Race Car Tech Discuss anything related to road racing and auto X.

Which rear dif ratio to go with??

Old 03-11-10, 07:59 PM
  #1  
No Traction
5 Year Member
Thread Starter
iTrader: (2)
 
FDAddicted's Avatar
 
Join Date: Jun 2008
Location: SouthWest
Posts: 64
Likes: 0
Received 0 Likes on 0 Posts
Which rear dif ratio to go with??

Not that I consider my FD a race car...
Currenty 320hp . Soon to be 400+ when motor gets a rebuild.

Im trying to get out of dragging the car, and want to start doing autocross.
Should I keep the 4.1 or drop down to the 3.90? Or is it to small of a change to make a difference? Maybe a different ratio? Any suggestions would be great..

Thanks..
FDAddicted is offline  
Old 03-11-10, 11:06 PM
  #2  
Senior Member
 
Join Date: Jan 2006
Location: nanaimo
Posts: 428
Likes: 0
Received 5 Likes on 5 Posts
just leave the 4.10's The 3.9 's would give you less rpm out of the generally tight corners in auto cross and bog you down. I have tried both and the only time you would want to go to a 3.9 or smaller if you have so much power that you just spin the tires when the car revs up. or the shifts come up too quickly.
racingdriver is offline  
Old 03-12-10, 07:59 AM
  #3  
All out Track Freak!
iTrader: (261)
 
Fritz Flynn's Avatar
 
Join Date: Jul 2001
Location: Charlottesville VA 22901
Posts: 10,324
Received 113 Likes on 96 Posts
Serious autocrossers run a 4.77
Fritz Flynn is offline  
Old 03-12-10, 12:23 PM
  #4  
The Silent but Deadly Mod
iTrader: (2)
 
Roen's Avatar
 
Join Date: Aug 2003
Location: NYC/T.O.
Posts: 4,046
Likes: 0
Received 1 Like on 1 Post
Who offers the 4.77?
Roen is offline  
Old 03-12-10, 12:27 PM
  #5  
Searching for 10th's
iTrader: (11)
 
jkstill's Avatar
 
Join Date: May 2002
Location: Portland OR
Posts: 2,192
Received 4 Likes on 3 Posts
Originally Posted by Fritz Flynn View Post
Serious autocrossers run a 4.77
+1

Going to finish up re-installing the suspension today so I can break in the Carbonetic diff with KG 4.77 gears. First autox with the new setup is Sunday.

4.10 gears for autox are really lame coming out of slow corners. I can only imagine how frustrating 3.90 would be.

Were I to do it again I would probably buy the 4.77 RX-8 gears from MazdaMotorsports.

The deal on the KG gears was too good to pass up though as it came with all the seals and bearings.

A good compromise might be 4.44 gears (also RX-8) if you didn't want to go as extreme as 4.77.
jkstill is offline  
Old 03-12-10, 03:44 PM
  #6  
No Traction
5 Year Member
Thread Starter
iTrader: (2)
 
FDAddicted's Avatar
 
Join Date: Jun 2008
Location: SouthWest
Posts: 64
Likes: 0
Received 0 Likes on 0 Posts
Well I would be serious if I had the time.. Realistically I will be able to track the car 2-3 times a year, if Im lucky.
4.77 might be to aggressive for me.
The 4.44/ 4.30 gears where what I started looking into. Since I still ran the 1/4 mile at the time, I was worried about traction issues.. Now that I am done with 1/4mile, I will look into those gear ratios.

Since I will be changing rearend gears, I was thinking about adding the brace to go with it. I have seen a couple of them on the vender's websites. Banzai, A-spec rx7store..ect... Do you guys recommend any of them?
FDAddicted is offline  
Old 03-12-10, 04:01 PM
  #7  
Lives on the Forum
iTrader: (8)
 
ptrhahn's Avatar
 
Join Date: Feb 2002
Location: Arlington, VA
Posts: 8,494
Received 20 Likes on 19 Posts
I'm pretty happy with the 4:10 on track, but with the short 5th gear, which I think is more important. I worried I wouldn't like the car on the street with both a 4:33 and the short 5th.
ptrhahn is offline  
Old 03-12-10, 06:46 PM
  #8  
vik
Junior Member
 
Join Date: Mar 2010
Location: Victroville
Posts: 10
Likes: 0
Received 0 Likes on 0 Posts
4.77 with a 6 gear tranny =]

Jk
vik is offline  
Old 04-14-10, 07:45 PM
  #9  
No Traction
5 Year Member
Thread Starter
iTrader: (2)
 
FDAddicted's Avatar
 
Join Date: Jun 2008
Location: SouthWest
Posts: 64
Likes: 0
Received 0 Likes on 0 Posts
I ended up staying with the stock 4.10 gears.. Cant beat a free rear diff.. Since it was free, i did have the bearings replaced and upgraded to the Greddy pan, and banzai rear diff mount.....
Just some random pictures of the damaged, and the rebuilt rear differential...


I noticed this.. It almost punched its way threw...

More damage

Im guessing this is what did the damage... but who knows

New set up.. Greddy Cover with Banzai diff mount.

Installed

Better look at the diff mount.
FDAddicted is offline  
Old 04-15-10, 05:43 PM
  #10  
Registered User
iTrader: (4)
 
justturbo2's Avatar
 
Join Date: Jan 2005
Location: new york
Posts: 1,571
Received 0 Likes on 0 Posts
Looks good. I like the greddy cover
justturbo2 is offline  
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
mustanghammer
Race Car Tech
28
11-22-15 07:10 AM
Marty RE
New Member RX-7 Technical
0
08-17-15 09:36 AM
Marty RE
New Member RX-7 Technical
0
08-13-15 11:19 AM


Thread Tools
Search this Thread
Quick Reply: Which rear dif ratio to go with??


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: