Converting 964 motor to GT-3
 

I recently purchased everything from the case out from a GT-3 cup motor that is being converted to 3.8L (water boxes, cylinders, piston, heads, cam boxes etc). My plan is to use a street car 964 or 993 case and adapt. Have any of you done that yet? What did you learn along the way?

Mark

You'll need a GT-3 case to finish your project as the air-cooled ones won't work. :)

I thought the GT3 case was the same thing as 964/993 case?

AFAIK, the early GT3 cases had a 964 part number.

Nope, the oil return tube holes are blocked off and the case is actually a bit thicker, I think by 2mm and there is some clearancing around the oil pump.

here is a photo posted by Bill Verburg in another thread:

http://forums.pelicanparts.com/uploa...1111359051.jpg

Thanks for the photo.

I found a new GT3 case, crank and rod set for sale so I jump on that. I'm still going to compare the case with an air cooled case for possible future motors. I'll post the differences when I get the parts and compare. I know the crank is simiar to a 964 crank with 3.0L rod journal diameters and larger radii. They don't use a damper because the Ti rods and pistons are very light which minimizes crank torsional vibration.

I plan to run low voltage wires from my Electromotive ignition to fire 6 coils at the spark plugs. I'm looking into tapping the timing or tach voltage output to control the intake cam timing (VarioCam). I may have to make up an amplifier/relay circuit to power the hydraulic solenoids at the cam boxes. I'm doing this to enable the use of my 50mm PMO carburators and stop the spending madness.

GT3 crank will go into a 3.0/3.2/964/993 case...won't it Steve?

subscribed

Yessir, with the right rods. GT-3 cranks use the same bearing size as the SC.

Don't use Glyco rod bearings for any high-RPM applications due to QC issues.

what kind do you prefer?

Rods?.......Steel ones,.....:)

Made by Brian Pauter.

Arrow's are good also, but more expensive.

No Carillo (sp) rods??

JP

Steve, would you cross drill the center main bearing on a GT3 crank? I'm told that Porsch doesn't do this and the RSR motors sometimes see 10,000 rpm without damage.

Each & every race crank gets the center main drilled. The bearing and case must be modified to suit.

Porsche loses an engine from time to time but don't overlook the fact that PMS rebuilds those motors every 25 hours. :)

We don't have that luxury and the lower end must go a few hundred hours.

Has anyone drilled the crank in 2 places so there are 2 rods between each oil pressure supply hole? If the problem is pushing oil against centripital forces, why not elliminate this all together.

Also, Ollies drills the crank but also cuts a groove around the crank so you don't have to cut the bearing. Has anyone seen a crank break because of this?

I thought the same thing and George at Ollies pointed out to me that the flywheel end of the crank has a similar groove to the one they cut and that end of the crank has the full torque output of the engine going across it.

Porsche Motorsport and dealers list same part number for Gen 2 GT3 bearings, are these OK?

I might ping Armando at CCR on the crank questions. Also Mike Stimson on general questions. Not sure if either have experience with cup motors, but both have a lot of experience.

Just buy a new case from the dealer, they are relatively inexpensive at about $1700 new.

This is a cup motor? As far as I know every year cup has the variocam removed. The mounting provisions remain, so you can bolt in the actuator from the street car easily, but I believe on all (or just most?) years the cup cars don't have it. I guess you're planning to buy the actuator and add it from the street car?