Why would you put 4 gears on a turbo and 5 on a non turbo
 

I've always wondered why a 930 came with 4 gears and the same year non-turbos had 5? Doesn't make sense. I would think you would want more gears for racing and less gears for every day driving, not the other way round.

Ours go to 11.

The 915 transmission used on non-turbo 911s at that time was not strong enough to support the power/torque of the 930 -- the 4 speed 930 transmission was. The later g50 5 speed transmission used on 87 and newer non-turbo 911s (and 89 and newer turbos) is strong enough.

4 speed was stronger and you dont need as many gears when youve got all that torque

I'm with everyone else here, it's because the 4-speed was the only transmission Porsche had available at the time that could handle the 930's power and torque. The G50, which was available the last production year of the 930 was even more durable, and from what I was told by another enthusiast, can handle 1000 hp.

Like others have written, the 930 box is essentially a strengthened 915. But as the gears are physically larger, I'm told, they couldn't fit 5 gears inside the 930 box. Hence, just 4 fwd speeds. For marketing purposes Porsche claimed that the additional torque of the turbo motor was enough that 5 gears were not necessary.

During the development and early days of the 930, the master plan was to kill off the 911 in favor of the 928. Stuttgart did not wish to spend any extra money developing a separate 5-speed gearbox for the 930. So the 930 made-do with the strengthened 915 box. As the 80s continued, it became clear that the 911 would continue (a la the 964), so money was appropriated to develop the proper 5-speed G50-50 gearbox which was fitted to the last year of the 930, 1989.

The 930 transmission was developed after the 915 box. The 930 box is actually a double over drive. 3rd and 4th are both overdrive. Honestly, you don't need another gear although some have changed their 3rd gear ratio to make it a more even spread between 2nd and 4th.

The early 75 - 77 930 trannys were different than the later 3.3L turbo boxes. The G50-50 used in the 89 930s was not just a normal G50.

The 930 tranny has stronger internals than the 915 tranny. Also, the 930 tranny goes to 65 mph in 1st, 95 in 2nd, 120 in 3rd, not sure what 4th can do, but that's enough for me.

I would be interested to know what is the tallest 4-th gear anyone has put into the road going 4-Speed 930 Tranny?

I have a modified(internally strengthen 915 5-Speed) mated to an 86' 930 motor.

My 2 thru 5th gears sound pretty much exactly like the first 4 gears on the 930 4-speed:

Mine:

2nd to 70
3rd to 100
4th to 120
5th to 155(indicated)

I've seen 150+ in third:( having my old girl for 30 years I'd always heard the 930 Trans was made for 750. True or not I liked that old wives tale:)

Also interesting is that Ruf got around only being able to put 4 gears in the 930 transmission by adding a fifth gear on the nose cone outside the box (where reverse normally is I believe)

No quite - I've never gone this speed in mine, but according to the factory owner's manual, 4th gear on a 1987 930 is good for 167mph. And an additional interesting tidbit in there - they claim it is safe to downshift from 4th to 3rd at 130mph in 4th.

I'm assuming that they didn't want to confuse you with too many gears to choose........ while you were spinning off the road....as the boost kicked in...............

no, the 915 was not strong enough. but porsche could have built a strong 5 speed.
but these cars were not built as race cars. they were built for 150 on the autobahn.
1st and 2second are VERY fast gears. flooring it in 1st is actually rather "violent" and it is something i dont do. i am guessing putting in another gear and having closer ratio gears was something that just was not needed.

i can do 60mph in 1st gear. with it as fast as it is already, imagine 30-or 40 in 1 st. yes i would love the gear ratios after that if i was on a track or racing,

It was a lessons learned from the 1974 24 Hours of Le Mans and from the 917's previous to that. With the 917's, they had 5 speeds and 4 speeds. The 4 speeds would lose a couple seconds a lap of Le Mans, but was much stronger, so was more likely to finish the race.

Like the 915 and 930 gearboxes, the cases were very similar, but the differences were in the beefier internals, bigger gears, bigger bearings, bigger shafts. With everything bigger in the same sized case, you have to give up a gear.

Porsche underestimated the torque of the 2.1L turbo they ran in 1974. If they hadn't, they might have won Le Mans in 1974 with a 911. You'll notice that all 934's and 935's used a 4speed.

1974 24 Hours of Le Mans - Wikipedia, the free encyclopedia

Porsche used a 4 speed because they thought 4 speeds were adequate, both for the street and the track. They made the gears bigger and the whole gearbox was beefed up, but it still had to fit in the space available. When they changed the clutch in the later cars, they actually had to move the engine towards the rear, as there just wasn't any more room left at the front of the gearbox.

The 930 gearbox wasn't "just laying around" when the 930 was developed. If it had been, they would have used it on the Carrera turbo race cars, which used a 915-based box that wasn't strong enough to cope with the torque and was know to fail. They lost a 5th gear in one at Le Mans that cost them a good finish. No, it was developed just for the 930, with an eye to using it in the 930-based race cars down the road. Porsche had also previously found 4 gears adequate in their other turbocharged race cars.
Some of the speeds you guys are quoting arre a little off the mark. There were slight differences here and there but a 930 would do around 53, 93 135 and 160 (power limited, not gearing limited in 4th) in the four gears. US cars probably wouldn't pull past 155 in fourth, the 3 liter cars maybe did 153. I've seen tests where the redline observed was anything from 6,250 to 6,800, thus you sometimes see different speeds quoted. I used 6,700, which gives the speeds I listed above, give or take a mph...

A 930 really doesn't need 5 gears, in it's stock form. If you bias the power towards the higher revs and reduce the lag, then a 5 speed might be useful. I prefer a 4 speed.

JR

It took me a while to get used to the 4-speed, but it's perfect for the 930, I preferred the longer gearing for sure in that car especially when on full boost, think a 915 would be shifting too much

Less Gears = Less shifting = Less time off power and in racing its really all about being on the power as much as you can, isn't it?....

And why overcomplicate something that works just fine....

Regards
Dave

Ha! Perhaps, but this would have only been applicable to numbnutzzz drivers that were unable to successfully operate the throttle! :D

That's a good 1 Al :D