Porsche 911 C4 Lightweight

January 15th, 2010

            As any car enthusiast tends to do I probably spend more time than I should looking through car classifieds on the Internet and in the back of magazines. Most of the time such searches are in vain, but once in a while we come across something that warrants further investigation. 

            In the October 2006 issue of Genroq, a Japanese car magazine, I found a listing for a 1991 Porsche 911 C4 Lightweight in Grand Prix White. After some Internet research and a slew of emails to Japan I planned a trip out to Fukuoka on the west coast of Japan in November to inspect first hand whether or not this 911 was the genuine item. 

            The 964 C4 Lightweight is somewhat of a black sheep in the history of limited edition/performance 911’s. It is not road legal in most countries and, as the C4 notation denotes, its four-wheel drive running gear from the 1986 953 rendered it in violation of most (if not all) existing GT competition rules of the time. As a result, unlike the 911R, 911ST, RS, or GT2 the C4 lightweight has no competition provenance of which to speak. 

            In total 21 C4 Lightweights were produced out of Weissach bearing six digit VIN’s using the format ‘964_001’. The body was stripped similar to the M003 RS option, use of Plexiglas for the side windows and aluminum for the doors and front and rear deck helped pare weight down to around 2,400 pounds. Four-wheel drive running gear from the 953, complete with manually adjustable front-rear and left-right torque bias adjustment, powered by a standard Cup Car engine mated to a close ratio gear box provided for an estimated 0-60mph sprint of around 4.5 seconds. Keeping the four magnesium Design 90 wheels planted to the road was a fully adjustable Cup Car suspension. 

            The car I was traveling to see in Fukuoka was VIN number ‘964_013’, the thirteenth lightweight to come out of Weissach.   The odometer showed 5,500km and apart from some slight paint wear the car was in very good condition; the engine bay was clean, the wheels free of any curb rash, and the body did not show any signs of previous bodywork. The previous owner had the engine sent back to Weissach in 1993 to fit larger heads increasing engine capacity to 3.8 liters. Additionally, at one point the final drive was changed to 3.44 from 4.65. 

            In February 2007 the car arrived in the Philippines. The first time we started the engine it was akin to a 21-gun salute using shotguns. Our first test-drive showed that the engine was running smoothly, the gearbox shifted nicely, and the absence of any major issues.   Due to the low mileage and good condition of the body we decided to focus any needed maintenance on mechanical issues. The laundry list of improvements included new tires, a new floater for the fuel tank gauge, reconnecting the oil cooler, and installing the original final drive. 

            Unlike your typical 911 the C4 Lightweight is not the kind of car you can drive at 9/10ths right out of the box. In order to get the most out of the C4 you need to invest the time and effort to get the chassis set-up right. For this purpose we scheduled a day at Batangas Racing Circuit for some track time. 

Six hours and 15 hot laps later with numerous adjustments to brake bias, camber, toe, etc. resulted in a set-up that is aggressive for the street but easy to manage on the track. Throughout setup, due to a lack of documentation on how to adjust the torque bias of the four-wheel drive, we decided to leave the system in its default setting. 

            As far as a driving impression, once you learn how to start off smoothly using a sintered racing clutch the C4 Lightweight is a relatively easy car to drive. Despite the Cup Car suspension it does not belie the fact that the components were designed more than 18 years ago. As such, the uni-ball suspension moves around more than some modern day offerings. You can really feel the weight transfer at work between accelerating, breaking, and entering into and exiting a corner. However, the moment of inertia helps the car to settle confidently into a corner as the tires find their grip, and with the right set-up the rear-end feels like it is pivoting through the turn following the front. Regardless of its four-wheel drive underpinnings, the C4 Lightweight feels 100% rear-engined when it’s on the move! 

At first, the weight transfer can feel a bit disconcerting, but after sometime you learn to trust what the car is telling you through the steering wheel and your ‘seat of the pants’ barometer. This car definitely handles as opposed to more modern machinery where ultimate grip tends to substitute for handling prowess. Needless to say, the 964 turbo brakes and calipers have no trouble hauling this 2,400lb ballerina down to a stop.

            Currently, after installing semi-slicks and straight-pipes for the exhaust, the car is a bit too extreme to be driven on public roads. Moving forward, we are still trying to find another ring and pinion set to return the final drive ratio to original and we will most likely refit more street friendly rubber and a quieter exhaust system. Otherwise, I don’t think we would be able to attend any Porsche Club meetings without seriously offending the neighbours!

Bryan jr.
January 2010