5 speed gearbox - how much power can they take?

[Escy]

I have considered the 987 3.2 box but they are harder to source and more expensive, plus i'm not sure how much work it'll take to fit into a 986.



That's a photo of my G86.20 (6 speed Boxster S) transmission with the Audi 2.7 Spacer plate fitted. There are 5 bolt holes which line up and both dowel holes line up (only one can have a bolt through it)

The other problem is there is no vehicle speed sensor on the diff housing (I assume the Boxster S uses the ABS sensors to generate it but i've not looked into it yet) and there is no mounting hole for the crank timing sensor on the flywheel sensor (that shouldn't be too hard to sort). The other problem is the starter motor location is in the wrong place, i'd need to notch the casing to fit it (it doesn't protrude that far into the bell housing.) Also, the Audi clutch plate won't fit the input shaft, not really an issue as both plates are 240mm but finding an off the shelf clutch plate that'll hold 500bhp might not be easy.

None of these issues are enough to stop me using the 6 speed but when the 5 speed bolts right up to the engine and has provisions for the sensors I might be making things more difficult than they need to be. That's if it can handle the power.

[itsnotanova]

Might be easier using the 2wd 01E. From what I understand, they're not too hard to find over there. We have to import them here.

[kcpaz]

Use the 987 6 speed and be done with it. It's a direct bolt on to the Audi engine, and it will bolt right into the 986 chassis with the matching mounts, and you can use the 987 shifter cables. The 5 speed WILL NOT be strong enough if the HP and TQ numbers you quoted are actual. The only tricky part will be the axle shafts since the 987 outer CV joints don't have the same reluctor ring for the wheel speed sensors as the 986 has. If you're resourceful though, the solution for that problem can be found using OEM parts from different years put together.

I'm doing the same thing in my race car, but using an ABZ engine. I originally planned on running the 5 speed since the ABZ doesn't make a whole lot of power, but changed my mind and switched to the 987 speed for the sake of reliability. I don't consider changing transaxles during my race weekend "fun".

[kcpaz]

Originally Posted by Escy

The other problem is there is no vehicle speed sensor on the diff housing (I assume the Boxster S uses the ABS sensors to generate it but i've not looked into it yet) and there is no mounting hole for the crank timing sensor on the flywheel sensor (that shouldn't be too hard to sort). The other problem is the starter motor location is in the wrong place, i'd need to notch the casing to fit it (it doesn't protrude that far into the bell housing.) Also, the Audi clutch plate won't fit the input shaft, not really an issue as both plates are 240mm but finding an off the shelf clutch plate that'll hold 500bhp might not be easy.

Neither the 5 speed, nor the 6 speed have a vehicle speed sensor in them for measuring vehicle speed. 986's and 987's use an output from the ABS to measure vehicle speed. On the 987 6 speed, the bellhousing casting has the location for the crank sensor just like the 5 speed, but it needs to be drilled out for the sensor and mounting hole, and tapped for the M6 retaining hardware, and you'll have to make some shims/spacers to set the sensor gap correctly with the reluctor ring on your flywheel. It's really not that difficult.