All: Most folks here state 3.42 is the most gear I should want for the street. However, I am going to put an OD transmission in my little Apollo (with sbb). I really would like to go 3.73 given I have the OD planned. I put 3.73 gears in my Fox Mustang this spring and have really enjoyed driving it to work everyday. I have had no problems with that application. I imagine both cars (Fox Mustang and Apollo) are of similar weight with similar RPM redlines (5800 RPM) I need to get my payment in the mail this week so I thought I would query the group one last time. 3.42 or 3.73?
For an OD, 3.73's are perfect. The 2004R has a .67 OD, that's a 2.50 final drive, 2000 RPM at 60 MPH. You can always fine tune with tire size as well. Putting a 28" tire out back brings the effective gearing to 3.54 and 2.37 in OD. I have the Gear Vendors OD and it is .78, 3.73's with a 28" tire (3.54), 60 MPH is 2200 RPM.
Larry: Moons ago when the motor was built, I started talking convertors (COAN was recommended). I remember filling out a questionnaire for the convertor guy which requested tire size and gear ratio. Given there are a number of variables I need to consider collectively, which do I choose first? Gear, tire, or convertor? My Apollo will likely have a shorter tire than your GS. Given the tire selection limitations on 14 inch rims, I wonder I if I have to choose the rim/tire first, and then back into gears? Or will the trans guy solve all of this for me with the convertor choice?
The converter guy will want to know as much as you can tell him about the car. The OD and tire size is just part of that. You can figure out the final drive easily once you know all the specifics. Typical tire size for the Apollo was FR78-14. That tire is 26.30" tall. So lets say you go to a 28" tire with the 3.73's. To figure out what the tire size does to the gears, just divide stock tire height/ new tire height, 26.30/28 and multiply that by the gears, 3.73. You get 3.50. BTW, noone says you have to stick with 14" tires, in fact I wouldn't, I'd go to 15" for more available tire sizes.
I put in 3.42 before I knew I was using the OD transmission. I ordered the converter from JW with the OD trans and 3.42. Is there going to be a problem if I switch to 3,73 ?
No not a problem it will be good on fuel if you have a strong enough engine to pull it along at low RPMs. My old 70 Skylark that I sold has a 3.42 gear, 2004R trans, and a Twin turbocharged Buick 350 and it ran super low RPM and still ran low 11s at the track on street tires. It cruises on the highway at 100-140 MPH no problem.
Consider that ALL: of the 84-87 Turbo Regals had 3.42 gears with the 200-4R trans with 215/65R15 tires (close enough to use 235/60R15's with virtually no speedometer error)
If you are not using a lockup converter then I vote you stay 3.42. If you do use a lockup converter then go 3.73. I actually went 3.90 in my car because I always thought it sounded cool
my 71 has a th400 with no overdrive and 275-15 tires and 3.73's, I drive it 100 miles to the track and back all the time with no problem..its about 3200 rpm at cruise speed (70-75 mph) and I've totally gotten used to it. Both my 65 and 73 cars have 3.42's, and truthfully, the difference between those and the 71 on the highway is not that huge....if youre going to run better than a 235 tire, I'd vote for 3.73's - if not, 3.42's...
