Diff's...... Tip owners look away now

[Louis]

Whole load of info here on rear diffs if you can be arsed trawling through it, all useful stuff and links though

http://www.clubvr4.com/forum/showthread.php?t=23198

[Kenneth]

Gowf, where did you get the 80/20 torque split from?

AFAIK, you will only get this if you use a open planetary centre diff in conjunction with the standard VCU. i.e. the cusco tarmac gears.

If you are talking a plate or helical LSD, surely you should have a 50/50 split?

[Gowf]

Hmmm, it was the kaaz plate diffs. We currently have an open centre diff with a vcu, and its more like a 60/40. I did read it somewhere, but i can't remember exactly.

[Kenneth]

Yeah, it is 60/40 bias to the rear, but that comes from the planetary gear in the VCU not the diff.

[Gowf]

Yeah, but that is removed when fitting a centre lsd. Just looking aparently the cusco's are a 65/35 split, I definately did read it somewhere but like i said i may be totally wrong.

I can see why the 50/50 split would be thought of, as would that not also be the same as welding the diff's? Which when thinking about it is what a plate diff would do anyway? hmmmm, im now on a mission to find that

[Kenneth]

Cusco tarmac gear is 65/35, but that is an open diff which uses a planetary gear arrangement. It is definitely not an LSD. Not sure if you are supposed to run it with the VCU.


With the diffs you have to be careful to differentiate between torque and output speed. Welding the diff locks the torque split to 50/50, but also the output speeds, which is what causes the handling issues.

[Kenneth]

I have done a fair bit of research into the different diffs etc... I plan on getting my drive train setup to my specification before going for more power.

I plan on having the following drive train arrangement

Cusco Tarmac Gear centre
Wavetrac front
S-AYC rear

[Gowf]

Just talked to a friend of mine who works at MML and apparently they recon that no ayc diff will cope with 500lbft. They also say, that just firing an lsd in the ayc casing is not the way to do it. So now it looks like im in rs uprated to GpA territory. Awesome, all i need to do now is sell a kidney

[Nutter_John]

Just talked to a friend of mine who works at MML and apparently they recon that no ayc diff will cope with 500lbft. They also say, that just firing an lsd in the ayc casing is not the way to do it. So now it looks like im in rs uprated to GpA territory. Awesome, all i need to do now is sell a kidney

Sorry they only accept kidneys without 20 years worth of alchool abuse

[Ryan]

Apologies for intruding with my techno-peasant brain but what sort of diff was Valmes using and how many did he end up going through?

[Gowf]

This i do not know. I have an sayc sitting here waiting to go in, but i dont want to put it in if its just going to go pop as soon as it goes up the strip.

[bradc]

I'm fairly sure Valmes had the normal AYC diff.

Think about this though. I'm making around 440lbft at the engine. In first gear this equals a massive peak of 5280lbft. I have a much longer first than stock which helps reduce that peak. Gareth's car still has the short first gear in it, meaning with the same torque output as me, he would make 6030lbft. Now he makes even more torque than me, so clearly his diff would have to handle much more torque.

In 2nd gear (again I have a longer ratio) we are at 3520lbft versus 3810lbft. Less of a difference, but a much lower overall value.

Perhaps changing to the ultra long RS 1st gear ratio like Kenneth has in his car is a good option? That would limit your 1st gear torque output to 5040lbft.

[Gowf]

Or launch in 2nd?

[bradc]

Perhaps yes, but then if you launch in 2nd you will have to be very careful with the initial shock load if you are revving the engine up fairly high to get a good jump off the line.

Limiting the boost in 1st would make the most sense to me.

[Gowf]

limiting the boost? It makes a bar on the line!!!!

[bradc]

Make less then

[Gowf]

Where's the fun if there's no launch control? Its all about the popping and banging. I can totally see what your saying though, but im still thinking that an rs diff is the way, the only downside is the price, and obviously the driveshaft issues im going to have

[Louis]

Surely there must me a few Evo's with standard S-AYC running big bhp numbers?

[Gowf]

Nope, they get rid and put proper diff's in. Same as all the rally cars do not run ayc. And if you look at Norris, he runs a skyline rear diff

[bradc]

Actually a lot of Rally, Targa and Track use EVO's over here are running SAYC now. All of those classes are limited by throttle body size or whatever and therefore don't go over 350hp or so. All of them love the handling advantage AYC in general gives, especially on gravel