Gear Selection

-
321Scamp

321Scamp

Well-Known Member
Joined
Jun 14, 2006
Messages
464
Reaction score
14
Location
Indiana
I need help picking a gear. The two I am looking at is the 3.21 and the 3.55. the car will acationaly see the highway, so I don't know if 3.55's will be to high for my 318 3 speed. What is anybody else running? I have 2.45's now.
 
I have a 318 4spd and run 3.91s. I'm looking for some low 3s myself for highway. Those 2.45s must be great for top end. Mike
 
If you are going to see a lot of highway and run 14" wheels I would run the 3.21's.


Chuck
 
The only really long highway trip it would see would be 200 miles once a year for the Nats. Most of the time it will be 55-60 cruising.
 
Just got my Mopar 8 1/4 Sure-Grip shipped to the house from Summit for $280.95. Their price $309.95 before shipping, I had them price match.

I talked to a friend of mine that said that the 3.55's is a good all around gear.
 
321Scamp said:
The only really long highway trip it would see would be 200 miles once a year for the Nats. Most of the time it will be 55-60 cruising.
Click to expand...

This very helpful in determining RPM at any given speed.


336 X MPH X GEAR YOU WANT / TIRE SIZE = RPM

EXAMPLE:

336 X 60 X 3.55 / 28 TIRE SIZE = 2556RPM

The slash is divide.
 
Good post mullinax95. I have 3.21's now with the stock tire height. The revs are not to bad, but, driving 70+ for any big distance could prove to be a bummer.
 
rumblefish360 said:
Good post mullinax95. I have 3.21's now with the stock tire height. The revs are not to bad, but, driving 70+ for any big distance could prove to be a bummer.
Click to expand...

Well thank you sir!

I found this on DodgeTalk.com because I have a Dodge Ram.

I did the math for my truck and I checked it going down the road just to see if it was close and dang it was smack right on the RPM that it equaled.

What my question is what does 336 have to with anything?

Square root maybe?
 
The difference in performance between the 3.21's and the 3.55's is very minimal. But the differnence in wear and fuel can be quite a bit over time because of the added RPM.

Chuck
 
Using the formula in my application at 70 MPH...

3.55's = 3265 RPM

3.21's = 2953 RPM

current 2.45's = 2254 RPM
 
Now, what gear fits the cruise RPM range of the cam and are you willing to deal/live with it?
 
321Scamp said:
Using the formula in my application at 70 MPH...

3.55's = 3265 RPM

3.21's = 2953 RPM

current 2.45's = 2254 RPM
Click to expand...

I'm guessing you have a 25.5, 26 to 26.5 overall tire diameter with the numbers you are showing. I checked only your 3.55 RPM. Are you sure you have the correct tire measurement?
 
i have 3.23's and a 26" tall tire I turn 3200 at 70 3400 at 75
 
"Torque converter slipage" is also a factor.
 
I have decided to go with the 3.55's. After doing some comparative research, it will be fine. My dads all original '70 T/A has a 4 speed with 3.91's and G-60 tires which is about 26". So at 60 his car is running about 3100 RPM. My car at 70 will be at 3200 RPM with the 3.55's. He also had a '69 Dart that had a 340 3 speed A/T with 4.11's and F-60's or about 24", 60 MPH = 3400 RPM. He ran his on the interstate a lot back then.
 
hey, let me know if you bought the 3.55 gears. I picked some Richmond Gear 3.55 gears for mine but decided to stay with the 3.21 gears i have already. The gears have less than 800 miles and a good wear pattern. Shoot me an offer
 
You must log in or register to reply here.
-

Back
Top