5 speed gearbox - how much power can they take? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Escy · 10-21-2015, 12:50 PM

Is anyone pushing a 5 speed gearbox? I want to put about 500bhp and 500ft/lb through one, the 6 speed will need some modification to work, the 5 speed would bolt straight up. I've read the 6 speed is stronger but I don't even know if that is man enough for that sort of power.

I'm just looking to see who's running what and at what sort of power level

JayG · 10-21-2015, 03:48 PM

what are you putting the Batmobile Turbine engine in it?

Escy · 10-21-2015, 03:52 PM

Audi 2.7 bi turbo

JayG · 10-21-2015, 04:34 PM

I don't think the 5 speed can handle that much power
Bear in mind the stock engine is ~200 HP with the 5 speed

If you take the time to do a search, you should find your answer
There have even been some recent posts about this
You even posted in one of them

You also may want to check boxa.net
it's a similar forum, but UK based

Escy · 10-21-2015, 10:33 PM

There doesn't seem to be many highly modified Boxster's in the UK. I thought I read on here about someone running a 996 turbo engine on a 5 speed.

The Radium King · 10-22-2015, 08:26 AM

i'd check the kitcar forums (like gt40) were they use this tranny on some bigger builds. given that it is an audi 012 unit there might be some info from those guys too as they do some big turbo builds.

most people who do forced induction on this board get shouted down so not a lot of info there. perhaps track down some of the LS swap guys on this board and see what they are running.

beyond that, there are differing opinions. some guys are running 300 hp 996 engines through them no problem, other guys are blowing them up at the track with 2.5 engines. they are a relatively small, lightweight unit.

What are the drawbacks of the 986 6-speed? it is the strongest of the lot. note that 987 trannys share the same bolt pattern and might be an option.

Escy · 10-22-2015, 01:46 PM

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 · 10-24-2015, 07:49 AM

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 · 10-24-2015, 08:12 AM

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 · 10-24-2015, 08:18 AM

Quote:

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.

Escy · 10-24-2015, 08:47 AM

I was planning on modifying the bellhousing on my G86.20, was going to put a hole in it for the flywheel sensor and add a few more holes for the missing bell housing bolts (the majority are fine anyway).

You don't happen to know what type of signal is generated from the vehicle speed sensor do you? I'm hoping it'll be the same as what my Audi ECU will want to see.

All the trans options are open to me but I want to go the easiest route. An 01E is dirt cheap, and will match the engine perfectly but i'll need to fabricate mounts and shifter linkage so that's my least favourite option at the moment.

Escy · 10-24-2015, 09:17 AM

I do like the idea of the 987 gearbox, it sounds like it could be the perfect bolt in solution. Do you know what clutch plate fits the 987 box? Is it the same as the 986? I prefer the clutch options available for the Audi 01E.

kcpaz · 10-24-2015, 11:41 AM

Quote:

Originally Posted by Escy

I do like the idea of the 987 gearbox, it sounds like it could be the perfect bolt in solution. Do you know what clutch plate fits the 987 box? Is it the same as the 986? I prefer the clutch options available for the Audi 01E.

I'm not an Audi guy, so I can't say for sure which clutch/flywheel package you would need. I know the 987 6 speed is very similar to the 01E, but I can't say for sure if the 01E flywheel and clutch would work. you should contact 034 Motorsports about it. That's who I got my ABZ flywheel insert and clutch kit from for my 987 6 speed

Escy · 10-24-2015, 01:13 PM

The Audi and Boxster clutch plates are both 240mm so i'll be using a flywheel and clutch pressure plate for the Audi but clutch disc won't fit the G86.20. Do you know if the G86.20 and G87.20 clutch discs are the same?

I've found a G87.20 for a good price so I might go for that. Can I use the 86 outer CV joint on the 87 shafts?