That was the plan, to leave the 5 speed in, but since I gotta pull the diff and choose a ratio now, may as well future proof it a bit. If you haven't noticed I prefer to err on the side of caution. In this hobby, there's a fine line trying to save a few hundred bucks on some parts vs just paying up for the proven solution. Tow bills, track time, etc. ain't cheap. The last weekend w/ SCCA cost $487 for the HPDE only. You add the tow/gas/etc. it all adds up. 6 speed tranny cost is $900ish. This ain't a cheap hobby.

 

QFT, because it's the exact reason my car is so close to stock.

Loving the conversation on 5 speeds. I've been wanting more power for years, and I'm trying to lay out plans for it now that I've got a second Miata. Between the complaints of shift quality on the 6 speed, the massive range of torque people claim the 5 speed can handle (Regular destruction in Spec Miata, or holding up to 300 ftlbs for years), and the sheer number of issues people have when adapting other transmissions, I've struggled to justify the costs of getting more power.

There's a Mazda Motorsports gearset now available for the 5 speed and I'm seeing some pretty great reviews for longevity and torque capacity. Given the buy in cost and issues with alternatives, I'm starting to think it's the route I'd take if I ever blew a 5 speed due to having more than 16 hamsters worth of torque.

 

Now you guys have got me thinking I should go back and look at my data and see if a 5sp wouldn't work better for me....

 

I will definitely give you an honest review of the 6 speed.. if it's really as bad as everyone says. Honestly I'd say that's one of the reasons I don't want to do a MR shifter off the bat. Some people say it's fine so perhaps it's a bit overblown. I think there's a variety of "ways" to break a tranny, which makes it hard to compare apples to apples amongst different cars, setups, drivers. Guys that drag race are banging gears (the faster the better), powershifting (not lifting throttle), dumping the clutch from a dig etc., which is hard on the tranny in different ways. For a track car and having some mechanical empathy on the tranny (shifting at a normal speed), maybe the 5 speed will last a while..?

That's interesting and never heard of that MM gearset. I googled it and part # is 0000-02-5800. On the MM store it lists the gearset for $2075. Is there a discount on that if you login? That does sound like an interesting option over the 6 speed. I'll keep the 5 speed and put it in the shed, so who knows it might be put back into service down the road.. A good thing about the 5 speeds is people are almost trying to give them away $ wise.

 

Ha, maybe.. you're N/A though so not having any lag at all when you put your right foot down has less of a "penalty" for rowing gears. The lag is minimal w/ the widdle 2560R but it's still there.

 

This is about where I'm at as well. There's a guy selling an nb2 6 speed locally for $800 and it'll need a shifter. 6 Speed and a 4.3 would be a wild setup, so then I need a different diff, and I don't want to do that twice which means sourcing a 3.6. But I also don't really want to pull the trans more than I need to, so then it's a clutch upgrade while I'm in there. Oh and... and... and... it never seems to stop

 

What clutch are you running now? Everything is compatible between the 5/6speed right? Also how much power can the Supermiata clutch hold?

Ya I don't want to take it apart twice. That's why I'm thinking this is the last time I'm going to change things (famous last words). I'm going to stop after these mods and just drive it (that's kind of where I'm at w/ the Honda). Maybe I'll turn up the boost a few psi but that's it. Regarding parts, damn miata parts costs look to be going up (probably because of people like me). But, I look on FB marketplace and people are asking 1400 for a diff? Come on man. Well I'm not hating if someone will pay it good for you. Good thing is Mazda made a crapload of these cars so there will be parts for a while yet.

I' m trying to justify to myself that I "need" a TIG welder so I can redo some stainless pieces and weld some Al. Garage is already too cluttered as is.

 

Interested in the comments on the 5-speed. I broke one in a bone stock NB8A, motorkanas and track days only. I have no plans to explore that option.

 

To contribute to the discussion, neat gearboxes is possibly developing and upgraded gearset for the 6 speed. It's estimated at something like $5k+.

I'm running the Flying Miata stage 1, but with my goal of ~350whp I think it'll slip. Again, it's all a ways out.

 

That's why 4.1s are awesome. Some of the benefit of a 5/4.3, still livable with a 6 speed. I was lucky enough to start with this, so when a good deal came up on a 6-speed, I didn't need to swap diff too. Then a trade opportunity came up for a 4.1 to 3.9 and I couldn't be happier. It's livable on the freeway at 70-80, and ok on the track too. Sonoma and Portland use 3/4/5, not sure I wanna use 2/3/4 with a 3.6. These days I'd rather save my 10/10s driving for wheel to wheel rather than my personal garage queen.

Anyways TLDR; 5/4.3 with a 1.6 lightweight clutch is awesome, but tough($$$) when you start wanting more power.

 

So the diff came in and I'll need to give it a little TLC. I will clean up the housing. I'm thinking hit it with a wire wheel until it looks pretty clean, but any tips on painting it? Should I use some kind of special primer? I will replace the axle seals and weld some plates over the notched side of the diff arms. I'll swap out the diff bushings as well probably with urethane.


I also need to order the replacement bushings for the shifter. I measured the "ball" part of the shifter and it's ~17.8mm, which should mean it's a NB2 (just wanted to confirm). According to a couple websites they said NB1 is 15mm and NB2 is 17mm. This is obviously larger than 17mm but NB2 is the one I'll order.



I got the 9LR street **** and the fluidampr crank pulley. I'm just waiting on the Xidas and should get them in January. Those are the big things and I'll swap the diff and tranny once I get the last of the seals/parts and get the diff prepped. Looking forward to putting my right foot down and not having the inside tire spin.

 

Hell yeah, it's all coming together!

I don't possess any pertinent knowledge on painting the diff. Just took a wire wheel to mine and sprayed it with whatever black paint I had lying around. You're not running poly diff bushings in the current diff, correct? They're for sure a big help with eliminating missed shifts on the 6 speed but get ready for serious decel chatter. That being said' I'd still do em again if I had another NA/NB.

 

If you really want it beautifully painted and perfect, I'd recommend using a needle scaler, wire wheel, and then scrub it with one of the many phosphoric acid based rust converters before paint. That's how I got a similarly crusty Michigan axle prepped to go under a clean Jeep. Given your location though, it'll never be subject to such rust causing conditions again, and that much work is a bit excessive. You could just knock off the scale so it doesn't rain down on you when you're working under the car.

I'm glad your experience with said "Prestigious" seller went better than mine.

 

I am running a set of poly bushings for the current 4.3 open diff and ordered some more poly bushings for this new diff (i could maybe swap them but they aren't too pricey). It def added some nvh and I agree anything to help keep the drivetrain from moving around helps, especially considering the tranny isn't mounted to the chassis so moves around a bit as is.

Well I hit it with a few diff wire wheels and sanding disc to get a lot of the rust off but did a thick (proly too thick) coat of rust reformer on the housing as I thought it would help convert any leftover rust. I had to wipeoff the excess after a couple hours, and it still has a bit of a white/shiney look, but I'll give it another couple days per the directions before doing a coat of primer and paint. I'm sure I'm overthinking it like most things but hopefully it'll turn out fine. I'll post a step by step of what I did when I finish painting it. How was your experience w/ them? I'd say mine was "pretty good." Their packaging is not great, and they put the wrong address on the diff and fortunately my neighbor called me to come get it last week.

 

Wire wheel + rust reformer is probably what I'll end up doing.

Share all the details because I'm probably doing this exact same project before 2025 is over

Excited to see the big transformation. Also welcome to the Big Wing Miata club.

 

I never got my parts and they put up a fight on refunding me.

My terrible experience with Prestige Spares - Miata Turbo Forum - Boost cars, acquire cats.

 

Your neighbor must've mistaken it for a 4.x open. Lucky break.

 

Sure will do. I've been snapping some pics. I'm not going for insta quality photos and cosmetic looks just want to prevent future rusting. Also, depends how you classify the 9LR street ****. Maybe I'm in the little **** club? lol

Ah sry to hear. I first ordered my square top from them a year ago (at under $200 shipped I couldn't resist), and fortunately turned out ok so figured I'd use them again for the tranny and diff. Given how it's hard to determine scammers from real sellers these days (and prices aren't cheap in the US) I figured I'd go w/ Prestige again, despite the different issues by different buyers. They definitely aren't perfect, and I can EASILY see how their questionable packaging results in damaged products. I almost expected to receive a damaged part and am happy things are in one piece.

 

Nice to finally get some time to tinker w/ car stuff again. Weather has sucked lately, super cold and snow covering the ground for the last 2 weeks. There's also been a new family addition a little over 2 weeks ago that's been taking up a lot of time. The kids are in love with the pup and it's nice having a dog again (we had to put down our old dog a year ago). Nothing quite like having a puppy for young kids. Same breed as our old dog, it's a lhasa apso. I'm a big fan of these dogs as they don't shed at all and get to be ~20 lbs.


Anyway, back to Miata stuff.. So backing up, I had to clean the nasty *** really rusty diff. I used various wire wheels to try and get the majority of the large pieces off. I also used a bit of sandpaper to get in the nooks and crevices. I ended up with this. Since the casting is pretty rough, you can't get it perfectly smooth and clean looking (or at least I didn't).



I wiped it clean with some acetone and then used rust reformer. It took 2 normal coats and a 3rd very light coat. I had the issue where the rust would "flash" through the rust reformer coating. Not sure what the technical term is. It goes on white and changes to more black after it does its thing. I will note I did them days apart like the directions recommend. This is the first coat.






2nd coat:




I did a 3rd light coat, and realized the rust flashing through would never be completely gone so went to primer. Just a regular rattle can gray primer. It's very cold in the garage so used a heater so the paint would cure properly. I did a few coats of primer.



Finally, did a few coats of high temp black paint. It's not perfect but much better than it was and looks pretty good to me. I still need to reinforce the diff housing.



Here's the diff all done sitting in the garage:

 

While the car was up in the air, I finally got the little parts I needed to install the 2 way valve on the gas tank breather line and delete the charcoal canister. It's just been open to atmosphere via the hard line that goes to the front of the car. The valve I used is a Mocal TPV8. It's a 2 way valve that let's air in/out at a certain vacuum/pressure. Not sure it's much better than just leaving the vent line open to atmosphere but I've had it sitting around. Removed the charcoal canister and hard line going to the front of the car. Probably saved a whole 2lbs!



Here's the new valve installed in place of the charcoal canister. I wanted to ask you guys. This line is just a direct vent to the gas tank w/o any other valve correct?