Recommend diff ratios - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
LinkBack Thread Tools Display Modes
post #1 of 2 (permalink) Old 01-05-08, 10:44 PM Thread Starter
Registered User
Join Date: Dec 2007
Posts: 6
Recommend diff ratios

Hi iv got a xc falcon with a 400hp 351 and 4 speed wide ratio toploader. Its currently got a 2.75 ratio which is way to tall. I'm wondering if any one can recommend a diff ratio that would be better suited. I only use it on weekends but I dont want it to be to drag like.

peeds13 is offline  
Sponsored Links
post #2 of 2 (permalink) Old 02-04-08, 10:27 AM
Registered User
Join Date: Feb 2008
Posts: 2
Re: Recommend diff ratios

I'm guessing you want to be around 3.54 a balance between off the line and top speed. I wouldn't recommend anything lower unless you plan on driving in a straight line or you completly updated the suspension.

Use this formula to figure out were you want to be

Maximum MPH in each gear:

Formula: MPH = rpm x tire diameter (in) / gear x final gear ratio (diff) x 336
Example: Maximum mph in 280Z 5spd 1st gear using 6500rpm redline.
MPH = 6500rpm x 24.0"(tire dia.)/ 3.321(1st gear) x 3.54(diff gear) x 336 = 39.5mph
Note: Top gear is most likely hp limited, and would not be able to reach max rpm.

RPM @ 65mph (Derived from Max MPH formula):

Formula: RPM = mph x gear x final ratio x 336/tire diameter
Example: RPM at 65mph for stock 280Z 5spd
65mph x 0.864(5th gear) x 3.54(diff gear) x 336/24.0"(tire dia.) = 2783 rpm
bxf250 is offline  
Sponsored Links

  Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > The Garage - Tech Forums > Trans | Driveline

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may not post new threads
You may not 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