Rear End Change - Hot Rod Forum : Hotrodders Bulletin Board -- Hot Rod Forum

Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend
User Name
lost password?   |   register now

LinkBack Thread Tools
  #1 (permalink)  
Old 01-07-2004, 11:36 PM
black66's Avatar
Join Date: Apr 2003
Location: West Coast
Age: 46
Posts: 452
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Rear End Change

I have a 1966 Impala. The summer of 2003 I built a SBC with 530 HP. Motor runs great. But my rear end is keeping the car from getting to its true potential. I figures my rear end gear ratio with a ratio calculator. But I think I did it wrong. It said my rear gear where 3.73. But that was with the tall tires. So actually my gear should be a lower numeric number. So where in the 3.3's I am assuming......

I have 25 3/4 tall tires (235/18/50's all the way around) I am pushing 2900-3000 rpm at 70. Is there a way to find what my rear end gears are now from this info??

And I am setting my car up to be fast from light to light. The car gets up and goes now. But I want to put a posi unit with better axles in this summer and want to go with 3.73, 4.11, or something in that range. I am not really worried about getting on the freeway. So my main focus is be 1/8 - 1/4 mile quick....... Thanks so much......



Last edited by black66; 01-07-2004 at 11:41 PM.
Reply With Quote Quick reply to this message
Sponsored Links
  #2 (permalink)  
Old 01-08-2004, 05:49 AM
Registered User
Last wiki edit: Mopar tapered axle rear brake conversion
Last journal entry: What I'm doing now...
Last photo:
Join Date: Jan 2002
Posts: 4,267
Wiki Edits: 49

Thanks: 0
Thanked 8 Times in 7 Posts
The taller tires will have some effect on the final drive ratio but they're not going to change the gear ratio of your rear end.

To determine what gears you have, get the entire rear end off the ground and rotate the passengers side tire one complete turn. Count how many times the drive shaft rotates for one turn of the rear tire. For example if the drive shaft rotates 3 and a half times then your ratio is 3.50 if it rotates just a shade over 4 times then its probably a 4.11 etc. Besides actually having the factory tag on the rear indicating the ratio or opening it up and actually counting the teeth, this is the easiest way to figure your gear ratio.

Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 01-08-2004, 04:35 PM
black66's Avatar
Join Date: Apr 2003
Location: West Coast
Age: 46
Posts: 452
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts

I will try that tonight........thanks....
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 01-08-2004, 04:46 PM
poncho62's Avatar Moderator
Last wiki edit: Streetbeasts links
Last journal entry: at car show
Last photo:
Join Date: Oct 2003
Posts: 17,579
Wiki Edits: 5

Thanks: 40
Thanked 562 Times in 420 Posts
The richmond gear calculater shows

26 in tire

It says 3.32

You have 3.31 gears
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 01-28-2004, 09:21 AM
M&M CUSTOM's Avatar Moderator
Last wiki edit: Transmission identification
Last journal entry: 1988 Suburban, the project continues.
Last photo:
Join Date: Mar 2003
Location: Northwest Pennsylvania.
Age: 44
Posts: 2,236
Wiki Edits: 9

Thanks: 0
Thanked 2 Times in 1 Post
For a 235/50/18 tire at 70 MPH I get:

2858 RPM's with 3.31 gears
2953 RPM's with 3.42 gears
3065 RPM's with 3.55 gears
3220 RPM's with 3.73 gears
Reply With Quote Quick reply to this message

Recent Transmission - Rearend posts with photos
Gear in this thread - Powered by O'Reilly Auto Parts

Quick Reply

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Please select your insurance company (Optional)


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

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

All times are GMT -6. The time now is 02:51 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2016, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright 1999 - 2012. All Rights Reserved.