A early 911 owner asked recently about installing a larger capacity starter on his up-graded 3.0 SC engine to help hot starting problems. The starter on rare occasions refuses to crank the engine - seems to happen when you least need it to.
Yes the higher capacity starters do help spin the engine in cold weather and when they are hot. I have installed the later 911 starter with 1.5 hp. This evolved from the early 0.8 hp starters that worked OK for engines up to 2.2 liters.
The factory installed 1.5 hp starters in the beginning of 1972, then in their wisdom reverted back to the 0.8 hp starter in May of 1972, using these until the beginning of 1974 when all production 911 cars came with 1.5 hp starters.
The 1973 Carrera 911 RS 2.7 came with a 1.5 hp starter and was available on special order. There are specialty retailers offering even greater hp starters for the Porsche. Some of these use Japanese starters with a Porsche type frame mount. These have very small size motors with very high out put from geared reduction. They are compact and reliable.
The factory 1.5 hp starter also came with another critical improvement. The battery-starter lead was increased in size from 25mm/2 (cross section) to 35 mm/2, (these had a yellow stripe applied around the cable at approx. 800 mm from the starter end). This cable enlargement was necessary to carry full battery capacity to the starter to enable it to deliver full cranking horsepower. While a 3.0 SC engine will need a 1.5 hp starter it will probably not get 1.5 hp worth of battery power until you have the correct cable size to transmit it.
Having experienced the need for more power to the starter on my little blue turbo car I realized the need to up-grade my old starter cable. I bought a good used cable and started the project by disconnecting the battery (installing a 9 volt radio code saver in the cigar lighter).
Remove the driver's seat, carpeting on the floor, center tunnel cover, console, floor board under the pedals, and trans. tunnel cover. The trunk carpeting needs to be pulled back a little.
Jack and safety stand the rear of your Porsche to allow plenty of room to access the starter area. Using a good flash light and a mirror inspect the old cable and pushed away the plastic covered body wraps that hold the cable in place away from all those pedal controls, wiring, fuel lines, and shift linkage. If you find other junk in there it is a good time to remove it. Also inspect the throttle rod plastic bushes. they turn yellow with age and deteriorate. The throttle pedal feels sloppy-etc. this is a great time to replace them.
The shifter and hand brake need NOT be removed.
Start in the trunk by removing the battery cable end. Solder a "end lug" onto the copper cable. Next wrap wire through the newly soldered cable end and the new cable 35 mm/2 starter end, this will enable you to pull the new cable through the body structure and have the new starter end lug arrive at the starter. You will need to coach the cable through with a little encouragement. The new cable is about 11.5 mm in diameter and the old one is 10.2 mm-get it? It takes time but when the new cable is installed on the starter you can back track forward pulling a little slack from the front as you go from rear to front to smooth out the cable routing. Secure the body wraps and work up to the trunk.
The cable may need to be shortened at the battery end, to avoid too muck extra cable length flopping around. I would recommend a new battery connector, anti-corrosion felt washers, and dielectric paste on the connections.
Remove the radio code saver 9v battery, and you are ready to try your full 1.5 hp starter system. I noticed a immediate improvement in the starter sound. The pitch of the motor was higher, and the starter cranked faster at every start. I also observed a higher voltage at the voltmeter (an add on), as soon as the alternator was charging.
I have also noticed brighter headlights at night, and the two fuel pumps run a little quieter. This may not solve a sick starter problem but it is a must to gain anything from a improved capacity starter and battery.
Lee Rice writes the monthly Technical & Safety column for the Orange Coast PCA (zone 8) Newsletter. He has generously allowed Pelican Parts to republish these articles here for the benefit of everyone who visits the site.