Dunno if it's typical. Seems like a bigger loss than I've ever heard for manual vs automatic.

The car was WRL power-to-weight classed based on the reduced hp so it was about as fast as I expected. Definitely slower than other 2.5 swapped NCs I've driven though. No amount of fast shifting will make up for 25hp lol.

 

got some pieces in from Domiworks. They are nicely machined and fit well. Ignore all the **** on my worktable. Unfortunately my brother's very fit wife died unexpectedly of Vfib ( I had never heard of it) last week so my project is on hold helping my brother get thru the ****. She was wonderful. Really a tragedy.

I'm still a bit on the fence, but am unconvinced about clutch wear fears as in my previous posts

adapter - needs a big starter cutout


. The parts shown are not really light - probably 15 lbs - so adding that to the TC means a ~ 50 lb flywheel. Yuck. Trans side of TC bell will be machined off as part of adapter as seen in some of the adapters done in the FB posts, and I'm going to machine the Domiworks pieces to remove weight too. Hoping to make more progress in about 10 days.

 

Hey OP,

What you are doing is exactly what I had planned for a while for my rods-only turbo VVT in a 95 NA chassis. I am running the Kraken full kit with a pulsar GTX2860r @ ~250whp. I will be following closely. Plese update us on any progress you are making as I am eager to see how it all works out.

 

an update: after a bunch of head scratching and playing around with parts, I finally came to a setup I think will work. Unless I've missed something with a brainfart (not unusual) the assy will consist of:

domiworks engine to trans adapter plate
NB miata auto trans flex plate
6 puck sprung hub clutch disc for an LS V8. I actually cannot remember it may have been for a 5.0 Ford, but key point is sprung hub for V8/Turbo Miata torques, and o.d. a bit bigger than the i.d. of the lip on the flex plate - you can see in the pics below.
the two splined hubs cut out of the ZF8 TC.

The splined hubs have been shown in previous posts. I had a morning shower aha thinking about the Miata auto trans flex plate - unfortunately my aha came months after paying for the Domiworks adapters. His stuff looks really nice, but I think the total kit cost can be much lower if you are going without the torque converter.

The auto trans flex plates are cheap as dirt - $30 or so.
sprung hub 6 puck disc $79 delivered, so ~~ under $150 all delivered.

I drilled the rivet on the metallic pucks and they came right off, then chucked the disc in my itty bitty lathe, and created an sub micron tolerance o.d. grinder set up. Call me Mr. Jank.
Ground the od of the disc to 10.040", which fits right into the lip of the Miata flex plate.
I'll space the disc out from the flex plate face to the edge of the lip to clear the crank bolts underneath.
I'll have to match drill thru the disc face and flex plate and will probably tack weld nuts to the back face of the flex plate to receive bolts from the front of the clutch disc.
the disc hub will be welded up as an assembly with the two splined hubs. I need to cut a spacer approx 3" od by 2.5" id to get the proper space between the two splined hubs then that will all be welded together.

Assembly will be bolt flex plate to crank, disc/hub spline assembly to flex plate. This basic configuration has all been done by the guys named above in much the same way so credit to them. If you're willing to do a bit of work yourself and either have tools or buddies with tools this part can be done pretty cheaply.

I'm more convinced than ever that the clutch "issue" is a figment of keyboard warrior imaginations.



sub micron precision od grinder


V8 6 puck sprung hub w pucks removed, in NB flexplate


NB flexplate

 

One of the other things I've learned is they apparently are output shaft speed limited in 7th and 8th gears - I think because the planetary set has to over speed by the underdrive ratio so it gets zinging up pretty good. Lawisme blew his ZF with a high speed 7th gear (and I'm talking hauling ***) K24 turbo NC pull. I think he was doing over 160mph. So a taller rear than the 4.3 will be rqd.

Food for thought.

 

I am glad you posted this because I saw him post the same thing a few weeks ago. I was going to start asking a few people about top speeds they reach on local tracks to me with 400-500hp miatas to see if I'm setting myself up for the same failure as Lawisme. With 230hp, I'm reaching 135mph with 6spd/4.3 at Road America. Not sure how much more speed I am to expect when I have twice the power

 

awesome work and engineering! Are you going to do a pilot of some sort to register the transmission input shaft into the back of the crankshaft?

 

Re: top speed and output shaft rpm - I contacted lawisme directly and he said he’d run his WAY over the output speed ZF recommends many many times. He also sent me a link to a 3.3 Miata ring & pinion - which I didn’t even know existed. I thought the lowest was a 3.6. Another option is the Caddy/Camaro diff (?) being run - I think those can have a 3.27. And, I think 150


or so will be fast enough for me. I’m old and my bones are brittle. And my plums have shrunk.

re: piloting trans input shaft- the shaft is recessed about 2” past the face of the trans, and, the torque converter is just bolted to crankshaft with the nose of the shaft sealing in it. I’m aiming for about .002 TIR

Shown are the two Domiworks pieces that won’t be needed. Though the black piece is aluminum, with it, the steel ring gear and piece of the cut up TC I showed earlier we’re still not what I’d call a low inertia “flywheel.” The auto trans flex plate, sprung hub disc, and small dia hubs connecting to trans otoh should have significantly less inertia than a 949 twin disc. Total assy weight looking like about 7 lbs, with half of that under 3” od.
😳

 

I love the creative solution you are brewing here. it should allow for a pretty responsive drivetrain with significant flywheel assembly mass reduction. Please keep the updates coming.

 

I've had a new family member - I'm a grandpa now - so have been a bit distracted. Gotta love grandkids - but then, helping "nesting" creations - re-painting wall cabinets, helping re-paint baby room and just enjoying the little bugger.

I am making drawings for the plug to use for centering while welding the pieces together, sleeves to connect the two hubs etc. I'll try to post some more pics in the next week or so.

 

Howdy Wombat! Any updates? I’m auto-curious!

 

man - "the next week or two" turned into eternity. Still bogged down in honey do's and baby sitting, but getting hot rod hangry so hope to get back onto it soon.

thx for reminding me where the priorities should be :-)

 

Well, I've gone and blown up my 6-speed and I think I will go the 8hp route as well. Nothing is solidified, but the transmission in the car is definitely done for. It didn't go out in the normal 4th gear explosion way though. On my way to work 2-3 weeks ago after hopping off of the interstate, the transmission got stuck in 3rd briefly while on the off-ramp and downshifting. I was able to get it out and then continued to drive normally for another week or so until a light but spirited drive one afternoon where it suddenly stopped wanting to shift into any gear smoothly. I took it back to the garage and changed the trans fluid, which revealed some nice metal chunks and 4/10ths of some metal ring (??). Also, the magnetic drain plug was covered and it had very shiny oil. I believe the trans had GL5 trans fluid in it, but I don't know what kind. I think this because when I put the Redline MT90 in it shifted almost better than ever without the engine running. regardless, ****'s fucked. 3rd/4th won't engage without manhandling it into gear. There is also a loud whine in all gears but 5th and 6th.






Regardless, I knew it was only a matter of time, and had already been doing some light research into other swaps available. In the spirit of pioneering new avenues, I found myself looking at the ZF 8HP transmissions. I had also driven my cousin's Dodge Hellcat with the 8HP90 and it was genuinely extremely impressive. I hadn't ever driven an auto transmission that felt that tight and responsive. Additionally, it pisses off all of my manual purist friends too so that's a huge plus. Anyways, the current plan is an 8HP45 or 8HP50 due to their smaller size. They're rated for 450nm/330ftlb and 500nm/370ftlb at the crankshaft, respectively. However, in practice, people tend to get a lot more out of these smaller gearboxes. I can't remember which gearbox it was but a guy on YouTube reported running around 700-800hp in an 8hp50 I believe so it should be enough for my measly 450 crank hp and 380 crank tq.

For conversion equipment and hardware, I plan on using the Adamat conversion kit (it is the cheapest) if I go with the 8HP50 or the Domiworks conversion kit with the 8HP45 with the stock (gasoline) torque converter to keep things simple and avoid any additional clutch wear from hard launches as I have planned to do. For mounting, I plan on making a homemade mount with polyurethane bushings for the transmission, the V8 Roadster differential mount/PPF delete kit, and a custom driveshaft. If you all have more information on the max output speed of the 7th and 8th gears that would be great because I was planning on using my 4.3 torsen and selling my 3.6 ring and pinion (I'm going to do more research into it myself regardless). For controlling the transmission, I plan on using a TurboLamik TCU. They seem to be the most flexible yet simplistic controller available. They also allow for use without an ECU that can do TQ calculations (the TCU has its own TQ calculations) or downshift throttle blips, which is great because for the first version of this I plan on continuing to use my MS2pnp. Eventually, I'd like to swap over to full drive-by-wire throttle body, Haltech 1500 ECU, and ethanol sensor but simultaneously I want to take it one step at a time and avoid scope creep. If I had to estimate a timeframe I'd say optimistically, it might take 6-8 months to complete. Realistically though, I think 1-2 years is more reasonable. We will see what happens, and I will try to come back here and create my own thread to document things.

For anyone else who has been considering this or is interested in learning more, a huge resource and source of entertainment has been Zero to Sixty on YouTube. They seem to be pioneering a lot of the tuning and installation efforts with these transmissions. Their last few videos where they have been tuning the RX7 have been really informative.

 

After some VERY LIGHT googling, I’ve found some people saying not to surpass 8100rpm on the output of the gearbox, which would be equivalent to 127mph with the 4.3:1, 133mph with the 4.1:1, 140 with the 3.9:1, and 150mph with the 3.6:1.

Based off of this I’m tempted to sell my 3.6:1 and then buy the 3.3:1 from Bofi, but simultaneously, I don’t know if having the capability to do 164mph in a Miata is the best idea… and if so I don’t know how happy the Torsen would be at that point anyways.

I was really wanting to run the stock differential to avoid further complication, but it is starting to seem like that isn’t the best option. I was already concerned about the hard launches with drag tires, and this just adds onto that. I’d hate to rebuild and reinforce my differential housing just to have battles with the axles or worse blow up the differential internally.

 

Watterson - glad another 8HP build underway. Where did you get the info on the 8k rpm shaft speed? I’ve heard about ~ 6500, and I think that’s about what the M4 BMW does w an 18”
tire & 3.15(?) rear @155 mph.

also - re torque converter - what is your logic on saving clutches if you run one? Not trying to start a pissing contest, just interested in logical thoughts about it.

Im hoping my build will be done in next 6 mos but my track record so far blows.

 

Re TC’s are you just doing drag racing? If so the rotational inertia will probably help.

 

I haven't seen anything concrete at all in terms of a hardcore cut off for maximum output shaft speed. I can't remember where I found the 8000rpm limit number, but it was just some random comment on Facebook, some forum, or Reddit. Earlier today I did a search on the TurboLamik Facebook though and found a case of a guy cracking the transmission near the output shaft flange.



Here is what he said:
With this, I'm thinking not to surpass 7500rpm or so, which is where I plan on setting my shift points. So basically just don't go into 7th or 8th at WOT. That should still be capable of 140mph with a 3.6:1 ring and pinion or 150mph with a 3.3:1. I'm perfectly okay with either limit, but theoretically at a track with a long straight, this could be an issue. Given, most people are probably going to swap differentials, which will give more final drive ratio options. I don't currently plan on doing that though.

It would be primarily street-driven, then autocross, then drag racing, and then track in that order. I just really don't like the idea of using a clutch to start the car's movement if it wasn't designed for that and easily replaceable. Also, not to mention the TC allows for loading up the drivetrain to avoid shocking the system under launches. If I didn't have the TC, I wouldn't be able to use the brake pedal to hold the car at the start line unless I used a transbrake method. I don't really like that idea though since it can lead to some pretty bad shock loading.

I wasn't really planning on talking about my differential ideas, but since I've brought it up I guess I will

I plan on using either the car's current Torsen II differential or the SuperMiata Tuned OS Giken differential. From what I read, the Torsen differentials (specifically the Type 1 that was on the pre-96 Miatas) have a bad rep of grenading themselves at the launch of a drag race. From what I've read the ring and pinion haven't ever really been the cause of failure, just casualties when the Torsen lets loose. I already have a 3.6:1 ring and pinion, but I think I'm going to sell it so that I can get the 3.3:1 from Bofi. It wouldn't be that much more expensive than what I can sell the 3.6 for, and if I'm putting the SM OS Giken diff in then it is only a drop in the bucket regarding cost. At this point, reinforce the differential, probably get some stronger axels, some 225/50/15 drag tires and shoot for 1.7 60 foot times.

 

So Curly just asked if anyone ever successfully installed an 8HP in a Miata. Specifically due to transmission tunnel clearances, and other than this wild build thread with a k24 I couldn't find anything. I figured I'd ask you if you ever got around to test fitting it? How do the transmission tunnel clearances look if not?

 

Any updates from you folks? This thread just came to mind yesterday. Buncha guys were buzzing on the NC FB group about the 8HP swap. I messaged Rapscallion Motorsports who make their own 8HP swaps for their shop NC’s, and was told this when I asked if they were going to release their kit for sale at any point.




Obviously the NC kit doesn’t apply to most of the cars in this thread but I thought their decision to go back to a torque converter was interesting given they’d run their track only cars converter-less for a while.

 

I have completed my swap. It’s not as easy on the NA/NB as the NC. There is literally no room for the exhaust in the tunnel. I had to do som surgery to make it work.