FAY

For instance, a vehicle (mass) is under power from its engine while traveling on a level road or on a very slight grade. It makes no difference if the engine power is accellerating (more inertia being developed in) the mass (vehicle) or if the power is maintaining (less inertia being developed in) the mass at a steady velocity, when the power (fuel) is eliminated the vehicle still continues rolling along the road while deaccellerating until it comes to a stop. The power while moving the mass caused the mass to have its own inertia to keep itself moving for a short time. The faster a mass is moving the more inertia is developed within the mass. The inertia in a moving vehicle (mass) helps the engine keep the mass moving; therefore, the engine has to generate less power (less fuel) to keep a moving body moving than when much more of the engine power was needed to started the mass moving in the first place.

Since the most torque is required to start the load or keep the load moving on a steep incline, that is where the Cummins is superior because an I-6 has heavier engine components and more main bearings to withstand the stress while generating more torque. When starting a load the engine speed is at a low rpm, thus the stress on engine components from generating that stump pulling torque is excessive, because at low rpm there is no inertia built up in the flywheel. V8 engines need an automatic transmission's slippage to allow the engine to speed up and develope much inertia in the flywheel before applying the grunt to move the load. With more inertia in the flywheel there is less torque force on the engine componets which are lighter in a V8. The I-6 is just better designed for heavier pulling. The I-6 is better balanced also.

XLR8R

Greater inertia inherent in a higher mass reciprocating assembly retards the engine's rate of acceleration, or ease of revving... but provides much more energy to transmit through the powertrain to the drive wheels.

Don't forget to consider the effect of the energy pulse on each combustion stroke, which is why the V-8s typically make their power at comparatively higher RPMs.

Torque is the rotational energy transmitted to the crankshaft.
Horsepower is the rate at which torque is applied, or produced.

FAY

When I say that inertia is built up in the flywheel it means energy from the inertia of all moving engine parts resulting in a form of torque at the output of all the reciprocating and rotating components in an engine. Combustion supplies the power to develop inertia energy in the mass of moving components.

If a V8 was fueled appropriately at lower rpms it could be made to produce higher torque at the same low rpm that peak torque is develped in an I-6. The reason the design engineers do not fuel a V8 in greater quanties at lower rpms is due to the fact that an excessive load resistance could result in damaged engine components that are lighter fabricated than those in an I-6. A V8 probably would stall out if loaded heavy at low rpm without an automatic transmission unless the clutch is slipped (burned).

Engine configuration dictates the maximum efficiency and torque from a given amount of fuel. The stroke in a V8 is not as much as in an I-6 resulting in a lower mechanical advantage, plus at slower engine speeds the rotational geometry of one cylinder bank slightly opposes that of the other cylinder bank during part of the crankshaft rotation and has more of a negative effect on power. V8 engines with a standard transmission do not produce enough torque to pull hard a low rpms as it could damage the light components. Lighter V8 components can rev faster than heavier I-6 components, so V8 engines are more suited to take advantage of the slip in an automatic transmission to rev to an engine speed that will not require the components to withstand as stressful a force in torque that and I-6 can withstand.

rockcrawler304

OUCH!!! My eyes are hurting.

Very good info here.

duratothemax

I know I have the actual ad somewhere, but here are pics that I had and pasted them onto one .jpeg pic. Ford 5r110 input shaft is courtesy of Suncoast's website, the allison input shaft is a picture I took when I built mine, and the 48re input is from an ATS build on Pirate4x4.

Not looking to argue or anything, take it for what its worth, I just saw that people were looking for this.

Ill keep looking for the ad itself.....

ben

wcbcruzer

Can't beat the Allison.

XLR8R

No wonder you need a billet input shaft for boost launches in the Ram!

The 48RE looks like my pinky,
the 5R110 looks like my thumb,
and the LCT-1000 looks like... well, I don't have anything that big

Is the Allison a much larger tranny than the 48?

duratothemax

Ive never seen a 48re in real life so I cant commment, but the ally is defiently good sized. 340 or so pounds dry with no converter. Converter is an extra 78 pounds. When I built mine, even with the stock transmission pan it took right around 5 gallons of fluid; deep pan takes more. Also beleive it or not, I DROPPED my allison off the bench when I was tearing it down. It was wieghted funky, I was trying to spin it around, and it was balanced wierd, slowly slipped and dropped all of its mass 3 feet onto the concrete floor. Stupid me. Bolt on a new bell housing (ally case is in 3 sections, so I didnt need a whole new case, just the bellhosuing) and the trans is still alive and well in my truck today

ben

XLR8R

Wow - 5 gallons of fluid is a lot!

HOV

Thanks for posting that. Looks like the Allison's input shaft is about as over-engineered as the Cummins engine is.

As for practical experience with the Allison, I had a 5-speed.

Pros:

Excellent shift management and engine braking in tow/haul mode
Easy to replace external spin-on filter

Cons:

Heavy
Power would not come on for a few seconds after shifting into gear
Power would be disrupted when going over bumps
Parking pawl was very clunky

In comparison, my experience with the 48RE:

Pros:

Smoother shifting
No pause when shifting into gear or going over bumps

Cons:

4-speed has wider gearing
Hunts for gears occasionally
No fluid pressure to TC in Park


All in all, I'd say that the 48RE is easier and better to drive around town, but the Allison was better for towing. Considering I do mostly unloaded driving, I'm fine with that.

duratothemax

very good points on the "cons"
TCM is really finicky and always making sure you arent trying to hurt the trans whenever you shift it, its annoying. I notice if Im going forward reverse forward quickly, like backing into a parking space, it will just kick itself in neutral because it thinks you are trying to go from reverse to drive while moving. Good thing I guess is that its not really possible for the driver to do something stupid...you can put it in reverse at 65mph on the highway.

speed bump thing is annoying, I think its the way the valve body is plumbed, to not let the trans completely "free wheel" in the lower gears.

parking pawl is very clunky, I hate when I back up into a parking space perfectly, then put it in park, and letoff hte brake only to have the truck "roll" forward or backward 2". Doesnt bother me that much tho I guess, the GM parking brakes SUCK so its good to know that there is a huge parking pawl holding the load there.

also, the grade braking is awesome but sometimes mine is retarded, just flat out doesnt work. Something to do with the complicated algorithm in the TCM?? It downshifts at the correct time maybe 80% of the time.

more ally parts with size references next to them.

ben

XLR8R

That's neat that it has a spin-on filter.

duratothemax

too bad the dealer rips you off for it. 39.95 at the GMC/Chevy dealer

7 bucks at the allison/detroit diesel dealer

mj007

All that says is that IH is using a Light Duty Diesel in a Medium Duty truck.

Begle1

Pfft. My poor little A-727 three speed takes 5 gallons too.