[DeTomaso] Final Drive Gear Question

John Buckman jb841 at cox.net
Sun Jun 24 13:36:01 EDT 2012


Shaun,

One of the shift shafts needs to be machined to clear the larger diameter of the .620 5th gear.  This is the highest 5th gear that is available for the dash 2 ZF.  I don't know if the machining is required for the other two 5th gears 
( .642 and .655 ).

With the stock 4.22 R&P and a stock .704 5th gear, *true* (not indicated) rpm would be 2650 at 70 mph.  This is 
with a 26.6" tire diameter.

With a stock 4.22 R&P and a .620 5th gear, rpm would be 2325 at 70 mph, a drop of 325 rpm.  This will make the 
cabin a little quieter.

Cost to have Lloyd install the .620 5th gear is around $2200, which includes the gear set, the machining, gaskets, 
and labor.

As we all know, gas mileage varies from car-to-car and from driver-to-driver, but with the .620 5th gear, you
should increase highway mileage by 1 or 2 mpg while cruising at 70-80 mph. 

With the stock cam and the .620 5th gear, performance (in 5th gear) is slightly less at low rpm's (which is to be 
expected).

Top speed at 6,000 rpm would increase from 160 mph to 181 mph, assuming your engine could overcome the 
additional drag.

John 


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