The best performing non-DCCD centre diff??
 

Ok, got into a bit of a debate with some friends on the weekend re: centre diffs. Of course there is Subaru's flagship DCCD which I have flogged in every shape and form of STi round the track while instructing (perks of the job!) and have now wired up in my 6 speed, tested round the track and fairly impressed!!

However to my knowledge Subaru have also released 3 other non-DCCD centre diffs with factory set pre-loads. These are 4Kg, 12Kg and 20Kg? Respectively...

The 4Kg centre diff being most common in most WRX in my experience is fairly doughy inducing heaps of understeer (which most attempt to somewhat 'cure' with suspension mods etc), the 12Kg seems to be superb offering a well balanced, more nuetral drive, but have never tried the 20Kg- which I hear can get a little tricky and end up throwing the car back into understeer issues again.

So thought I'd throw out this question to the guys who have tinkered with any/ all 3 of these variations or had them inclusive within vehicles (eg- early STi's) to get their opinions... what are the differences? And which did you feel was the best??

there is also an 8kg

There are also the Cusco Tarmac Center diffs which is very similar to running a DCCD box with no power going into it.

And Cusco and ATS also make 2 way plated mechanical center diffs. Similar in operation to a 2 way rear LSD. It locks up hard under power and throttle off. And opens up when coasting.

I haven't driven on either of these though.

Just to clarify Joel, To my knowledge the 12 and 20Kg/m were not STi and STi/Ra default fitment. To assume that any STi or Ra automatically has one would be incorrect.
I've never found anything other than a boring old 4kg/m softie in any road going non dccd STi. If the car was rallied or 'dirt trial' raced in Japan you may be lucky enough to find one fitted.

I've tried all of them.
Stock 4 kg needs help to stop excessive front wheel spin.
12 is my pick as better than the rest. Does the job nicely, no nasty side efects.
20 behaves like a 12 but has noticable bind on tight turns.

My old series 1 Legacy had approx 220 horsepower at the most. A 20kg/m may have been more beneficial if the car was more powerful. I now have a DCCD centre in there and I'm seriously considering going back to a 12. The DCCD is less predictable.
I did loads of *handbrake turns with the 12 and the 20, so don't let anyone tell you it can't be done. *must have a hydraulic handbrake, plate rear diff also desireable.

cusco tarmac gear is the diff of choice for a tarmac based car, 65/35 rear front power split, has turned our car into an oversteering demon, but with a working front diff, entirely driveable, will not fall apart like a electronic dccd centre at around the 300hp mark and is about the $1200 mark making it excellent bang for buck

I was very happy with my 12kg center and it did reduce understeer whilst allowsing predictable tail out action. I have never heard the stories of not being able to use the handbrake with the 12kg but I can also confirm handbrake turns can be achieved with a 12kg center.

i like burnouts in general, so any diff that encourages it, can only be a good thing.

[QUOTE=Denver;445024]will not fall apart like a electronic dccd centre at around the 300hp mark[/QUOTE]

Is that true? A regular occurrence like gearboxes?

protofail kept toasting his, he did some digging and found a lot of people making over 300 ATW had simular issues, switch to tarmac gear, problems go away..

being electrically controlled, increasing the power input by a very large amount will in time kill it, especially if your motorsporting a lot, mechanical solutions are generally the only reliable way to do these things as power increases will not affect them as much...

I am of agreeance, in any form of motorsport or ahrd use the DCCD centre is really only good on a stockish powered car

[QUOTE=jEstEr?;445288]I am of agreeance, in any form of motorsport or ahrd use the DCCD centre is really only good on a stockish powered car[/QUOTE]

As a general rule for 5 speeds yes. The 6 speed ones are considered to be much better (especially 06 onwards) and are suitable for rallying.
Back in the day of 5 speed group N Subarus, no one used the DCCD with any success. They used to open up after a few kays of hard driving.

Not to mention, 6 speeds generally have an 'auto mode' or can be hooked up to similar aftermarket setups which saves being set in 'lock' mode all day long.

PS- Yes Doug, wasn't really sure what comes out with what (hence the question mark in the poll).

Anyone have any super handling probs with the 20Kg on tarmac. Stace, someone mentioned you once ran one in one of your vehicles...??

[QUOTE=dtrally;445305]As a general rule for 5 speeds yes. [/QUOTE]

yah thats what i meant

[QUOTE=subarooboy;445308]Not to mention, 6 speeds generally have an 'auto mode' or can be hooked up to similar aftermarket setups which saves being set in 'lock' mode all day long.
[/QUOTE]

So will running an aftermarket controller which has an auto mode help save it a little?

[QUOTE=Denver;445268]protofail kept toasting his, he did some digging and found a lot of people making over 300 ATW had simular issues, switch to tarmac gear, problems go away..

being electrically controlled, increasing the power input by a very large amount will in time kill it, especially if your motorsporting a lot, mechanical solutions are generally the only reliable way to do these things as power increases will not affect them as much...[/QUOTE]

glad i read this! mine seemed to be coping well with 310 hp atw, better get mms to pull all the DCCD gear out when we swap the box and put a cusco 35/65 tarmac diff in there, i'd rather sell one in working condition than break it and have nothing to show for it :p

[QUOTE=subarooboy;445308]Anyone have any super handling probs with the 20Kg on tarmac. Stace, someone mentioned you once ran one in one of your vehicles...??[/QUOTE]

ive had 4kg/12kg and plenty of DCCD centres. (all my current gearboxes have dccd, and i pack spares!)

i dont do any circuit work (maybe once in a blue moon), only rarely do drags.

basically the heavier the diff, the better the handling, a DCCD at full lock is equivelent to a 20kg centre (run full lock at the drags).

although, if you work the DCCD centre hard, they loosen up and eventually suffer eternal rear bias only, which in my opinion- effectively the same as leaving the diff unpowered, and near the same torque split as one of those cusco centres.

possum bourne motorsport were at one stage offering rewinds on 5 speed centres.

to be honest, dccd for me is about having fun. i'm a hoon at heart, so i just like turning tires. if you want to be fast on the track, i'd be opting for a 20kg, and relinquishing the car from daily duties.

[QUOTE=V3 RA;445383]glad i read this! mine seemed to be coping well with 310 hp atw, better get mms to pull all the DCCD gear out when we swap the box and put a cusco 35/65 tarmac diff in there, i'd rather sell one in working condition than break it and have nothing to show for it :p[/QUOTE]

just leave the diff un powered.

5 speeds will break no matter what centre is in there.

[QUOTE=tuna;445385]just leave the diff un powered.

5 speeds will break no matter what centre is in there.[/QUOTE]

i wont be keeping the RA 5 speed in there, im surprised that lasted as long as it did...was more thinking of selling the whole lot i.e front diff, centre diff all the DCCD gear and gearbox. A few people showed interest when i initially popped the motor and was going to part it out completely and start a fresh in a few years time.

I've never tried a Cusco 35/65 but I reckon it's too much rear. I drove a R32 GT-R once that had lots of power ~ 450 horse, it wasn't fast on the skid pan as there wasn't enough going to the fronts and too much to the rears. I felt unbalanced, nervous and less fun than a 200 horse Subaru after you get tired of smoking them as you spin it backwards. I'm thinking 300 horse and 65% rear drive in a GC8 you better have sticky tyres and 2+ cans of Red Bull before you get behind the wheel.

cue rob spiraling off into the dirt at collie

i have been running the dccd centre in my 5 speed in a dedicated tarmac rally car. I have blown one up so far but I think that had more to do with 1) driving back from collie with a rear right broken driveshaft and then doing a couple of stages at targa west 08 with a broken rear left driveshaft. When it was stuffed all it diff was absolutely bake the front tyres.

I also run a 1.5 way in the front and the thing drives like a front drive car anyways. Takes massive provocation to get the back to step out even with a 2 way in the rear.

Also bear in mind that in targa spec my car only has about 165kw at the wheels because of the pea shooter.

I think that as I prepare the car again I will put in a fixed diff in the centre.

I usually run the dccd at the first orange light because i feel that suits me but i have no qualitive data on different settings.

Brendon

I'd defn go the 12kg, don't think they came standard in anything tho'...only a rally upgrade to my knowledge. There is a difference in how the early Sti/StiRa 5 speed open fronts behave and influence handling depending on ratio that I found.

[QUOTE=jEstEr?;445288]I am of agreeance, in any form of motorsport or ahrd use the DCCD centre is really only good on a stockish powered car[/QUOTE]

I'm glad I have the above (stockish powered car) then!

[QUOTE=nauli;445521]I'm glad I have the above then![/QUOTE]

Thats for a 5 speed DCCD box though. You could have heaps of power!

[QUOTE=Denver;445024]cusco tarmac gear is the diff of choice for a tarmac based car, 65/35 rear front power split, has turned our car into an oversteering demon, but with a working front diff, entirely drivable, will not fall apart like a electronic dccd center at around the 300hp mark and is about the $1200 mark making it excellent bang for buck[/QUOTE]

Spot on.

I have a front (helical torsen) lsd and rear (plated) lsd on my GC8 MY00 - it simply just "punts hard". You you can power in and out of corners, throttle steer stupid and really only have to watching out for swapping ends when you go hard in the wet. No more under steer. ever.

Note however, you've got do these other to front/rear lsds otherwise it won't work properly or safely. As you would also imagine it's well worth upgrading all your other suspension parts too.

Final word - without a doubt these are the best handling mods you can do a bar a DCCD, which even then you'll probably prefer to drive it in a 35/65 set-up.

Cheers

[QUOTE=97RA;445516]I'd defn go the 12kg, don't think they came standard in anything tho'...only a rally upgrade to my knowledge. There is a difference in how the early Sti/StiRa 5 speed open fronts behave and influence handling depending on ratio that I found.[/QUOTE]

I couldn't agree more with this observation! Unfortunately, apart from a few after work laps (with street tyres, exhaust silencer etc) I never got to test the 12Kg out on the track when fitted up to 4.11 box... was too afraid I'd break another box! But I swear it would've been beaut!!

[QUOTE=dtrally;445476]I've never tried a Cusco 35/65 but I reckon it's too much rear. I drove a R32 GT-R once that had lots of power ~ 450 horse, it wasn't fast on the skid pan as there wasn't enough going to the fronts and too much to the rears. I felt unbalanced, nervous and less fun... [/QUOTE]

From memory Doug... it didn't appear you were having "less fun" that day??:D LOL!

dunno how you could feel like you went slow in a gt-r, provided you keep the boot into it which keeps the atessa system locked up and pushing drive to the front wheels, they can be driven like a RWD car but will pull where you want them to, they shit all over a WRX for drive out of corners, even with huge amounts of mumbo, but you can't button out, the second you do, its all over..

Tom
So what center diff do you have?

[QUOTE=Tom;446917]Spot on.

I have a front (helical torsen) lsd and rear (plated) lsd on my GC8 MY00 - it simply just "punts hard". You you can power in and out of corners, throttle steer stupid and really only have to watching out for swapping ends when you go hard in the wet. No more under steer. ever.

Note however, you've got do these other to front/rear lsds otherwise it won't work properly or safely. As you would also imagine it's well worth upgrading all your other suspension parts too.

Final word - without a doubt these are the best handling mods you can do a bar a DCCD, which even then you'll probably prefer to drive it in a 35/65 set-up.

Cheers[/QUOTE]

There really should be a poll choice for a CIG locker and no front shafts :)

Hi Maddog

In my ranting enthusiasm, I probably didn't clearly state that I too am using a Cusco Tarmac Gear. They're simply the best.

Cheers