Keith Tanner said:Your 2001 5-speed has a 4.3. You'll definitely want a new rear end with that trans.
Thanks! Do you think the 3.9 would be my best option then? Hopefully I can find one, seems like they're a little difficult to find.
Keith Tanner said:Your 2001 5-speed has a 4.3. You'll definitely want a new rear end with that trans.
Thanks! Do you think the 3.9 would be my best option then? Hopefully I can find one, seems like they're a little difficult to find.
codrus (Forum Supporter) said:Keith Tanner said:The stock transmissions don't seem to explode on clutch drops, they just shear the teeth off the gears under power. Keeping the fluid fresh and cool would probably help a lot, as would taking an extra half second to shift. The Torsen rear ends are good in the sub-400 range as long as you avoid wheel hop. Not indestructible, but failures are rare in my experience.
Yeah, I think the transmission acts as a fuse to prevent the rear ends from blowing up.
My 5-speed failed the way you say (sheared all the teeth off 3rd gear). The 6-speed that I blew up was the input shaft bearing, probably due to excessive heat from lots of track days. Were I still running a turbo Miata at the track I would be looking for transmission oil coolers.
That sounds pretty gnarly. How much power were you pushing in the Miata?
Japanspec said:Keith Tanner said:Your 2001 5-speed has a 4.3. You'll definitely want a new rear end with that trans.
Thanks! Do you think the 3.9 would be my best option then? Hopefully I can find one, seems like they're a little difficult to find.
They were only found in 1999-03 6-speed cars, which are relatively thin on the ground especially since the 1999 was a limited production special edition. Add in high demand and yes, they're a little difficult to find.
3.9 was the factory's choice in North America. The 3.6 - which is available through Mazda Motorsports and the aftermarket - was the choice in Europe, and seems to be the favored choice for higher horsepower folks. Personally, I like a 5-speed with a 4.10 behind it and my four cylinder Miata doesn't make enough power to trouble the transmission :)
I did the K swap on my Exocet. Great motor and a hoot to drive, but by the time I got done with it the price tag was a whole lot more than $10K. Started with a used motor that had a bent rod so did a short block with 12.7 pistons, rods, etc.. Decided it needed E85 which leads to bigger injectors. New intake, throttle body, header, custom 3" exhaust. etc. And since we're that deep into the motor, of course it needs a new timing chain assembly, oil pump, seals, head bolts, VTEC hardware, etc.. Full head refresh. Got a low mileage 6 speed, and of course a new high performance clutch setup. In the end it was pushing close to 270HP and a ton of fun to drive. But every warning about engine swaps blowing out the budget came true.
If I had to do it over again I'd just turbo it with a 6 speed.
Japanspec said:codrus (Forum Supporter) said:Keith Tanner said:The stock transmissions don't seem to explode on clutch drops, they just shear the teeth off the gears under power. Keeping the fluid fresh and cool would probably help a lot, as would taking an extra half second to shift. The Torsen rear ends are good in the sub-400 range as long as you avoid wheel hop. Not indestructible, but failures are rare in my experience.
Yeah, I think the transmission acts as a fuse to prevent the rear ends from blowing up.
My 5-speed failed the way you say (sheared all the teeth off 3rd gear). The 6-speed that I blew up was the input shaft bearing, probably due to excessive heat from lots of track days. Were I still running a turbo Miata at the track I would be looking for transmission oil coolers.
That sounds pretty gnarly. How much power were you pushing in the Miata?
The 5-speed I blew up with it making 260 at the wheels (an FM2 kit with a 2560). By the time the 6-speed blew up I'd gone to an "FM2R"-ish setup, using a 2863 with an external wastegate, it was making around 320 rwhp in track config (up to 350 on the street, but I turned the boost down a bit for the track).
As far as rear end ratios go, in a 300rwhp Miata the 6-speed with the 3.9 is faster at the track, but the 6-speed with the 3.6 is more friendly for street and autox use. Mine has a 3.6.
Thanks guys! I'm a bit bummed out about the gearing ratio now when I think about it. The 6 speed doesn't sound great for drivability on the street, but is stronger than the 5 speed. The fact that 3.9 diffs are difficult to find just makes it more of a bummer. I would like it to be usable on the street, so finding the right gearing seems like its going to be tough. Of course there is the OS Giken, but thats quite a bit expensive.
The OS Giken doesn't come with a ring and pinion, so it doesn't solve your gearing problem :)
The 3.6 is available through Mazda Motorsports, part MA02-27-110.
3.9 is M061-27-110C. $547 for the ring and pinion, on the shelf in the warehouse in California.
Keith Tanner said:The OS Giken doesn't come with a ring and pinion, so it doesn't solve your gearing problem :)
The 3.6 is available through Mazda Motorsports, part MA02-27-110.
3.9 is M061-27-110C. $547 for the ring and pinion, on the shelf in the warehouse in California.
You're right, it doesn't...I forgot about that! Hmm seems like the best option would be to find a torsen 3.9 diff. Going to be searching for quite a long time. I'm guessing a 4.10 torsen with 300whp wouldn't be that great on the street, would it? I don't have too many issues with my 4.3 and 5 speed right now with 230whp, but then of course going to a 6 speed and 300whp would definitely change things.
3.6 Torsen diffs are pretty easy to get out of England for about what you'd pay for a Torsen diff here. I also bought a 6 speed out of England for considerably less than they're selling for here, including shipping. Of course, those are used parts.
As noted, the Mazda transmissions will be the weak point, especially on sticky tires at the track. There is a BMW option available now for trans swaps, which seems to be the ticket for high HP BPs.
Has anyone mentioned the obvious option of sell it and buy a car with 4-500 HP stock? Play with that until bored then add another 100-200 to it. Like a corvette BMW or Pony car.
Not to derail but this is always my advice when someone wants to add a V8 to a car that came with one or adding $10 worth of supercharger and support to a mustang vs swapping to the one that came that way.
Please disregard and carry on if this is out of line. Personally I would not listen to me either. As I add thousand of dollars into my old Mustang.
Rodan said:3.6 Torsen diffs are pretty easy to get out of England for about what you'd pay for a Torsen diff here. I also bought a 6 speed out of England for considerably less than they're selling for here, including shipping. Of course, those are used parts.
As noted, the Mazda transmissions will be the weak point, especially on sticky tires at the track. There is a BMW option available now for trans swaps, which seems to be the ticket for high HP BPs.
Tell me more about this BMW trans option. Is it accomplished with an adapter plate or is it a complete bellhousing?
akylekoz said:Has anyone mentioned the obvious option of sell it and buy a car with 4-500 HP stock? Play with that until bored then add another 100-200 to it. Like a corvette BMW or Pony car.
Not to derail but this is always my advice when someone wants to add a V8 to a car that came with one or adding $10 worth of supercharger and support to a mustang vs swapping to the one that came that way.
Please disregard and carry on if this is out of line. Personally I would not listen to me either. As I add thousand of dollars into my old Mustang.
A Miata is a Miata. Corvettes and BMWs feel like 3/4 ton pickups in comparison, and I have driven video games that had more driver feedback than the newer Mustangs provide.
I have a 3.6 diff in my turbo Miata. My family was looking for something to get me for my birthday this year and since I already have everything a man could reasonably ask for they got that. $750 on eBay for a used and slightly rusty complete rear end. I think it came from Australia.
Yep about getting trans and rear ends from England, there's a guy on Facebook and Miata turbo that does pallets of them. I had my 3.6 diff built locally with new ring and pinion.
Even with the 3.6 diff I hated the six speed. The shifts are vague (and I had the Miata roadster short shifter too) and the gearing is truly terrible.
If you're getting into track work, even your current Miata power levels is going to be a handful for a novice, not to mention even well built turbo cars are going to struggle in ways they never struggled on the street. I'd make that a priority, maybe a TNiA event?
Here's the BMW trans kit, I believe someone asked about.
https://kpower.industries/collections/transmission-upgrades/products/mazda-bp-to-bmw-e36-e46-transmission-adapter-package
Japanspec said:Thanks guys! I'm a bit bummed out about the gearing ratio now when I think about it. The 6 speed doesn't sound great for drivability on the street, but is stronger than the 5 speed. The fact that 3.9 diffs are difficult to find just makes it more of a bummer. I would like it to be usable on the street, so finding the right gearing seems like its going to be tough. Of course there is the OS Giken, but thats quite a bit expensive.
While 3.9s might be relatively rare as Miatas go, I don't think I'd describe them as "hard to find". They did make 50K+ of them and they show up for sale fairly regularly. There's one on ebay right now for $1300 buy-it-now (which is higher than I'd expect) and looking at the miataturbo.net classifieds I see 4 or 5 of them sold in the last year ranging between $600 and $1000.
akylekoz said:Has anyone mentioned the obvious option of sell it and buy a car with 4-500 HP stock? Play with that until bored then add another 100-200 to it. Like a corvette BMW or Pony car.
As mentioned, it's still not a Miata, which is way different dynamically than pony cars or 'Vettes. And the consumables cost will be far higher than a Miata doing the same lap times.
We had a '17 Mustang GT and an '18 ZL1, tracked them both. Both are gone, and we still have our Miata because not only is it a LOT cheaper to run, it was more FUN to drive.
accordianfolder posted the BMW trans link. There's even a couple of folks using that kit to run a BMW auto with flappy paddles on high HP Miatas. Big investment, but pretty cool if you're looking for the ultimate.
accordionfolder said:Even with the 3.6 diff I hated the six speed. The shifts are vague (and I had the Miata roadster short shifter too) and the gearing is truly terrible.
I'm going to have to disagree with this. The shift feel varies a bit and it's never quite as good as a Miata 5-speed, but assuming all the parts are in good working order (the plastic bushing at the bottom likes to break) it's better than 90% of the manual transmissions out there.
As for the ratios, with a 3.6 the 6-speed works out to have very close to the same total ratios as a 5-speed with a 4.3 for 1-3. Top speed in 4th and 5th drops by about 5 mph, but how often are you winding out 4th except on the track? IME, this is not an issue.
FM's gearing calculator is good for exploring this: https://www.flyinmiata.com/tech/gearing.php
In reply to codrus (Forum Supporter) :
The other option is to pick up a 3.9 open and throw an OS Giken diff in it for serious track work. I'd do that before spending much over $1k on a used Torsen.
codrus (Forum Supporter) said:I'm going to have to disagree with this.
Me too. It isn't as good as the 5 speed, but it's still pretty good, especially with a MiataRoadster shifter.
I'm currently running a 6 speed with 4.1 in our NA, naturally aspirated. I tried the 4.3, which everyone raves about with a naturally aspirated Miata, but it was too short for the tracks we run.
Rodan said:In reply to codrus (Forum Supporter) :
The other option is to pick up a 3.9 open and throw an OS Giken diff in it for serious track work. I'd do that before spending much over $1k on a used Torsen.
Did they make a 3.9 open? I'd have to check my notes, but off the top of my head the 6 speed was always paired with an LSD.
I'm not a fan of the 6 speed shift feel myself. I'd use it if I had to, but I prefer the 5. FM actually backdated their MSM to a 5 speed because of the shift quality of the brand new 6 speed. It's not the cool thing to do but every single staff member preferred it that way.
6 with a 4.3 is goofy short. I expect "everyone raves" means there are two people on a single forum who won't shut up about it :)
In reply to Rodan :
There is a guy with a twin turbo LS swapped RX-7 using a BMW DCT with an aftermarket controller. He loves it. This is where my interests lie.
Just my opinion in regards to feel!
Also everyone raves about the 6 speed durability, but for track work you're still on borrowed time. And what monster decided that this was a great gearing for 3-4-5!? 5th gear being 1:1 is a crime against humanity and means you're always shifting into it, and then you've got a 6th gear that's the same ratio as 5th in the 5speed, ha!
Here's an interesting thread about modifying the countershaft in the 6 speed. Supposedly good for 350+ ft/lbs
Keith Tanner said:Did they make a 3.9 open? I'd have to check my notes, but off the top of my head the 6 speed was always paired with an LSD.
My automatic '99 came with a 3.9 open diff. Since nobody wants open diffs, I figure it would be pretty easy to find one in a pick n' pull. I held onto it for possible use with a turbo car (with either a Torsen or OSG diff).
6 with a 4.3 is goofy short. I expect "everyone raves" means there are two people on a single forum who won't shut up about it :)
Accomplished racers on other forums, but yeah, it was goofy short. 
Rodan said:Keith Tanner said:Did they make a 3.9 open? I'd have to check my notes, but off the top of my head the 6 speed was always paired with an LSD.
My automatic '99 came with a 3.9 open diff. Since nobody wants open diffs, I figure it would be pretty easy to find one in a pick n' pull. I held onto it for possible use with a turbo car (with either a Torsen or OSG diff).
6 with a 4.3 is goofy short. I expect "everyone raves" means there are two people on a single forum who won't shut up about it :)
Accomplished racers on other forums, but yeah, it was goofy short.
1999 automatic came with a 4.1. All NB autos did. Might want to count those turns :)
I assume "accomplished racers" means Emilio for a pure dedicated track car on specific tracks, and then his advice gets repeated. If your car has license plates instead of number plates, it's goofy short. I do have a friend who lives in Germany who loves it, but it's behind a stock 1.6.
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