Our RVs today are powered by the most sophisticated and powerful engines
ever built and we're running them at higher speeds while driving the biggest, heaviest and most
complete RVs in history. All of which means there has never been a greater demand for Gear
Vendors Under/Overdrive auxiliary transmissions.
Whoa!
An overdrive for your vehicle that already has overdrive. Think that doesn't make
sense?
It does. In fact, it goes right to the root of the problem.
One difficulty with those sophisticated engines in today's motorhomes and tow
vehicles is CAFÉ. That's not a drink, it's a governmental control on all automotive manufacturers:
Corporate Average Fuel Economy.
Every manufacturer has to meet requirements of fuel economy over their entire
product line. And with big engine trucks, SUVs and RVs the most popular with the public, fuel
economy becomes a difficult problem. Manufacturers solve that problem through gearing. The
newest transmissions have lockup torque converters to keep the RPMs lower after each shift. This
is fine on an empty half-ton pickup that's going through the EPA test course, but not near what
you want if you are towing 10,000 lbs. Or more or have a motorhome that is always heavy. Yet
you get the same transmission as the EPA-certified light duty truck.
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And that creates a problem for us RVers, which Gear Vendors Under/Overdrive
resolves through corrective gearing, called gear-splitting.
Let's consider a specific transmission. The E4OD/4R100 is Ford's heavy duty
transmission used in heavier half-tons and all three-quarter and one ton trucks and motorhome
chassis. It is a four-speed transmission, including overdrive. The 4.10 rear-end is one of the
most common differential gears, pretty standard for towing and motorhome loads. When you buy a
GEAR VENDORS, you get gears, so let's look at a common set-up with 4.10 gear as an example. The
ratios of this transmission are very similar to those found in the GM and Dodge products as
well, and they all use a lockup torque converter:
First gear has a final drive ratio of 11.11, meaning the engine turns over 11.11
times for every full turn of the wheels. That's powerful. Very powerful. Pretty hard to imagine
a situation in which you could need to go lower, certainly not often.
Second gear has a final drive ratio of 6.31. Third gear has a final drive ratio of 4.10 and
4th or overdrive has a final drive ratio of 2.91.
Those are huge gaps between the gears and each shift means a major change in
engine speed. An engine speed has everything to do with power.
Ford's popular 6.8 liter V-10 engine develops 265 HP at 4,250 RPMs.
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Revving the engine in first gear to that speed and shifting to 2nd drops the RPMs to 2,422 (53%).
At this RPM, the engine produces only 175 HP. Besides a huge loss of 90 HP, you also have reduced
the engine's torque multiplication from 11.11 to only 6.31. You lose all this because it is such a
large step from one gear to the next.
If you could keep the RPMs up and reach a gear in between those two, your power
would obviously remain high. In fact, with a GEAR VENDORS Under/Overdrive 1st over produces a
ratio of 8.67 (only a 22% change), which would put engine ROM at 3,314 and 250 HP. That's 75 more
ponies without any modification to the stock engine. What's more, most of us don't care to rev
to 4,250 before we shift anyway, and GEAR VENDORS is then even more important.
And that's what Gear Vendors does throughout the gears: It gives you a gear just
about halfway between the stock gears. So shifting up or down; you don't have as large a gap.
RPMs remain high and so does the horsepower.
With the installation of a GEAR VENDORS Under/Overdrive, you'll have eight forward
gears. You'll be doing exactly what the 18-wheelers are doing, using gears to keep up the RPMs
and the resulting horsepower when you are tacking the hills, and using the low RPM torque when
cruising on the flat highway. The more gears you've got, the easier it is to find the performance
and economy originally designed into the motor.
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