Maybe check that the cv axles were perfectly straight and level between the diff and hubs at launch. They are supposedly strongest during the times when the joints are straight. But then again, you aren't breaking the joints.

Yep breaking the actual shafts. Never had a problem the joints. I attached a pic of the broken insane shaft. I just emailed them pics and a return form. Lets see if they warranty.
https://cimg3.ibsrv.net/gimg/www.mia...d7d51d5413.jpg

I'm investigating potentially using two left side 88-91 929 axles with early 1.8 stubs with spacers between the stub and axle. I will have to source some na fc rx7 hubs as well apparently.

It looks like using 929 axles and spacers is an upgrade in the rx7 community, maybe even over the turbo axles. https://silhouettepower.com/collecti...37073959911588

Just to catch y'all up on axle conundrum.

Still haven't heard back from the insane shafts folks. I've emailed them a couple times their rma form, sales receipt and pics of broken axle, no reply yet. I've also called and left a voicemail, no reply to that either.

The currently car has 1 stock, 1 insane axle. If I do get a replacement from them I will be selling the Insane shaft axles. I do feel they were stronger, just not enough so for what I'm trying to do.

So moving on to improving them. I got in a couple left side 929 axles. Now those puppies are looking strong! The axle shaft is 28mm as does not neck down anywhere, even going into the cv race. In fact I pulled off one of the boots to have a look into the cv joint. the axle actually steps up larger to go into the cv race. The cv joint are also significantly larger. Since I have so many broken shafts and a broken insane shaft I can look into where the boot areas would be and measure the areas where those axles step down to measure the minimum diameters since that is where they've been breaking. The stock axles neck down to about 22mm, the insane shaft necks down to about 23mm. The 929 axle is 28mm minimum. So if I can pull this off with as minimum expense as possible I should be a huge upgrade.

Now for the challenge. These axles use an rx7 style stub shaft. No biggie, I just picked those up along with a rx7 carrier and axles for $100 from a cool sort of local fellow.
These axles are too short by about 3/4" or so. Also the centering ring on the 929 axle is a little larger than needed to fit into the rx7 stubs. Im assuming the spacer made by sillouettepower accounts for that. I emailed them to confirm before I order but no reply as of yet. there is a chance a may have to spin my own spacers. Not a huge deal though. I can figure that part out if need be. The good thing about swapping to these axles is I can swap to a turbo 2 style diff and carrier later if need be, the outboard stuff will be done.

Also these require a 28 spline rx7 style hub. This is where it gets interesting. I emailed Martin at monster miata asking him about possibly broaching some miata hubs with the 28 spline rx7 style spline. That guy actually took the time to pick up the phone and call me if you can believe that! Talk about customer service!! Well it turns out he actually has those on the shelf. So I ordered two. If I decide to move forward on any other swaps to the rear, he will be the first one I check in with before spending any big bucks.

Below is a pic of the size difference of the 929 axle vs the insane axle. The insane axle is slightly larger than the stock axle as well, though just barely. Howevre notice the difference in the size of the outer cv! stock is on the right.
https://cimg3.ibsrv.net/gimg/www.mia...6672676171.jpg

No clue where your alignment is at currently, but I wonder how much of that you would be able to make up just by setting all of the eccentrics to pull the control arms to maximum inboard position.

Not nearly enough.
In fact I had to extend the top arms to get positive camber so tires will be flat at launch. Also I'm still gathering parts and taking measurements. It could need as much as an inch spacer. Also need to adapt to different centering dimensions since I'm using the na rx7 stubs as opposed to the t2 stubs., that can be accomplished in the spacer as well. The t2 stubs would have the same centering dimensions as the 929 axles. Good chance I will order two 5" x 1" aluminum lathe stock and make them. Cheap and easy enough.

The new fuse will likely be the stubs, differential or driveshaft joints. After looking at these axles I find it extremely unlikely the axle will break before those other things. If I start breaking stubs or differential I'll address going to t2 diff or something else.. I'm only looking to pick up a couple tenths though, so hopefully those fuses don't blow before then.

Lots more axle info:
So I got the spacers made, larger 28 spline hubs and everything needed to convert to 929 axles
https://cimg1.ibsrv.net/gimg/www.mia...15b8576997.jpg

I installed them in the car and took for a rip. I noticed a slight vibration at heavy load so jacked up car and ran on jackstands to observe if spacers were machined true and center, they were not as evidenced in video clip Dang it!! If its not one thing its another LOl...
Time to regroup a bit.
Since I now have 28 spline hubs I can no longer use miata axles, but fc rx7 axles bolt right in, so that's what's on the car now. I also have a couple spare rx7 axles too. I have a lot of measurements of various axles I have on hand in pics below. It looks as rx7 axles are potentially a little stronger than miata axles as evidenced in pics. The miata axles neck down to ~22mm inside the boot areas going into the cv joints. The rx7 axles look to be between 24-25 in the boot area going into cv so the shaft should be a little stronger. I have been breaking the miata axles in the narrower area where it necks down. The rx7 cv joints are larger as well so the cv joints should be stronger too. However I have yet to fail a cv joint, just the axle shafts themselves.. Hopefully these rx7 axles will get me by while I decide if I want to remake the spacers to use the 929 axles with the miata diff or just save the 929 axles for when I do a ford 8.8 conversion or for a turbo2 differential setup to use them with. Apparently the 929 axles are stronger than the turbo2 axles according to sillouettepower.
https://cimg3.ibsrv.net/gimg/www.mia...e130f1c75c.jpg

Below are pics of the 929 axles and measurements
https://cimg9.ibsrv.net/gimg/www.mia...59fdde8c15.jpg
https://cimg1.ibsrv.net/gimg/www.mia...f35b411e5b.jpg
https://cimg3.ibsrv.net/gimg/www.mia...808137d58c.jpg
https://cimg5.ibsrv.net/gimg/www.mia...d5f8a90ac0.jpg
https://cimg7.ibsrv.net/gimg/www.mia...27ebe87b7b.jpg



Below is pic of 929 spline size vs miata (I removed the sensor ring for install as it interfered with spindle)
https://cimg5.ibsrv.net/gimg/www.mia...f4cfdbf168.jpg




Below are miata axles
https://cimg7.ibsrv.net/gimg/www.mia...eb4b846686.jpg
https://cimg9.ibsrv.net/gimg/www.mia...c43992b06f.jpg
https://cimg1.ibsrv.net/gimg/www.mia...56a064d2e6.jpg
https://cimg2.ibsrv.net/gimg/www.mia...de913d668b.jpg
https://cimg1.ibsrv.net/gimg/www.mia...ffb38e174f.jpg




Below are fc rx7 axles
https://cimg7.ibsrv.net/gimg/www.mia...d0edb00264.jpg
https://cimg9.ibsrv.net/gimg/www.mia...d55491c523.jpg
https://cimg1.ibsrv.net/gimg/www.mia...d160128187.jpg
https://cimg4.ibsrv.net/gimg/www.mia...369db7fb97.jpg
https://cimg6.ibsrv.net/gimg/www.mia...5e9c87fd73.jpg


I am hoping to have everything in hand to do a 8.8 swap or t2 swap by the end of the year to get it done while track is shut down. I really want to start testing using some nitrous at the track, but the weak driveline has been stopping me. Hopefully that will be corrected beginning of the year as well as some weight reduction. Should get some pretty solid passes in if can lose a couple hundred lbs, stronger rear and spraying 50-100hp worth n2o eventually.

I would just like to start this off with HOLY COW. I have an NB Miata with an auto and there is hardly any information online about auto Miata's with turbos. I've been trying to gauge how i could do it for so long and you sir have been a godsend. After spending the last 30 minutes of this reading i do have to ask. What are you using for engine management? I may have missed it in one of the posts but I absolutely want to go this direction. I also wanted to know how you felt about the auto that came in the NB miatas (Aisin 03-70le i believe). Thank you for all the help : )

I am using a "fishdog" from speedyefi. It uses an ua4c board made by wmtronics.

The transmissions I run are the early jatcos. I have never been into an aisin transmission so cant help you much there. Pat ran that transmission for a while before switching to a c4 so you may want to ask his thoughts.

I have heard a lot about this pat person but have yet to find a way to contact him. Could you point me in the right direction? Also that's awesome information about that ECU. If I'm not incorrect, you are using the transmission that came in NA miata automatics. From what ive heard those are controlled by a unit in the stock ecu and are not a separate module. Does the Speedyefi control the transmission in your build?

PS: Sorry if these questions are stupid im still learning about miata autos haha

Just send him a private message through this forum or ask a question on one of his threads. He will respond to you eventually. I know he ran the Aisin transmission before swapping to a c4, but was not happy with it. However he did not really pursue building it up either. He just stepped up to a big boy transmission.

The transmissions I run are very heavily modified throughout and are basically manualized, so mostly don't rely on ecu for shifting. I shift manually all but first to second shift. I do use an ecu map to control first to second solenoid, but all else is manual in so far as shifting gears goes. I only use first gear at the track and on slicks. Street driving is all manual shifting no ecu control.

The na miata 94-97 use the factory ecu and a tcu for transmission control, but I believe the ones prior to 94 are all hydraulic with the exception of the lock up solenoid which is controlled by the ecu. You could use one of those transmission and use a simple switch for lock up in 4th gear. Its not rocket science, but automatics are complex and do require you study up if you plan on building one successfully.

I dont know what you are trying to achieve, but your stock automatic may hold 250hp or so as it is. That is if its in good shape and you don't cook it.

Don't expect to duplicate my results though unless you really know what you're doing in so far as going into the transmission.

Being fully honest i didnt think putting a turbo on an auto Miata was possible. Every time I asked in a forum places people just told me "manual swap it". Which yes this is the easier route, but personally I have to drive my car in stop and go traffic ALOT and dont want to destroy my left foot LOL. And i appologize for not explaining it better, i mostly was excited to see hope. My goal is nothing crazy as its my daily. Its a 2003 NB Miata with an auto and I want to put a turbo on it to run at a max 200 wheel hp. To start i dont even want to go that crazy. But i guess talking with you was my first step in learning about miata autos as there is so little information present online. I'm not trying to duplicate the spooling system you have, for now I just want to go with a basic automatic turbo Miata. I know a lot about engines but little to nothing about how transmissions work. I should probably start by learning that LOL. If I do have questions would you be willing to answer some? You seem like an amazingly experienced mechanic that I could learn lots from :) If not I understand completely people have lives to life :P

If you are only looking for 200hp and your engine and tranny in good shape I would just go for it with what you have personally. For easy management you could run an aftermarket ecu in parallel with factory setup. You could use the aftermarket ecu for fuel and ignition and factory for everything else

@Kango , you are looking for @patsmx5 .

IIRC, there is a modulator (externally accessed part) from another transmission that allows the Mazda automatic to hold more torque.

DNM

Hey Dnm. Thanks for linking right to Pat. I didnt think to do that. I assumed he had already been to some of Pats' threads.

Are you referring to a vacuum modulator? I dont think his tranny uses a vacuum modulator. I could be wrong since I've never personally laid hands on one of these things.
However, I did look up the tranny used for the 2001-2005 miatas. It looks like it uses a throttle cable for pressure control. That can be adjusted slightly for more pressure but at the expense of harsher shifting when just putzing around. At his projected power level i wouldnt bother doing anything to the transmission. It should be fine if its in good shape.
If the info and schematics I found are correct I see a couple positives and negatives if wanting to build this transmission for something more serious, Like 400- 500hp.
It does use 4 pinion planets, which should be ok for 400 or so. The valve body uses separator plate with orifices that can be modified for faster filling and draining of the packs for faster shifting. However the issue I see is that it would not be easy to add to clutch frictions and steels count in any of the packs. It doesnt look to use cushion plates which can be removed to make room in the packs for more frictions and the retaining plates dont look thick enough to do a lot of machining to make room. I suppose if you could locate some thinner steels and adjust pack clearance by slightly machining retaining plates it might be doable?? Again, since I havent seen or been into one of these in person, take the above with a grain of salt lol... I could be wrong.
Probably best though if one is considering bigger power with this tranny to just follow Pats lead and look elsewhere.

https://cimg6.ibsrv.net/gimg/www.mia...fb2ea9f040.jpg


Well snap!! All this transmission talk last few post jinxed me LOL..... Glad I found this before it totally let go. This thing lives right by my leg. I should really get a blanket on this thing.

Direct drum developed a crack. Most likely started on one of my trips at the dragstrip trying to launch at high boost with the transbrake and launch control when the axles started breaking. Once the crack started it likely just propagated from there. Looks like I will be foot braking this as before until I decide how I want to proceed. Car ran a best of 6.57 at 108 and change foot braking, but not much left on the table to get off the line harder. With the transbrake I feel I had some performance left to be tapped into, but the driveline parts just couldn't handle the shock of the instant hit of power application. For now the tranny is repaired and back in the car. All is well again.

However I have some decisions to make. Should I keep everything as is and try to be satisfied with a best transbrake run (so far) of 6.56 at 109.8 (not likely I can control myself lol)? Should I sell it and move on to the next one? Keep the miata engine and swap out driveline for stronger stuff?

Sad thing is years ago before I swapped out the 5 speed to the jatco I had a c4 I built up and planned on going with. I also had the jatco to use for the bellhousing. When I opened up the jatco I noticed the clutches and drums were very similar sized, so I thought to myself, Self you can build this puppy up for the easy button, which I did. I then sold the c4 when it looked like the jatco will hold. The jatco did well for years until I recently decided to go crazy with a transbrake setup looking for more.

However the main issue with the jatco is there is no aftermarket support for stronger hard parts,, whereas the c4 is still supported. The jatco you are stuck using factory hard parts. The jatco may hold ~500ish hp for a couple years though if modded but with no transbrake. I've never dynoed my car nor do I care to, but wallace race calculator has me between 520-530hp based off best 1/8th mile trap and est weight. I would think the jatco would live a pretty long life if built similar, but at a lower hp level, say maybe 400ish, in case anyone else out there is eyeing these things for their projects.

The problem with the c4 is build-able cores are getting a little harder to find locally. If I keep the miata and the bp engine I will most likely wind up using a c4 and ford rear, but not 100% sure I wont swap everything in the future, including the engine.

Or go on a drastic weight reduction endeavor with the miata and see how quick that will get you.
I am currently attempting to take 200 lbs out of my miata kart to bring it down to 1,750 lbs.

Maybe. Right now its back together as it was. I most likely will keep the car as I've had it for so long and had a lot of fun with it. Undecided how far I want to try and take it though and if Im staying with the miata engine or not.

If you get to 1750 you should fly. Thats really light.

https://imgflip.com/i/71rv0k

FWIW I have an auto from a 2003 sitting in a box. I modded it a bit to shift faster and hold more power. I'd say it's good to 300whp. I got it to hold about 350whp by developing some electronics to limit torque on gear changes. Less fun but more fast. Would sell for very cheap if you're interested.

As mentioned, I now run a Ford C4 Auto which is a lot stronger, but it was stupid expensive to get finished. But it works really well for how I use it.

Small update..
Went to the track last friday for tnt to beat on the car a bit. Track was not really prepped since the following saturday was basically a 28 tire race which they dont really do much prep, if any at all. Tire spin was an issue for me. Best pass I had to peddle a couple times to only a 6.94. This was also on lower boost and launch rpm to try and preserve driveline parts a while longer.

I am still tentatively planning to 8.8 swap in the near future to start cranking the power and launch aggression in this junk back up. Need to do some maintenance on the rear bushings as well. Mine are energy suspension about 5 years or so and apparently wearing out. I was getting some tire rub in the upper forward portion of the wheel wells. The wheels are biasing forward under heavy power. I checked all the rear suspension stuff for cracks/looseness, everything looked good that I could see. I also need to limit the amount of rear squat at heavy load when launching to help with tire clearance, keeping tires planted flat and axles at less of an angle.

Its been a while since I tinkered with this junk miata so I messed with it a little this weekend. I was going to build a cheap header for it, likely still will eventually. However when I got the cast ebay manifold off I looked at it and decided to try a few ideas to improve on it first. The pic below is the before pic. It was mostly as cast but slightly radiused ports from when I first got it and installed a number of years ago. Of course it also has the pipe for the spool shot system.
https://cimg8.ibsrv.net/gimg/www.mia...adab9bef7c.jpg


After looking it over I decided to open it up and shaped it a bit to closer match the gasket area. Its hard to see in the pic but I also welded in a center divider. The divider goes from where the wastegate pipe is welded up to about half way up the open area where the turbo mounts. I would have liked to have brought the divider all the way to fill the entire cavity, but i couldn't do that due to the inlet from the spool shot system. The idea behind adding the center divider is to help add a little bit of a barrier to try and mitigate some of the cylinder dilution of exhaust gasses during overlap of the exhaust valves between cylinders 1/3 and 2/4.

And yes, I know this is cobbled junk and the work is crude, but the idea is to test these things without spending a huge amount of time unless it is absolutely necessary.

I got all this done and put car back together to test. I only got to do a couple short pulls at my test spot today due to some people in the area, but the manifold mods appear to have made a positive change. It seems to spool a little better and may have slightly improved power. I need to do more testing to confirm results but it definitely didn't hurt.

https://cimg4.ibsrv.net/gimg/www.mia...d77a383808.jpg


I also want to give a huge shout out to 208 fab. He cut me a great deal on a ford 8.8 diff. I hope to have that ready to go in by the end of the year.