Question about selecting gear ratio - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

 14Likes
  • 5 Post By Alan F
  • 1 Post By Jim Mac
  • 2 Post By big gear head
  • 1 Post By Skier_Bob
  • 3 Post By Lew540
  • 1 Post By hydro462
  • 1 Post By Alan F
 
LinkBack Thread Tools Search this Thread Display Modes
post #1 of 12 (permalink) Old May 22nd, 20, 11:49 AM Thread Starter
Pete
 
Join Date: Sep 2015
Location: New England
Posts: 14
Question about selecting gear ratio

I am thinking about getting a 12 bolt to replace the 8.2" 10 bolt I have in my 68. Currently a 3.08 open diff.



I have a mild 396 with a TH400 with 26" wheel diameter and the car is slow from a stop. I have some money but no experience on doing an engine build but a rear end swap looks like something I can do quickly so I can still enjoy the car this summer.



I was thinking of purchasing a complete rear end and thinking about what gear ratio to select. I have seen all the comments on not putting short gears in cars due to noise and high RPM on the highway. Well I live in the country and have only taken the car on the highway once. I just want something fun to drive around back roads and is quick but not fast. Again not worried at what RPM I will cruise at going 65 MPH since I rarely go anywhere with a speed limit above 45. Just want something that will be fun from a dead stop.



I was thinking at least 3.73 or maybe 4.10 with a posi would be a good choice.
bladerunner is offline  
Sponsored Links
Advertisement
 
post #2 of 12 (permalink) Old May 22nd, 20, 12:03 PM
Gold Founding Member
 
Join Date: Aug 1998
Location: 30.1298228, -97.9771166
Posts: 6,732
Garage
Re: Question about selecting gear ratio

Based upon your intended use a 3.73:1 would be fun. 3.31 would be practical but not enough difference from 3.08 to notice. Iíd stay away from a 4.10 if you do any distance at a fixed highway speed.
blm, pannetron, Kirk's67SS and 2 others like this.

I donít like being manipulated!
Alan F is offline  
post #3 of 12 (permalink) Old May 22nd, 20, 12:40 PM
Senior Tech Team
 
Join Date: Dec 2004
Location: tucson az
Posts: 14,287
Send a message via AIM to Jim Mac
Re: Question about selecting gear ratio

I've got 3.55 in my 66, 3.31 in the 70. either gears are great around town gears. jim
Kirk's67SS likes this.

Jim

70 chevelle, SS clone 454 4 speed
71 camaro. (owned since 1978!) 6-71 blown small block 400
66 chevelle 350 4 speed 3.55 12 bolt
66 el camino 350 th350 parts hauler
Jim Mac is online now  
 
post #4 of 12 (permalink) Old May 22nd, 20, 1:14 PM
Senior Tech Team
Freddie
 
Join Date: Feb 2000
Location: Central City, Ky.
Posts: 9,450
Re: Question about selecting gear ratio

Play around with some of these calculators and see if it helps any. Wallace Racing - Automotive Calculators
pannetron and Kirk's67SS like this.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
big gear head is offline  
post #5 of 12 (permalink) Old May 22nd, 20, 10:35 PM
Lifetime Premium Member
 
Join Date: Jan 1999
Location: New Orleans, LA,USA
Posts: 1,357
Re: Question about selecting gear ratio

3.73! I have 4.10 rear. think about tire size to help. shorter tire will increase rpm too.... so see if 27" or larger would work for you.
pannetron likes this.
Skier_Bob is offline  
post #6 of 12 (permalink) Old May 23rd, 20, 3:45 AM
Lifetime Premium Member
Marcus
 
Join Date: Sep 2005
Location: Sweden
Posts: 6,260
Garage
Re: Question about selecting gear ratio

3.55 would be my choice.
Or if you plan lot of highway driving 3.31.
What ever ratio you decide get a Us gear set imho.

Chevelle Malibu ss 64
489 BB with parts from Lewis racing
Alumitech radiator with dual spals
Th 400 Edge 9.5" converter
57 3/4Ē wide 12 bolt: Eaton posi, Us gear 3.31, Toms KA 33 splines axles
Malibu ss 64 is offline  
post #7 of 12 (permalink) Old May 23rd, 20, 8:10 AM
Lifetime Premium Member
rick
 
Join Date: Jul 2012
Location: st. pete. , fla
Posts: 6,499
Garage
Re: Question about selecting gear ratio

I have a 3.73:1 posi in my 68, makes it fun around town but with 27" tall tires it's spinning about 3K rpm at around 65


To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.
shovelrick is online now  
post #8 of 12 (permalink) Old May 23rd, 20, 8:57 AM
Senior Tech Team
Lew
 
Join Date: Nov 2015
Location: Potomac, MD
Posts: 1,007
Garage
Re: Question about selecting gear ratio

Go with a 3.73 to start (drive it this summer) and then if you want more put a Gear Vendors Overdrive on and you will have a 2.90 final drive then. Nice thing about the Gear Vendor is you keep your trans in place it bolts to the back to the Turbo 400. It comes on/off electronically or if you want to do it manually then put a dimmer switch on the floor. If you have a 3.08 now, the GV OD (with 3.73 / 2.90 OD) will be similar except about 200 rpm lower at cruising 65 mph then you are now.
Kirk's67SS, bladerunner and flht01 like this.
Lew540 is online now  
post #9 of 12 (permalink) Old May 23rd, 20, 9:08 AM
Tech Team
 
Join Date: Jun 2018
Posts: 85
Garage
Re: Question about selecting gear ratio

A 4.10 will get you about 52 MPH at 3000 rpm, and 60 at 3500 rpm. This calculator is accurate for my car. RPM/MPH From Gear Ratio Calculator by Wallace Racing
aimhard is online now  
post #10 of 12 (permalink) Old May 23rd, 20, 9:08 AM
Senior Tech Team
Jeff
 
Join Date: Jun 2009
Location: Pittsburgh, Pa.
Posts: 2,705
Re: Question about selecting gear ratio

The higher numerically you go the less torque multiplication you'll get from the torque converter.. This is where a lot of people screw up on street builds... Keep the 3:08 and change cams to something with more dig, more off idle torque. Make sure you specify "off idle torque", when looking.. There's a guy that makes cams on here that was going to make one for my 454 with tremendous low end torque..

The standard rear end differential also makes for a smoother driving and turning car... Both back wheels propel the car with this rear end its just that once one side starts spinning the power flows to that wheel.. If you learn to control rear wheel spin and install adjustable rear control arms with Delrin bushings, this makes the standard rear end the best choice..
bladerunner likes this.

Last edited by hydro462; May 23rd, 20 at 9:26 AM.
hydro462 is offline  
post #11 of 12 (permalink) Old May 23rd, 20, 12:10 PM
Gold Founding Member
 
Join Date: Aug 1998
Location: 30.1298228, -97.9771166
Posts: 6,732
Garage
Re: Question about selecting gear ratio

Quote:
Originally Posted by hydro462 View Post
The higher numerically you go the less torque multiplication you'll get from the torque converter..
I think you might be referring to the change of rear gear to effect the stall speed of a torque converter, wherein stall speed would be lowered and the engine speed would be making less torque, however negligible, at the new stall speed. If not, would you mind elaborating on this? Thank you.

Otherwise itís generally acknowledged that a higher numerical rear end ratio increases torque to the wheels. The biggest takeaway is that a change in rear gear ratio will have an effect on torque converter stall speed.
bladerunner likes this.

I donít like being manipulated!
Alan F is offline  
post #12 of 12 (permalink) Old May 23rd, 20, 1:26 PM Thread Starter
Pete
 
Join Date: Sep 2015
Location: New England
Posts: 14
Re: Question about selecting gear ratio

Quote:
Originally Posted by Lew540 View Post
Go with a 3.73 to start (drive it this summer) and then if you want more put a Gear Vendors Overdrive on and you will have a 2.90 final drive then. Nice thing about the Gear Vendor is you keep your trans in place it bolts to the back to the Turbo 400. It comes on/off electronically or if you want to do it manually then put a dimmer switch on the floor. If you have a 3.08 now, the GV OD (with 3.73 / 2.90 OD) will be similar except about 200 rpm lower at cruising 65 mph then you are now.

I was reading about a Gear Vendors OD and I think it would be a great option.



Thanks for the advice everyone. I am definitely leaning towards 3.73
bladerunner is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Chevelle Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address. Note, you will be sent a confirmation request to this address.

Email Address:
OR

Log-in










Thread Tools Search this Thread
Show Printable Version Show Printable Version
Email this Page Email this Page
Search this Thread:

Advanced Search
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome