Red9

What is the difference between the respective crankshafts and also the 993 RS ?.Are the 993 cranks different in the different models? EG from 95 to Vario? Is the standard Vario crank up to engine upgrades?

Bill Verburg

The same crank was used from '95 on for all 993 models including RS, TT and GT2.

The 993 crank was considerably beefed up compared to the 964 version.

Steve Weiner-Rennsport Systems

Bill:

Just a data note on this,........

964-993 RSR's and 993 GT-2's used 964 cranks for their strength as well as for their wider rod journals. Even the 9500+ RPM GT-3R uses a 964-type crankshaft.

Red9

To be clear on this-- the 964 type crank with the wider Rod Journals is used on the Turbo,GT2,RSR------ Correct? What about the 993 RS ? Did all 993 N/A engines have 993 type crank?Have ther been issues with 993 Crank in uprated engines?

NineMeister

The 964, 993 and GT3 cranks all share the same 76.4mm stroke and 60mm main bearing journal diameter, so with respect to the crankcases, all are interchangeable.

The 964 crank has the same 55mm diameter x 22mm wide big end journal as the older 930 (3.2 carrera and 3.3 turbo) crank and runs with a damper on the front pulley to reduce harmonic vibrations.

With the introducion of the 993 engine, Porshe changed the crank design to reduce the inertia & weight of the engine. All 993, 993RS, 993TT and 993GT2 standard engines were fitted with the same crank which had the same journal diameters as the 964 but was made with thicker crank webs for additional stiffness. This change necessitated a reduction of the big end journal width from 22mm to 19mm, which ironically made the crank heavier but the added stiffness meant that it could run without a damper and with lighter rods & pistons* made the overall assembly lighter.

With the GT3 engine Porsche returned to the 22mm wide big end journal but reduced the diameter to the 911SC size of 53mm which has the effect of reducing the surface velocity of the bearing, allowing safer high rpm use. Other changes to the oil flow allows this crank to be safely used at 9000rpm on track.

I currently run a stock 993 crank in my 400+bhp n/a RS engine and have seen no problems on track using up to 7900rpm, I also have customers with standard 993GT2 engines running the same crank at 500+bhp on track so I would say that there is not a major problem with using this crank in mildly modified standard engines. However if you wanted to run the engine at higher rpm I would recommend fitting the GT3 crank. For turbo engines where high rpm is not required the 964 crank is preferred for its maximum big end bearing area to cope with large rod forces (read torque).

* Connecting Rods
The 993 connecting rod obviously has a matching 19mm wide big end, but to reduce weight further the little end was also made narrower at 20mm compared to the previous 25mm of the 964/930 conrod. The piston was also altered, having the same 23mm pin dia but used a shorter pin with narrower bosses.
The early 993 n/a engines were fitted with a fairly lightweight rod which was subsequently replaced by the stonger version that was fitted to the RS & turbo engines as standard, and I believe that this heavier rod is now the only one available from Porsche.

The 9m race engine runs with a connecting rod with a 19.5mm wide x 22mm dia little end, again without any problems to date after 3 seasons racing.

Bill Verburg

According to the Porsche Mortorsport Technische Innformation Ersatzteile Katalog Rennversion 'Modell '97, 993 GT2 uses the same crank as the other 993 models and as Colin indicated the later reinforced rods, this is the set up w/ Raceware rod bolts that I have in my 3.8.

Red9

What Bill asserts is different to some respected opinions. Bill is backed up by part numbers as far as I can tell-- even 996 turbo crank does not appear to have different part nos. Can anyone throw some light on this -- with different relevent part nos.