nfury8 wrote:With a 235/75-15 tire and a 3.55 gear, you should be at about 2900 rpm when going 70 mph.
3.23 gears would drop you to about 2630 rpm.
A .74 OD and 3.55 would change that to about 2140 rpm.
OD and 4.10 would be 2470 rpm. This seems like the best of all worlds.
Good RPM range and the low gear grunt of 4.10's.
I tend to agree with the above, if your going to leave the 435 (or use any 1 to 1 output trans) I would
be looking at 3.23 rear gears, it gets you close to mid power band. Yes, you will loose some pulling
power but should be very useable still. Otherwise leave the 3.55 and well enough alone....
If you still think OD might be the choice......
Over drive gear set will depend on what gear set the trans uses on the OD application. The gear
below OD will still be 1 to 1 and give you the 'grunt' power when needed. Using above, the 4.10, or 3.90
set would be about as good as it gets....... go to low with the rear gear set and frist
gear may be come un-useable as anything other than granny on a 5 speed OD trans,
however, that may not be such a bad thing in a truck.....
play with the numbers and make a good choice for your use......
everything is a trade off....
I use the 3.55 in my 68 with a 838 727 p235R15-75, it had 2.91 set in it when it came to me, fine on the
open road @70 plus, but sucked fuel around town which is were it gets most of it's use (engine worked too
hard at lower rpms around town in 3rd and I end up running it in 2nd a lot). If I were to take it
to the track a lot I would be droping the gears at least one step to 3.90 or 4.10 since the engine will turn 6000rpm at the top. If I did more Highway driving I would be looking at a 3.23.
I entend to keep my 66 truck as is with it's 3.55 with the 10-31's set since it gets used to haul often but sometimes
gets on the open road with a load and is overall the best for my use....
BTY, years ago I had a 75 Ply Volary 225 1b 833OD 225r14-70 with 3.55, even with a full load in the car, GF and her
2 kids with gear, it would get 26mpg @ 70 on the open road......were I'm headed with my Scamp(without GF included