warp2diesel wrote:
[quote=But the difference in towing capacity is large between the same truck and those 2 different gear ratio's.My father's '01 SD originally came with 3.73's and could not pull much more then 16,000lbs,he had the gears changed to the OEM option of 4.30's and can tow over 20,000lbs now with the same truck.Can't give you any empty mpg #'s since it never is driven without a gooseneck attached(be it the 38' horse trailer or 45' flatbed),he used to get about 8-9mpg's with the 3.73's but now can get about 12mpg's with 4000lbs+ more in towed load at 75mph.But who knows since his 7.3 PS must be finally getting broke in with 700,000 miles on the odometer.
A smart transmission would adapt from empty to a goose neck 20,000# trailer with out changing the rear axle.
It is totally correct the same engine will need to turn more revs per mile with a 6,000# truck pulling a 20,000# load than with just the 6,000# truck, laws of physics dictate that. A smart transmission would adapt to the load and obtain the best possible fuel economy for the conditions.
brown stinkies can the excess paper work and "Lock and Tag Out" the Bean Counters (Each Engineer and Technician gets a key and lock) and any good Engineering team can make the Smart Transmission happen.
Will the 6,000# truck towing 20,000# ever get 34.5 MPG, no. But it will get better MPG than it does now.[/quote]
Turning different REVs at highway speed with a different load? Only if the converter isn't locked up. Then, you are wasting MASSIVE amounts of fuel to keep the transmission fluid warm. Not a bright idea. My 30' RV has a 3-speed TH475 transmission (Chevy P-30 chassis) and a 454 putting power through it into the 4.56 rear end. At 60mph, that engine is close to 3k RPM, all day long. Why? Because I'm in top gear (1:1) and the converter is locked shut. The transmission is nothing more than a straight shaft. Whether I'm pulling just the 12k lbs of RV or I add another 4k of Jeep Grand Cherokee to the tail... It will always run at 3k at 60mph.
Now, lets talk about the upgrades I have done to this engine.
Stock, it gets 6mpg.
I have removed the dual airpumps (stupid inventions) converted the 5 V-belts to a single Serpentine and ONE extra V for a safety, replaced the manifolds with dual headers connected to completely separate 2.5" exhausts that run straight back through dual truck mufflers (one per side) without ANY bends or restrictions... Replaced the intake manifold with an Edelbrock Performer and the carb with an Edelbrock 750cfm... Extreme set of spark wires and an HEI coil for the fire... 4" air intake line that is insulated from the engine bay's heat and connects to a K&N behind the headlights... Tuned the HELL out of that Carb so that it is running DEAD PERFECT stoich at cruising speeds, varies a bit on acceleration or coasting, I would have preferred it be a bit lean but don't want to cook a piston.
And driving cross-country drafting behind semi trucks with the onboard generator running both roof airs (1gph) at 65-70mph... I was pulling 9mpg steady the whole way.
Is the engine capable of better economy? Certainly! The economy doesn't change when I added that Jeep behind the RV, which says the engine is being wasted on that gearing. Gas engines cannot vary their fuel consumption substantially based on loading, they HAVE to maintain stoich 14:1 or darn close, or risk burning a piston. In fact, a gas engine has to spray even MORE fuel when heavily loaded to cool the combustion chambers, b/c lean = death. Diesels can go to 200:1 when not loaded. Because my RV doesn't change it's MPG when I add 4k lbs to the back, obviously the engine doesn't think that it is loaded heavily. Remember also, this is NOT a computer controlled engine. So when I am unloaded, this engine is creating LOTS of available power that is just heading out the tailpipe. Sad. That should never happen, but this is only a 3-speed.
So how to fix the economy? GEARS! The 454 engine is a SLOOOOOOOW turning block. For the RV setup, it has a redline of 4500 rpm. Considering that this 30 foot RV can easily keep up with traffic, it has an enormous amount of power available. Turning it slower with more gears STILL makes use of that same power band, but to a more economical and fuel-efficient way. When you have 500 lb-ft of torque to apply with every rotation, who cares if it is applied slower once you are at cruising speed?
Adding more gears costs the BUILDER more, and they don't see the benefit. Remember GM and the transmission drain plugs? Adding one cost them more, but they didn't see any benefit. Only the buyer / mechanic would. So they didn't do it.
This is the same thing. GM only GRUDGINGLY started even offering three gears, their motto for years had been that two was more than enough for anyone. But their other motto was "we build stinky poo, you'll buy it anyway."