Rod requirements
Discussion
For 3.3 930 or 965 engines you do not have a worry unless you are going to take the engine over 7500rpm* as the stock 930 rods are very strong. If you need a reference for this statement ask Richard Chamberlain, he uses balanced & shot peened 930 rods in his "935".
The 964 based engine also uses 930 rods, so there are will be relatively few issues with running a 3.6 on a 964 crank.
The 993 based engines are a different matter. In order to reduce inertia, Porsche designed and fitted a stiffer crank with narrow big end bearings to all 993 engines. The good news is that this eliminated the need for the harmonic balancer (heavy fan pulley) as used onthe 964, the bad news (for turbo engines) is that the connecting rods were significantly lighter. For the TT engine Porsche beefed up the rod (and subsequently fitted this heavier rod in to the RS & all production engines) but this rod is still a weak link when it comes to handling high cylinder pressures, both in terms of its own stiffness and the area of the narrower big end bearing. The quick fix for very high torque 993TT and GT2 engines is to fit the 964 crank with 930 or aftermarket rods.
* I should qualify that I would only use 930 rods at this rpm on turbo applications, by their design the 930 engine has smaller lighter flat top pistons and the overlap loads are less than on an atmo engine due to the intake pressure.
The 964 based engine also uses 930 rods, so there are will be relatively few issues with running a 3.6 on a 964 crank.
The 993 based engines are a different matter. In order to reduce inertia, Porsche designed and fitted a stiffer crank with narrow big end bearings to all 993 engines. The good news is that this eliminated the need for the harmonic balancer (heavy fan pulley) as used onthe 964, the bad news (for turbo engines) is that the connecting rods were significantly lighter. For the TT engine Porsche beefed up the rod (and subsequently fitted this heavier rod in to the RS & all production engines) but this rod is still a weak link when it comes to handling high cylinder pressures, both in terms of its own stiffness and the area of the narrower big end bearing. The quick fix for very high torque 993TT and GT2 engines is to fit the 964 crank with 930 or aftermarket rods.
* I should qualify that I would only use 930 rods at this rpm on turbo applications, by their design the 930 engine has smaller lighter flat top pistons and the overlap loads are less than on an atmo engine due to the intake pressure.
My understanding is that on the 993tt (on the 996tt the numbers are slightly different) there are 2 issues with the stock rods. At peak torque levels of somewhere north of 750NM, a stock rod will bend, simply too much force. Here is my little beef - You won't have 750+ real NM (not the chassis dyno unloaded stuff) and have straight stock rods.
My experience was an engine which was putting out 757NM on the engine dyno, probably closer to 800NM on the road whilst overboosting bent a set of GT2 rods - I'm not sure how these differed to stock 993tt, but apparently some early 993tts were fitted with them, I think they were supposed to be closer matched and stronger (but not certain) - anyway, they all bent
The answer to this first problem is Carillos - fit them and forget. Its what all the EVO racers ran with 850NM torque.
The second "rod" problem is a bit more complicated. My understanding is that at high real power levels and at high revs 6000-7500rpm an inherant imbalance manifests itself and throws one of the rods, usually through the side of the case. It is always the same rod. The top racing teams have a fix for this, but its only really necessary above 520 real hp
My experience was an engine which was putting out 757NM on the engine dyno, probably closer to 800NM on the road whilst overboosting bent a set of GT2 rods - I'm not sure how these differed to stock 993tt, but apparently some early 993tts were fitted with them, I think they were supposed to be closer matched and stronger (but not certain) - anyway, they all bent
The answer to this first problem is Carillos - fit them and forget. Its what all the EVO racers ran with 850NM torque.
The second "rod" problem is a bit more complicated. My understanding is that at high real power levels and at high revs 6000-7500rpm an inherant imbalance manifests itself and throws one of the rods, usually through the side of the case. It is always the same rod. The top racing teams have a fix for this, but its only really necessary above 520 real hp
Gassing Station | Porsche General | Top of Page | What's New | My Stuff