some engine details wanted
Lead Driver
Joined: Apr 2008
Posts: 6,942
Likes: 13
Going up an inch or two is hardly a difference you will notice. Even before my new engine, when i went from 265s and 4.11s to 255s and 3.73s the difference was negligible. Now, if you were going from 235s to like 37s, then yea, thats a big difference, but the difference between a 235 and 315 is only about 2" depending on the tire. That would drop your rpms about 200 at a given speed.
Here is a fun little toy Gear Ratio Calculator
Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
Likes: 21
HP is simple a mathematical calculation of your Torque at a certain rpm. If memory serves hp=(torque x rpm)/5252. So more torque at any given RPM will also give you more HP. The HP # for diesels do't go up as much with the added torque simply because the RPM # is much lower......it takes alot of torque to reach 300-400 hp at such a low rpm. The opposite of that is my cammed gasser track car. The cams didn't add a lot of torque, but it shifted the torque peak to much later in the RPM band. This resulted in a large increase in HP......and a vehicle that is not great off the line, but pulls very hard at higher RPMS.
My van has 235/85r16 with a c6+DNE2 OD and 3.54's. It does fine at 65-75mph on the highway and doesn't have an issue towing a trailer in the 6000-7000lbs range. Definitely not overly fast doing it, but it handles it fine.
For the best of both worlds you could add an aux O/D to your e4od and put in 4.10's or even 4.56's. You would have the gearing to get a heavy load moving as well as the number of gears to keep your rpm's lower at hwy speeds if you wanted to.....but for the $$ I would stick with the e4od/3.55s and add a turbo.
My van has 235/85r16 with a c6+DNE2 OD and 3.54's. It does fine at 65-75mph on the highway and doesn't have an issue towing a trailer in the 6000-7000lbs range. Definitely not overly fast doing it, but it handles it fine.
For the best of both worlds you could add an aux O/D to your e4od and put in 4.10's or even 4.56's. You would have the gearing to get a heavy load moving as well as the number of gears to keep your rpm's lower at hwy speeds if you wanted to.....but for the $$ I would stick with the e4od/3.55s and add a turbo.
Fleet Mechanic
Joined: Oct 2012
Posts: 1,943
Likes: 21
They are not manufactured anymore. I purchased mine used from a forum member.
The only aux overdrive that is still being manufactured as a bolt on unit is the Gear Vendors.......and they are very pricey new.
Postmaster
Joined: Dec 2011
Posts: 3,860
Likes: 7
I don't own one.
Gear Vendors also makes a bolt-on overdrive unit that bolts to the back of the trans or transfer case, and gives you an extra top gear(overdrive) on top of whatever gear you are in. So you can "split" gears.
Here's a nice chart with ratios: https://www.gearvendors.com/fdrive.html
Remember that a final drive ratio is "how many revolutions of the engine it takes to turn the wheels one revolution", so you can then take an RPM * 60, divide it by the final drive ratio, multiply by tire circumference(2 * pi * radiusOfTire) and divide by 12 to get into feet, by 5280 to get to miles.
so:
( RPM * 60 / finalDrive) * (2 * pi * r) / (5280 * 12)
2000 rpm, 2.43 final ratio(GVOD + ZF5 in OD), 15.85 radius tires(235 85 R16):
(2000 * 60 / 2.43) * (2 * 3.14159 * 15.85) / (5280*12) = 77.6 MPH
Plug it into a calculator and play with it if you want.
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