LSD recommendation FD3S Road course
 

Hi,

Like the title states I need some recommendations on a good LSD for Road course racing.. Any advise would be nice as I am really a novice at this.

Thanks

what's your budget?

an OS Giken is going to be your best bet... but they're expensive.

Run a stock lsd diff.

It a torsen and works fine. They are just about perfect for roadcourse racing. The only guys who need to change them out is the drag guys who dump the clutches and break the little gears, and slalom guys who lift the insde rear tire due to the sharp corners . I have roadraced one for over 10 years and up to 740 hp. A friend has an ls7 rx7 fd and its been fine . But you must add an electric pump and small cooler or you will cook the seals.

I would consider switching over to a ford 8.8, unlimited ratios, easy to install (sandberg cradle) and it is pretty hard to break compared to the stock diff.

BigAl...

Not to mention that with the Ford 8.8 IRS you have a few more options on the type of LSD you can go with, that and those LSD options are all are a lot less expensive than the aftermarket units for Mazda 8" unit.

What site sells the conversion kit for the cradle that holds the Ford 8.8 IRS diff?

Oops, missed the FD part... Roninspeedworks has a FC kit and I believe they are working on one for the FD? Might try shooting them an email.

I went with the 8.8 with samberg cradle. I can say the car was no faster. By the time you freshen the seals and bearings, upgrade the ltd slip, buy the cradle, buy the adapter axles, custom driveshaft, I spent close to $4000.

8.8 isn't to make the car faster, it's to make it more reliable and gain access to a greater range of final drive ratios (which, with tuning, will make it faster on specific tracks)

If you want an awesome LSD in the stock casing, OS Giken is the way to go.

I recently switched from an FD torsen to an OS Giken in my FC Turbo and like it much better.

cradle 670
axles 600
dshaft 400
master rebuild kit 75
Seals 25
total $1770

I've done this swap 4 times and have yet to change the ltd slip, all four times it was for a dedicated racecar and the diff has performed flawlessly! The bearing rebuild can easily be done on your own. The only variable is the cobra rear diff, I've seen them as low as $150 and as high as $500

I think you might have over paid for some of the parts by over two grand :blush:, these are all current prices.

BigAl...

The FD Torsen is what, a type 1 or type 2 unit? I know the 1.8L Miata unit that I have for my 7" n/a FC is a type 2 unit. The OS Giken is about the best clutch type unit out there, plus it can be customized to suit your needs/desires.

Al, what type of LSD do you have or have you used in you Ford 8.8?

BTW that is a really sweet race car you built!

I am in Canada so there was shipping.
cradle 670
axles 600
dshaft 400
yoke ?
dr shaft bolts?
kit/ seals 100
ring pinion 200 ( stock is 3.55)
bushings 200 ( always toast)
t2r torsen 600 i think
used irs assembly 900 (to get cv's , otherwise you have to buy those from driveshaft shop.)
labour 300+ ( not everyone can set up gear lash.

Total $3770 before taxes and shipping.

i use the stock ford, it hasn't failed me yet!

thank you, it was a lot of fun to build

BigAl...

Stock FD is a type 1. More potential torque split, but more nvh.

I talked to os giken before I bought mine and they put the high preload springs in it because I'm using big Hoosiers. They were super nice to deal with.

Cool. If it is a stock '03-04 Cobra unit, then it is a TrackLok clutch pack type that has the CF discs, which are better suited for high HP levels and track use.

If I am not mistaken the T1 style Torsen units are not as strong as the type 2 Torsen units. Also the type 2 Torsen units are more similar in design and function to the Eaton TrueTrac design LSD.

Sounds like you got a sweet setup with the OS Giken unit - glad it is working well with the Hoosiers on your car.

yes you must use the 03-04 cobra with the 31 spline axles.

BigAl...

+1, I've been using the 1.5 way for years and it works great. I don't see a need for an upgraded diff if your on the road coarse... It's the drag launches that break them, not cornering :lol:. I don't even run a diff brace... The OS Giken is also very easy on diff oil, its always clean when I change the fluid whereas with the stock diff it turns black after the first track day.

thewird

What oil so you run in yours?

I started off with amsoil SG 75w140 with no friction modifier... Well see how it goes. I don't want to pay for the giken oil :p:

The FD Torsen is what, a type 1 or type 2 unit? I know the 1.8L Miata unit that I have for my 7" n/a FC is a type 2 unit. The OS Giken is about the best clutch type unit out there, plus it can be customized to suit your needs/desires.

I have been wondering what the different bias ratios etc were on the Torsens available for the Mazda 8" rear.

I put an FD Torsen in my FC and it feels very different than my FD and I just got an RX-8 and it has a different feel as well.

Which of these Torsen have same and which have different part #s? ( I was going to explore part #s but Mazda Motorsports site is down).

What are the differences?

infini FC RX-7
series 1 FD RX-7
series 2 FD RX-7
series 1 RX-8
series 2 RX-8

Some part numbers-

FD differentials (all Torsen?)

1993 FD RX-7 manual transmission-P099-27-200B, P099-27-200C, P099-27-200D
1993 FD RX-7 auto transmission-R008-27-200, R008-27-200A (nla)

1994 FD RX-7 manual transmission-P099-27-200E
1994 FD RX-7 auto transmission- R008-27-200B (nla)

1995- same as 1994

Note- besides the two listed as no longer available (nla) the rest of the FD Torsen part numbers are listed as superseded.
--------

RX-8 Torsen differentials (open diffs listed separately)-

Beginning of US production to Feb 2010 production-RS01-27-200A
Feb 2010 to Oct 2010-RS01-27-200B
Oct 2010 to end US production- RS01-27-200C

All Torsen differentials listed as backordered (not in US).

I've used Redline for the diff's whole life. However I'm considering getting the OS Giken oil now that I have a a lot more power with the 20b.

thewird

The RX-8 is some funky cone clutch type. Its not a torsen AFAIK.

The FD may have had a type1 from the factory in 93 but mazda switched all their replacements and OEM versions sometime around 94 from type 1 torsens to type 2 torsens. In both the MX-5 and the rx-7s.

When you buy a used FD torsen it it's often a toss up.

stock torsen is great and os giken is best. wouldnt recommend too much in between. only upgrade if you are a dedicated race monster car racing other monster cars.

i reccomend the factory LSD.

let us know when you break it road racing....

however; the 4.44 R&P from a rx8 might be a worthy investment for a FD that lives over 4k rpms

Rear end stability/handling with torsen vs. clutch
 

So does anyone have any practical experience with how the car feels going into and out of corners with a clutch type (osgiken or otherwise) vs. the stock torsen? I've been driving the fd so long with it's torsen that i'm curious of what a difference the clutch type would make. I've read threads (in other not rx7 forums) where they talk about cars with torsen's being unstable and that at the limit on a track you're better off with clutch types. That over rumble strips/curbs the tires get air and upset the car as well.

I guess the question is can you compensate for this with driving style and suspension setup? Is this just less of an issue with the rx7?

From what i've read it appears to not have an absolute answer and that ultimately you're better off focused on improving everything else before you even start thinking about it.

Just curious, so thanks for any answers i may or may not get ;)

It's really simple. You get more grip and stability with an OS Giken. In other words, you go faster.

thewird

indycars use torsen . they seem pretty stable. and torsen is awesome in the rain as it doesn't cause a big push

the racing type clutch plate LSD is going to be much better at putting the power down compare to the stocker for sure !! There is no question about it. OS Giken has a smoother power delivery, Kaaz have good US side service. I would pick between these 2 proven ones.

I've roadraced my fd since 1997.

I was running a stock diff with 70,000 kms for over 10 years of dedicated roadracing, with and without slicks. I ran it 4 years with a 20b turbo with 740 rwhp and a nascar tranny and had no problem hooking up the power. Never had a failure or changed any parts in all that time. The car is always one of the fastest cars in the rain while all the guys with lockers and clutch diffs were all over the road. For roadracing there is absolutely no need to change it. My friend runs an ls7 7 litre rx7 fd racecar with the stock differential and the same results. I would spend the money on top grade Penske or Ohlin shocks or some big brakes to go faster and be more consistent.

For those of you running clutch type LSD's for road racing, are you using a 1-way, 1.5-way, or 2-way?

1.5 way is what you want...