3.55:1 ring and pinion

[Get Down]

I have a 1949 3100 with a 1962 235 3 speed on the colum and original rear. I'm considering a 3.55:1 ring and pinion. I've read that I'd be able to cruise 70 mph on the highway all day long. Has anybody done this? I'm curious if it was well worth the purchase and if your happy. Also any pros and cons on changing out the gears. Thank you in advance for any replies.

[mr48chev]

70 might be pushing the limits a tad but you could go to a calculator like this one http://www.ringpinion.com/Calculators/Calc_RPM.aspx and figure out what difference between the current 4.11 gears and the 3.55 gears you could expect . Meaning if you know what rpm your truck comfortably cruises at say 55 now you can figure out what speed the 3.55 gears would be at the same rpm.

Every vehicle has it's "sweet spot" in the rpm range where the engine seems to purr along and at the same time give the best fuel mileage. I found that out on my OT rig last summer on a trip to Texas. Even on the 80 mph speed limits in some states my car was a lot happier at 75/76 as gas mileage dropped 5mpg at 80 over what it was at 75.

[OrrieG]

Use a calculator like this:

http://www.coastdriveline.com/htmlfo...lculator2.html

to determine speed and rpm for different ratios and tire diameter. I do not know if it has a factor for wind resistance, but it will get you close. I could not quickly find it but one of the landspeed sites has one where you can put it drag coefficient, hp and hp loss to drive train components for more accuracy.

Here is a graph that show hp for various stovebolt 6 engines. It is not shown but maximum torque on a 235 is at about 1800 -2000 rpm.

[Speedbumpauto]

Not to change direction, but I thought the 49 had a torque tube. I don't see the 62 engine/trans fitting the "original" rear end without lots of work. I may be wrong but the rear may need to be verified before ordering parts. Just sayin.......

[Get Down]

Thank you guys for the info I will use the calculator to see what I come up with. I was hoping somebody made the change and could speak directly on the difference. I guess there are more factors to consider like tire size speed and rpm. Reading a few different articles I though this was the cats meow while maintaining the original drive train.

As far as the 62 235 being in a 49 I believe the 62 was bolted up to the original trans and rear. That's how it appears to me.

[T Hilde]

My '49 has a 267 sbc with a 3.55 rear and 70 mph is easy to do. I have 28" tall tires and it's about 2400 rpm(although it's a cheap tach).

Speedbump, I did see a 250ci 6 hooked to a torque tube 3 speed. The bell housing was a rare 2 year production run as I remember.

[Get Down]

Patrick's has a good article refrencing my 62 235 in my stock 49

http://www.patricksantiquecars.com/articles.html

[wolffcub]

What is your tire size?

[Get Down]

Wolffcub I'm considering running 235/75r 15's

[curmudgeon]

Plug in your ratios and tire size into these calculators to help determine the set up that works best for you:

http://www.miata.net/garage/tirecalc.html

http://tri-5.chevyrides.com/rpm.php

A 235/75-15 is 28.9" in diameter, with a 3.55 rear, 1.00 ratio in 3rd will have the engine spinning at just under 3000 rpm at 70 mph. I live in Northern California, which requires one to be always on the the highway, where 70 mph is the slow lane for me. My set up is similar, a '62 261 engine, slightly more torque and with 28" tires but a 3.08 rear and also a top ratio of 1.00 puts the engine at around 2600 rpm at 70, a good cruising rpm with a little extra for passing. If you plan a lot of highway time, a trans swap with overdrive is the way to go.

[Highsider]

My 235/75-15 rears are closer to an even 28" plus a little more.

[Get Down]

Curmudgeon thank you for sharing your set up, food for thought for sure. This is why I'm trying to see first hand if it would be worth changing the gears. My truck is more a just around town truck or a nice Sunday cruise kinda truck. But I would like the option of jumping onto the interstate and crusing at highway speeds and keeping up with traffic.

[curmudgeon]

For your intended purpose, a 3.55 rear with a stock 3-speed Saginaw should be OK and a worthwhile upgrade. The original rear is 4.11 x 2.95 stock trans 1st gear = 12.1 off the line ratio. A 3.55 x 2.95 = 10.4 ratio, still low enough to take off but don't plan on hauling heavy loads. By comparison, I'm using a 3-groove Saginaw 4 sp, 3.11 (1st gear) x 3.08 rear = 9.6 take off ratio, a little clutch slipping to get started on a hill, but good spacing for the majority highway driving I do. Patrick's recommends the 3-groove Saginaw with 3.55 rears, but that's with the stock, larger diameter tires than I use (I'm running 225/70-15's all around).

[wolffcub]

Im using a t5 with a 3.23 rear and 235/60r15 rubber. In 4th (1-1 ratio) you can compare your 3 speed to it. I can do 62.5 mph at 2600 rpm in 4th and 5th drops me down to 2000 rpm at 62.5 mph. Truck still climbs in 5th but nothing to be crazy about, a quick shift to 4th on the highway get me passing cars with ease.

I used these calcs to help me out.

This one i like as you can see two options at the same time

http://www.teammfactory.com/gear-calculator

click on the axle pic on this link and download the excel file. Its a great tool for also seeing options. I have the newer file for this one from the creator on my pc and can email it directly to you if you want.

http://www.12bolt.com/gearing_calculator

Never trust the tire diameters that are posted in the auto generator of any calculator. they are not the same in real life as the tire width vs aspect ratio equation. Mine actually come in at 24.75" when the calc shows 25.66"

This is my setup currently.