jdistefa

Ooooh just discovered this thread. Subscribed

Cupcar

This is long to respond to a PM I got.

Yes, both arms pictured are Porsche RSR parts. They have an 18 mm spherical "Unibal (German speak)" or "Monoball (US speak)" bearing instead of the usual rubber bearing element. The stock bearings at the upright are "Unibals" in all 993's race or street - as is the forward bearing of the stock Track arm that is bolted to the subframe. The only rubber elements in the stock control arms are those bearings that are bolted directly to the subframe.

RSR Unibal



I noted is that the stock rear suspension has two types of rubber elements, one for the Camber and Toe arms and one for the Track and "Kinematic (caster) arm". I noted that the annulus of rubber in the bearing design is thinner in the Toe and Camber arm, thus allowing less potential deflection than the Track or Kinematic arm do. This variance in motion between the two types of elements and the hardness of the rubber in the elements determines the amount of "Kinematic effect" which is a toe in of the outside wheel and toe out of the inside wheel during cornering to stabilize oversteer with a countering self steering rear suspension motion.

This Kinematic effect is accomplished by the geometry of the rear control arms which converge on a virtual axis that is outside and behind the tire patch center thus allowing a rotation moment about the outside Toe arm bearing when the Track arm bearing deflects under load.

The rubber bushings in the RS car are of harder rubber than the normal car in the Kinematic and Track arm bushings to decrease the amount of this Kinematic change and thus make the car handle more like an older semi-trailing arm 911.

Note the difference in the rubber elements in picture below, RS replacement on left, stock Track and Kinematic in middle and Toe and Camber bearing on right. Simply replacing all the elements with the RS part would allow more potential motion in the camber and toe elements than design specification although the difference in motion would be eliminated since all bearings would be the same then. The RS bushings are much harder and denser than stock.

RS Replacement-----------------Stock Kinematic and Track---------------Toe and Camber


I at first thought that I might use a combination of rubber elements for the Camber and Toe arms with Unibals at the Kinematic and Track arms, but decided to go all Unibal when found I couldn't buy the correct thin annulus bearings for the Camber and Toe links.

CalvinC4S

Glad to hear your going GT3 bottom end and stopping there. That will make for an amazing motor true to the dynamic of the 993.

When I read about your plans to go water pumper, IMHO would have put the car in the Frankenporsche LS1 camp.

Cupcar

Hmm...and my wife would like Bob to grow up.

Frankly, the only happy people I know are into some toy be it a horse, boat, plane, bicycle or whatever. The others seem to be looking for what those on
Rennlist have.

RAB

Looks good

You got some nice parts.


Richard

camlob

That was a nice explanation Bob Thanks for it. Really appreciate the effort.

lopro

interested read, I just went thru the whole thing and learned lots about 993. thanks for posting, good luck with your build and keep going. Most of all have fun.

ironimages

I love/hate this thread.. Love all the information and watching the build, hate it as it will most likely cause me to spend more money on my car. Keep the updates coming!

SeattleAllroad

trophy

What are you going to use as pistons and cylinders? I have a GT3 Crank and Rods coming for my engine rebuild, but havent decided on P&C's yet.. Would love to know whick way you are going.

Cupcar

I am a ways off on this part of the project. My plan is to finish the chassis and do a quick re-seal of the stock engine along with a LWF install and then reinstall the engine to drive the car for a while.

The working plan is to use LN cylinders with 102 mm JE custom 993 pistons with the compression height reduced 3 mm. JE says this would be no problem. I will probably use a factory 3.8 GT3 ring package which is ~ 1.2, 1.5 and 2 mm, the JE stock ring package is 1.5, 1.75 and 3 mm. This would be a ~ 494 gram piston.

BTW, Stock 993 100 mm pistons run 596 to 614 grams and Mahle 102's are 614 to 622 grams. Stock 993 rods are 508 to 550 grams and Ti GT3 130 mm rods run ~ 424 grams.

Having said that, a friend is a Mahle Motorsport dealer and said he would check for me if they could do a custom 102 mm set using the GT3 3.8 piston's forging blank machined to a 993 crown configuration. This possibility has not been investigated yet and I suspect would be too expensive to me even if possible. This would produce a very light ~ 445 gram piston however.

The thought of knocking over 200 grams (around 1/2 pound) off each piston and rod assembly gets my juices going.

trophy

The thought of dropping that much weight off pistons and cylinders is pretty exciting. It is one of the reasons I bought the gt3 crank and rods.

I was looking at going to 104mm pistons to build a 3.9... I will give L&N a call to discuss the possibilities.

Either way love your plans and the process you are taking.

KMASS993

Why no GT3 engine? Is it difficult to get the plumbing and integration done? or is it more a performance issue? I have always dreamed about the GT3 engine and 993 combination but really have no idea what is involved

Cupcar

Actually it would be pretty easy, the water lines go down the center tunnel and a radiator is installed in the trunk. Since the GT3 crankcase is the same as the 993's, the gearbox bolts up and the mounting of the rear is a pretty straightforward modification of the 993 mounts. Wiring is not all that hard. And there is no engine sheet metal surrounding the engine so no PIA there. One can use the stock 993 oil tank and oil cooler with minimal modification.

Basically, if you have any hot rodder genes at all it is a pretty easy swap.

Why not?

Because the chassis is so nice, I was getting shy of aborting my car into a hot rod, then and a day in my buddies new RS 4.0 made me realize one can have too much power on the street.

Then CA smog would involve switching drive trains for smog test every 2 years...So I nixed the idea and fell in favor of keeping my car air-cooled, less powerful and CA smoggable.

camlob

Yup Steven the JE pistons are light. Give Charles a call. I like your crank Your car will be a keeper!