NB 5 speed to 6 speed swap
 

I've searched, but I'm still a little confused. Please forgive me if you guys have read this before. I've seen a lot threads, but I'm unclear if I need anything in addition to the trans.

Thinkibg about buying a 6 speed for my NB track car. I don't care about freeway cruise rpm's. I think the closer 3-4-5th ratios with my 4.3 rear end will help get off the corners better. In another older thread, I saw that I need a new shifter in addition to the trans. Is that true? I was thinking what I had would work.

If the 6 speed needs a different shifter and it's not included with the trans when I buy it, any suggestions where to find one?

6 speed does use a different shifter. Either find a used stock 6 speed one, or spend big bucks on a miata roadster short shifter kit. For every 6 speed I have bought I have gotten a shifter with it.

I've got one w/shifter on a pallet in my shop. We are not going to use it.

https://cimg5.ibsrv.net/gimg/www.mia...305c826c80.jpg

price and location? I'm NW of Chicago, so I expect freight will be an issue.

From what I remember, we paid 550 a couple of years ago.

I think it's NB1 low mileage 6-speed but quite frankly I can't really remember the details.

I haven't even unwrapped it to look at it yet. Just stuck it on the shelf for later.

For every time you find that perfect gear coming off a corner you'll be forced to make a mid corner shift or have to choose a higher gear. I'm running a 6 speed with 3.90 gears and I find them too short. Granted I'm running 200+ hp. You might not find it to you liking, I certainly wouldnt spend $600+ and the time on the swap if I didn't need the strength.

The 6 speed will be faster on a road course than the 5 speed. Both 949 and TSE have proven it with lap times; 3rd-5th gears are nicely spaced in the 6 speed. The 6 speed is also significantly stronger. The 5 speed is a wear item even in Spec Miata. The 6 speed / 3.90 is about perfect for my fairly stock Miata at most East Coast road courses, so I'm not surprised it's too short with an extra 60hp.

That's exactly why we got this one, for the 3-4-5 spacing. We just found a better solution so now Wil not need this.

The gear spacing isn't much different between the 5 speeds and 6 speeds. I really just depends on what final drive you pair them with. A 6 speed with a 3.9 is nearly identical in 1st-5th (within 1-4mph @ 7250rpm) to a 5 speed with a 4.77. You just just an extra gear in the 6 speed. The 5 speed can be fragile in high power applications and there are only so many final drive ratios out there to shorten everything up to take advantage of available power. Since the 6 speed is shorter to start with, you can really have some fun with short final drives at lower power levels.

Thanks for your help guys. I found both 5&6 locally. Decisions decisions...

Let me know if you want a gearing comparison spreadsheet I've setup to look at different transmissions, final drives, and theoretical tire sizes

Anyone doing a 6sp swap with a 3.9 rear end should have enough power that a 5sp isn't a viable option. For NA cars, the 6sp/4.30 combo is what you want, and to get the same gears in a 5sp, you have to buy 5.12 gears, and at 7400rpm, that's 121mph calculated and maybe 115mph GPS at the top of 5th. The 6sp gives you all the extra grunt, plus an extra gear for highway cruising or for the occasional long track.

Can confirm. 6spd/4.30 is win.

So much win, in fact.... that i have it in 2 cars, and have the set sitting here to go in a 3rd.

You're correct. My thought basis comes from a dual purpose street/track car that gets driven on the interstate. So compromises have to be made sometimes.

I can tell you one thing, a 6 speed and 3.90 sucks for Road Atlanta in NA (150-160whp) car. If I go back, my compromise is going to swapping in a 4.1 or 4.3 for the event (or just have a dedicated track car). Vmax on the back straight was calculated at 125 which was right at the top of 5th (perfect, no extra shift), but man did it suck having to short shift into 5th in a few places (down into 12 and through the Esses).

Interstate is fine. The RPM difference at 70mph cruise really isn't that drastic, and it's not like a dual purpose Miata isn't a horrible rattltrap on the highway for hours on end anyways. :)

Hell, i still get 30mpg at 70-75mph with my 6spd/4.30 combo.

At 75mph its a 300rpm between the 3.90 and 4.30 on a 6 speed. It just wasn't something I wanted to do. I found the 5 speed with a 4.30 to be a little harsh on my commute, but I also wanted shorter gears for the track use. So with a 6spd and 3.9 I got both shorter gears and lower RPM (-225rpm) cruising.

I would love to see that spread sheet I'm planning on kswapping with a turbo and want the most top end possible I'm thinking 6 speed with a 3.9

Check out the gearing calculator on the Kpower.industries site. All the transmissions/rear ends you could want to compare are pre-programmed into it.

As stated above, the Kpower website has a nice quick calculator

If you want something more in-depth, I made a tractive force calculator that you can download on this thread
https://www.miataturbo.net/race-prep...ulator-107689/

As a fellow kswapper currently on a 6spd, you are going to want a more robust option than a miata trans once you go turbo... so just keep that in mind...