Fordmods Logo

diffs - please explain! 

 

Page 1 of 1 [ 9 posts ] 

 
 Post subject: diffs - please explain!
Posted: Mon Jan 22, 2007 5:52 pm 
Getting Side Ways
Offline
User avatar

Age: 39

Posts: 1442

Joined: 26th Apr 2006

Gallery: 6 images

Ride: 97 EL XR6

Power: 162 rwkw

Location: liverpool
NSW, Australia

ok, from what i thought, the higher the diff ratio the quicker you get thru your gears, but top speed is lower.

ive got a manual with 3.45 gears and a big cam, so im lacking a little down low, if i wanted to get a quicker 1/4, id assume that a set of 3.9's, or 4.11s, would get me there quiker.

now ive heard some people on here swear by lower gears, and some on higher gears.

how would a set of 4.11's slow you down on a 1/4 mile?

 

_________________

07 BF MKII XR6T
310rwkw @ 13psi - Tuned By CMS

Top
 Profile  
 
 
 Post subject: Re: diffs - please explain!
Posted: Mon Jan 22, 2007 5:58 pm 
Tyre Shredder
Offline
User avatar

Age: 46

Posts: 378

Joined: 3rd Dec 2004

Ride: EB V8

Location: Blue Mountains
NSW, Australia

FAST-XR wrote:
ok, from what i thought, the higher the diff ratio the quicker you get thru your gears, but top speed is lower.

ive got a manual with 3.45 gears and a big cam, so im lacking a little down low, if i wanted to get a quicker 1/4, id assume that a set of 3.9's, or 4.11s, would get me there quiker.


In a word, Yes.

 

_________________

Production Editor of Performance Motoring at Express Media Group
shollier@expresspublications.com.au
Phone: (02) 9741 3838 (direct line)

Top
 Profile  
 
 
Posted: Mon Jan 22, 2007 6:06 pm 
Technical Contributor
Offline
User avatar

Age: 39

Posts: 5855

Joined: 5th Nov 2004

Gallery: 8 images

Ride: '95 EF's

Location: Leederville
WA, Australia

4.11's = more gear changes over the 1/4!

 

_________________

R.I.P. Scotty

Top
 Profile  
 
 
Posted: Mon Jan 22, 2007 11:07 pm 
Getting Side Ways
Offline
User avatar

Age: 39

Posts: 1442

Joined: 26th Apr 2006

Gallery: 6 images

Ride: 97 EL XR6

Power: 162 rwkw

Location: liverpool
NSW, Australia

so with 4.11s your saying that ill be be hitting 5th?

 

_________________

07 BF MKII XR6T
310rwkw @ 13psi - Tuned By CMS

Top
 Profile  
 
 
Posted: Mon Jan 22, 2007 11:08 pm 
Tyre Shredder
Offline
User avatar

Age: 46

Posts: 378

Joined: 3rd Dec 2004

Ride: EB V8

Location: Blue Mountains
NSW, Australia

You already use fourth? Then I'd be looking at why you have such little low rev torque, nor the high rpm power (& revs) to justify this big cam.

 

_________________

Production Editor of Performance Motoring at Express Media Group
shollier@expresspublications.com.au
Phone: (02) 9741 3838 (direct line)

Top
 Profile  
 
 
Posted: Mon Jan 22, 2007 11:19 pm 
Getting Side Ways
Offline
User avatar

Age: 39

Posts: 1442

Joined: 26th Apr 2006

Gallery: 6 images

Ride: 97 EL XR6

Power: 162 rwkw

Location: liverpool
NSW, Australia

well if i just hit fourth at the line, its still a gear change, and if it happens earlier with the 4.11s is that a bad thing?

 

_________________

07 BF MKII XR6T
310rwkw @ 13psi - Tuned By CMS

Top
 Profile  
 
 
Posted: Mon Jan 22, 2007 11:36 pm 
Tyre Shredder
Offline
User avatar

Age: 46

Posts: 378

Joined: 3rd Dec 2004

Ride: EB V8

Location: Blue Mountains
NSW, Australia

I take it this is for the 97 EL XR6, right? What is your current terminal speed? At what rpm do you change gears? & at what rpm are peak power & peak torque achieved?

You need to make the most of your combination & that means matching all components from the intake & exhaust, cam, head (ported or not), gears etc. You may find avoiding the change into fourth saves more time, or you may decide to go with 4.11s & make some use of that change into fourth.

I still don't see why you are changing into fourth at the line instead of just holding third, especially since a big cam that has sacrificed torque would require more rpm to be effective.

 

_________________

Production Editor of Performance Motoring at Express Media Group
shollier@expresspublications.com.au
Phone: (02) 9741 3838 (direct line)

Top
 Profile  
 
 
Posted: Tue Jan 23, 2007 10:09 pm 
Getting Side Ways
Offline
User avatar

Age: 56

Posts: 6467

Joined: 18th Dec 2006

Ride: 93 ED sedan

Power: 161 rwkw

Location: Rockhampton
QLD, Australia

I would suggest advancing the cam timing first, try 2dgs then 4dgs, to see if this helps. its easier to do this than change diff gears.
There is a formula for workin this out, as in revs & gears.

RPM x total outside tyre dia in inches x 3 (this is a constant)
______________________________________________ = speed MPH

Total gear ratio ( g'box ratio x diff ratio)

Eg; 3,000 rpm becomes 3.000 or
2,500 rpm becomes 2.5 ok?

So 2.5 (rpm) x 26" x 3 = 195
________________________ _________ = 56.52mph

( 4th) 1 x 3.45 (diff) 3.45

56.52mph x 1.61 = 90.99 kmh



Use this to sort out rpm verse tyre size and diff gears.

 

_________________

http://youtu.be/jJTh9F3Vgg0

Top
 Profile  
 
 
Posted: Tue Jan 23, 2007 10:36 pm 
Oompa Loompa
Offline

Age: 36

Posts: 28

Joined: 5th Oct 2005

Location: adelaide
SA, Australia

going from 3.45 to 3.9 is putting in a lower ratio.
3.08 is higher than 3.9.
higher ratio = long legs
lower ratio = short but quick
Top
 Profile  
 
Display posts from previous:
Sort by  
 Page 1 of 1  [ 9 posts ] 

Who is online

Users browsing this forum: No registered users and 24 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

 

 

It is currently Thu Mar 28, 2024 8:32 pm All times are UTC + 11 hours

 

 

(c)2014 Total Web Solutions Australia - Australian Web Hosting and Domain Names