I'm running 308 rear with T10 tranny (don't know ratio) and she will cruise 70 to 80 all day long. :anim_25:
:gba:
bowtie-trifive

 

Changing from a 3.36 to a 3.08 will drop your RPM at 62 MPH from 2567 RPM to 2353 RPM assuming a 28" tire. ....http://www.ringpinion.com/Calculators/Calc_RPM.aspx If your are actually taching more than that, the torque converter or transmission may be slipping excessively.
Changing to a 700R4 will drop the RPM at 62 to 1750 RPM with the 3.36.

 

Very good info here, and thank you for this link. I just measured the rear tires at 25" (235/60/15) and using the 62 mph (which is a "guess-timate" because the speedo is not 100% accurate), I get an rpm of 2875. With an AOD that rpm would be 1960 or 2230 at 70 mph. Right where I want to be.

I also liked bigblock261's comment about the spread between 1st & 2nd being more friendly to a smaller engine. Not sure why, but 200R4's are hard to find and not very well-liked in our area. I have spoken with several self-proclaimed transmission gurus about the 200 as a lower cost alternative to the 700 and none of them have much good to say about the 200. Any idea why? It seems that many folks here at Tri-Five have and like the 200.

 

Small motor, tall gear.

The 283 is a fine motor, but a bit low on torque for a 3.08 rear gear. The cruise rpm will be lower, but I think the car will be somewhat anemic in all three gears.

As you have stated, you need overdrive. TH 700-R4, or TH 200-4R if you want to keep your present driveshaft and save a few bucks. With the 200, your transmission crossmember will have to be moved back a bit. The ratio spread between low and second gear is friendlier to a smaller motor with the 200.

Just my humble opinion.

 

Wouldn't aerodynamics/weight play a role in this calculation? With a 26" tall tire then you're a little closer to the 3000rpm mark, about 2700 or so. I would save up and go with the 700r4, but until then if your 283 is healthy it should cruise at 3000-3200 all day long.

 

Wouldn't aerodynamics/weight play a role in this calculation?

Weight and aerodynamics has nothing to do with the nymber of revolutions the engine makes when the tire goes around once. They are directly coupled together with a manual transmission and the calculator allows for some slippage of an automatic torque converter.

 

Keep saving for the overdrive! I've been saving for a manual 5 or 6 speed for a while but I know it will be worth the wait in the end.

 

I say put a 200R4 in it.

Change rear gears may be cheaper but so much better to go with the OD. Save up and you will be much happier in the long run.

 

Our `56 wagon has a 283, TH350 and 3:36 gears. Most of the driving we get to do with this car is around twon, so that set-up works fine. But, if I want to go out of town to an event, show, cruise etc, then I am running 3000 rpm to maintain 62 mph. Because of my limited "top speed" I hate to drive any of the freeways. I have wanted to drop in a 700R4 for several years, but frankly, I can't afford that kind of dough right now. Someone suggested to me that I might want to change gears to 3:08 or even higher. This would certainly be more financially do-able, but what would I gain and what would I lose?

I have an original 56 convertible with 265 P/P and P/G trans. I swapped out the 3.55 rear for a 3.08 and gained 10 MPH @ 60, Not sure of the RPM but it made it safer to run at highway speed without really winding the engine up.
I also have a 355, 700R and 3.36 gears in my 55 wagon and it also works great. Obviously the O.D. trans would reduce your RPM more but either will work for you. :anim_25:

 

255/70 15 rear tires would be low cost alternative also or something similar taller than 25 inch rear tire.

 

The 3.08 gears are the answer as long as you're not a red-light bandit . You'll cruise @ way lower
RPM's , probably about 2500 @ 62 mph , and save a ton of fuel . The overdrive trans would be a great option for a next expense though ; then you could stick your 3.30 gearset back in . Bob

 

Dollar for dollar , you could make your own overdrive setup with a pair of 235-75R15 rear tires , a much larger circumference (taller) tire , if you didn't mind the rake . I really can't see a 283 doing much damage to a 200R trans . They're not popular with the big-motor guys because they have much smaller clutches , and won't take the abuse , but GM built them and they're not junk . You could probably find a trans kit for one if you did the homework too . Good luck and have fun . Bob