Last Updated: 12/10/2013
I recently purchased the
The basic mechanical process of the modification is fairly obvious; remove the air cleaner housing, the alternator, the A/C compressor and the cast aluminum bracket that mounts on the driver’s side of the engine block and balance shaft housing. The new bracket is attached (using the same mounting holes), the alternator is mounted to the new bracket, the new fan belt is installed and the job is basically complete.
As in all of these projects, the reality is somewhat more involved. The first thing that I noticed was that the new belt was wider than my original belt. The crankshaft and alternator pulleys on my car have five ribs, not six. I did a little research and found out that a 5PK720 belt is no longer available. The alternatives are a 5PK710 and a 5PK736. I called Jason, explained the problem, and he readily sent me a replacement belt. I opted for the longer belt (5PK736) figuring that I can always shim the new bracket out from the block if there is not enough range in the adjustor. I suspect that the narrower pulleys are fitted to the earlier cars and mine (October, 1984 manufacture) had not been updated.
As I removed the old alternator bracket, it became apparent that one of the mounting bolts was shorter than the other three. I then realized that the new bracket was thinner than the old one by 10mm. A quick trip to the hardware store for new bolts (M10x1.5x70) solved this problem. (Note: You need to inspect the threaded mounting holes in the block and balance shaft housing. This bracket has probably never been removed from the car and there may be some corrosion on the threaded surfaces. You may want to install threaded inserts before proceeding.)
The conversion should now proceed smoothly. The A/C compressor comes out from beneath the engine (Take care not to lay it on it’s side as the lubricant will leak out. It can be safely placed “nose down” until the oil is drained.). The Freon lines need to be disconnected. The dryer and condenser need to be removed. The condenser is most easily removed by first removing the front spoiler. You must then take out the radiator as the condenser is mounted to the perimeter frame of the radiator. The aft end of the Freon lines need to be disconnected under the dashboard at the ventilation unit. Take your time; it seems like they are supported to the chassis and firewall about every 8”. The total weight of the parts removed is 25 lbs.
Once the new bracket is mounted (mounting bolts are torqued to 36 ft/lbs), the alternator is installed from underneath the car. Depending on the age of the alternator, you may want to have it re-bushed prior to installation. Any auto electric shop can install new bushings and diodes. The power steering belt must be removed before the alternator belts can be exchanged (You may want to replace it at this time. Add it to your parts list). The same type “drop link” adjustors are used for both belts. I found that the adjustor for the compressor used a larger bolt (at the compressor end) than the alternator required. You have several choices here. You can “sleeve” the bolt hole in the alternator end of the adjustor, you can drill and re-tap the mounting hole in the adjusting flange of the alternator to accept the larger bolt or you can order the correct adjustor from Porsche (part # and price). Fortunately, I happened to have the correct adjustor on hand.
With all of the correct bits and pieces at hand, this should take an afternoon (3-4 hours). You end up with 25# less weight in the front of the car, a small amount less parasitic drag on the engine and the alternator sitting as low in the car as possible. If your car competes at close to the minimum allowable weight, you may now have the opportunity to add ballast at a more advantageous location. I have found that the best ballast is the lead anode plates found at the larger marine supply shops. They are available from 5-50 lbs and are usually flat and pre-drilled for mounting.
Credits: Kevin Kehoe