mx5-kiwi

Am in the early fine tuning stages of my road/race car in it's current state.

Pondering my next lap time improvement upgrade/purchases.

A comment I notice Emilio made on a thread just read has me wondering if people have any comment on OS Giken or equivelant v torsen 1 and 2 diffs (I have a 4.3 v1 and a 3.9 v2 - I think I prefer the v1 style).

At this point traction isn't a serious issue but as i improve it will be. I definitely notice the difference between the torsen v1 and v2 but the different ratios probably exagerate that....

So my questions are...

- Significantly faster on track or not? (most races I do are in the 15 minute range, 8-12 laps)

- Huge NVH increase/ no difference?

- Road driveability good / bad ?

- Perhaps the difference is negligible and i should focus on other areas first..track time, more boost, 8-9" rims etc....

tomiboy

iTrader: (3)

GRM had an article comparing LSDs on a Miata

Leafy

iTrader: (1)

Theoretically it should be better than the torsen. In Practice, the more I deal with gikens the more I want to keep my torsen. Too much lockup and the car pushes like mad, not enough lock up and you spin the inside wheel. Not enough preload its an open diff all the time, too much pre-load and the car pushes. IMO as long as you can keep both drive wheels on the ground all the time the torsen is the better diff. If you cant keep both drive wheels on the ground, then after you spend a couple years dialing in the giken it will be better.

One caveat, I've only dealt with gikens that came from them when they had the drifters running the show. The guy who actually knows things has supposedly come back to giken USA, which means you might be able to get a cam profile that works better for actual racing.

jmann

Leafy I've heard pretty much the samething. I am spinning the inside tire on most corners with the torsen diff and was wondering about the giken and have been told what you are saying that it is really hard to get it set up to where you aren't understeering [to much lockup] or spinning the inside wheel [ not enough lockup]. For 2 grand I am sticking with what I have for now. Maybe they well improve it in the future.

Savington

iTrader: (31)

You've heard wrong, and Leafy is wrong as well. The OSG doesn't cause understeer on entry - IMO it's practically invisible compared to a Torsen until you're on power on exit, at which point it hooks both wheels and allows you to be on the power hard and early without wasting anything. IMO, it's one of those parts that needs no "well, it improves here but detracts there" justifications - it simply does everything better than a Torsen and is a total no-brainer if you're willing to spend the cash.

The whole "a torsen is better if you can keep the wheel on the ground" is total BS as well - Torsens will only transmit torque in proportion to the force on the inside rear, so as you corner harder and harder, it moves less and less power to the outside wheel (where you want it). The OSG doesn't give a **** - it will always move the torque to the outside wheel like it's intended to. The result is dramatically improved corner exit speeds and lower laptimes in pretty much every example you can think of.

Significantly faster. Even without a turbo, expect gains of 1+sec on 2 minute road courses. With a turbo, it will be more.

No NVH increase. The diff doesn't even pop/click in parking lots - it's transparent until it needs to work.

Road driveability is flawless - again, it's transparent.

Leafy

iTrader: (1)

I never said it understeers on entry. The issue is understeer mid corner and exit when you try to power out and the diff locks. 100% lock is too much, 80% lock is too much, 60% lock is not enough. There needs to be a 70% lock option but that isnt possible without a redesign of the diff that uses more clutches. I can say that because I've physically pulled a Giken apart and flipped around the clutch plates to change it.

The OSG cant move any torque, it is a clutch type. The max TBR on a clutch type is 1, which is lower than the TBR of either of our torsen options. The most torque it can apply to the outside tire is 50% of the total torque, and that would be at 100% lockup.

Savington

iTrader: (31)

That's not something I've ever experienced, and I have hundreds of hours in OSG-equipped cars over the last 3+ years. Not sure what was wrong with the OSGs you've driven, but all the ones I've driven have been either factory OSG or 949Racing Hi-power tunes and they've all been magical.

jmann

I too was talking about mid corner and exit and this is by people who are using it. Entrance into a corner has more to do with balance than the diff. IMO.

shlammed

iTrader: (8)

I had an OSG in my miata.

They are like stock drivability wise and noise wise it was more quiet than my 1.6 vlsd.


As far as the handling issues im not sure what you guys are talking about, you should go learn to drive. if your understeering you should ball up and use the right foot a little more and im not suggesting you go drift.

chances are the understeer is because your not on the gas enough and your trying to slow down to get back on line if your understeering mid corner.

cheezitnation697

iTrader: (1)

Maybe a newb question but if it can ony apply 50% power to outside wheel? what is the difference between the osg and a torsen or open diff in that sense?

cheezitnation697

iTrader: (1)

agreed, sometimes you have to slow down to go faster..

Leafy

iTrader: (1)

The open will always transfer 100% of the torque to the wheel with the least grip. The torsen will transfer a certain amount of the torque based on the TBR and the amount of grip, up until there isnt enough grip on one of the two tires then it acts like the open. The Salisbury style clutch type of the OSG will lock the axles together anywhere between 50% and 100% depending on how you setup the clutch disks the design of the control cam. The control cam acts differently based on the total torque transmitted through the diff. Then there is the normal clutch type that we arent talking about here, which is basically an open diff except the two axles are linked by some sort of friction apparatus (the VLSD works like this), which basically locks the two axles together until there is a large enough difference in force between the two axles to overcome the friction force of the diff.

The trouble with the OSG seems to be in the control cam. On exiting the corner when you've got the car floored, the diff locks, doesnt allow speed differentiation between the two wheels and the car pushes. If you let off the gas enough to unlock the diff and be able to turn, you're just going slow and giving up time.

A properly setup Salisbury type clutch lsd will be faster than a torsen. Most of us dont have the time or the money to spend hundreds of hours testing and adjusting the Giken to get there.

Scrappy Jack

iTrader: (2)

Is it possible that Leafy and jmann's buddies are talking autocross-specific experience and Savington is speaking to road course work? I imagine "mid 'corner'" in a parking lot/on an airstrip is significantly different than on a circuit.

Savington

iTrader: (31)

It must be. Based on his posts, I don't think Leafy's ever driven one on a road course (or if he has, it wasn't set up correctly at all).

Leafy

iTrader: (1)

That would be correct. Never had a mid corner speed with one over 60. And never in a miata with more than 180hp. And never in a car with smaller than 275 hooisers. I could see how a car with more power or less grip would be able to power on enough to get past pushing and into sliding. But the giken problem is worse and worse the higher speed the corner is at least up until 60.

Savington

iTrader: (31)

Within that narrow specification window (very wide tire, relatively low power, zero elevation change and low cornering speed with tight relative radius), I could see how any clutch-type would push a bit. For every other case, including normal cars on 205/225 R-comps with 150-400whp and cornering speeds ranging from 50mph to 120mph with elevation change and curbs, the OSG does a better job than the Torsen.

concealer404

iTrader: (3)

Got it. Torsen to pop down the street to get groceries, OS Giken for cross country work.

Savington

iTrader: (31)

That's not what I said.

concealer404

iTrader: (3)

Sorry, i should have added a smiley of some sort. Was just attempting to add some brevity to the discussion. Clearly i have failed.


I know what you said and understood it.

Savington

iTrader: (31)