Notices
RX-8 Racing Want to discuss autocrossing, road-racing and drag racing the RX-8? Bring it here. This is NOT a kills/street racing forum.

Let's talk about diffs, baby.

Old 07-23-2018, 11:50 AM
  #1  
Registered
Thread Starter
 
Mr. Pockets's Avatar
 
Join Date: Mar 2008
Location: Champaign, IL
Posts: 468
Received 8 Likes on 7 Posts
Let's talk about diffs, baby.

Hi.

I had a glorious weekend at Pitt Race, but the current weakest link on the car appears to be the diff. Mine may be worn out. I was getting a ton of wheelspin out of slow corners - specifically 5/6 and 17/18.

I understand 1, 1.5 and 2-way diffs in theory. And I see there are a lot of options out there. My priority is getting traction out of corners, and I don't want to change the feeling of the car under braking. I worry about a 1.5 or 2-way diff causing instability in the rear. On a track like Pitt Race, with its sort of insane final corner complex, that would be a whole lot of no fun.

I see diffs from Kaaz, Cusco and OS Giken. They ascend in price in that order. I hear a lot of nice things about OS Giken.

Please let me know what you've tried or use. Thanks!
Mr. Pockets is offline  
Old 07-23-2018, 11:59 AM
  #2  
Not ******
iTrader: (1)
 
John V's Avatar
 
Join Date: Jan 2004
Posts: 686
Likes: 0
Received 9 Likes on 9 Posts
The 1/1.5/2 "way" differential discussion always confuses things. It makes a lot more sense to talk about how strongly a differential locks (or doesn't) when it's forward-driven versus reverse driven.

In general, your car will be more stable when the differential is locked up, i.e. limiting wheel speed delta. Two-way differentials are typically used for track work because they are the most stable under braking. They don't typically work for autocross because they make the car push on turn-in. There is a continuum between a "1.5-way" and "2 way" differential. It comes down to driving style, tuning, etc. Personally, I like a differential that is as open as possible on decel and locks up aggressively but progressively on accel. Some would call this a "1-way" differential. I'd call it a "1.5 way" because the preload of the clutch packs still means there is always greater than zero lockup.

Tunability is important. The OSG is very tunable, but maybe not by the user... typically people send them back to one of the US-based service locations to have the lockup characteristics tweaked.
John V is offline  
The following users liked this post:
Mr. Pockets (07-23-2018)
Old 07-23-2018, 02:11 PM
  #3  
Registered
Thread Starter
 
Mr. Pockets's Avatar
 
Join Date: Mar 2008
Location: Champaign, IL
Posts: 468
Received 8 Likes on 7 Posts
Originally Posted by John V View Post
Personally, I like a differential that is as open as possible on decel and locks up aggressively but progressively on accel. Some would call this a "1-way" differential. I'd call it a "1.5 way" because the preload of the clutch packs still means there is always greater than zero lockup.
See, I think this is what I want. I don't think I want a diff to mess with the car under decel.

Originally Posted by John V View Post
Tunability is important. The OSG is very tunable, but maybe not by the user... typically people send them back to one of the US-based service locations to have the lockup characteristics tweaked.
Tuning the diff opens up a whole new can of worms. As much as I want to pretend I'm pro, I have to be honest. I'm a weekend racer, and much of my time is spent instructing and supporting students and our program. So I'm not sure tunability is high on my list of priorities.
Mr. Pockets is offline  
Old 07-23-2018, 03:58 PM
  #4  
Registered
 
Join Date: Jun 2016
Location: Rochester, NY
Posts: 52
Likes: 0
Received 1 Like on 1 Post
Originally Posted by Mr. Pockets View Post
Tuning the diff opens up a whole new can of worms. As much as I want to pretend I'm pro, I have to be honest. I'm a weekend racer, and much of my time is spent instructing and supporting students and our program. So I'm not sure tunability is high on my list of priorities.
That's the problem, isn't it -- if you don't like how the car behaves with the diff setup they give you, then you need to pull the diff and mess with it in hopes that the next time, it'll be the way you want it.

if you've used the stock diff in while it was still good and enjoyed the handling characteristics, then I'd seek out another one -- less to worry about, else you fall down the rabbit hole of diff types and tuning.
gigglehurtz is offline  
Old 07-24-2018, 06:10 AM
  #5  
Not ******
iTrader: (1)
 
John V's Avatar
 
Join Date: Jan 2004
Posts: 686
Likes: 0
Received 9 Likes on 9 Posts
And you also have to know whether it's the diff or something else in your setup causing the problem you're chasing. It's easy to convince yourself you're fighting a suspension problem when it's really a diff problem or vice versa.

If you have a suspension that generally works well it is hard to go wrong with a helical differential, especially one with some sort of preload like a T2R. They do not have the usual bad habits of a clutch-type diff on corner entry. They are very consistent and don't wear out over time like the stock RX-8 diffs do.
John V is offline  
Old 07-24-2018, 02:07 PM
  #6  
Registered
 
Join Date: Jun 2018
Posts: 27
Likes: 0
Received 0 Likes on 0 Posts
I am not familiar with the 8 diff. but could it be welded?
chavelo is offline  
Old 07-24-2018, 02:35 PM
  #7  
^^^ Fluent in snark.
 
NotAPreppie's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL, USA, North America, Earth, Sol System, Sector ZZ9 Plural Z Alpha, Milkyway, Universe
Posts: 3,252
Received 431 Likes on 352 Posts
The RX-8 has a Tochigi Fuji unit that is a cone-clutch torque sensing type and functions like a 1-way LSD.

https://www.rx8club.com/series-i-tec...01/#post278604

I'm thinking any gear-type LSD would be a good replacement (Torsen, Wavetrac, Quaife, etc).
NotAPreppie is offline  
Old 07-24-2018, 02:53 PM
  #8  
Not ******
iTrader: (1)
 
John V's Avatar
 
Join Date: Jan 2004
Posts: 686
Likes: 0
Received 9 Likes on 9 Posts
Originally Posted by chavelo View Post
I am not familiar with the 8 diff. but could it be welded?
Sure, if you want to ruin the handling.

Wavetracs are junk.
John V is offline  
Old 07-24-2018, 08:52 PM
  #9  
Registered
 
Join Date: Jun 2018
Posts: 27
Likes: 0
Received 0 Likes on 0 Posts
Could you be more specific, and do you have first hand experience that it would ruin the handling, I have no experience with autox set ups, but it works fine in drag racing and road racing. it may be old school, but I do know it works, it is not for a daily driver as it is a pain at low speeds.
chavelo is offline  
Old 07-25-2018, 06:17 AM
  #10  
^^^ Fluent in snark.
 
NotAPreppie's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL, USA, North America, Earth, Sol System, Sector ZZ9 Plural Z Alpha, Milkyway, Universe
Posts: 3,252
Received 431 Likes on 352 Posts
Locking the rear wheels together sounds like a recipe for miles of understeer followed by snap oversteer.
NotAPreppie is offline  
Old 07-25-2018, 06:28 AM
  #11  
Registered
 
Join Date: Jun 2018
Posts: 27
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by NotAPreppie View Post
Locking the rear wheels together sounds like a recipe for miles of understeer followed by snap oversteer.
That has not been my experience, look it up.
chavelo is offline  
Old 07-25-2018, 06:38 AM
  #12  
Registered
 
Join Date: Jun 2016
Location: Rochester, NY
Posts: 52
Likes: 0
Received 1 Like on 1 Post
Originally Posted by chavelo View Post
Could you be more specific, and do you have first hand experience that it would ruin the handling, I have no experience with autox set ups, but it works fine in drag racing and road racing. it may be old school, but I do know it works, it is not for a daily driver as it is a pain at low speeds.
I challenge you to find a modern, competitive, road race car running a spool where running a limited slip diff is an option.

Yes, it's possible to set up a car around a diff... but this is beyond the scope of the OP.
gigglehurtz is offline  
Old 07-25-2018, 06:50 AM
  #13  
^^^ Fluent in snark.
 
NotAPreppie's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL, USA, North America, Earth, Sol System, Sector ZZ9 Plural Z Alpha, Milkyway, Universe
Posts: 3,252
Received 431 Likes on 352 Posts
Originally Posted by chavelo View Post
That has not been my experience, look it up.
That's not how this works. You make a claim, you support your claim. You don't make a claim and tell other people to support your claim for you, especially when that claim is prefixed by a personal anecdote ("That has not been my experience...").

Last edited by NotAPreppie; 07-25-2018 at 06:55 AM.
NotAPreppie is offline  
Old 07-25-2018, 06:52 AM
  #14  
Not ******
iTrader: (1)
 
John V's Avatar
 
Join Date: Jan 2004
Posts: 686
Likes: 0
Received 9 Likes on 9 Posts
Originally Posted by chavelo View Post
Could you be more specific, and do you have first hand experience that it would ruin the handling, I have no experience with autox set ups, but it works fine in drag racing and road racing. it may be old school, but I do know it works, it is not for a daily driver as it is a pain at low speeds.
Spools work great for drag racing, but when most of us say "handling" we mean turns.

They can be made to work for road racing and autocross. I had a spool in my car when I bought it and it does exactly what you expect - unless you set up the car with a lot of rear roll stiffness the car will simply not work well in the first half of a corner. They work fine once you're on the power, but you sacrifice a lot of corner entry speed.
John V is offline  
Old 07-25-2018, 07:26 AM
  #15  
Registered
iTrader: (2)
 
Join Date: Jun 2011
Location: Destin
Posts: 305
Likes: 0
Received 2 Likes on 2 Posts
I will also say that a welded diff *can* be made to work but is not the best option. We ran one in our lemons car and while it was workable for road course, to autocross the car you had to adopt a ‘throw it in sideways’ approach to get the car through any corners succinctly.
roflcopter is online now  
Old 07-25-2018, 09:20 AM
  #16  
Registered
Thread Starter
 
Mr. Pockets's Avatar
 
Join Date: Mar 2008
Location: Champaign, IL
Posts: 468
Received 8 Likes on 7 Posts
Originally Posted by NotAPreppie View Post
The RX-8 has a Tochigi Fuji unit that is a cone-clutch torque sensing type and functions like a 1-way LSD.

https://www.rx8club.com/series-i-tec...01/#post278604

I'm thinking any gear-type LSD would be a good replacement (Torsen, Wavetrac, Quaife, etc).
Unfortunately, I don't see any helical LSDs out there for the RX8. It looks like the FD RX7 torsen diff may fit, though...
Mr. Pockets is offline  
Old 07-25-2018, 10:33 AM
  #17  
Registered
 
Join Date: Jun 2018
Posts: 27
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by NotAPreppie View Post
That's not how this works. You make a claim, you support your claim. You don't make a claim and tell other people to support your claim for you, especially when that claim is prefixed by a personal anecdote ("That has not been my experience...").
I am not making any claims, since I am talking from personal experience and not looking for support, if you have not looked it up, or familiar with it then dont try to bash me.
chavelo is offline  
Old 07-25-2018, 01:50 PM
  #18  
^^^ Fluent in snark.
 
NotAPreppie's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL, USA, North America, Earth, Sol System, Sector ZZ9 Plural Z Alpha, Milkyway, Universe
Posts: 3,252
Received 431 Likes on 352 Posts
Nobody is bashing you.

I'm just trying to teach you how to communicate effectively. If your evidence is personal anecdote then don't tell people to "look it up" because we can't look up your personal anecdote.
NotAPreppie is offline  
Old 07-25-2018, 04:36 PM
  #19  
Registered
 
Join Date: Jun 2018
Posts: 27
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by NotAPreppie View Post
Nobody is bashing you.

I'm just trying to teach you how to communicate effectively. If your evidence is personal anecdote then don't tell people to "look it up" because we can't look up your personal anecdote.
Wow, you are very sensitive, what did you have to eat this morning.
Anyways did you look up yet.
Let me know when my next class will be teacher
Why are you so upset?
chavelo is offline  
Old 07-25-2018, 04:59 PM
  #20  
^^^ Fluent in snark.
 
NotAPreppie's Avatar
 
Join Date: Mar 2006
Location: Chicago, IL, USA, North America, Earth, Sol System, Sector ZZ9 Plural Z Alpha, Milkyway, Universe
Posts: 3,252
Received 431 Likes on 352 Posts
Alright, well, you're clearly trying to start something here and this thread is about diffs and not trolling so I'm just going to ignore you and move on with my life.

Last edited by NotAPreppie; 07-25-2018 at 05:03 PM.
NotAPreppie is offline  
Old 07-25-2018, 05:00 PM
  #21  
Registered
 
Join Date: Jun 2016
Location: Rochester, NY
Posts: 52
Likes: 0
Received 1 Like on 1 Post
Originally Posted by Mr. Pockets View Post
Unfortunately, I don't see any helical LSDs out there for the RX8. It looks like the FD RX7 torsen diff may fit, though...
It fits, and works quite well so long as you're not bouncing the car off of every curb at WOT.
gigglehurtz is offline  
Old 07-26-2018, 10:50 AM
  #22  
Registered
Thread Starter
 
Mr. Pockets's Avatar
 
Join Date: Mar 2008
Location: Champaign, IL
Posts: 468
Received 8 Likes on 7 Posts
Originally Posted by gigglehurtz View Post
It fits, and works quite well so long as you're not bouncing the car off of every curb at WOT.
What do you mean by that? I wouldn't say I'm 'bouncing off every curb at WOT,' but I do that on the ones that make me faster.

Also, when you say it fits, what else would I need from an RX7 to make one work in the 8's differential case? Do the RX8 axles have the same splines? I found a used one on eBay, and it says it needs new 'side flanges.' I'm not sure that the RX7 or 8 have such a part.

Last edited by Mr. Pockets; 07-26-2018 at 10:57 AM.
Mr. Pockets is offline  
Old 07-26-2018, 04:39 PM
  #23  
Registered
 
Join Date: Jun 2016
Location: Rochester, NY
Posts: 52
Likes: 0
Received 1 Like on 1 Post
Originally Posted by Mr. Pockets View Post
What do you mean by that? I wouldn't say I'm 'bouncing off every curb at WOT,' but I do that on the ones that make me faster.

Also, when you say it fits, what else would I need from an RX7 to make one work in the 8's differential case? Do the RX8 axles have the same splines? I found a used one on eBay, and it says it needs new 'side flanges.' I'm not sure that the RX7 or 8 have such a part.
I didn't need anything else for the FD Torsen to fit in the RX-8 diff. Side flanges sounds like stub shafts, which FD diffs don't have either.

You just put the ring onto the FD Torsen, lash appropriately, and off you go.

The problem with a Torsen is that if a wheel is unloaded (say, hopping a curb), it spins up, just like an open diff. Then, when the wheel touches back down, all of that force goes into the diff, which can cause catastrophic failure. In general, Torsens don't like shock loads, but it seems that especially Type 1 Torsens don't live very long when exposed to shock loads.

Last edited by gigglehurtz; 07-26-2018 at 05:23 PM.
gigglehurtz is offline  
The following users liked this post:
Mr. Pockets (07-27-2018)
Old 07-27-2018, 07:00 AM
  #24  
Registered
 
trackjunkie's Avatar
 
Join Date: Oct 2017
Location: South Central PA
Posts: 312
Received 11 Likes on 10 Posts
i have a OSG diff and 5.1 FD waiting to go in the car. unfortunately my next event is not till end of september, so no feedback till then. if you're interested in an OSG diff, let me know i can get one at very good price.
trackjunkie is offline  
The following users liked this post:
Mr. Pockets (07-27-2018)
Old 07-30-2018, 12:55 PM
  #25  
Registered
Thread Starter
 
Mr. Pockets's Avatar
 
Join Date: Mar 2008
Location: Champaign, IL
Posts: 468
Received 8 Likes on 7 Posts
Originally Posted by trackjunkie View Post
i have a OSG diff and 5.1 FD waiting to go in the car. unfortunately my next event is not till end of september, so no feedback till then. if you're interested in an OSG diff, let me know i can get one at very good price.
The 5.125 final drive is magical. You're gonna love it.
Mr. Pockets is offline  

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:
You have already rated this thread Rating: Thread Rating: 0 votes,  average.

Quick Reply: Let's talk about diffs, baby.


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.