Been doing some research lately as to what gearbox I want to run once I finish my P12 head swap/full build on my sr. My goal is 500-700hp (still in early planning stages, running turbo numbers/figuring out what I really want from this) which has got me thinking about what to replace my sr 5 speed with. Obviously there are plenty of options. Lets run through them quickly.
Z32 TT gearbox- 5spd, requires adapter plate, can use sr clutch/flywheel, similar gear ratios to sr box, weight ~140lbs
Z33 gearbox (cd009)-6spd, requires adapter plate/custom bellhousing, can use sr clutch/flywheel, shorter gears, weight ~115lbs
*I didnt include s15 6 speeds or rb25 boxes in this comparison because theyre hard to find in the states and most likely couldnt hold this much power/torque. Obviously they are still options in the real world, but didnt make sense here.
*Needless to say any option is going to require a custom driveshaft and a custom transmission xmember.
*Im not including any comparison/info on speedo correction because I dont know much about it, and its been covered many times before.
Now heres the kicker, doing this research I discovered a couple shops (overseas) that make adapter kits for BMW transmissions. Both 5 and 6 speed zf/getrag boxes are known for holding very high power/torque, theyre pretty plentiful in the states, shift very nicely and quickly, and weigh fairly little. Ill compare the getrag 420g (E46 M3 gearbox) here.
Getrag 420g- 6spd, requires adapter plate, cut and shut bellhousing to relocate starter motor, must use conversion clutch/flywheel, shorter gears than the cd009, weighs ~102lbs.
This was enough to get me interested, one shop in particular has a few solutions to this.
http://www.pmcmotorsport.com/swap-so...arbox-bmw.html
Heres another option:
http://www.abc-clutch.com/portfolio/...ox-adapter-kit
and there are a few others that dont include clutches or flywheels.
These kits seem to be fairly similar in terms of cost to a full cd009 conversion, and carry the same benefits as well as a bit of weight savings. 5 speeds weigh about mid 70lbs, so pretty significant if you sacrifice the 6th gear. Couple things Id like people to weigh in on since I dont know if it would work, but say I wanted to use my os giken twin plate clutch/flywheel setup on the bmw box, since both utilize 240mm clutches could I swap the clutch disks to 240mm disks with the correct bmw input shaft splines and be able to use that setup?
Another maybe stupid thought, would it in theory be possible to use the SMG II gearbox from an e46 m3? It would bolt up to the adapter plate, and there are some standalone ecu's that should be able to control it alongside the SMG's TCU might be a relatively inexpensive route to a sequential gearbox?
Another benefit I can see to using a bmw box is this
https://cae-racing.de/CAE-Ultra-Shifter_49
If youve ever had the pleasure of shifting one of these, youll understand the allure. One of the best feeling things in a car hands down.
Its worth noting that Collins has an adapter for these BMW boxes to 1j's and 2j's so those of you running those engine swaps feel free to weigh in also.