Confirming limited slip in G50/52

[Ken Wright]

I can use a fiber optic scope to see my differntial and there is a hole in the case that reveals a gear that is consistant with a Torsen type diff.

However, when the car is in gear the axles spin in diffent directions. When in neutral they spin in the same direction.

How can this be confirmed as a limited slip?

Thanks,

Ken

 

[Jac Mac]

There should be a certain amount of 'breakaway' torque to overcome when checking with car in gear and having opposite rotation per wheel. Dependant upon the model or application this can be quite low or higher for some types . They need a certain amount of pre-load in order to function correctly, particularly where a wheel gets airborne.

 

[Erik Johnson]

raise the car so that the rear is off the ground, spin one wheel, if the other wheel travels in the same direction, it is LSD, if goes in the opposite direction it is an open differential.

Hope that this helps

Erik Johnson
Carquip Sales
(303) 443-1343 ext 2 work

 

[Randy V]

raise the car so that the rear is off the ground, spin one wheel, if the other wheel travels in the same direction, it is LSD, if goes in the opposite direction it is an open differential.

Odd but the Torsen differential in my FFR Racecar (used the Torsen T2 from Maximum Motorsports) reacts in the same manner as an open differential except when being driven my the engine and having some sort of bias.. Then it will direct the torque as required..

So - with both wheels off the ground and the transmission in gear, if you spin one rear wheel the other will turn in the opposite direction.

No direct link to the product but if you click on the product tab and then product searc and enter "torsen t2" that will get you there..
Maximum Motorsports :: The Leader In Mustang Performance Suspension

Are these types of differentials ever used in the Porsche boxes?

I really liked what the T2 did for the corner entry and exit on my racecar..

 

[Jac Mac]

Torsen units for some lower power applications have no internal preload or 'breakaway' mechanism and react as per a 'normal' open differential when tested gently in the manner Randy & Eric mention. If you move one wheel quickly while holding the other the torsen type will start to work, while the open type will not. You must remember that the tests above are not what the diff unit experiences in the ' real world ' where power/force is applied by the carrier/ring gear.


I agree with Randy though, the Torsen types are the most user friendly & probably incur less mechanical stress on components along with being consistent in operation.

 

[Erik Johnson]

Here are a couple of things to consider in your differential selection process.

A torsen differential is not a Limited Slip Differential, it is a Torque Sensing or Torque Biased differential. While this does allow for both wheels to drive under torque loading, it does not offer any locking effect on the decel side of operation, as a Plate Type, Ramping LSD does.

So why does this make any difference. Well in a street driving application, many people actually like the TBD (Torque Biased Differential) better then the LSD for that very reason. However for very aggressive drivers, and for the track, the greatest advantage in my opinion for the LSD is in the breaking effect, and ability to drive into a corner harder, using to LSD to correct the cars track if needed, and to allow the car to slow quicker using the LSD's braking lockup.

These are pretty difficult things to really adequately describe on paper, but the difference on the track is extreme.

The typical LSD that comes in a G50/52 is not a torsen type diff. It is a plate type ramping LSD, so to test this would be the same as I mentioned earlier in this thread, however, it should be noted that if the diffential has been heavily used and is warn out, it will effectively operate as an open differential. IE one axle will spin forward and the other will spin backward due to the fact that there is no longer any preload on the diff.

I hope that this information has been at least a little bit helpful, and please do not hesitate to contact me for better clarification, as needed.

Warmest Regards,



Erik Johnson
Carquip Sales
(303) 443-1343 ext 2 work
(720) 980-9407 cell

 

[Howard Jones]

Eric, let me ask you a question on the breaking effect of a LSD verses a Quaife type (torque bias). I have found that I can get the best break rate in my car (Quaife R21 Renault) by simply going right to the limit of adhesion with the brakes until just before the turn in point and then as I begin to release the breaks complete the down shifts with the clutch in and then blip the throttle and let the clutch out in the new gear. I very seldom try to use the engine to improve the brake rate anymore because I think all I do is unsettle the car.

As far as power transmitting ability I find the Quaife is almost un-noticed. It just seams to transmit power to both wheels with out any feedback except no independent wheel spin.

I really like my Quaife and would recommend one to any GT40 builder. They do add to the cost but I believe they are really worth it. How do other TBD's compair to Quaifes in your opinion.

 

[Erik Johnson]

Howard your explaination makes sence to me given what you are working with. In your case you would be using the gearing in the gearbox to slow the car more so then engine and differential.

The question I have for you is what do you do when the brakes run out? Your Renault very well be light enough that you do not have to worry about brake fade, but what happens when you go in too hot?

One of the nice things about the LSD - plate type is that you can use the differential lockup on the decel side to change the cars angle to the apex. Now this is technique is not for the timid and it take some practice to get used to, but because the rear axle is under lockup if you turn the steering into the apex a bit more sharply the rear will have the tendency to step out a bit and allow you to get the car back on line. Then you simply apply heavy accel to induce a bit of understeer through the apex.

It really has a lot to do with weight transfer and differential lockup in this regard, and because a torque biased (quaife) progressively locks to almost 100% this type of driving technique is practically not available to you.

Please do not misunderstand me here though, I have a lot of people that very much like the quaife differentials, but they really are not designed, (in my opinion) for very aggressive track driving.

There is another condition to consider for you very agressive drivers. If you are in the middle of a turn with a quaife differential, and happen to loose grip on a tire, or hit a corner bump, as you will sometimes find wrapping an apex, and raise a wheel off the ground, you no longer have any lockup on the differential. It is essentially an open diff until the wheel has grip again, then there is a delay while the quaife relocks again. This can be very unnerving to the car and driver alike.

This is just one other reason that any, Torque Biased Differential is not ideal for the track. If the same thing were to happen with a normal LSD, then you would have an equal amount of drive on both wheels at all times, even with one wheel in the air. This mean much better handling without any surprises.

In relation to one TBD to another, I think that I will avoid that discussion for the time being. I will say this though, if you are considering a TBD for street or autocross driving, then my recommendation is the unit that Guard Transmission makes.

I hope that this information has been at least a little bit helpful, and might help with the understanding of the differences.

I am always here to help, so feel free to contact me with any questions that you might have.

Warmest Regards and safe driving to all,

Erik Johnson
Carquip Sales
(303) 443-1343 ext 2 work
(720) 980-9407 cell

 

[Randy V]

Howard your explaination makes sence to me given what you are working with. In your case you would be using the gearing in the gearbox to slow the car more so then engine and differential.

The question I have for you is what do you do when the brakes run out? Your Renault very well be light enough that you do not have to worry about brake fade, but what happens when you go in too hot?

One of the nice things about the LSD - plate type is that you can use the differential lockup on the decel side to change the cars angle to the apex. Now this is technique is not for the timid and it take some practice to get used to, but because the rear axle is under lockup if you turn the steering into the apex a bit more sharply the rear will have the tendency to step out a bit and allow you to get the car back on line. Then you simply apply heavy accel to induce a bit of understeer through the apex.

It really has a lot to do with weight transfer and differential lockup in this regard, and because a torque biased (quaife) progressively locks to almost 100% this type of driving technique is practically not available to you.

Please do not misunderstand me here though, I have a lot of people that very much like the quaife differentials, but they really are not designed, (in my opinion) for very aggressive track driving.

There is another condition to consider for you very agressive drivers. If you are in the middle of a turn with a quaife differential, and happen to loose grip on a tire, or hit a corner bump, as you will sometimes find wrapping an apex, and raise a wheel off the ground, you no longer have any lockup on the differential. It is essentially an open diff until the wheel has grip again, then there is a delay while the quaife relocks again. This can be very unnerving to the car and driver alike.

This is just one other reason that any, Torque Biased Differential is not ideal for the track. If the same thing were to happen with a normal LSD, then you would have an equal amount of drive on both wheels at all times, even with one wheel in the air. This mean much better handling without any surprises.

In relation to one TBD to another, I think that I will avoid that discussion for the time being. I will say this though, if you are considering a TBD for street or autocross driving, then my recommendation is the unit that Guard Transmission makes.

I hope that this information has been at least a little bit helpful, and might help with the understanding of the differences.

I am always here to help, so feel free to contact me with any questions that you might have.

Warmest Regards and safe driving to all,

Erik Johnson
Carquip Sales
(303) 443-1343 ext 2 work
(720) 980-9407 cell

Erik -
Absolutely no offense intended here - but - You really need to drive a car with a Torque Sensing differential in it on the track... I had one in my Cobra and was on 3 wheels plenty of times and not once did I ever get an increase in RPM or a slow-down as in loss of driving force. It was totally seamless.. No problems with trailing throttle oversteer when I would chose to trail-brake a corner.
The corner entry was seamless as both rear wheels would evenly send the torque back through the differential to the driveshaft.

I won 3 of my 5 triple-championships in the SCCA's Central Division with this car so I would consider myself to be a somewhat discerning and aggressive driver.

I do believe that you will find Torque Sensing differentials in far greater numbers than conventional LSD differentials in the cars of the Champions. There's clearly a reason why Torsens are higher priced than Auburns et al and more highly sought after..

Others may chime in with differing opinions - but this one is mine..

 

[Erik Johnson]

Dear Randy,

No offense taken, not at all. The reality is that there is what works on paper, and what works in real life. Most of my track time is in a rear engined 911, and prohaps that makes things work somewhat differently, but the concepts are still the same.

A Torque Biased differential does not transfer power to both of the rear wheels, if one of those wheels is off the ground. Now you may not notice it as much in some cars as you will in others, which could be the case for your car of choice, and it could very well be that the time it takes for your diff to relock is so short that you simply did not notice, but as a rule the concepts that I presented should be sound.

I completely agree that with 5 championships to your credit that you would be a good person to give sound advice in this regard.

I personally do not have any issues going either way LSD or TBD, I do however like the LSD better for track applications, due to the locking effect on Decel which is not available with a TBD.

Still we all know what they say about opinions right?

I really appreciate your input on this subject. Anyone else have an opinion either way on this?

Thanks again.

Erik Johnson
Carquip Sales
(303) 443-1343 ext 2 work
(720) 980-9407 cell

 

[Garry]

:inquisitive: Very interesting! Still learning.
Garry