Mr. Pockets

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!

John V

iTrader: (1)

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.

Mr. Pockets

See, I think this is what I want. I don't think I want a diff to mess with the car under decel.

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.

gigglehurtz

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.

John V

iTrader: (1)

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.

chavelo

I am not familiar with the 8 diff. but could it be welded?

NotAPreppie

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).

John V

iTrader: (1)

Sure, if you want to ruin the handling.

Wavetracs are junk.

chavelo

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.

NotAPreppie

Locking the rear wheels together sounds like a recipe for miles of understeer followed by snap oversteer.

chavelo

That has not been my experience, look it up.

gigglehurtz

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.

NotAPreppie

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...").

John V

iTrader: (1)

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.

roflcopter

iTrader: (2)

Mr. Pockets

Unfortunately, I don't see any helical LSDs out there for the RX8. It looks like the FD RX7 torsen diff may fit, though...

chavelo

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.

NotAPreppie

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.

chavelo

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?

NotAPreppie

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.

gigglehurtz

It fits, and works quite well so long as you're not bouncing the car off of every curb at WOT.

Mr. Pockets

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.

gigglehurtz

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.

trackjunkie

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.

Mr. Pockets

The 5.125 final drive is magical. You're gonna love it.