RX7 fd3s transmission in MX5
 

Because I have many answers about this modification, I decided to open a topic for this.

Well

The miata transmission is very nice, but can't handle safely more than 250 WHP.

At stock situations or at light turbo setups you 'll not deal with problems, but with 300+ WHP the 2th or 3th gear sometimes will gone :magna:

So there are two solutions
1)exotic stuff gears (os giken, quaife etc) but very expensive
2)adaptate transmission from another car, more inexpensive from the first solution but very difficult to do a perfect job.

So I put a turbo trans model "R" from RX7 fd3s (93-95).
It was from the beginning a difficult modification but the engineer succeed in this 100%.:bowdown:

The gear lever is exactly in the same position like the stock, and the "sense" of changing gears maybe is better than a stock transmission miata.
The 1-2-3d gears are a little shorter than stock gear ratio
The 4th is the same 1:1 ratio
And the 5th is much longer than stock ratio!! And this is very nice for a 380+ hp turbo miata! :cool::cool:

The modification based to a new housing between the block and the RX7 transmission. We modificated the miata housing (bellhousing? ) and connect to its end, the end of the RX7 housing.It was a very difficult job because it had to be perfect at straight line with the stock one.
You will see at the fotos what exactly we have do because my english are not so good to explain exactly what I want to tell.:hustler:
The driveshaft was cut and modificated to match to the RX7 transmission.

god i'd consider keeping my miata if this were an easy task.

Bigturbo do you have the old rx7 bell housing still? What about and adapter plate?

would you consider making the adapter plate for selling purposes?

not for profit but yeah, i would love to have another trans option

I would just provide the plans if i could, and have someone else waterjet em.

Technically the issue with the plates is you usually can't take advantage of all the bolts/holes originally designed to be used with the trans or block. What bigt did is stronger (weld job dependent) solution. That said, the adapter plates seem to hold us power as anybody has thrown at them. I'm still undecided on my approach.

great idea indeed, cut the miata tranny and weld up to the fd tranny, keep bolt patern same...hmmmm

I wouldnt really be worried about it. I would be more worried of the bolts ripping out of the block before them failing.

aluminum = requires some skill to weld

cast = inconsistant to weld

cast aluminum = expensive to pay a pro to weld.

Would industrial epoxy work as good as weld?

No.

Right thats why i want to devise a way with no welding, complete bolt up.

Τhere is no problem with the weldings, the job that have been done is very accurate, and don't forget that the stresses in these points are not so much because tha car is a RWD and not a FWD that they have much more stress at the transmission housings

I hope that you understand right the modification.

The RX7 transmission is not like miata trans, it is 2 pieces, the front housing, and the trans. The miata trans, is one piece.

The front side of the miata trans has been cut, and weld to the end of THE FRONT HOUSING OF RX7 TRANS. So the new "custom" housing came and seat to the RX7 trans like the stock RX7 front housing, using the stock bolts etc.

I used a stock 1.8 bp flywheel with a custom 6-pad clutchkit.

The center of the disk has been modified because miata's trans and rx7's trans has another frame in the center shaft.

When you welded the cut miata bellhousing to the FD transmission bellhousing, were you able to bolt the bellhousing back on as if it was stock?

Another question you might be able to answer. On the TII transmission the bellhousing also bolts on in the same fasion as the FD does. Are the TII and FD trannies the same length? IE, if you did this cut-n-weld mod to a TII tranny, would it sit in the correct location?

Another question I thought up, are the input shafts the same lengths on these transmissions?

bigT, your last post is more confusing.

I've got two of the S3 R trans and they're four sections: tail, intermediate, the gearbox and bell housing. As I understand it, the Miata bell housing is welding to the part of the S3 housing that bolts to the front of the gear box. That's what it looks like in the photos. Essentially the mounting of the S3 box is cut out to form a plate to weld the Miata housing too.

mouse- the rx7 shaft is shorter. Using the 1" aluminum adapter plate, there's roughly 1/2" spline penetration to the clutch hub with a miata set up.

I was hoping to build an OE bolt up solution without having to do gear swaps for my FE. My assumption was that input shafts were the same across all R trans - for the 929, rx7 TII, truck/ute and bongo van. They're not. The van and truck get the longest, the rx7 is in the middle with the 929 (going to the v6) the shortest. Here's pic of a TII gear box bolted up to a van bellhousing - that added an extra 7/8" inch of space over the TII housing. Problem with the truck/van trans is the sucky gearing. I'll probably end up doing similar to bigT - using the bell that bolts up to my block, sectioned to fit the TII shaft. May cost, but once you've got it, it's done and can just move over to the next box if needed.
http://i158.photobucket.com/albums/t...Ishaft_600.jpg

Adapter plates could be far more an easy way to go than welding. Also it has been used for decades in the beetle world, where the engine don't even have mounts and just hang from the transmission with no fails or so. People stuff EJ20T and 13B there with no problems.

http://www.kennedyeng.com/

May be some thing can be done with Kennedy but will cost probably 400 and more

I'm still trippin about the fact that you have a greddy E manage

Ok now I'm a little confused. So if you go bigturbo's route, do you have to change input shafts, or are the differences in length negligible?

no- the advantage of bigT's solution is that you can cut the bell to position the input shaft where you want. Of course that'll also dictate the position of the stick thru the hole if you don't compensate for that. The miata solution typically is the adapter plate because it is easy and cheaper than the welding- and it works for as much power as anybody has made.

So does anyone have a rx7 bellhousing?

Subscribing...pretty impresive bigturbo...
I wanna see someone start pumping out adapter plates to allow for bolt on trans's...very interesting topic guys

With the adaptor, I've read through crash41301's swap a few times. I'm getting tripped up with the clutch fork pivot bolt/ throwout bearing mod. Can you possibly give me a better description of what to do here? How do you get the throwout bearing to sit 1/2" farther forward?

Loki - I have one rx7 bell, attached to the box. But I'm not going to give it up yet, not until I've completed the project. What I did was just call around to mazda shops until I found that had two of the boxes that were in the way. They gave them to me. Same shop gave me three 1.6 engines like five years ago. The owner is a racer, so he'd rather give them to me than the junk man. IMO a lot of these owners will take interest if you tell them what your up too - like a 300hp miata...

I thought there was somebody in fla on m.net that did a bunch of adapter plates... don't know if it ever came to fruition. I do think that Loki could probably sell at least 5 of them- more if he pushed them on m.net. Just need to figure out what it's worth to others, and to him.

I can't. I'm not doing it that way- different engine. I'm using a van bell housing which has the normal clutch fork position. I've already been through the resolution for the process on my own tho. I'm using a b2000 truck bell on a miata housing with an 80s 626 flywheel, 1.8 Miata clutch & pp. I made all my adjustments to ensure proper engagement/disengagement through the slave rod length- trial and error.

I have explain it many times. One of them, is here

Did you swap out tranny interals for better gearing?

The lever it's almost at the stock position (1 cm behind) as you can see at this foto
https://www.miataturbo.net/forum/att...1&d=1201133301

For some of the other questions, sorry but I cannot follow some of the elaborator meanings (not very good english :dunno: )

If I had better explains to some meanings maybe I could help better.
But I thing that the most have understand tottaly about the modification.:)

Nope, I just buy from a friend (only for 200$ :cool: ) an RX7 fd3s '95 model transmission with very little kms. It was at very good situation so I put it as it was.

how much did you cut off of each bellhousing?

car
 

Dude, This is sweet. And to mod and weld something that works great under that force is awesome!!!!:bowdown:

hmm do any b6 or bp trannies have bolt on bell housings?
if so then an adapter plate between the gear box and the bell housing would be a an easier and better solution to an adapter between the block and the tranny.

How's this holding up now that you've been driving it for a few years?

Don't know why you would want an FD tranny. They aren't exactly known to be reliable. Ask me about my two broken trannys from my FD sitting in my shed.

Tell me about your two broken trannys from your FD. I'm looking into this swap with either a FD or the TII FC tranny which is pretty much the same.

The first one shredded 3rd gear shifting from 2nd WOT when the car was stock. Approx 250ish whp. The second I blew the 5th gear syncro (known problem in the FD trans) at 380whp. The current one is holding strong. We'll see how it lasts.

FD guys swap TII trans in because they are stronger. Go for the TII.

Guys on the FD forums are known to refer to the FD trans as glass... lol

From what I have seen doing research, the only differences between the TII tranny and the turbo FD tranny are the syncros which made it shift better (although it would appear otherwise in your situation). Powerwise I'm being told it's a wash. I've gotten all this information from FD owners.

You're right on the smoothness of shifting. The TII won't be right there... but from my understanding it will hold more power and take a bit more of a beating before any issues arise.

Realisticaly, for a Miata power wise you're OK with either. Syncro wise, I would say to go with the TII. Or have an FD box rebuilt with all new syncros and run good fluid from the get-go.

What's odd is that those transmission are both essentially the same unit- based on the same Mazda R gearbox. I suppose it's possible that changes to improve drivability were done at a compromise to strength. You never hear of people braking the TII version in a Miata- and this is the only case I know of that is using the FD box.

bad ass swap. FB rx7 guys have been using the Miata gear sets for years not I was waiting for the reverse to happen.

It's holding up just fine and the car's previous dyno was ~380rwhp. Its getting a Megasquirt now and we are hoping for 400+rwhp at 28psi.

Dimitris

I am working for a rotary shop, and so I am seeing my fair share of FC/FD gearboxes. Almost all FC gearboxes have syncro problems. FDs don't. The only FD gearbox that I've seen breaking was on a RX-8 swap (FD 13BT+FD 5-speed tranny), where the input shaft literally snapped. The gears were fine. Horsepower was ~500rwhp at 15psi.

Dimitris

500whp and 15 psi with which turbo Dimitris?

My rx7 fc tranny holds perfectly 28 psi with gt2871r but I have some syncro problems.Who cares.

It's a Garret GT3582.

Dimitris

i have seen these trannies hold up to 600hp with ease..

I think I found a solution to the bellhousing issue with the Mazda TII transmission.

You may be able to use a TII tranny with a Ford Ranger 83-88 toyo-koyo bellhousing.
Its a 2.0 block and/or you can use the ranger tranny which has a longer input shaft but its internals are very similar to the mazda turbo style with the oil pan fins on the bottom,