V

Great summary Bill as always, thanks.

Not get off topic here, but what do you mean by "effective LSD"? Care to elaborate? Is the one I mentioned above (Guards LSD 50/80) suitable for a 2wd 993TT? I assume it is overkill for a mostly street car but it's also nice to know that your car is properly setup once you take her to the track.

Also using different pads is a good idea. For example if you use 993RS/TT front and 993RS rear, why not use a performance pad like Pagid up front and just the standard pad in the rear to shift stopping power forward? I will be using the standard pads all around though since I HATE brake squeal and standard seems to be the ticket to minimize squeal..

Bill Verburg

The standard 22/40 or 25/65 lsd 993 lsd(option 220) are ineffective 2 plate lsds, they are not set up for performance use. Their plates are prone to rapid wear and they are set w/ very low levels of break away torque.

GT can rebuild them to perfomance spec, w/ better friction disks and higher break away torque spec but cannot change the basic 40/64 or whatever spec.

Both 4 plate Porsche Motorsports lsds used in the /3x transmissions and the Guard GT lsds are effective out of the box. 50/80 w/ performance disks and high break away torque is more of a track only lsd. As I noted earlier even the current batch of RSRs has backed down to 40/60 w/ high breakaway torque specs w/ 6 - 8 friction discs.

break away torque is an artefact of the assembly process. There are sets of driven and drive plates that rub on each other creating breakaway forces. They come in various thicknesses and are preloaded by the stacked tolorances. Obviosly worn disks are thinner, reducing the initial breakaway torque w/ use, hence the double strike against the oem street lsds which are set up loose and quickly get looser w/ use..

the 40/60 # comes from the machined angles in the outer load carrying members that the pinions ride in, different angles cause different levels of dynamic pressure on the stacked discs. The spec is given as drive / coast levarage.

V

That's what I thought.. So either a Motorsport or a Guard GT lsd with something like 40/60 would be about right for a trackable street 2wd 993TT? I really need to learn how stuff like this works, so informative posts like your last are very much appreciated. That (IMHO) is what RL is all about.

Bill Verburg

Thought I'd resurrect this thread w/ some additional info

I went through and calculated the actual brake torque exhibited by all the various 993 brake setups, all are @ 70bar line pressure. It turns out that 993RS is not as rear biased as I had at first thought and in fact is right inline w/ the bias exhibited by all 911s up through '83, i.e. 1.491

Paul902

Bill, as always, you are the master of data. Can you repost the table with headings, though?

Bill Verburg

Sorry about that, edited w/ headings

trophy

Hey Bill, Great Chart.

If I sent you the specs from the Stoptech kit would you add it to this chart?

Bill Verburg

Sure, can't guarantee when though
I need some of details that aren't usually published

piston sizes of course and effective rotor size, if this last isn't available the rotor and pad sizes can be used

jstyer

Few questions... Since the 993tt rear caliper has smaller pistons, and less breaking torque then the 993 rear caliper, is the primary purpose of switching to tt rear calipers just to be able to run larger rotors, and therefore better heat dissipation characteristics?

Also, if the regular 993 system is at 1.640 f/r ratio without the 40 bar p/v, why run it at all? It seems to me that 1.640 is not far off from early 911 territory.

Bill Verburg

yes, You'd get better bias by running stock rears, that setup(993RS/tt/993) would be very close to what they ran on 964 Cup cars w/o a p/v


Correct, I run the 993RS setup on my '76 w/o a p/v it is fine that way. Someday I'll experiment w/ the 993

trophy

Rotor Details:
F: 355 x 32
R: 332 x 32

Pads:
F & R: 131.56 x 71.12 (Same as RS/TT Rears All around)

I'll get you the caliper piston details tonight.

No rush, just interested to see.

trophy

Stoptech Piston Sizes:

F: 40 / 36
R: 28 / 28

Bill Verburg

trophy

Thanks Bill, does it change much if you use the front pad height as 71 mm vs 74 mm?

The Stoptechs use the smaller pas front and rear...

Bill Verburg

The shorter pad makes the effective rotor diameter a little bigger and will commensurately increase brake torque