Re: [Amc-list] T-5 OD gear

[adh@xxxxxxxxxxxxxxxxx (Sandwich Maker)]

" From: farna@xxxxxxx
" 
" The 0.62 OD gear is probably going to be a bit tall with a 3.55
" axle. I have a 0.70 OD (early AW4) and cruise at 76 mph @ 2400
" rpm. With a 0.62 OD my car would be running 85.6 mph at the same
" rpm, 71.3 @ 2000 rpm. You need to cruise above 1800, preferably
" around 2000, with the 4.0L for best efficiency. 2500+ rpm will
" cause the computer to enrichen the mixture enough that you'll
" notice the mileage difference -- found that out on my 93 Cherokee
" years ago. My Renix engine acts the same. That's why I geared and
" adjusted tire size to cruise around 75 @ 2400 rpm. I generally
" cruise at 70 (2200 rpm). I'm running 205/70R15 tires, yours may
" be smaller. A 205/70R14, for example, would run 82 mph @ 2400 rpm
" w/3.55 gears/0.62 OD, 69 mph @ 2000. That might be better. Just
" means you'll only use fifth on the interstate (or similar
" highways).

this points up camming differences.  the original mustang pulled that
0.62 5th with iirc a 2.73 axle, but that was the factory setup from
the start, and the engine must obviously have been set up for it.

cherokees with the 4.0 and auto are geared 3.55.  the smallest tires
they run are 215/75r15s, with 225s and 235s more common.  4th isn't
usable at all below about 50 and not of much use until you get over
60.  65 is about 2200-2300 and that's comfortable.

cherokees with the 4.0 and stick are geared 3.07, and that's widely
considered to be tall gearing for them.

iirc the stock 4.0 cam has something like 270* duration.  if you swap
it for something oriented for lower-rpm operation - like a 2bbl 258
cam with 257*, or a '60s-'70s 232 cam with 244* - you can efficiently
pull all sorts of tall gears.
________________________________________________________________________
Andrew Hay                                  the genius nature
internet rambler                            is to see what all have seen
adh@xxxxxxxxxxxxxxxxx                       and think what none thought
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