Sam's build thread

[Sydneykid]

I have used these guys;
ford 9" clutch pack limited slip differential 9 inch clutch pack 9" posi plates 9inch lsd,F100 DIFF

A lot of the Sports Sedan guys use spools, but I have seen a couple of these around;
Powertrax Grip Pro - PowerTrax

The problem with a plate style diff in high powered V8's is that, due to the torque and HP, they wear out the clutches very fast, plus pass a lot of heat into the oil. So they need very regular maintenance and frequent oil changes. That's why spools and ramp style LSD's are more popular.

With the V8 Supercars Albins offered an LSD as an alternative but they decided to go with the control spool centre on maintenance grounds.

Cheers
Gary

[metalhead]

Is yours a Detroit locker now? Does the Eaton Posi fit yours?

Mine is an Eaton style posi now (factory fitted) but with a few changes from stock - solid steel clutch plates, shimmed to fit the case with a small amount of friction, and preload springs removed. Locks up fast and smooth under power but is basically unlocked off the throttle. No chattering, very smooth and positive engagement. It's actually unnoticeable driving quietly on the street, whereas it used to chatter and clunk noticeably before the changes. Eaton don't make a clutch posi centre for the 9" as far as I can see.

I have used these guys;
ford 9" clutch pack limited slip differential 9 inch clutch pack 9" posi plates 9inch lsd,F100 DIFF

A lot of the Sports Sedan guys use spools, but I have seen a couple of these around;
Powertrax Grip Pro - PowerTrax

The problem with a plate style diff in high powered V8's is that, due to the torque and HP, they wear out the clutches very fast, plus pass a lot of heat into the oil. So they need very regular maintenance and frequent oil changes. That's why spools and ramp style LSD's are more popular.

With the V8 Supercars Albins offered an LSD as an alternative but they decided to go with the control spool centre on maintenance grounds.

Cheers
Gary

I was hoping you might have some thoughts Gary. I found that most seemed to be running spools. The powertrax grip pro is a torsen/gear style diff isn't it? Though looking on their website they also have a "Grip LS" clutch style lsd for a 9", is that what you were referring to?

Those clutch plates are for a factory lsd aren't they? Does the factory LSD stand up to competitive use?

The current diff has stood up ok, it's done ~45,000km and still locks up very effectively. Probably does have some wear on the clutches though, as it has developed some side yoke play. I'd be keen to have steel clutch plates again, as I think that's probably fairly key to longevity and not needing to rebuild/repack every few events. My brother has an OS Giken LSD in his mx5 that he's been happy with - was secondhand when he got it and has done a lot of work both street and track in his car. Much less power and weight though obviously.

What's your opinion on gear vs clutch LSD's for higher powered rwd cars? I don't want to lose the predictability that the current diff offers. Almost every experience I read preferred the performance and consistency of a clutch LSD on the track, and running motorkhanas and khanacrosses I feel like I would risk losing and regaining drive as the inside rear got light on tight turns. But it can be hard to gauge how qualified people's opinions are online...

I don't think a locker (or even more so a spool, even if it weren't a street car) would work well without a lot of other changes - the car is quite twitchy and needs to be able to be balanced on the throttle, I expect the sudden engagement/disengagement would unsettle the car badly.

[Sydneykid]

Power Trax is a torson ramp style, the Pro is their competition version. There's a few SS's running them, but from what I have heard most use a spool (low initial cost and next to zero maintenance, plus light weight). With low chassis weight (1125 kgs inc driver) and ~700 bhp they are very twitchy. Plus they use 3 or 4 diff ratios around the various tracks, so low initial cost is more important than if they were buying just one.

I had a quick talk to a friend of a friend who does lot of work on 60's American Muscle cars and he suggested Eaton. They make what they call a Truetrac which has gentler ramp angles on the helicals so they tend not to clunk and are not light switch like in their on off action. That maybe a better choice for a combo road (less) and track (more) car with a 9". They also have a plate style LSD (Eaton Posi LSD) which he suggested for a combo road (more) and track (less) car. But I think they only make them for 8.8". Eaton Posi | differential | limited slip | Eaton

FWIW, carbon composite clutch packs are pretty common these days as they are bit gentler on lock up (than steel) and last a long time.

Cheers
Gary

[sambb]

surprised a geared torsen style LSD is suggested in a RWD car. Is that because you can set them up with lots more front anti roll than a FWD and get the inside front in the air and concurently keep both rears firmly planted on the taarmac?

[Sydneykid]

surprised a geared torsen style LSD is suggested in a RWD car. Is that because you can set them up with lots more front anti roll than a FWD and get the inside front in the air and concurently keep both rears firmly planted on the taarmac?

We certainly run more anti roll on the front of a RWD car than we do on the front of a FWD car, a lot more. Because we aren't concerned with adversely affecting inside wheel power down. As we have talked about a few times, we run positive rake (nose down) on a RWD car, plus a higher (than the front) rear roll centre. This increases the diagonal weight transfer (to the outside front wheel) and unloads the inside rear wheel, especially useful in a car with a spool. I run a slightly higher rear roll centre with a spool than I do with an LSD. We also run a much higher front spring rate than the rear, so the spring rate counteracts the swaybar rate to some extent (pushes down on the inside front wheel). But we also run a lot of rebound in the front dampers to reduce the corner exit understeer as the spool (or LSD) will make it push under acceleration. We also run about the same droop in the front suspension as in a FWD car for the same reason.

For me I find that a RWD car is tuned (for balance) mostly by adjusting the rear roll centre and the front swaybar. I rarely adjust the rear ride height or the rear swaybar and pretty much never adjust the front ride height.


Cheers
Gary

[sambb]

I understand the thinking behind getting the inside rear to lift in a RWD with a spool, but I'm surprised that could would work with a torsen RWD diff that can go open in the same circumstances or am I missing something? When you see pics of RWD cars holding the inside front up through corners, is that a setup for open diff RWD cars?

[sambb]

Gary RE the Kaaz diff I'm working on, I have a question about oil. The Kaaz oil is an 80W90 mineral based. The factory oil for the box is a 75 monograde synthetic. I'm currently using Motul 300 75W90 for the wavetrac. So I have two questions: For a street/track car with a diff like this, is it absolutely necessary to go for the name brand 'tailored' oils from the diff company or are there generic clutch LSD friendly oils that in your experience work just as well or better. ie could using a readily available mineral based LSD oil an then adding friction modifier if need be, be an equivalent route performance-wise and maybe more cost effective?
Secondly, what are my synchros going to think of a mineral based heavier weight oil that might contain fiction modifier?

[sambb]

Dammit. The crown wheel is the smaller 113mm. So that's an early HWY and now the later JDB box both having the 113mm. Was hoping I'd get lucky but apparently not. I'll call Brian at Gti import to get a price on a 114mm crown wheel and pinion and weigh that against machining costs. I'd assumed you'd machine the gear but the gearbox guy said that in DSG box's he'd had done the machinists had taken material off the diff casing!

[Sydneykid]

I understand the thinking behind getting the inside rear to lift in a RWD with a spool, but I'm surprised that could would work with a torsen RWD diff that can go open in the same circumstances or am I missing something? When you see pics of RWD cars holding the inside front up through corners, is that a setup for open diff RWD cars?

In a RWD car I generally end up with inside wheel lightness on acceleration, away from the apex. This is due to the high front anti roll rate plus the low (relative) rear spring rate and the rear suspension geometry. The rear squats under acceleration, adding weight to the rear wheels, when added to the roll from the cornering G force the inside goes light as a result. So it's not that I target it specifically, it's a by product. At times an unwelcome by product as too much and it can lead to corner exit understeer. Hence the use of front damper rebound to slow down the lightness caused by the front end lift.

Torsens are tricky to set up for, we want the inside rear wheel to go light on corner entry so they unlock. If they stay locked we end up with turn in understeer. But we also want them locked for acceleration on corner exit. We use the chassis dynamics and the tools at out disposal to balance out these contradictory requirements. Tools = swaybars, spring and damper rates, roll centres, ride heights, etc. My go to tool in a RWD race car is the rear roll centre. As we use a chassis mounted watts linkage the roll centre moves (in relation to the ground), simplistically such that it's higher under braking and lower under acceleration. So we get more diagonal weight transfer to the front outside tyre under trail braking, but we get less (weight transfer to the front outside tyre) under acceleration on corner exit.

Very small changes in rear roll centre can make a lot of difference. For example I can eliminate a lot of corner entry understeer by raising the rear roll centre 5 mm. Moving it 10 mm higher can result in an oversteering pig. That's why back in the LRA days we used to adjust the rear roll centre on the V8 Supercars with a crank handle during pit stops.

Cheers
Gary

[Sydneykid]

Gary RE the Kaaz diff I'm working on, I have a question about oil. The Kaaz oil is an 80W90 mineral based. The factory oil for the box is a 75 monograde synthetic. I'm currently using Motul 300 75W90 for the wavetrac. So I have two questions: For a street/track car with a diff like this, is it absolutely necessary to go for the name brand 'tailored' oils from the diff company or are there generic clutch LSD friendly oils that in your experience work just as well or better. ie could using a readily available mineral based LSD oil an then adding friction modifier if need be, be an equivalent route performance-wise and maybe more cost effective?
Secondly, what are my synchros going to think of a mineral based heavier weight oil that might contain fiction modifier?

In the FWD car with the KAAZ LSD we use Nulon (obviously) Full Synthetic 75W-85 Smooth Shift Manual Gearbox and Transaxle Oil. It doesn't specify LSD's but chemically it's suitable and it has a number of advantages for that application (ie; inside knowledge).

Cheers
Gary