Jump to content

M10, S14 & M20 6 Speed Adapter Plates with How-To Guide


Recommended Posts

How-To Guide now on Page 3 of this thread.

 

Evening All

Every few months on here I see the same threads about how increasingly expensive and unobtainium 5 speeds are. That’s not to mention the close ratio 5 speeds.

 

I have recently completed my ’02 build with an M20 3.1l engine mated to a Mazda RX8 6 Speed manual transmission using an adapter plate of my own making. In the process of doing this I have come to learn all of the technical hurdles in mating the RX8 gearbox to the BMW M20 engine, of which there are many, none of which are insurmountable.

 

There is little fundamental difference between an M20 and an M10 as far as the clutch and transmission setup is concerned. In my spare time I have also made a trial M10 to RX8 6 speed adaptor plate and have access to the facility of getting a CAD drawing made to replicate it.

 

What is so great about this transmission? Well it’s basically the best transmission you could fit for the money by a distance.

1)      They are cheap to buy

2)      The gear ratios are superb

3)      They will handle lots more power

4)      They will have longer life span

5)      They shift much better (no separate platform)

6)      They don’t leak like a sieve

The key aspect when it comes transmission swaps is the gear ratios. The RX8 6 speed ratios are perfect for the M10 because they are basically the same as the Close Ratio Getrag 245 and Over-Drive Getrag 245 in the same transmission. So you get the driving perfection of the CR ‘box with the OD 6th cruising gear on top for only $250. A factory CR transmission is >$2500 these days and are notoriously unreliable.

 

***There were 2 variants of the RX8 transmission with slightly different ratios, essentially they are the same but the S1 is closest for the factory 245CR ratios

 

RX8 (S1)

RX8 (S2)

245(CR)

245(OD)

1st

3.760

3.815

3.764

3.682

2nd

2.269

2.260

2.325

2.000

3rd

1.645

1.536

1.612

1.330

4th

1.187

1.177

1.229

1.000

5th

1.000

1.000

1.000

0.805

6th

0.843

0.787

N/A

N/A

 

There are obviously downsides,

1)      No speedo cable drive

2)      The shifter will move back circa ¾ to 1 inch

3)      It is possible you will need to modify the tunnel slightly… Im not totally sure on this, it might fit as is…  (it won’t fit without mods on an M20 install because it sits much further back in the tunnel) If mods are required for an M10 install it wont be a lot and would be un-noticable inside the car.

4)      It is not a straight bolt in job there is some bits of machining work involved that you will likely have to sub out unless you have access to tooling.

5)      Weight, they are around 15kgs heavier than a 5 speed.

 

Everyone says that a 5 speed transforms the car, albeit in different ways depending which one you choose. Well this 6 speed is double the transformation, I can attest to that.

 

Although I have access to an M10 engine and transmission to do lots of fundamental works I don’t have a car I can install this set up in to prove it. However as I have said, there is not a great deal of difference between mating it to the M20 which I have done without issue. I am 99% confident that it would work.

 

I am at the point now where to progress this it would involve me spending chunks of my own cash to get it drawn up, and test adaptor plates laser cut etc. Im just a private individual, so Im reluctant to do this if there is no appetite for this set up. After all, I will get no benefit out of this because I already have one in my car! So I guess Im trying to gauge what the interest would be in these and whether I should pursue it or drop it.

 

Maybe there is someone out there willing to aid start up costs for one of the first plates… Ideally it would be great if I could get a plate to someone who is able to dive straight into installing the transmission and report back on things like the tunnel fitment etc and that, yes, it does fundamentally work, even though I know it will...

 

Some final food for thought

1)      It would be interesting to know if there was any interest in the M20-RX8 adaptor plates

2)      M42/M44 adaptor plates could also be possible (not really looked into this so much)

3)      M30 bolt patterns are the same as M10 so I assume they would work on those engines too

 

M10 to RX8 Prototype Adaptor Plate:

 

1218225604_2018-11-0218_16_57.thumb.jpg.c294264334c04121c68072db5993612b.jpg

 

 

 

 

 

My M20-RX8 combo: 

 

1272020122_2019-01-3020_30_49.thumb.jpg.11bfc0a606b5975a207056dd6a79bfab.jpg

 

 

Installed in the car

1093525372_2019-02-0119_29_26.thumb.jpg.b7ed1ecacf542bba7aed90bfc06f9f79.jpg

 

 

I welded in the tranny mounts but you could bolt them in if needs be:

 

1495602162_2018-04-2218_03_14.thumb.jpg.7179a3db47ae740cc83eb588c2153c8c.jpg

 

 

The shifter is about 3" back in my M20 car which is fine if you have the seat right back as far as possible which I do anyway (I always thought the shifter was too far forwards), it would be only 1" back in an M10 car which I dont think people would notice when driving. You can see the tunnel shape is still pretty much normal.

 

1886342898_2019-03-2917_09_28.thumb.jpg.c9778b3eb09deadcc47f8047f27904ae.jpg

 

 

 

Edited by camperman
  • Like 4
Link to post
Share on other sites
  • Replies 86
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

Popular Posts

Just got back from a 2500 mile trip to the French Pyrenees using my M20 6-speed setup, without issue ( see 02 beauty shots thread). I have been continuing with this M10 project. I have finalised the p

How-To Guide now on Page 3 of this thread.   Evening All Every few months on here I see the same threads about how increasingly expensive and unobtainium 5 speeds are. That’s not to men

Pictures to go with this.    

Posted Images

Love where your head is at. Seems very doable and likely fit the needs of more than one 02 owner. The downsides are not small, but also not a big deal for those not interested in "can convert back to OE as needed".

 

I have two 02s, one with 5spd OD (e21) and one with 235/5 CR and both fit the purposes of the cars and how they are driven. A six speed would be cool - CR + OD in one...

 

Jason

Link to post
Share on other sites

Well I'm pretty sure there will be interest in this project especially if the price of the plate and Mazda trany could be brought in around the price of the now rare o/d 5 speed I mean who wouldn't want a c/r box with a o/d on top of that:D?? 

Link to post
Share on other sites

how's the driveshaft situation looking? Outlet from the trans to the driveshaft? Looks like cross-member transmission support is not so plug and play.

How does the input shaft work out? No adaptors?

Clutch slave? Looks like its mounted high on the rx8 trans? How does that work with the stock slave? It needs a long line run to the top of it?

What type of machining is required? The starter ends up in the wrong spot as far as I can tell. 

Is that plate thick enough for the strength factor?

  • Like 1
Link to post
Share on other sites

It's an interesting thought for sure. I'd like to hear more about the particulars of the issues you had with your M20 adaptation in order to better understand what else would need modifying to make it work with an M10.

Link to post
Share on other sites
9 hours ago, theNomad said:

how's the driveshaft situation looking? Outlet from the trans to the driveshaft? Looks like cross-member transmission support is not so plug and play.

How does the input shaft work out? No adaptors?

Clutch slave? Looks like its mounted high on the rx8 trans? How does that work with the stock slave? It needs a long line run to the top of it?

What type of machining is required? The starter ends up in the wrong spot as far as I can tell. 

Is that plate thick enough for the strength factor?

 

The propshaft uses the front end of the RX8 propshaft, its a spline fit that just pushes into the transmission. Obviously as with all transmission swaps you have to get a propshaft made using the front end one and the back end of the other to the length you require. An advantage to this is that you have no guibo and no centre bearing.

 

1603949203__1.jpg.7daa9addfd850fac670721d98c8dc3fb.jpg

 

The cross member would be up to the installer how they want to do it. You could just bend some metal and drill holes and bolt it all together quite easily, or weld it in as I have done.

 

Other than the adaptor plate itself the input shaft is not altered.

 

Im not sure of the LHD clutch slave positioning and piping. Obviously you will need to route either a long custom flexi-hose (these are available pretty cheap, my custom one was $20) or install a section of hard line closer to the transmission then a shorter length of flexi. 

 

The main thing is that the bell housing face will need machining down.

 

You dont use the RX8 starter mounting position, the starter stays in the M10 location using the M10 starter.

 

My plate is 8mm but some people go thinner to 6mm. The tranny bolts on at 6 points using M12 bolts some of which have a nut welded to the back to give 20mm of thread, and dont forget that the only force the plate really sees is torsional. My M20 makes way more torque than an NA M10 will likely ever make and I have total confidence in it.

 

 

Link to post
Share on other sites

In light of swapping motors and getting a better transmission, you can put a F20C out of a S2000, and get the complete package for about 5-7k.  I am not sure where the shifter lands.  I am not sure about the impact to value, and ease of selling, but on the surface you get a 200+ hp motor, and a 6 speed transmission. 

 

 

Link to post
Share on other sites
48 minutes ago, Lorin said:

Interesting project.

 

Why not just bolt on a BMW 6 speed to your M20  with all OEM parts and no adapters?

 

33 minutes ago, iinca said:

^Exactly,,,

Well firstly im mainly discussing the M10 here so they wont bolt up to that.

 

Secondly because the gear ratios are much more spread out for the M54 6-Speed Transmissions so they are much more for cruising and not in any way sporty. "Shite" is the term I would use. I was replicating the original CR/OD ratios that the M10 and M20 originally came with in the '02/E21/E30.

 

The E30 325i, 325is, M3 etc had much the same gear ratios as as the earlier Getrag 245 OD/CR transmissions. Nothing like the M54 ratios (below). They are probably not too bad on an M20 if you want amazing cruising and you gear the diff accordingly to make 1st gear useable but you would need decent torque even by M20 standards to pull 6th.

 

There are also flywheel/input shaft complications regarding the dual mass flywheels, I think you'd have to run a dual mass flywheel in order to get them to work and they are also... not the best

 

On an M10 depending what diff you run you will either never use 1st because its far too short or wont have the torque to pull 6th, the gears are simply too spread out, unless you have forced induction I suppose.

 

M54 6 speed ratios

   
1st 4.35
2nd 2.50
3rd 1.66
4th 1.23
5th 1.00
6th 0.85

 

 

Edited by camperman
Link to post
Share on other sites
34 minutes ago, Dudeland said:

In light of swapping motors and getting a better transmission, you can put a F20C out of a S2000, and get the complete package for about 5-7k.  I am not sure where the shifter lands.  I am not sure about the impact to value, and ease of selling, but on the surface you get a 200+ hp motor, and a 6 speed transmission. 

 

 

 

Yes obviously this is a great idea if you dont mind running a foreign engine which personally I dont like the idea of. I'm less bothered about running a foreign transmission no one can see but maybe thats just me. Its each to their own at the end of the day, I understand that. If you simply want a the very best 4cyl and transmission available then your right thats the best way to go. It will cost you a packet though and is way more involved than this swap.

 

On the other hand if you want to stick with the humble M10 which many people do, and want the best transmission out there to match it for less than $800-1000 all in then maybe this is the way to go.

  • Like 1
Link to post
Share on other sites

This is pretty intriguing. I am doing an M20 swap as well, but I was planning on putting the 5 speed in there with it (will also have an E30 rear subframe). 

 

What modifications did you have to use for the clutch slave cylinder? 

What modifications did you have to do to the trans tunnel?

What clutch disc/flywheel/pressure plate did you use?


The work looks well done. And maybe I missed it, but what would be the cost for a M20 adapter plate? 

 

Either way, like someone else said, I like where your head is at here. And you might want to see if there is any desire for the M20 adapter over on some E30 forums like R3V, bimmerforums, etc. those guys might love the idea of a 6 speed swap (especially someone with an auto...)

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.




×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.