1979 911Sc Tranny Diagram 9Shifting at speed) question

[FinallyGotOne]

I was just checking out my manual again as i was curious about the speeds i can go in certain gears.

from about 5MPH at 850 RPM to about 6750 RPM at 40 MPH in 1st gear

dropping to 2nd at 3900 RPMs to 6750 RPM to 69 MPH

then 4700 RPM shft to 3rd to 6750 RPM's to 102 MPH

drop to 5900 RPM through 6750 RPM to 130 MPH

5750 RPM to 6750 RPM maxing out at 155 MPH.

says based on 185/70 VR15 and 215 60 VR 15 tires and wheels.

is this real life info? or dyno with no drag, etc...

the full power curve only goes to 131 MPHat about 5300 RPM's and the acceleration curve shows 5th gear at max of 141 with what appears to be tapped out horses.

also it says the "ring ratio is at 3,87:1 no of teeth 8:31"
what exactly does this ring ratio info mean, and how does it affect performance.

So it does not all seem to jive, unless the tranny is simply capable of holding the above maximum statistics, but the engine itself with weight is not able to hit the max marks.

it shows 0-60 in aboutr 6.5 secs and 100MPH in about 15 sec's.

please feel free to expound all you want.

I dropped about 200 pounds I think by going to all fibergalss bumps and skirts. I really need to get to a weigh sytation so i can really weigh my car thou.

I wonder how much faster my speed and quickness is with the pounds i drop, and when at what point it just sort of makes very little difference. Like changing out my seats for race seats, or killing the A/C all together. Since i do not road race it, 1/100th of a second is no use to me.

I am finally no longer interested in "dragging off the line" anymore, but would like a bit more power trowards the middle and top end of 2nd gear.

[FinallyGotOne]

bumpity bump

[emcon5]

The tranny gearing chart in the manual is just math. With a 3.18:1 first gear ratio, a 3.875:1 final drive ratio, and 225/50-16 tires, you get ~5.9 MPH per 1K RPM.

The 5th gear number is theoretical, as your car doesn't have the power to overcome the drag needed to get to that speed.

The 8:31 is the number of teeth on the ring and pinion gears respectively in the final drive. You divide the teeth to get the ratio, 31/8 = 3.875:1. In other words, the pinion gear turns 3.875 times for each revolution of the ring gear.

Tom