Pros and Cons of a Six-Speed Tranny on an NA8?

[mx54life]

Man I am now swamp with things that I think need to be accomplished while half of the engine is out. Which brings me to the transmission. And since I am gonna change the clutch anyways why not do the swap now right? I do have a six speed from a 2001. But suddenly I come to realize that the NA's never had 6 speed so there's got to be pros and cons. I am supercharged to begin with so please shed me some reality please?...........Will this be a good upgrade? I was told that the first gear will be very short. I love to rev the 1st a little.......

[Greasemonkey2000]

NA8's have 4.1 rear diff ratio so you will end up turning higher rpms(w/ 6 speed) vs the 5 speed but better acceleration so kind of a pro and con.

Personally unless it is strictly a track/autox car i wouldn't do it without swapping in 3.9(or 3.63) gears or diff but that is just my humble opinion.

[mx54life]

NA8's have 4.1 rear diff ratio so you will end up turning higher rpms(w/ 6 speed) vs the 5 speed but better acceleration so kind of a pro and con.

Meaning good acceleration but poor top speed? Will that be better for a supercharge miata or not? I love the way the car runs now but I missed my six speed NC so without thinking I snag this tranny :-(

[speedypenguin]

You'd be shifting very often if you pair the 6spd with a 4.1

I found that the 6spd paired with the 3.9 was decent in my old NB. If you want quicker acceleration with your supercharged setup, getting the 6spd would get you that. Or...add more power. ;)

[mx54life]

You'd be shifting very often if you pair the 6spd with a 4.1

I found that the 6spd paired with the 3.9 was decent in my old NB. If you want quicker acceleration with your supercharged setup, getting the 6spd would get you that. Or...add more power. ;)

I want more balance so I guess I will have to hunt the 3.9 diff then before I install this six speed. I have an LSD from another 94 will that be still a 4.1 ratio diff?

[Greasemonkey2000]

iirc, all 94-05 5 speed miatas would have a 4.1 rear diff, 6 speeds had 3.9 and the msm had 3.63...someone correct me if im mistaken.

[smy0003]

I thought the msm had a 4.1.
I think australia were the only country to get the 3.63.

[Greasemonkey2000]

Stock rear end ratios for North America

1990-93 5-speed 4.30
1994-97 5-speed 4.10
1999-05 5-speed 4.30
1999-03 6-speed 3.909
2004-05 6-speed 4.10
2006-15- all trans 4.10
2016-?2.866

From Flyin Miata: https://www.flyinmiata.com/tech/gearing.php


Looks like i didn't recall correctly. :fp:

[mx54life]

Stock rear end ratios for North America

1990-93 5-speed 4.30
1994-97 5-speed 4.10
1999-05 5-speed 4.30
1999-03 6-speed 3.909
2004-05 6-speed 4.10
2006-15- all trans 4.10
2016-?2.866

From Flyin Miata: https://www.flyinmiata.com/tech/gearing.php


Looks like i didn't recall correctly. :fp:

Thanks. So my former 06 NC 6-speed had 4.10? I didn't feel I have to shift all the time IIRC. What would be different if I put this 01 6-speed then, the gear ratios are not the same?

[smy0003]

The 6-speeds in the NC had different ratios to the nb 6-speeds, to make things more complicated ;)

EDIT:
Have a play with this:
https://www.flyinmiata.com/tech/gearing.php

You can run a bunch of different combinations through it and see what will suit you the best.

[Greasemonkey2000]

So in short just swapping to a 6 speed it looks like you will gain acceleration(shorter gears) but in turn shift sooner, obviously gain an extra gear but turn another 112 rpms in final gear even with an extra gear at 65 mph and lose 5 mph of top speed all other things equal with stock size tires.

I guess in theory not bad and if i had a 6 speed and hadn't already invested in a sts, clutch and flywheel for a 5 speed, as i have, then i would go ahead with the 6 speed swap. One other consideration is that everyone says the 5 speed shifts better/smoother than the 6 speed.

[ScratchNSniff]

I want more balance so I guess I will have to hunt the 3.9 diff then before I install this six speed. I have an LSD from another 94 will that be still a 4.1 ratio diff?

If you end up wanting a 3.63 R&P let me know...

[mini_fd]

Con: finding and actually getting in reverse in one try.

[HarryB]

Anyone knows if the gears are the same face width on 5 and 6 gear versions?

[Phatmiata]

I wish we could have got that group buy finished with Bill at MiataRoadster, then you could have a great rear end ratio, transmissions aside

[mx54life]

I wish we could have got that group buy finished with Bill at MiataRoadster, then you could have a great rear end ratio, transmissions aside

When was that?

[RotorNutFD3S]

If you have a friend with a stockish Mazdaspeed Miata, see if you can drive it. That'll give you the closest feel in terms of effort (and slightly different power) to what you'll have with a 6-speed and the 4.10 rear end in your own car.

[Greasemonkey2000]

When was that?

More pertinent question is how much which i think the final cost was going to be around $900 for just the gear set which i believe was 3.36, iirc. There was a group buy early this year/late 2014 that didn't happen due to not enough people.

[Mr.Woolery]

-If your goal is great acceleration at the cost of LOTS more shifting and lower top speed, use the 6-speed with the 4.1 diff. Downside is that 1st gear will seem almost useless.

-If you want a nice balance of acceleration, still a lot of shifting and normal top speed at higher RPM's, use the 6-speed with the 3.9 diff

-If you want it to act like a 5-speed with a nice cruising lower RPM overdrive 6th gear, use the 6-speed with a 3.6 diff. Less shifting, generally acts like a 5-speed otherwise (unless you're on the highway in 6th), lowers high speed cruising RPM, increases MPG...and is mechanically the strongest setup combination of all the options within the OEM parts range.

I personally think a forced induction Miata with a 6-speed and 3.6 diff is the best street powertrain setup out there. I would've gone that route myself, but went with a 5 spd and a 3.9 diff because, at the time, I didn't know better.

[kung fu jesus]

Cons: price.

Replacing a blown 6sp is more costly and harder to source.

The 6er has never really impressed me either, in feel. I seem to miss more shifts in the 6 than the 5sp.

[RotorNutFD3S]

I personally think a forced induction Miata with a 6-speed and 3.6 diff is the best street powertrain setup out there. I would've gone that route myself, but went with a 5 spd and a 3.9 diff because, at the time, I didn't know better.

Both setups are really nice, I've had both. I've found that I prefer the 5-spd/3.9 in my current Miata, longer gearing than the 6-spd/3.6 combo (comparing gears 1-5) which the turbo loves but the car doesn't choke off the line because of it. And like KFJ said, the 5-spd isn't as finicky when it comes to shifting. At the same time, I'm under the 250 wtq level that seems to destroy 5-spds, higher tq setups are likely going to need a 6-spd to survive.

[mini_fd]

From driving a FD 5speed and going back the 6speed 10ae, I keep missing 3rd gear.

[kung fu jesus]

I concur on the 3rd gear miss, and reverse.

I rebuilt the shifter on mine and motor mounts to alleviate, but it didn't help much. Maybe muscle memory or hands made of ham was the issue?

[mx54life]

I am now in search for the holy old Mazda that bears the 3.63 r/p. Am I too late?

[Satisaii]

Never came on a Miata. Think you can still get them new.

I have a Rotrex with the 3.6 and 6 speed. I had the 5 in it, but knew it was going to break eventually. Love it for highway cruising. Hate the feel of the 6.

[kung fu jesus]

You can source them if you put in the time and have the money. If you can't find them stateside, it might be something to look for in Australia or NZ. Don't forget, you are basically rebuilding the pumpkin, so bearings, lash, seals also should be considered. The second item being the tricky part, probably requiring a professional.

[mx54life]

Yes they are stateside too in limited numbers, 1979-1982 Mazda 626 5-speed. If you get lucky I was told the entire pumpkin could be bought for $150. Professional fee is between $350-450 to have the ring and pinion installed.

If not b/n from Corksport is $650.

[smy0003]

We got the 3.63 diffs down here. Way too tall for an NA car and I have no idea why mazda had to give us a different ratio to the rest of the world.
You could grab one from here for pretty cheap, especially with our dollar tanking.

[mx54life]

We got the 3.63 diffs down here. Way too tall for an NA car and I have no idea why mazda had to give us a different ratio to the rest of the world.
You could grab one from here for pretty cheap, especially with our dollar tanking.

How much for a good set of 3.63 ring and pinion ship to 95747? Maybe you can give a lead or I pay your time? They were in the old Mazda 626 1979-82 but are now getting scarce here stateside.

[smy0003]

There's a couple of shops in Aus that regularly part MX-5's and have a regular stock of diffs. They sell the entire diff assemblies as a whole. I'll PM you the details as the shops are not sponsors on here.

[kung fu jesus]

You can share those links as a resource. What we don't like are non-sponsors advertising their goods here. Posting progress of development is interesting, but once pricing is included, it becomes advertising. This becomes particularly so if the person posting is affiliated or employed by that company. :)

[smy0003]

Cool, just didn't want to get up any ones nose since I'm new here. Not affiliated with either so:

First is Automotive plus up in Queensland
http://store.automotiveplus.com.au/

Second is MX5 Mania in New South Wales:
http://www.mx5mania.com.au/drivetrain.php

Both ship big parts like engines and diffs on pallets and bring containers in from Japan, so I don't see why they couldn't ship a diff State-side. Although, I don't know if either would, so you'd have to email them and see.

Be warned though. There was no such thing as a 3.63 ratio torsen, all the 3.63 diffs are open. Same size as all the other diffs so you can swap in a torsen or clutch pack diff if you want to.