If you change the gears to 4.10s or 4.56s, since you gain acceleration, what do you loose?

 

Fuel economy. Maybe engine longevity (if you believe an engine has just so many revolutions in its life).

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99, XL, SC, SB, auto, 4.6L, 255x70R16, 3.55LS, 2wd, Med Tor, Dk Grph, Raider LoRider Tonneau, Valley class III hitch, bed mat.
Computer Code YBQ3
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[This message has been edited by Tiger (edited 05-02-2000).]

 

Without any other parameters as benchmarks, it's a toughie to properly answer, but here goes the broad brush.

If you're planning on towing, you give up some speed in each gear. That might not be a problem, depending on where you need the power -- for example, if you're now pulling a grade at 3000 rpm in second gear, you may find that you now have enough torque to maintain that speed in third.

The obvious thing that you lose is rpm at cruise. The less obvious is that you may even be able to go faster (top end) if the reason for your speed limitation now is running out of hp -- not running out of rpm.

If you're running a Lightning or other quick-revving engine, your quarter mile times can actually be hurt if your engine can't spin up fast enough -- due to high inertia of the flywheel/torque converter -- spending too much hp spinning up the flywheel and not moving the vehicle.

In Overdrive vehicles, where the .7 or so OD permits such a dramatic lowering of the engine rpm at cruise, radical gear ratios -- even over 5:1 are bearable on the highway.

You also give up some strength in your axles because you can add more torque to them with the new ratio.

On the plus side, spinning your engine faster means smaller power pulses for a given speed -- which means less torque demand on the front-side of the axle -- namely the transmission and drive shaft.

Higher numerical ratios also mean smaller pinion gearing, which means less life of the pinion gear -- due to both the reduced size and the increased sliding of higher ratio hypoid gearing.

What is your present situation, and what would you like to end up with?

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Y2K™

XLT SC SB 5.4L 3.73LS

 

I currently have 3.73s in my F-150. I am thnking of changing the gears to 4.10s or 4.56s to make my truck accelerate faster. But other people said you couldn't go as fast.

 

Don't confuse "fast" with "quick." In general, numerically higher gears make the truck quicker, it accelerates harder and will haul or tow more weight. You lose speed in every gear and carry more RPM at cruising speed. You may or may not lose fuel economy, depending on driving habits, usage, tire size and what the original and new ratios were.

In general, a change of one ratio, such as 3.73 to 4.10, probably isn't worth the time or money involved. Going to the 4.56s will give you a very noticable gain in acceleration, but you will be pulling 22% more revs at all speeds. Unless you're planning on running tall tires to compensate, that may be more change than you really want. Most people think of 3.73s as a performance ratio.

 

I agree with that StrangeRanger.

I had the 3.55 with P255's on my last F150 -- was ok, but left me wishing for more.

Got the 3.73 on my Y2K, however the tire size is LT245 -- around 4% bigger than the last truck -- and with the 3.73 some 5% slower, the net is around 1% change overall -- not enough to make any difference (cannot even spin the tires from a WOT Braketorque launch -- perhaps it's the superb traction of those Goodyear RT/S that everyone is raving about - not).

My Ranger has 3.73 in it -- but there's a BIG difference between the two trucks -- due to the little one's P225r15 tires.

Bottom line -- figure out what you want your cruise speed RPM to be -- and go with the axle ratio to get you there.

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Y2K™

XLT SC SB 5.4L 3.73LS