I did this mod on my car about a year ago. What you will need depends on which clutch you choose to go with.
Option 1 would be to use your stock twin disk clutch. This will require you to purchase a new main shaft from SOS that supports the stock twin disk clutch used with the 5-spd transmission. The main shaft in the 5-spd is the basically same as the 6-spd with the exception that the 5-spd main shaft has a longer splined section. The longer splined section on the 5-spd main shaft is used to grab both friction disks in the twin disk clutch set. If you set the transmissions side by side (6-spd vs. 5-spd) you can see the different spline lengths. So, if you decide to use your stock twin disk clutch you will need to purchase the new main shaft AND have it installed. I am not sure what it would cost to open up the transmission and install the new main shaft but, I do know there are more and more clutch options available for the 6-spd today than there was one year ago. I will also note that if you choose to purchase the 5-spd main shaft and have it installed in your 6-spd you CAN run a single disk clutch at a later date without having to reinstall the 6-spd main shaft. In other words the stock 5-spd transmission (with the longer splined section) can operate with either a twin disk clutch or a single disk clutch. The 6-spd transmission (with the shorter splined section) can only support a single disk clutch set up.
In summary if you choose option 1 you will need the following:
1) 6-spd transmission
2) Main shaft from SOS
3) Reverse Lockout Kit
Option 2 would be to keep the original 6-spd main shaft thus requiring you to use a single disk clutch. Clutches…I would recommend against the CT (PG 1 or 2) single disk clutch. The pedal effort is extremely heavy with the PG 2. If you have an early model NSX (assuming you do since you are installing the 6-spd) AND you decide to go with the CT clutch I would recommend that you go ahead and replace the clutch slave cylinder and the soft line. The stiffer clutch (additional pedal effort) puts more of a strain on the slave cylinder and will most likely finish it off leaving you stranded. If you do some research you will find a few clutch options for the 6-spd transmission. I know SOS carries a clutch for the 6-spd. Brad at Autologic also carries a clutch for the 6-spd. He has a Clutch Masters single disk clutch set that he sells. He has this clutch installed in his car right now and has been running it for months now with no problems. Ok enough with clutches, just do some research and you will find that there are more options out there for the 6-spd (other than the CTPG clutch).
In summary if you choose to go with option 2 you will need the following:
1) 6-spd transmission
2) Single disk clutch
3) Reverse Lockout Kit
4) Flywheel bolts (maybe as this depends on which clutch you choose, read below)
You hear people talk about the fly wheel bolts. The flywheel bolts are different for the stock twin disk clutch and the stock single disk clutch. The flywheel bolts for the 5-spd are shorter than the bolts for the 6-spd. The stock single disk clutch uses a dual mass flywheel which requires longer flywheel bolts. To the best of my knowledge, most aftermarket single disk clutch sets use the shorter (5-spd) bolts. So you should be able to use the flywheel bolts from your 5-spd with most aftermarket single disk clutch sets. I do know that if you decide to use the stock single disk clutch then you WILL have to purchase 8 new flywheel bolts that hold the stock single disk clutch. When current 6-spd owners choose to go with an aftermarket clutch they must purchase the shorter (5-spd) flywheel bolts. This is why you see the websites telling the 97+ owners that they need new flywheel bolts. They basically need to purchase the shorter (5-spd) flywheel bolts. Since you already have the shorter 5-spd bolts you should be fine.
The reverse lockout kit…this is basically a switch that prevents you from selecting reverse gear or the reverse gate. The kit locks out the entire reverse gate so you can’t even get close to the reverse gear. I have the CT reverse lockout kit and am happy with it. I know that CT designed their kit using the vehicle speed. Once the vehicle is over a certain speed (I think it’s like 5 or 10 mph) the reverse gate is locked out. There may be other options out there but I would check to see that they are designed using vehicle speed and not RPM. I personally have run the car hard through the first three gears, pushed in on the clutch, and lazily (after the RPMs have dropped very low) selected 5th or 6th. If the kit was designed using RPM I would ask if in the above case would it be possible (even though the car is traveling 60+ mph) to hit the reverse gate/gear when trying to select 5th or 6th. The reverse lockout kit that CT sells also comes with a little 6-spd shift pattern and a new dust shield. The dust shield is different for the 5-spd and 6-spd transmissions.
Any finally one last thing, when installing the 6-spd I noticed mine had an extra sensor with two wires hanging out…the sensor was for the electric assist steering that is standard on the 97+ cars. If your new 6-spd comes with this you can simply remove it and then use the plug from your 5-spd. We don’t have power steering so we don’t need that sensor.
Sorry this post is so long but I thought it would help you and maybe others that may be interested in what is involved with the swap. It is really straight forward; the 6-spd bolts right up using the same bolts that held the 5-spd in place.
Paul
P.S. I purchased my 6-spd from the same guy (David) in Dallas. When I saw the 6-spd on eBay I drove from Houston to purchase it b/c I found it hard to believe that someone would sell a NEW in the box 6-spd transmission for a $1000 less than Niello (even with the 30% discount). I got there and sure enough David had a 6-spd in his NSX and a NEW 6-spd sitting in a box on the floor. I purchased it and it was worth every penny!
