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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Strength is number one. Close behind is the gear ratios. The normally aspirated gets you through the large rpm drop that comes with the first to second shift sooner. The rpm drop with the later shifts is a lower rpm drop so one maintains a significantly higher average power level.

With a typical motor that dose not have variable cam, intake, or exhaust phasing or boost tapered by rpm the area where the motor makes it's most acceleration is arguably about 1500 rpm wide in most cases at best.

The 930 transmission has two significant issues.

1) First gear is on the tall side. This it mostly relevant to street drivability or drag starts. Thus if full boost is at 3500rpm we are at about 27 mph before we start to really get going. Put in a 915 and we are going to be going at about 20mph.

2) The RPM drop between gears and especially first to second with about a 2700rpm drop on a 930 transmission. This puts us in a lower part of the power range than comparable cars.


930 rpm drops:
2nd, 2700rpm at 53 mph
3rd, 1900 at 94 mph
4th 1800 at 137mph
red line at 197 mph.

915 rpm drops (NA G50 is simmilar):
2868 at 40mph.
1890 at 70mph
1345 at 95 mph
1368 at 120 mph
Red line at 155 mph

All are approximations.

If we could just tighten up the first to second rpm drop to 2000rpm our Power/weight ratio at the shift point would increase about 30%.

If we tighten up the rpm drop from say about 1850 to about 1350 or 500 rpm less we pick up about 15% more power at the beginning of later gear shifts.

Again, the difference in going from a 930 gear set to a NA gear set is about 30% more HP with the first shift and we are in second at 40mph instead of 53mph. In later gears we start out at up to 15% more power at the beginning of the next gears.
Old 03-13-2010, 07:52 AM
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