Mission impossible: modding a Unimog

[Cd]

Originally Posted by mnmarcus

What? Oh wait a sec. 1 mpg is a 25% increase in FE... Even then, I wonder what numbers you are using???

From Unimog links:



FA (?) 48.18 sq. ft , EE .19, drive train efficiency .9, #2 diesel
CRR (?) .015

Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

Gets 13mpg @~37mph... close to 50:50 aero and rolling resistance.

I got 9.36 mpg at 50mph with .75 Cd and a 66:34 aero to rr (respective)ratio. At .30 Cd I got 15.5 mpg, a 65% improvement in mpg and a 44:56 aero to rr ratio.

I stand by the fact that aero improvements are almost always beneficial. Would adding another axle to this vehicle cut rolling resistance by a lot?

So did I do the math wrong ?
That doesn't surprise me a bit - especially since i was on crismas vacation and using my cell phone to write that.

Isn't .75 - 65% something like .26 though ?

I guessed at 4 mpg. So this monster actually gets better F.E. than several SUVs ?

That's just sad !

[mnmarcus]

I don't know what the mpg he's getting is. The Unimog link said 13mpg. I don't know what the speed for that would be. My point was effective aero modifications can make a huge difference in mpg. Although this truck has a huge rolling resistance, improving the aero dynamics from cd .75 (your #) to cd .30 (your #) would improve the mileage by 65% at 50 mph.

Isn't .75 - 65% something like .26 though ?

I don't know what you mean by this. I got the 65% from the difference in mpg at 50 mph. One was 9.36 mpg and the other was 15.5 mpg. So...

9.36 X 1.65 = 15.444
Was wondering if I said that right as I was typing...

Of course I don't know if any of this is correct for his unimog. Just pointing out that that aero mod would have a huge impact on FE.

I guessed at 4 mpg. So this monster actually gets better F.E. than several SUVs ?

I don't know what mpg this Unimog gets at what speed. If it's better than any modern SUV it would have to be because of a massively under-powered (no offense), semi-efficient diesel engine, at a much lower speed! The frontal area and weight seem to make 13 mpg a pipe dream...

[comptiger5000]

I would expect slightly better mpg than a school bus, so I could see getting 10 - 11 mpg at the right speed. I doubt it'll do much better, however. It's pretty big and heavy, although the smallish diesel certainly helps.

[autoteach]

My bus gets 11 to 12 mpg. I dont know if it can do much better than that.

[Mario_Marques]

Performance & fuel economy
-Turbocharger
-Propane injection
-water injection
-less restrict exhaust
-Porting the engine head and intake manifold(expensive costs)

Man, i'm used to tune turbo diesel engines in my country, unimog it's different but still a diesel engine, those ideas work here, so they will work there.

Regards.

[TheEnemy]

Can I have your axles?

check the gears on the hubs, makes sure they are lubed correctly.

My 84 CJ makes that much power with a 258, and has trouble maintaining highway speed.

A swap with a modern turbo diesel and a 5 speed gearbox would probably do wonders for both drivability and mileage when you have the money.

From what I have heard though you have to watch your hubs at speeds over 55mph though, they supposedly heat up.