop fabricate a longer exhaust pipe section, insert an extension in one wiring loom and you have a frame of any length you need.

2. If you choose to implement a 3 point pivot sub-frame that pivots in the rear you can end up with a flat frame from cab to rear. Attach the front of the pivot frame in the forward section of the stepped down frame so its top lines up with the upper section of the step frame. Establish your rear pivot height to maintain the flat frame. Success depends on how tall your sub-frame section is and how much pivot you allow before you hit the bump stops.


Automatic vs. Manual engine output

Another major difference between the two platforms is starting with the FE series redesign a few years ago there has been no automatic transmission available in the FG.

There is a significant difference in output ratings between the 4M50T7 motors used in the manual transmission FE and FGs and the 4M50T8 used in the automatic FEs.

4M50T7: 147 HP @2700; 347 Ft/Lbs @ 1600
4M50T8: 175 HP @2700; 391 Ft/Lbs @ 1600

Click here for the relevent Fuso documentation: http://www.hackneys.com/mitsu/docs/fuso-power-train.pdf

I talked with two different Fuso service managers and two different Fuso parts managers. All four stated there were no differences in camshafts, valves, heads, fuel pumps, injectors, fuel rails, etc. between the T7 and T8. The only part number difference between the two motors is the EFI control unit.

It seemed to me that this could possibly be an easy chip swap between the two EFI controllers, but I did not take on the project of researching, procuring and testing the T8 chip or EFI controller.

One of the Fuso service managers talked with his Fuso factory rep and was told the T7 motor was downrated due to torque capacity limitations of the manual transmission. I have no reason to dispute this but thought it more likely the T8 was uprated to compensate for the torque losses inherent in an automatic transmission's torque converter, thus yielding similar driveshaft power from both drivetrains.

Doug

Isuzu NPS 300 vs FG Stepped Frame

I realize that the new Isuzu NPS 300 (Australia) has now gone to a Straight Frame verses the Stepped Frame of previous models and wonder what other major components had to change to make this possible?

How has Isuzu NPS pulled off this change and Fuso FG is still stepped? Is there additional benefits to the Straight Frame as done by Isuzu?

Curious....KEENO

I realize that the new Isuzu NPS 300 (Australia) has now gone to a Straight Frame verses the Stepped Frame of previous models and wonder what other major components had to change to make this possible?

How has Isuzu NPS pulled off this change and Fuso FG is still stepped? Is there additional benefits to the Straight Frame as done by Isuzu?

Curious....KEENO

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Well the rear springs are now obviously raised higher above the diff so that reach the higher chassis. To do this they simply packed them up. The higher rails also mean that a 2 piece rear tailshaft wasn't going to work so they went to a single piece unit and hey that's about it.

John,

hopefully i will start building my new chassis soon, it won't have the step in it, straight rails 150mmx 50mm x 6mm tube, with toyota 200 series front coilover suspension.

hopefully i will start building my new chassis soon, it won't have the step in it, straight rails 150mmx 50mm x 6mm tube, with toyota 200 series front coilover suspension.

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Alan , if you're thinking of attaching coil overs to the original shock mounts , I don't think they'd be strong enough. Just getting in early. Good plan though.

This photo also shows the difference in strength between the frame
of a medium duty truck (the FG and FE) and a heavy truck (the FM
in the background. The heavy frame looks to be three times thicker!

Is there any reason for the stepped frame other than to reduce height?

no, i will be making new brackets, i figure there are plenty of aftermarket coils and shocks available for 200 series so should be able to get it riding pretty good.

whatcharterboat said:

Alan , if you're thinking of attaching coil overs to the original shock mounts , I don't think they'd be strong enough. Just getting in early. Good plan though.

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Bumping this for comments on the stepped frame design. I was talking with a friend of mine recently about TATRA trucks, which use a backbone instead of traditional frame rails. This places the engine very high in the chassis, but it does not seem to be an issue as these trucks are not rock crawlers. The MAN and HEMTT trucks are similar in design with regard to powerplant placement though they may not use the torque tube design.

So the questions that came up are:

What are you accomplishing by raising the front frame section?

The cab is higher but this could be achieved with a simple body lift. The engine and transmission are higher (compared to straight frame rails) which is bad for on and off road handling. There is more articulation for the front axle, but this should not be an issue, as this is not a rock crawler and the rear axle is limited by its location on the straight frame. If you mount a box, the box must sit up higher in the front due to the step frame or it must be behind the drop in order to sit on the straight frame section, thus causing you to lose valuable frame space (unless you are parking a motorcycle or two spare tires or other items between the cab and the box.)

If the FG were to use a straight frame (like the FE) the engine and trans would be located in the same place, there would be few if any differences between the two with regarding to mounting and location and the front might lose some suspension travel or articulation compared to the step design.

In a backbone chassis, the engine cannot be lowered in between the frame rails as there arent any, so you are hampered by that design, with regard to powerplant placement and CoG. It seems the FG essentially has the same characteristics as you are raising the cab and the powerplant to make more clearance for the front axle? This may be silly, but I think the FG looks quite silly with the cab raised up and a large wheel gap. Look at a new jeep or a 4wd truck, there arent huge differences front and rear like that.... Maybe its exacerbated by the cab sitting over the front tires and not having a body like a car or truck.

Maybe the cab wont fit correctly if the engine is raised in a straight chassis to clear the front axle. Is front axle clearance really the issue here or is there something else? Seems like a front mid engine chassis would not have the problems that a front engined truck or SUV (4WD) would have..

:coffeedrink:

DzlToy said:

the front might lose some suspension travel or articulation compared to the step design.

Is front axle clearance really the issue here or is there something else?
:coffeedrink:

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If the FG were to lose any suspension travel, the travel would become completely non-existent

Near as I can tell, the reason for the step in the frame is just to get clearance over the front axle.

I have the chassis half built for my mits 4x4 there is no step, I will use a spacer block between the rear springs and diff to compensate for no step.

Hi Kerry and Dzltoy,

The "step" can be seen as a way of accommodating the front diff obviously but if you are trying to understand why >> maybe look at it another way. What would happen if you put a front diff under a FE>> the front half would be exactly the same as it now on the FG but the rear of the chassis would be around 200mm (estimate) higher than it should be. So you would have 2 choices (1) step the rear chassis down so that the springs can bolt straight to the top of the diff or (2) use serious spacers between the diff and the springs.

Fuso chose (1) so they only build one lot of chassis rails and cut them and add the step to make the FG chassis.
Isuzu in the current model chose (2). They used to have a dedicated chassis for the earlier 4x4 NPS (instead of a 2wd chassis with a stepped section inserted) so it had one piece stepped chassis rails and a separate 2wd chassis with straight rails . Now it looks like they use a version of the 2wd chassis (less tooling I guess) but use big spacers between the rear springs and the diff.

Hope I haven't really confused everyone I think of the "step" not as a step UP to make clearance for the front diff but as a step DOWN to answer the problem at the rear .

Or what Alan said .........

I will use a spacer block between the rear springs and diff to compensate for no step.

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Ok John, lets take your example and say that I just pick up a 2wd FE out of the local paper and want to make it 4wd. I would add springs to the front (straight) frame section and bolt in the solid axle, probably something about the size of a Dana 60.

Now I am not intimately familiar with the Fuso chassis as you and some others are, but I would "assume" that by installing the correct length of leaf spring and shackle, the diff would not contact the body or engine.

I dont see where this would necessitate a cab lift or changing anything on the rear of the truck. It would be the same as picking up the front end of the truck with a crane or wrecker (exageration, of course) and pulling it down the road.'

In the US, most full size trucks and SUVs sit higher in the rear than they do in the front to compensate for heavy loads and towing, especially pick up trucks. In the case of the Fuso, the springs and axle are rated high (you probably wont get 7000 pounds in the bed of an American pickup truck) So I see no reason to change anything with regard to the rear suspension during this "conversion". Therefore, if you raised the front it seems the two would be even now or maybe the front a bit higher?? So maybe the step is to make the frame rails parallel to the ground again, yet keep the cab and engine high enough to clear the diff?? I dont see how the rear is now 200 mm higher than it should be, as you havent done anything to it...

Thanks for your thoughts...

Cheers..

Dzltoy>>

So maybe the step is to make the frame rails parallel to the ground again, yet keep the cab and engine high enough to clear the diff?? I dont see how the rear is now 200 mm higher than it should be, as you havent done anything to it...

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Sorry maybe I should have added that about the chassis staying parallel to the ground. Well the same attitude anyway.

When I said

What would happen if you put a front diff under a FE>> the front half would be exactly the same as it now on the FG but the rear of the chassis would be around 200mm (estimate) higher than it should be.

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>> I should have been clearer. The chassis still needs to maintain the same attitude. So if you lift the front so it's high enough for the front diff , the whole chassis is lifted, not just the front , otherwise it would be sort of pointing up hill all the time. Castor would be wrong, etc.

Anyway, that's my best guess why Fuso did it.