Trans Upgrade: K or BP Engine to BMW E36/E46 Trans
 

Copied and pasted from our blog post here:


It’s time to share some long-awaited news about the transmission project we’ve been working on. Due to the huge power potential of a boosted K series engine, a stronger transmission option has been a really common request over the last year.

The wait is almost over. We have just finished a bolt-in transmission upgrade for a BMW E30, E36, or E46 transmission (1982-2006 BMW 3 series) in an NA and NB Miata.

The project originally began for the K series swap community, but we know our turbo BP engine friends have transmission struggles. Because of that, we have designed a transmission setup for both the K series and BP engine platform!

https://cdn.shopify.com/s/files/1/11...G?v=1492013070

In fact, phase one of our testing has involved installation of an E36 5 speed trans and Getrag diff in our BP-powered test car.

We looked at many transmission candidates for this project and ultimately settled on the the BMW 3 Series family of transmissions for their strength, dimensions, availability, and gear ratios.

BMW uses transmissions built by Getrag and ZF, and all E36 (92-98) and E46 (99-06) transmissions have the same bellhousing bolt pattern. As a bonus, the E30 5 speeds also share the same bolt pattern, except rotated 10 degrees. The ratios will appeal to some customers so we'll have a specific adapter for that trans as well.

Although many transmissions will work with these new parts, we narrowed it down to the following three options that seem like the best fit:

1. E36 5 speed ZF trans (same trans for M3 and base models)
2. E30 5 speed Getrag 260 trans (available in 6 cylinder cars, longer gearing than the ZF)
3. E46 ZF 6 speed from 2003-2006 330i and Z4 (non-M3 6 speeds)

Strength

First and foremost, we needed a new gearbox to solve a problem: broken transmissions in high HP applications.

Lucky for us, these transmissions can be found holding 1000+whp on a drag strip. There is some debate as to how much each gearbox can reliably hold, but ZF and Getrag underrate them from the factory. 800+whp has become common for a boosted E36 or E46, so based on the number of high HP turbo BMWs out there, we’re well within the limits with our turbo 4 cylinders.

Just for fun, here's an E36 M3 street car with the stock transmission running an 8.94 quarter mile with 1051whp and 870wtq. The action starts 90 seconds in.



Size and Packaging

At first glance, these transmissions are quite small, particularly the 5 speeds. The entire trans is only 22” long, and the 6 speeds are about 4” longer. They are wider than a Miata trans, but both 5 and 6 speeds fit in the Miata trans tunnel without modification. The 5 speed requires a few smacks on the top of the tunnel to make clearance for an unneeded bracket, which could also just be cut off the gearbox.

A 5 speed weighs just 77 lbs, with the 6 speed coming in at 96 lbs.

From left to right, E30, E36, E46, Miata 6 speed:

https://cdn.shopify.com/s/files/1/11...G?v=1492013200


Price and Availability

These are available everywhere, as you can see from a quick search at car-part.com. Here are common price ranges we’ve seen, as of April 2017:

5 speed ZF $200-300 (we paid $275 shipped for ours)

5 speed Getrag 260 $200-400 (we paid $300 shipped)

6 speed ZF $500-750 (we paid $500 shipped)


Rear Transmission Mount, Driveshaft, and Differential

Since a stock block K20 can put down 600+whp when boosted, we knew that a rear end upgrade would be in order for many customers, although not required.

This transmission was also chosen because it pairs well with the GM Getrag ratios used for the V8 swaps (3.23, 3.42, 3.73, and 3.90). These diffs are dirt cheap, and are available with a strong clutch-type LSD.

For testing, we picked up a 3.42 LSD for $124 and a 3.73 LSD for $180.

Here's our 3.42 installed in our subframe, thanks to parts from V8 Roadsters:

https://cdn.shopify.com/s/files/1/11...G?v=1492014358

https://cdn.shopify.com/s/files/1/11...G?v=1492014348

Since this setup is designed for high HP applications, we have opted to delete the PPF like the V8 cars. Since the new mounts and frame rails add a good deal of rigidity to the chassis, the PPF isn’t missed. We used upgraded rear transmission mounts and differential mounts, so shifting is precise, even with stock BP engine mounts.

Here's our Driveshaft Shop axles and hubs from V8R, along with our custom driveshaft:

https://cdn.shopify.com/s/files/1/11...G?v=1492015437

Expect to see a rear Miata Torsen mount available that will allow a Miata rear end to be used with these transmissions as well.


Shifter

These transmissions operate with a selector rod that attaches to the back of the gearbox, so the shift lever distance from the bellhousing face can easily be adjusted just by changing the length of the selector rod. This is good news for us, as we’ve been able to fine-tune the shifter position for the same stock Miata shifter position.

We followed the lead of many BMW racers by deleting the upper shifter arm and have replaced it with a solid mounted plate that bolts to the top of the Miata trans tunnel and accepts the shift lever ball.

https://cdn.shopify.com/s/files/1/11...G?v=1492015235

We've already ordered a shorter, straight shifter for testing from a Z4 3.0 to replace the part you see pictured from an E62 M5. There are many versions of shift levers available from BMW, and we're honing in on the perfect candidate for the Miata.

https://cdn.shopify.com/s/files/1/11...G?v=1492015286

We’ve also designed an adjustable selector rod so the shifter position can be set in the right location regardless of which trans is used. The double sheer design of the rod also eliminates slop, resulting in a high level of precision and shifter feel. It will certainly be a nice upgrade for the current 6 speed Miata trans users.


Gear Ratios

Gearing in these transmissions shines with high HP cars, which works well for our purposes. The E36 and E46 gearboxes have short gearing, with the 1:1 gear being 5th in both the 5 and 6 speeds. Both transmission ratios are nearly identical, while the 6 speed adds an overdrive gear on top. The Getrag 260 trans from the E30 is a longer ratio 5 speed, which will be preferable for certain BP-powered cars. We only plan to make an adapter plate for this trans that mounts to the BP, not the K.

Since the E36 and E46 transmissions have shorter gears, they will do best when paired with a longer ratio rear end, especially for street cars. For many BP powered cars, we like the 3.23 and 3.42 Getrag ratios, or the Miata 3.63 and MFactory 3.30. BP cars for track use will do well with a 3.90, and K powered cars will shine with a 3.73 or 3.90.

The 5 speed ZF is a particularly great option for any track car that has no need for an overdrive gear. It’s by far the most popular transmission used in E36 and E46 BMW race cars, and also my personal favorite. Cheap, lightweight, very strong, and short gearing.

If we could change anything about these transmissions, we’d like to see a little longer 1st and 2nd gear, but some things are a trade-off. Track users will gear the car to optimize 3-4-5 top speeds, and street car users will probably prefer a longer ratio rear end to lengthen 1st and 2nd, and give a lower cruising RPM on the highway.

I’ve been (aggressively) commuting the last few days in a BP-powered car with a ZF 5 speed and the 3.42 Getrag and the gearing is great. A 3.73 or even 3.90 would probably be fun too.

To reduce the “what’s the best setup for my car” questions, we’ve gone ahead and added a gear ratio calculator to the website, under the Resources menu. It includes all NA and NB Miata transmissions, all three BMW transmission options, and all Miata and Getrag rear end options.


Clutch Options

Again, because these transmissions come from cars with high HP levels from the factory, clutch options are fantastic for our purposes.

Our flywheel is designed to work with any E46 or E39 (5 series) pressure plate. Yes, the E46 M3 and E39 M5 use the same pressure plate as the base model cars. Because this pressure plate is used for the 400 HP V8 in the M5, BMW guys are holding 400-500wtq with their stock clutches. The benefit to us is that we can run an inexpensive OEM replacement clutch kit that can handle most turbo 4-cylinder builds and still maintain nice street manners.

Here's our prototype BP-E36/E46 flywheel and adapter plate:

https://cdn.shopify.com/s/files/1/11...G?v=1492014595

Production adapters will of course will be ground smooth and zinc plated. The flywheel weighs 13.5 lbs, and we have a few tricks we may implement to get the weight down even further. The K series adapter and flywheel are built in the same manner. We'll post up pictures as soon as the final adapter plate design is here.

The OEM BMW flywheels are all dual-mass, so the clutch discs are very light and also unsprung. Most BMW enthusiasts replace the stock flywheel for a lightweight aluminum unit and still run the OEM unsprung disc.

https://cdn.shopify.com/s/files/1/11...G?v=1492014632

Since the disc surface is solid (no pucks), there is still smooth engagement, and we were pleasantly surprised by how easily we were able to modulate the clutch. The pedal feel is perfect with the Wilwood 13/16” master cylinder.

https://cdn.shopify.com/s/files/1/11...G?v=1492015066

The 5 speeds and 6 speed clutch discs have different spline counts, so it’s important to pair your transmission with the matching clutch disc. Our kit will include the appropriate clutch kit, so no worries there.

Thanks to the short length of the trans, installation is even easier than stock when lowering the engine and trans through the engine bay:

https://cdn.shopify.com/s/files/1/11...G?v=1492016106


The final transmission kit will include the following parts:

Steel 0.5” adapter plate, zinc plated (K series or BP)

Aluminum flywheel (K series or BP) that accepts an E46 clutch kit

Driveshaft specific to your application, rated at 500+hp

Rear transmission mount assembly (5 speed or 6 speed specific)

Performance poly transmission bushings

V8 Roadsters frame rails (optional for 5 speed, required for 6 speed)

Billet aluminum solid mount shifter plate

Adjustable length selector rod

BMW clutch kit with correct disc that matches your application

BMW shift lever

BMW shifter ball bushing

BMW clutch fork pivot pin

BMW clutch fork wire clip

BMW/Sachs E36 slave cylinder

Wilwood 13/16” Master cylinder kit with braided stainless clutch line

Reverse light switch jumper

GPS-based speedometer adapter



Additional options:

Rear mount for Miata diff due to PPF delete

Getrag diff upgrade from V8R (stage, 1, 2, and 3).


As mentioned above, the PPF (power plant frame) gets deleted. While I’m sure some transmission adapter would have been possible, it seemed silly to adapt a flimsy PPF to a different trans and diff, so we opted to design it from the ground up and add frame rails into the package like the LS and LFX swaps. The car feels perfect, nothing is lost, and the chassis seems to have gained some rigidity as well.


Release date:

2017 availability is the goal, but there is no exact estimate at this point. Parts will go into production after some very rigorous testing. Be sure to subscribe to our newsletter for the latest information and pricing.

Saved first post for future updates.

FINALLLYYY!!!!

yes, Yes, YES!!!
Thank you señor

Link to the gearing calculator: K Miata Gearing Calculator

In for 1000whp K miata. Parachute should be included in the kit.

Haha glad you like. We've been slaving away at this for a few months now. It feels so good to have a confirmed working setup. I should be thrashing it on track this week at least once, weather permitting.

Ballpark it.

How many 6 speeds do I have to blow up before this makes sense. ;)

Not too many. a six speed setup involves a $600-700 trans, a $400 shifter kit to make it feel decent, and a lightweight flywheel and clutch for another $600 or so. So assuming you're already spending that, this setup is going to be pretty reasonable.

But the $400 shifter and clutch can be swapped between blown 6 speeds :D

:likecat:

:likecat:

Think about that empty feeling you have listening to others out on track while you sit in the pits with a crap Miata trans blown to bits... the answer is not even 1 for me.

Well yes, if you're upgrading from a nice 6 speed setup to this, you will be spending some money twice. But then you won't be breaking transmissions.

Oh my god, Why didn't I think of this. I had so many of these transmissions from my e30 days. So cheap.

Some of that will hold resale value as well, for when you move to the ZF :giggle:

No, I get it, its a bitch of a thing. I've watched a couple guys do this now at the track. I also watched someone from out of town pay $1,500 (iirc) to a local for a 6 so he could finish his track weekend.

I understand this means different things to different people, but trans swap for me is an economics decision. Gone are the days of unlimited "for the lulz" spending that got me where I am today, so I have to have a better reason to justify it other than "its better." If this is {the cost of a couple 6 speeds plus clutch, flywheel & MR shifter, give or take} then yeah, I might do this if/when my 6 lets go. But if its $4,500 +/- then I'm going to turn down the boost and drive with a bit more mechanical empathy, because I can make a $700 6 speed last for quite a while if I have to.

But I also know I'm not always the target audience :party:

I'm just glad there are options, and that the cost is (probably) reasonable. :bigtu:

I get it. This setup will be nowhere near $4500, especially if you're retaining a Miata diff. Adapter plate and flywheel will be comparable in cost to our current offerings, and then you need the extras outlined in the first post, none of which are more expensive than you'd expect.

Plus you get the added bonus of a trans that shifts much better than the Miata 6 speed.

You. I like you. :love:

I was talking this over with my BMW race guy..no sacasm, I love the way his ZF shifts. Makes something stupid like 400tq at 20psi and does constant burn outs and launches and no regard for the longevity of it without a single issue.

Well done. :likecat:

OP, what a great idea! Seriously, y'alls "thinking outside the box", is a real home run!

This is awesome news :likecat:

I knew of these tranny and their strength, I never even considered these trannies because I'm used to foreign parts costing an arm and a leg at the pick a part. Like if you asked me cold how much an E46 tranny was at the pull-a-part I'd guess like $1200 minimum, probably 2k+ for one thats not totally clapped out, and thats close to custom gearset money, so no further thought went towards it.

Who would have though a new company would be able to kick so much ass in the miata modification market in such a short time.

Damn. Nice work guys. I am super stoked to be placing some orders with you in the future. :likecat:

Edit: A small suggestion for the gearing calc - make it so you can view the results of two ratio presets side by side with all other settings the same (redline/tire size). This was you don't need to have two windows side by side to quickly see which trans you would want in your car.

Awesome news!

Coming fresh off a race weekend with a MSM 6-speed in our car, even at 25k miles fresh I would rather do many other things than shift a Mazda 6-speed.

:rly:

looks very interesting. out of curiosity, what is the weight on that adapter?

Thank you very much everyone. We work hard to make products a reality that we wish already existed!

This trans setup will be fun, I think it checks many of the right boxes for guys needing a stronger trans option.

7.5 lb, paired with a 13.5 lb flywheel.

That's very cool and definitely something to think about.

Out of idle curiosity (I like a real manual, and even if I didn't I hear they're not not all that reliable), does the E46 SMG fit? :)

--Ian

Hope you're talking the SMGII :P

I would've never guessed E30/36/46 manual trannies were plentiful and cheap.
Kudos!

.

Great transmission choice. These transmissions are really cheap in Europe, you can pick up a 5 speed from around 100 euros and a 6 speed from around 250 euros.
The GS6-53DZ (diesel ratios) is really plentiful/cheap here and is rated for ~500Nm / 400 ft/lb. Not entirely sure whether the diesel box fits in the same place as the petrol one, I thought the bellhousing was slightly rotated compared to the petrol one. Also the ratios are worse. But I guess the diesel boxes are not present in North America.
These boxes are almost the default choice in the European drift scene right now. You can get almost any adapter plates for these here: Toyota UZ, Toyota JZ, Nissan SR, BMW M60 / M62 / S62, Mitsubishi 4G63.

Still I am wondering what the final cost would be for a BP engine with Mazda diff. The amount of parts needed is quite a lot. With a boosted K and the Getrag diff I think it makes an awesome package though and almost a no-brainer.
Maybe this kit enables me to build a very cheap K powered E87 1 series (because those cars are massively plentiful and cheap here) :giggle:

Sorry for the shameless plug, but this is super exciting, and it makes me miss my old e30. I had used the MZ3 shifter, it's taller but the pivot arm is a bit longer reducing throw. This is making me nostalgic for my s50 e30 days where I fashioned a plate with the UUC ERK:

Sigh, way to give me a reason to further prolong my build lol

Nope, you can still get it running with everything you have.

No way, really? Are you positive about that? I never would of guessed that...I appreciate that amazing observation Captain Obvious...

:rofl: just not letting you use this as a crutch for an excuse. You're so close to the finish line.

/derail

Congrats guys! I look forward to seeing this move into production.

GPS based speed adapter?

On one hand, that's incredibly cool and means that you should theoretically have more accurate speedometer readouts, but I do kinda worry about not having a direct mechanical or electrical input from the transmission. What happens when you go through tunnels? (about .00001 of my driving time). How fast does it respond to changes in speed? Much slower than a direct wired connection I am sure.

I hope they can find a way to give options on that.

This looks awesome. How does this effect downpipe clearance? 3" downpipes are already tight with the little NA 5 speed. I'd like to see one installed with a downpipe for reference. Very cool though.

+1

Yes, same idea. I actually have a Z4 3.0 shifter on my desk and I'm about to put it in the car. I think it's going to feel better than the M5 shifter in there right now.

We had the same thoughts. Dead nuts accurate and super simple to install. Plus you can change ratios, wheel size, or anything at all and it will be accurate. It's a really common thing in the hot rod community. The trade-off is possibly losing GPS signal. The module we're using has really good reviews. I should have it this week and we'll install and test drive. It seems like the gauge action is like stock. The other option is adding an ABS wheel speed sensor and developing a processor to send that signal to the ECU and cluster. We can do it, but the GPS setup will be cheaper and simpler, and won't require people to hunt for spare ABS knuckles, sensors, and rings.

Stock Miata exhaust fit comfortably back on the car without issue, with both 5 and 6 speeds. There is actually quite a bit of clearance, and it definitely will fit a 3" K series exhaust. If anyone wants to ship me parts to test fit on this car and return, I'm happy to do so.

Is there any low hanging fruit on downpipe clearance. Like tabs that can be cut off the trans or anything?

Nothing worth cutting off the trans. I can get under the car and take some pictures with the stock header and exhaust though. I don't envision it being a big issue, the trans is really not that large. The only place clearance gets tight is on top of the tunnel.

​​​​​​​I will shoot you an email.

Cool, thanks.

Do you expect to offer individual components of the kit? Or all in one package. I assume it will be like the k swap, where you can buy individual components. If so, awesome :D

Yeah, we'll make separate parts available, shouldn't be an issue.

Awesome. Looking forward to seeing it run.

We'll take some video. It's just not that exciting with the stock engine. But I've been doing non-stop burnouts and donuts with it so far. Oh, and commuting like a normal person too. I'm getting a couple track days on the calendar right now too.

Will you have one at MRLS?

Yup, probably 2 or 3 of them actually. Come on by and we'll take you for a ride. If all goes according to plan, the white turbo car will be there to make cool noises.

I'm only a few miles away David. I have a custom 3" exhaust based on a BEGI manifold and FM downpipe elbow. If it's something that won't take long I'd be happy to bring my car over and let you swap over and back. We can do it over the course of a day together or I can leave you the car for a week or so.

Sweet. I'll stop by for sure. Can you have a kit ready for me to take home?

Or install in the parking lot friday night :giggle:

Yes it should. They are physically on the outside the same case. It's just the SMG pump and a few other things internally. If you do a little bit of searching, there are even instructions on how to convert the SMG transmission to a regular manual with some mods.

A customer of mine on a high power 1.6L (530hp/390tq) had the FD gearbox and installed an M3 E46 gearbox - 3" DP and exhaust, no clearances issues. Custom fabrication (not a Kmiata kit or anything) but it goes on to show that there should be no clearances issues with a 3" exhaust.

You could use the xenocron wheel speed sensor.

Let's talk at #gridlife about the e30 behind the BP option for my new to me endurance NB.

I am in talk with KMiata now to possibly get some setups out to him in various forms for some test fitting. Hoping to get MKTurbo, TSE, and a Begi/FM setup.

Yes, Lars and I will see what we can come up with for some test fitting.

Good idea on the Xenocron speedo setup, I'll check it out.

Allen, sure we can talk anytime for parts for your NB, just let me know.

Swapped in the Z4 shifter and I'm quite pleased. Size, shape, and throw is similar to stock. When you shift it, you can tell there is something a lot more stout down there.

https://cdn.shopify.com/s/files/1/11...G?v=1492543406

https://cdn.shopify.com/s/files/1/11...G?v=1492543426