A few months ago we talked about turbo engine modifications. After some thought, I’ve realized that a lot of people are modifying their 911 and 911 Turbo engines and are starting off with what I consider to be a shaky foundation. So, for all of you following my columns, let’s back up a little and talk about building an engine that goes beyond making gobs of power. Let’s build one that stays together. Let’s build one with a “Bullet proof bottom end.” 

 

I have found one of the weakest parts of the 911/930 engine to be the connecting rod bolts. These are the bolts that hold the connecting rod cap to the connecting rod, housing the connecting rod bearing that rotates around the connecting rod journal of the crankshaft. If you can, imagine an old locomotive, with a big external connecting rod going right to the drive wheel. This is what the connecting rod assembly looks like, on a smaller scale. Through the crankshaft, the connecting rod and its bearing turn the up and down motion of the piston into circular motion which then gets transmitted through the flywheel. On a downshift, the rod bolts want to stretch past their normal length. If the downshift is done at an engine rpm high enough, the bolts will stretch causing the clearances to become too large in the connecting rod cap (the big end), letting the bearing spin in its bore. This usually ruins the bearing, rod, and the crankshaft. The end result being another major engine rebuild. Since we’re here already, let’s start out right. A company called A.R.P. makes an after- market rod bolt that is much stronger and will take much more abuse than the stock unit. Going even further, you could opt to use Pauter racing rods when building a high performance Porsche engine. These racing rods come with even stronger bolts to hold it all together when the revs really go high.

 

Another modification that should go along with the crankshaft/connecting rod package should be the actual preparation of the crankshaft. The first thing to do here is to send the crank out to a crankshaft specialist to get it magnafluxed. Magnafluxing is an operation that is used to find any hidden cracks and imperfections. This procedure will let us know if the crank is worth using and deserving of further modifications. If it is deemed good, we then recommend center drilling the number four main journal. When used in conjunction with a specially grooved main bearing, this modification will feed the numbers two and five rod bearings directly with oil. The number two and five rod bearings are normally the last to get oil, making them more susceptible to oil starvation and thus spinning their bearings in their caps. With the above modifications performed, engine failure because of spun rod bearings is almost eliminated, within reason.

 

In the engine case there is lots of air that is being pushed around by the pistons as they fly up and down in their bores. It is a good idea to smooth out any obstructions inside the case. This will increase horsepower by reducing air turbulence inside the case. One of the most effective internal case modifications is called knife-edging or boat-tailing. This is where a machinist will take and reshape the backside of the case webbing (the side the piston sees as it reaches the bottom of its stroke) reducing air resistance inside the case.

 

In any high horsepower (over 350 hp) Porsche engine, the case should also be shuffle pinned. Porsche engines are seamed right in the middle and built up around and outwards from the crankshaft. Here is why the experts shuffle pin the case halves. When the engines are modified and run under high loads the case halves tend to “walk.” Shuffle pinning is nothing more than installing non-movable dowel pins that will stop the halves from moving under the high loads of a high horsepower Porsche engine. This makes a stronger engine case.

 

There you have it, starting at the crankshaft and working outwards, we have begun to build a high horsepower engine that will stay together. The list of modifications is endless and much leg work should be done before beginning. Remember, always start with a good foundation or the house may not weather the storm.