Why 912 gears in tranny? Options

[HeloMech]

So I was going over what has been done to the 74 1.8 914 I'm picking up. There was mention of having put 912 gears in the tranny. What's the reason for this? pros? cons?

[Aaron Cox]

QUOTE (HeloMech @ Oct 26 2005, 11:58 AM)

So I was going over what has been done to the 74 1.8 914 I'm picking up. There was mention of having put 912 gears in the tranny. What's the reason for this? pros? cons?

5 speed or 4?

A F M S X iirc is a 912 5 speed. very short 5th.... and make good gears for a track box.
if a 4 spd...

A H Q X...

let me know if you are unloading em, weve got some 914 gears (all but a 5th) you can have.

[Dave_Darling]

A similar question came up on the Bird's Tech Support system recently. My reply is below:

QUOTE

The 914's 5th gear is the tallest of any installed in the 901-type gearboxes. The stock ZD 5th gear of the four-cylinder 914s was a 31:22 gear, which gave a 0.7097 ratio. Couple that with the 7:31 ring andpinion, and you get a very tall gear indeed. The ratios for the four-cylinder 914 transmission were: 11:34, 18:34, 23:29, 27:25, 31:22. If my information for the four-speed 912 transmission is correct, the ratios were: 11:34, 19:32, 24:27, 28:24. I believe the four-speed 912 gearbox used the same 7:31 ring and pinion as the 914 gearbox does. I hope this helps!

There was also a five-speed gearbox used on some 912s. A Google search on "porsche 912 gear ratio" should turn up some info.

--DD

[lapuwali]

QUOTE (Dave_Darling @ Oct 26 2005, 12:27 PM)

A similar question came up on the Bird's Tech Support system recently. My reply is below: QUOTE The 914's 5th gear is the tallest of any installed in the 901-type gearboxes. The stock ZD 5th gear of the four-cylinder 914s was a 31:22 gear, which gave a 0.7097 ratio. Couple that with the 7:31 ring andpinion, and you get a very tall gear indeed. The ratios for the four-cylinder 914 transmission were: 11:34, 18:34, 23:29, 27:25, 31:22. If my information for the four-speed 912 transmission is correct, the ratios were: 11:34, 19:32, 24:27, 28:24. I believe the four-speed 912 gearbox used the same 7:31 ring and pinion as the 914 gearbox does. I hope this helps! There was also a five-speed gearbox used on some 912s. A Google search on "porsche 912 gear ratio" should turn up some info. --DD

A F M S X

Most 912s in the US were five-speeds, btw. The five-speed was standard from '65 to '69 in the US, and the four-speed was an option in '67-'68.

[Joe Ricard]

Not to hi-jack but I just picked up a free either 66 912 box or 69 911T box.

Haven't looked at the Numbers yet but I am optimistic about the gears inside. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Aaron Cox]

QUOTE (Joe Ricard @ Oct 26 2005, 02:46 PM)

Not to hi-jack but I just picked up a free either 66 912 box or 69 911T box. Haven't looked at the Numbers yet but I am optimistic about the gears inside. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

nice.

4 speed boxes pay off well (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

BTW - 911 box would have a GA mainshaft if its a five speed....
ie - the same 2nd as a 914.6

[Bleyseng]

912 Transmission 5-speed 902/1, #163001-165214
923/02
902/02
902/50 (close-ratio 5 speed)
Gear ratios, 902/1 and 902/02 5-speeds 11:34, 18:34, 22:29,25:26, 28:24
Grade climbing, standard 5-speed,2490 lb. load 46, 25, 16, 11, 8%

4-speed 902/1(USA), #234001-238942
902/01
Gear ratios, 902/01 4-speed 11:34, 19:32, 24:27, 28:24
Grade climbing, standard 4-speed,2490 lb. load 46, 21, 12, 8% N/A
Axle ratio 7:31:1 7.31:1
Final drive ratio 4.428:1 4.43:1
Oil Capacity 2.65 quarts N/A
Taken from the 912 Registry Specs.

I have taken the 3rd gear "M" (22:29) and 4th gear "S"(25:26) and installed them in my tranny leaving the "ZD" 5th for freeway driving. Should make a good close ratio 914 box for AX and track with the 50 series tires I run.