Posted by J.R.
on 9/21/2012, 3:40:52, in reply to "Re: FC-150 Highway driving"
71.9.65.20
Good info re. overdrives, in general, and specifically for Jeeps can be found at http://hermtheoverdriveguy.com/
Having used overdrives & auxiliary transmissions on lots of different stock & modified vehicles, I have to agree with the main substance of Jesse's commentary, but if you're aware of what RPM range your engine delivers its best torque at, and shift accordingly, you can see some definite improvements in versatility and possibly also in highway cruising speeds. However, an OD alone is NOT going to instantly create a comfortable 70mph freeway cruiser with the stock engine. Now if you install a Warn overdrive, AND turbocharge / intercool your F134... it just might take on a revised over-the-road personality. If you do... please post pictures! 
BTW the Borg-Warner (30%) overdrive from a T86 transmission requires some adapter pieces to fit it up to the rear output of a Dana 18 transfer case. Once fitted it would be used in 2WD, in the forward speeds only, and could sometimes be helpful for 'splitting gears' in highway driving, as well as obviously giving the rear axle the 'feel' of a 3.77 ratio in 3rd gear/overdrive. Again one would need to have a good grasp on the engine's torque curve to use the available gear ratios to best success. Cable lockout & electric solenoid wiring are easy to route.
One caveat on the B-W overdrive, out of concern for uneven & sudden torque loading on the Model 18 transfer case, I won't use the under-the-accelerator downshift/overdrive-disengage switch on my FC170's installation. Behind a high torque engine, that sucker sure slams the drivetrain hard when it kicks into direct gear at W.O.T., even in a 2WD passenger vehicle & even at very high road speeds. Conservative no doubt, but IMO a simple hand push button switch for the B-W overdrive unit should make it easier to keep it together longer. That may or may not be a valid concern with a stock F134-powered FC150(?).
J.R.
SoCal
--Previous Message--
: I 'm not going to burst your bubble, but 50
: mph in an FC-150?
: I am all for OD units, in any vehicle, they
: reduce the heat and wear and tear of the
: engines, when driven at the moderate design
: of the working rpm curve, of the engine
: torque range. The OD may also add more life
: to the existing gears if they are in good to
: new condition when the unit is installed.
: They are also considered to be a if you can
: believe, a benefit in mileage, if you plan
: to drive the vehicle for a few hundred
: thousand miles, you may save enough to pay
: for the OD conversion in an FC. However if
: you are going the same distance quicker by
: going faster, then the RPM / torque lag, may
: make for worse mileage.
: If your expectations are that you think that
: spending an extra grand will allow you to be
: able to go faster in an FC-150, more than 50
: mph, or if you expect to be able to maintain
: HWY speeds of the other traffic, with an OD,
: (I have owned a few of these), it is not
: going to happen, you may get a few more mph
: on flat ground or down hills, but not that
: much more, because the improvement is best
: at 35-45 mph when your rpm will be at it's
: peak, so an OD that makes 25% less rpm, does
: reduce the engine rpm speed but does not
: increase the speed by 25%. At top end you
: are already wound out way past the rpm
: torque curve, because at the higher rpm with
: higher OD gears, you will run out of torque,
: imagine the traffic slows to 45 mph then it
: immediately builds back up to 70 mph, you
: will get run over. The OD gears are
: multiplying the rpm of the driveline and
: quickly dividing the torque that the engine
: has to work with.
: What this means is you can coast and
: accelerate to top speed to go faster mph
: down a hill, faster at 25% more rpm speed,
: but you will also slow down the rpm speed by
: 25% quicker with any incline, because an OD
: will not increase the engine torque to match
: the mph. Sure you can switch out of OD to
: get the torque back, but do not attempt this
: unless the vehicle behind you is 10 car
: lengths back, and you installed and turned
: on the emergency flashers on. it would be
: sort of like pulling a parachute. (have your
: speedometer checked)
: A repowered FC that has an engine that
: develops more than twice to three times the
: amount of torque compared to that of the
: original engine can have a much better
: benefit from an OD.
: The ugly truth is that any FC is going to be
: able to do as good as it can, with or
: without an OD unit, but the faster it moves
: in speed, the more it is fighting to
: displace the air in front of it. FCs are not
: very streamlined, the faster you make an FC
: move against the air or wind, the more
: output or torque is needed.
: So as far as OD units, they are all good,
: they have benefits, but doing the math of
: how fast a 3500 pound flat nosed FC travels
: against a self generated wind load, is going
: to be different from how fast a 2700 pound
: flat fender Willys moves.
: The clue should be that the shifters are not
: easily found or sold for FCs.
: Jesse Ybarra
:
: --Previous Message--
: I have a borg warner overdive on a T-86
: transmission i'll sell. If you want it email
: me at dirtboy170@ yahoo.com and i'll send
: you pictures.
:
: --Previous Message--
: Hi all, Anybody have any ideas on how I can
: get a higher gear to run my 3 speed FC down
: the road. I know Walck's carries an
: overdrive unit that attaches to your
: transfer case for over $1,000.00 but the
: units linkage and shifter has to be
: remodified to fit in an FC. How about using
: a 2 speed rear? I can get the rig up to 50
: mph now but the rpm's are way up there. I
: don't want to blow out the 4 cyl. engine.
: Gary.
:
:
:
:
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