Fitting a Limited Slip Diff.

[Fred W.]

Hi all
I have a good 'looking' Porsche G50-01 gearbox. There a couple of things I would like some help with. Im about to buy a Quaife Limited Slip Diff as it sounds like the best/easiest upgrade, right? I assume installation will be straight forward but while I have the box apart what else can be done to upgrade it, what should I inspect if I only change the diff? This box will have to handle the power of a chev Ls2 a 400 HP motor. Any thoughts. If I went nuts on it what could be done?

 

[flatchat(Chris)]

An ATB is the go --- "Automatic Torque Biasing" diff :- (avail. Quaiffe) rather than an LSD -- even an open diff is not that much of a problem in these things when you dial out the chassis flex and set the suspension up correctly

The characteristics of the differential are that it progressively locks as torque increases; there are no plates or clutches to wear out, unlike the more conventional limited-slip designs.

Since you have it apart --check it over thoroughly -- a taller 1st gear set, could be a better option (see Albins)
Generally they are a good tough box and can easily handle anything a Chev can through at it :laugh:

 

[Fred W.]

Chris

Thanks for the thoughts. The diff I have lined up from Quaife is indeed a ATB diff but I have to admit I did not know what ATB meant so thanks for spelling that out. The question of the first gear being to low I have seen written about before. It sounds like an expensive mod. The gear is integeral with a shaft, is that right? Is the mod of some great benifit? Thanks.

 

[flatchat(Chris)]

Is the mod of some great benifit?

Only if you're racing it --when you'll have to short shift to 2nd real quick:shifty:

 

[Pablo]

Not everyone in the Porsche world thinks highly of ATBs ... which is probably why all Porsche pro teams use plate-style LSDs exclusively.​

Link deleted for whatever reason​

 

[Erik Johnson]

Well I thought that I would put my .02 cents in here.

The ATB or torque biased differential is a great street diff, however, does not lend itself well to the track as there is not lockup on the decel side of the differential.

As to changing out the 1st gearset, this can not be easily done with a G50/01, as the 1st gearset is intregal to the mainshaft. You would either need to pick up a two-piece mainshaft with the new first gear, or have one welded on. (I can help you with that here.)

As to what is possible, well that all depends on what your budget is.
Cryogenic treatment of the internals will give you much longer life to the gears.

A billet side plate might not be a bad idea, however with only 400 HP I feel that this option is a bit overkill.

I would caution you however with regard to the differential. Regardless of if you go with the ATB or the more traditional plate type differential, these are NOT plug and play upgrades. You will need to make sure that the ring and pinion is set up correctly, otherwise you could possibly do damage to the gearbox, and potentially lock it up completely, in a worst case scenario.

I would do some case work though, make sure to open up new oiling passages to ensure that your gearoil flows correctly front to back. Keep in mind that the biggest killer of gearboxes is heat. I would go so far as to recommend that you install cooler in and out ports (8 AN) and use a good oil cooler and pump, again I can help here too.

The G50 is a great option for mid-engine use, we build many of these for these types of applications, usually we change out the 4th and 5th gear ratios with taller gearing that is better suited to the V8 application.

I would be happy to discuss this in more detail with you should you have some time. Feel free to contact me with any questions that you might have. I am always here to help.

Warmest Regards, and happy building.

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

PS Make sure that you use a good gearoil, either Swepco 210 or LE 9920 would be my recommendations.

 

[Cliff Beer]

Ditto what Erik said re: ATB v. LSD on the street and track. The ATB works great on the street, it gets you basically what you need which is limiting (very effectively) the amount of wheel spin of the less loaded tire on acceleration. It's my understanding that many race teams not only prefer the LSD over the ATB because of the better handling on decel, but also because the LSD is adjustable - they can vary and set the breakaway tension by using different plates and pressure upon the plates - and this is helpful for tuning the car to a particular track. The ATB has no such adjustability on the fly.

 

[Howard Jones]

I would like to throw my 2c in here. On track can mean a lot of things. Full on racing, wheel to wheel for financial reward is an entirely different ball game than open track, armature type events. ABT type diffs will be the best OVERALL type for a street legal car that is run on track in track day events. These type of events don't have the class rule packages that insure that participants in real racing are trying to extract every .01 sec per lap and therefor are tuning such things as limited slip ratios, changing gears ratios to suite each track every weekend and all the other stuff including a much higher maintenance pace that goes with full on racing.

Open track events are sort of run what you brung events that typically don't require that kind of performance optimization. Most people who what to go faster put on slicks and or add more power. The former works better that the latter in my opinion.

I have a Quiafe in my GT40 and I really like it. So much so that I had one installed in my G50 for my SLC.

As far as mods to do to a G50. After a TBD I would consider changing 1st and second gear to ratios that suit a V8. Something on the order of 2.6 first and 1.75 second is about right with a 3.5 final. This will get you about 55 mph in first without wringing the snot out of it. The rest of the Porsche gear ratios are good with a moderate final drive ratio like 3.5 to 1. With a .8 5th you are looking at a top speed of about 165ish at 6.5K RPMS. That's plenty.

Pumping oil onto the R&P and the gear-set is a good idea but unless you are running a race pace with a lot of power for an hour or more you don't need a cooler. My R21 Renault oil stays below 180F
if run on a hot day for 30 min or less at quick lap speeds but not by any means full on race speeds. 10 to 15 laps at a time is typical at open track events and I have found that that's not long enough to over heat the gearbox oil. My 302 is making right at 300HP at the wheels.

 

[flatchat(Chris)]

All good info here --- Howards comments are on the money in this application.
Unless you're doing 6 -24 hour enduros -- then build a race car !

I've seen more blown up motors (especially Fords:heart than G50s --- they are the best value IMHO -- the next best would be the ZFQ, Ricardo, Hewland etc

Perhaps? -- the GT40 with more weight over the rear wheels may suit an ATB over the LSD

 

[Pablo]

TBD works well in autocross or mid engine cars ... but even with mid engine, the LSD is king for high speed track.