901/05 hillclimb gearbox

gestalt1 · 09-24-2008, 03:25 PM

hi all, i opened up my 901/05 gear box to see what ratios it has and as suspected it has the vowel box (AEIOU) gears for hillclimbs. i punched the #s into the gear calculator and found that at 60mph i'll be running 3500rpm. this car is going to be used as a fun car for track and a little street use. i think these gears will be great on the track but i'm concerned about the drive home being a little tiring. does anyone else run these rations or something close? the 911 is a 68 that will be an under 2000lb 911r clone with a short stroke 2.5 engine.

GrantG · GrantG's Garage

I used to have gears that were fairly similar (I don't know what the ratios are for those letters, but I had similar mph/revs in 5th). It is not too bad, unless you take a long trip on the highway with high speeds. Driving at 5,000+rpm for hours at a time is a bit tiresome.

But, driving on the track with low/close gears is worth the trouble (as long as your track isn't fast enough to cause you to run out of revs in top gear). Your car will feel really lively. LSD is a must with those gears with plenty of applied torque to light up the tires on corner exit.

What's the redline of that 2.5L SS?

If you tell me the actual gear ratios (numerical) and Ring & Pinion and tire diameter, I'll send you a graph & spreadsheet.

Flieger · Flieger's Garage

gestalt1 · 09-24-2008, 06:21 PM

i actually have the spreadsheet to calculate the speed in gears etc.. very useful tool. the engine is not built yet but i'm thinking that 8k rpm redline would not be difficult with the 66mm counterweight crank. i find the trans charts interesting because this transmission is not listed - there is no doubt that the # is 901/05. not sure why but it does have the same ratios as the 902/50. also, good point about the LSD, i was hopeing to stay with the open diff for now (save money) but it might make sense to go with an LSD. too bad there arn't hills around chicago!

GrantG · GrantG's Garage

Quote:

Originally Posted by gestalt1

good point about the LSD, i was hopeing to stay with the open diff for now (save money) but it might make sense to go with an LSD. too bad there arn't hills around chicago!

You won't regret an LSD. I have a Guard clutch-type asymetrical unit and it really helps with braking and corner entry stability in addition to the better traction under power.

8k redline and low gears is a great mix (make sure your cam makes power up there).

gestalt1 · 10-30-2008, 04:17 PM

Well, i actually took the gearbox apart and found I was wrong about the gears in it, it has A,F,M,S,X. Basically it is the same as the 902/1 and 902/02. Some of the teeth on the gears have a little rust on them, is this a problem? Also, the case is aluminum, is there any advantage with the aftermarket billet intermediate plate over the stock aluminum one?
thanks!

Steve@Rennsport · 10-30-2008, 05:32 PM

Quote:

Originally Posted by gestalt1

Well, i actually took the gearbox apart and found I was wrong about the gears in it, it has A,F,M,S,X. Basically it is the same as the 902/1 and 902/02. Some of the teeth on the gears have a little rust on them, is this a problem? Also, the case is aluminum, is there any advantage with the aftermarket billet intermediate plate over the stock aluminum one?
thanks!

Thats really a GREAT overall gearstack,...

If you have any surface rust, just clean it off with Scotchbrite and inspect the surfaces to make sure there is no pitting whatsoever.

Aftermarket billet intermediate plates are far stronger and more rigid than OEM ones.

jpnovak · 10-30-2008, 06:24 PM

I thought 901/05 was the designation for a special order box. I recently got one that was A, F, J, O, V. Talk about short gears.

gestalt1 · 10-30-2008, 06:29 PM

thanks Steve for the info. I was also told it was a special order gearbox that supposedly had hillclimb gears in it. the seller was not sure what they were, the price was cheap so i did not really care. it would make sense that porsche had a separate # for gearboxes with non-standard ratios.

Jandrews · 10-30-2008, 06:46 PM

I have a '71 911/01 gearbox with A,F,N,V,Zd Kind of the opposite end of the spectrum...I never use 5th gear on the track, but it is nice for the ride home. This gearbox sits in front of 2.7RS motor with MFI (210 HP or so). 2nd gear is good for about 62 mph at 7,300 rpms, 3rd about 92, and 4th about 125....just about the max for the track I drive.

I would second the recommendation for the billet intermediate plate if you are going to be putting a fair amount of power behind it.

JA

Brant · 10-30-2008, 07:36 PM

You'll like the short box on the track

I'm currently running F/J/O/S/V and love it
900rpm between 4th and 5th!

zap26 · 02-27-2011, 09:41 AM

I have two boxes a 901/05 and a 911/01, I was thinking of using the 911/01 gears in the 901/05 as I need the earlier style box to work in my project, any ideas if this swap would work if not Ill try and sell the 911/01 and examine the gears in my 901/05, Thanks for any help and input

911pcars · 02-27-2011, 09:49 AM

My 911 had a 4-speed in it. When I converted to a 5-speed, I obtained a 901 with a 6:29 rear end. At approx. 60mph, the engine buzzed at 4000 rpm, but great for low end umpf. I later replaced it with a 915 with more normal gearing.

Sherwood