Re: AMC 4-cylinder in a Spirit (Revisited)

[Amcjrb@xxxxxxx]

There is another reason why a Jeep or truck with a 4 cylinder engine would use different gears than an amc Spirit.  It the size of the rear tire.  As the rear tire size increases (in diameter and therefore circumference) the effective gear ratio drops numerically.  If you think in terms of engine RPM per mile per hour , a Spirit with 205 70 R 14's and 3.54's is on par with a Jeep with 235-70-R15's and 4.10's. In any case, the trend is to keep the rpms per mile per hour the same, as the tire diamter increases, you need lower (higher numerical) gears.  Thats why when you run your 35: super swampers you need 4.55 gears.
Jim Bolton   

On September 27, 2005 Tom Bunsey wrote:

> Frank & Company:
> 
> Please pay attention to my entire post, AND to the original question concerning gearing.
> 
> (1) I don't argue that the 4-cylinder in a TRUCK would have 4.10 gearing.
> 
> (2) But he doesn't want to put the engine in a truck; he wants to put the engine in a CAR. FOR GAS MILEAGE!!!!
> 
> We aren't talking TRUCK gearing; he wants to know what PASSENGER CAR gearing to use. We're not talking about load hauling a ton of wood or whatever in a pickup TRUCK, we're talking about a passenger car rated at about max 700 pound payload (see owner's manual for details).
> 
> What I am saying is that when AMC used a similar sized engine in a Spirit, these were the rear end ratios they used.
> 
> Historically, trucks use deeper rear end gearing than the same engine in a passenger car. You know this, I know this.
> 
> The guy raising the issue wants to put this engine in a passenger car. He isn't going to haul firewood, or plow his driveway, or go off road with it. He is going to drive the car on the highway!
> 
> As I recall, the 1982 Spirit with the IRON PUKE and the 5-speed was rated at 37 mpg, highway. With a 3.08 gear. And a .85 5th gear (overdrive).
> 
> THIS IS WHAT IS WANTED. Mileage!
> 
> NOT pulling Jeeps out of ditches!
> 
> Tom Bunsey
> 
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