901 'box into Turbo
Discussion
Does anyone have a definitive answer on whether a 901 (5 speed) gearbox can be installed to replace the 4 speed on my 1980 (930/3.3) Turbo.
I heard that the 4 speed was spec'd because the 5 speed won't handle the torque but have been told by a guy who races a 930 that the 5 speed will work fine.
Is the straight answer 'yes' or 'no' and if 'no' - can you let me have your justification please?
Cheers
Demo
I heard that the 4 speed was spec'd because the 5 speed won't handle the torque but have been told by a guy who races a 930 that the 5 speed will work fine.
Is the straight answer 'yes' or 'no' and if 'no' - can you let me have your justification please?
Cheers
Demo
First of all I think you mean 915 gearbox, not 901, the 901 was only fitted to the 2.0 litre 911's and would not take to torque of anything over 300Nm, which basically rules out any 911 engine making more than 180bhp.
So, given that we are talking about a 915, to answer your question: yes, the 915 gearbox will fit into a 3.3 turbo shell, move the engine forwards by 30mm, reduce flywheel mass and give you 5 gears. But if only life was that simple.....
Gearboxes are torque conversion devices and generally are oblivious to the power of the engine that you strap on the back, but the gears themselves have a torque rating that they can comfortably cope with before they break. Porsche rate 915 at about 300Nm (approx 220lft) but it is generally thought that this rating is conservative to the point of being almost 50% of its ultimate capacity. In practise the maxumum torque that a standard 3.2 Carrera gearbox will accomodate is around 400-440Nm, although with expensive modifications it will cope with 540Nm (400lbft).
So, what does this mean in real terms? In a nutshell you can drop a standard (but fresh) 3.2 Carrera gearbox into a standard 930 and it will cope admirably, but if you modify the engine to more than 350bhp you are asking for trouble with 1st & 2nd gears and the differential beariing support area of the box. For more powerful engines my recommendation is to modify the casing of the gearbox with a steel insert & cover to support the bearings and to revise the lower gear ratios with stronger/taller gears that will take the torque. A further option which works on all 915 boxes is to replace the 915 syncros with the 930 turbo syncros, these last longer and allow faster "racing" gear changes.
The shopping list of parts that you will need are:
915 gearbox
915 gearbox mount (may need modification)
915 gearlever assembly
1978-80 SC flywheel & spigot bearing (fits all years)
915 ring gear
915 heavy duty clutch package (std will barely cope)
915 clutch release arm/omega spring
911 3.0/3.2 engine front tinware (either side over box)
Space for engine mount or bend rear beam in press
3.2 "S" pipe (oil feed pipe from tank to oil cooler)
930 gearbox output flanges (use the ones out of your old 4 speed)
I think that just about covers it. If you are serious about building a 915 for high torque you will have to contact me direct on 01925 242342 during the week as there is too much information to write down on a Saturday morning!
So, given that we are talking about a 915, to answer your question: yes, the 915 gearbox will fit into a 3.3 turbo shell, move the engine forwards by 30mm, reduce flywheel mass and give you 5 gears. But if only life was that simple.....
Gearboxes are torque conversion devices and generally are oblivious to the power of the engine that you strap on the back, but the gears themselves have a torque rating that they can comfortably cope with before they break. Porsche rate 915 at about 300Nm (approx 220lft) but it is generally thought that this rating is conservative to the point of being almost 50% of its ultimate capacity. In practise the maxumum torque that a standard 3.2 Carrera gearbox will accomodate is around 400-440Nm, although with expensive modifications it will cope with 540Nm (400lbft).
So, what does this mean in real terms? In a nutshell you can drop a standard (but fresh) 3.2 Carrera gearbox into a standard 930 and it will cope admirably, but if you modify the engine to more than 350bhp you are asking for trouble with 1st & 2nd gears and the differential beariing support area of the box. For more powerful engines my recommendation is to modify the casing of the gearbox with a steel insert & cover to support the bearings and to revise the lower gear ratios with stronger/taller gears that will take the torque. A further option which works on all 915 boxes is to replace the 915 syncros with the 930 turbo syncros, these last longer and allow faster "racing" gear changes.
The shopping list of parts that you will need are:
915 gearbox
915 gearbox mount (may need modification)
915 gearlever assembly
1978-80 SC flywheel & spigot bearing (fits all years)
915 ring gear
915 heavy duty clutch package (std will barely cope)
915 clutch release arm/omega spring
911 3.0/3.2 engine front tinware (either side over box)
Space for engine mount or bend rear beam in press
3.2 "S" pipe (oil feed pipe from tank to oil cooler)
930 gearbox output flanges (use the ones out of your old 4 speed)
I think that just about covers it. If you are serious about building a 915 for high torque you will have to contact me direct on 01925 242342 during the week as there is too much information to write down on a Saturday morning!
DDan, I am afraid you need to go back to school and read up on your 911 history. The 964 had a 5 speed G50 box, it was only the 993 variants that had the 6 speed version. Like UV said, the strongest of all the G50 boxes are the turbo variants from the 930 and 965, the best for this job being the G50/50.
However these are an absolute sod to fit into the non-G50 shell because there are structural modifications required. We have and can do the job, but if I tell you that we start by putting the car on a jig and cutting out the centre of the rear torsion tube you can begin to understand the work required, you need to budget for at least £3000 + parts to do it properly, so the cheaper option is usually to sell the car and buy a G50 version.
However these are an absolute sod to fit into the non-G50 shell because there are structural modifications required. We have and can do the job, but if I tell you that we start by putting the car on a jig and cutting out the centre of the rear torsion tube you can begin to understand the work required, you need to budget for at least £3000 + parts to do it properly, so the cheaper option is usually to sell the car and buy a G50 version.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&rd=1&item=2493484643&ssPageName=STRK:MEWA:IT
Sorry - thrown by this item available on e-bay (item number 2493484643) - it is a 6-speed box but has a 964 part number so thought it might be a late 964/Turbo 2 box.
Anyway - question still stands would it fit?
Sorry - thrown by this item available on e-bay (item number 2493484643) - it is a 6-speed box but has a 964 part number so thought it might be a late 964/Turbo 2 box.
Anyway - question still stands would it fit?
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