Upgraded Transmissions for 986? 987?
 

Hey guys, it's been a while.

So I'm about to boost my 3.8L M96 on my base 986. I'm actually still using the base 986 5 speed, which has held up admirably for the last 50k miles on the upgraded engine. However, now that I'm looking into increasing the horspeower even more, I feel the need to upgrade my transmission.

I heard the 987S transmission bolts up, but there's some work required. I tried searching it but there's not a lot of documentation. Anyone have a lead on some info?

I am still using stock base 986 rear uprights - I am considering upgrading to the S uprights, especially if it's necessary for transmission upgrade.

I´m afraid aI cannot advice you on the gearbox question, however I would really like to know more about your plans for the engine..

I'm having the work done by Turbokraft here in Arizona.

I currently have a re-sleeved M96 to 3.8L. Makes roughly 300 wheel on a good day.

I am going to need a solution to get a beefier transmission, though.

California Motorsports is your best bet & they have moved to AZ

Hmmmm....a boosted 3.8 may negate the need for expensive 3.8 heads....very interesting

Jaykay,

I believe that the 3.8 and 3.4 heads are the same, of course I could be wrong.. :p

I remember reading this when I was going to send my 3.4 (987S) to Hoffman Automotive when planning to build my LN 3.8 engine

What year is your engine ?

so, 986 5- and 6-speeds, and 987 5- and 6-speeds, will all bolt up. not sure about the 987 units, but 986 5- and 6-speed transmissions have different input shafts requiring different clutches (and probably pressure plates, fasteners, etc., while you are in there). transmission mounts should be the same, but the brackets differ. reverse switch plugs are different, as are clutch slave cylinders and lines. most likely you have to change exhaust mounting hardware, and shift cables are specific to each transmission.

the real work is with the axles. there are differences in length, flanges at the transmission, and wheel bearings/carriers. i can't recall, but 986 6-speed transmission axles require beefier bearings that may not fit into the 5-speed uprights? can't remember, but check parts catalogs to determine diameters, splines, etc., for fitment.

as far as what to choose, size=strength with transmissions. the 987 6-speeds are actually smaller than the 986 6-speeds, so you may wish to consider a 986 6-speed. cheaper and easier to find as well.

The cheapest and easier options is to swap in everything 6-speed from a 986-S.

I don't know why you'd go with 987-S stuff, especially since it would be significantly more expensive.

In WRL there are a handful of 986 boxsters running a cayman 6 speed. It's supposedly stronger and geared lower. I don't see a difference in performance between the 986 and 987 6 speeds on the track though. Both transmissions are pretty durable. I personally don't think it's worth the hassle to put a 987 6 speed in a 986. The 986 6 speed is an easier swap and roughly $1000 cheaper. There's no getting around swapping to the S carrier if you go with a 6 speed. Another option is the 987 5 speed. While not nearly as strong as the 6 speeds, it's supposedly stronger than the 986 5 speed and it swaps into a 986 with no major modifications. A bonus for the 987 5 speed is that you can find them for $300-700 and it weighs less than a six speed

I have an L&N 3.6 Built by flat6. Within 10-15k miles of the build I lost 2nd gear in my 6 speed. The car is a 986s. My indie rebuilt it and it was great For another 25k. recently I’ve started having some shift issues. Not sure why right now but I am babying it for now. Not sure the 986 6 speed handles the additional power too well. My indie told me he had had far less trouble with 5 speeds.


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Radium King and others, thank you so much for the info.
Still doing a lot of research. Seems getting Boxster 986S parts and swapping that into my base 986 may be the best route, as the 987 doesn't offer strength and is significantly higher in trouble and cost.

It's worth mentioning that I baby car - it is a daily and not tracked. The engine is from an 03 986S