Originally Posted by Peter Zimmermann
Let's look at this a little closer. The weight of a filled 915 RoW version 915/67 with cooler is approximately 60 kg (132 lbs). The cooler weighs almost nothing (I can testify to this because I've cleaned a number of them), so let's call the USA 915/68 at 130 lbs. The weight of a filled RoW G 50 version 950/00 is 66 kg (146 lbs), which is virtually identical to the USA version 950/01. So we have a weight difference between the two transmissions of 16 pounds.
The 915 flywheel weighs 12 lbs, and so does the G 50 flywheel, so that's even.
The stock 915 clutch weighs 18 lbs, the G 50 clutch weighs 29 lbs. So, in total, the G 50 package is approximately 27 lbs heavier, which was offset (in 1986) by an increase in rear torsion bar size from 24.1mm to 25mm. Something else comes into play here that contributes to the 915 car "feeling quicker" to some drivers. Back in the day of Hemi-Cudas, 427 Vettes, etc., the ticket to really quick quarter mile times was having a "short", 4.11 rear end (final drive) ratio, or an even shorter 4.56 ratio. Of course, the big compromise with a short ratio was having to run at much higher revs at freeway speeds. Cars with a taller, aka longer, 3.00, or 3.30 rear end (ring & pinion ratio) just wouldn't come out of the hole as quick, and the race was usually over in 2nd gear. In 1974, 911s were fitted with a 7:31 ring & pinion, which is a final drive ratio of 4.43 (remember, the bigger the number the shorter the ratio). Later SCs and early Carreras w/915s had an 8:31 (3.88) final drive ratio, BUT, G 50s are fitted with a 9:31 (3.44) final drive ratio. Yes, the factory fitted all new, "shorter" ratios to 1st-5th to try and make up for it, but, while striving for better mileage and reliability, couldn't overcome that "longer" ring and pinion, which can make, combined with the extra pounds, a G 50 car feel more sluggish than a 915 car. A lightweight clutch will help the G 50 car, but on a road course there should be very little difference between the two because the rpm drop between second and third, between third and fourth, and between fourth and fifth, is very similar when comparing a 915 to a G 50. Yes, the 915, in some situations, will "feel" quicker, but can it generate quicker lap times on a road racing course? I doubt it.
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