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K or BP Engine to BMW E36/E46 Transmission Upgrade

Old 04-22-2017, 05:11 AM
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Originally Posted by aidandj
What are the chances that this would work with a miata twin disc flywheel, and a bmw pressure plate and clutch disc. a 7.25" disc would fit on the comp clutch flywheel, but i dont know about the pressure plate.

Now that would be crazy.
Hard to imagine a better Miata clutch!
That is the custom clutch version is it not?
I talked to custom clutch about a dual clutch that I thought was the 949 clutch...and mixing that with a T5 6 months ago...
The head of oddball clutches said it was totally doable.


Getting it to fit a BMW doesn't seem like a quantum leap, but who knows.
I can look up the email of their head wizard of weird clutches if you want?

What is the BMW clutch diameter KMiata?
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Old 04-22-2017, 09:08 AM
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It's not a custom clutch. It's a comp clutch. And it has to do with the spacing not the size. You want a 7.25" because of the smaller MOI.
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Old 04-22-2017, 10:16 AM
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Got bored and made some graphs. Figured out that the E36 5 speed and the Miata 5 speed share some pretty similar ratios, the E36 being much lower. Gears 3-5 line up very well when comparing the MIata 5 speed with 4.1 rearend and the E36 with the new 3.3 rearend with the E36 having slightly lower 1 and 2 gearing.



The E46 6 speed is basically the 5 speed plus an overdrive gear. Mapping the 6 speed with the same 3.3 compared to the Miata 6 speed with 3.9 (my current config) makes some interesting results. E46 1-5 has the same spread as Miata 1-6 with a super nice cruising gear on top of that (3000rpm at 80mph anybody?).

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Old 04-22-2017, 11:16 AM
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I'm still curious about why it's specified non-M e46 6speed trans. Ive been able to find more m3 transmissions than 330i/z4 unless they are all just the same. Everything is attractive about these solutions, I'm still in the honeymoon phase
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Old 04-22-2017, 01:30 PM
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Nice graphs Dane, thanks for posting!

Originally Posted by nbfather
What is the BMW clutch diameter KMiata?
240mm clutch disc.

Originally Posted by psyber_0ptix
I'm still curious about why it's specified non-M e46 6speed trans. Ive been able to find more m3 transmissions than 330i/z4 unless they are all just the same. Everything is attractive about these solutions, I'm still in the honeymoon phase
Non-M trans is specified for two reasons. The first is the 330i trans is less than half the cost used, and is still very strong.

However, the main reason is the rear mount style. BMWs use two rear isolators below the mounts. This works perfectly with the shorter 5 speed trans, but the 6 speed is 4" longer, and as the tunnel narrows, we lose all ability to clear a 3" exhaust if we stick with the factory isolators. The M3 trans has the prongs on the back of the trans cast into the casing, just like the 5 speed. But the 330i trans conveniently has this bracket on the back that can be unbolted:


Since it can be removed, we have built a 6 speed-specific mount that replaces the OEM bracket and uses a GM style rear isolator, just like a T56. It makes everything fit much nicer and allows for easy 3" exhaust clearance. I'll post pictures of both the 5 and 6 speed mounts once I have final samples that look beautiful. They are being fixtured right now.
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Old 04-22-2017, 01:42 PM
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Also, on a somewhat unrelated note. This Getrag diff is fantastic. For those who don't know, its a clutch-type diff vs. the gear-type Torsen.

I drove the test car for two hours straight at Gingerman yesterday evening, and I was pleasantly surprised by how much better the rear end of the car hooked up compared to a Torsen.

Considering the diff cost me $124, its an upgrade I'd like to see a lot more customers choose. They are dime a dozen. My used parts guy offered me three of the 3.42 LSDs for $300 delivered!

Sure, you need to buy the parts to make it all work, but afterwards you have some really nice benefits. Dirt cheap diff options, good ratio selection, upgraded axles, optional upgraded hubs, near-solid diff mounts, and a super easy PPF delete. I certainly would choose this over a 3.63 or 3.3 in the Miata carrier, specifically if you're paying someone to swap the gears. if you go with our trans upgrade, you need a custom driveshaft anyway, plus the front diff mount to delete the PPF, so this is a perfect combo.
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Old 04-22-2017, 02:40 PM
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^^ that's exactly why i'm holding off on changing gear ratios on my car. When I am ready to go, I will spend the money on the getrag.
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Old 04-22-2017, 05:08 PM
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Super thanks for the clarification! The search for a 330i trans continues!
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Old 04-22-2017, 07:46 PM
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Originally Posted by aidandj
Except pilot bearing, shaft length etc. And then having a shitty hydraulic tob.
Pilot might be interesting, good point. Figured it was the same size, and that the length was already right. The hydraulic tob is much nicer feeling that the miata setup though, and you would probably just buy the whatever tilton 52mm (or whatever size you need for the 949 pressure plate fingers) one that fit the BMW lever.

Originally Posted by acedeuce802
I wonder if there's a button flywheel that uses the Miata crank pattern. Then you sandwich that flywheel up against an automatic flex plate (I'm unfamiliar with Miata autos and don't know if they have the standard thin flex plate like the 'Merican world). My 5.5" LS1 button flywheel weighs like 2 lbs, then I'm not sure about the flex plate. Also, hydraulic release bearings aren't shitty, just inconvenient that they're embedded in the bellhousing. I'm super excited to get mine running to feel the AP Racing release bearing, I've read several accounts of how much less hysteresis there is than a typical production style slave cylinder and the pedal feel is awesome.
You just send the flexplate and some input shaft measurements to quartermaster and $800 later you have a button flywheel and twin disk clutch that fits your setup, and a hydro TOB that doesnt that you can ebay for $200.
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Old 04-24-2017, 02:50 PM
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Dumb question: what's the difference between a hydraulic TOB and a concentric slave cylinder like on the C5 Corvette? Just that the bearing on the hydraulic version is attached to the hydraulics and not a separate part?
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Old 04-24-2017, 03:01 PM
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How much do we bribe you guys for a PPF delete "kit," retaining Miata trans?
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Old 04-24-2017, 03:23 PM
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Originally Posted by huesmann
Dumb question: what's the difference between a hydraulic TOB and a concentric slave cylinder like on the C5 Corvette? Just that the bearing on the hydraulic version is attached to the hydraulics and not a separate part?
Same thing, different name. I don't think I've ever seen a concentric slave cylinder without the bearing built in.
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Old 04-24-2017, 04:13 PM
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Originally Posted by huesmann
Dumb question: what's the difference between a hydraulic TOB and a concentric slave cylinder like on the C5 Corvette? Just that the bearing on the hydraulic version is attached to the hydraulics and not a separate part?
They are the same, but different markets call them differently. Production cars generally refer to them as slave cylinders, and motorsports generally refer to them as hydraulic release bearings.
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Old 04-24-2017, 04:25 PM
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Originally Posted by concealer404
How much do we bribe you guys for a PPF delete "kit," retaining Miata trans?
Haha. We could easily do it, but I'm curious to hear why you want it.
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Old 04-24-2017, 04:30 PM
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Originally Posted by KMiata
Haha. We could easily do it, but I'm curious to hear why you want it.
PPFs are gross and we could get away with less aggro motor/diff mounts while still having less driveline slop.

Less weight. More room for exhaust. Less things on car.

Bonus points for giving multiple mounting points for use with V8R setback engine mounts.

You know... since you guys are already going to be making mount kits for Miata diffs.
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Old 04-24-2017, 05:14 PM
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is there something specific about v8 rails and trans mounts? I have FM rails and really would like to avoid re-drilling the floor if holes aren't aligned. Though I'll do what I have to do run a BAUS trans setup. Just kinda bummed to add more holes.
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Old 04-24-2017, 05:49 PM
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Originally Posted by psyber_0ptix
is there something specific about v8 rails and trans mounts? I have FM rails and really would like to avoid re-drilling the floor if holes aren't aligned. Though I'll do what I have to do run a BAUS trans setup. Just kinda bummed to add more holes.
But adding holes is weight reduction!

If you go with a 5 speed, no need to change a thing, just keep your existing frame rails. Only the 6 speed rear mount ties directly into the frame rails due to the added length, and then you'll need our specific ones with the mounting pads welded on.
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Old 04-24-2017, 05:50 PM
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I can't find the original picture I saw. But does the 5 speed mount bolt to the trans tunnel walls?
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Old 04-24-2017, 05:59 PM
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Originally Posted by aidandj
I can't find the original picture I saw. But does the 5 speed mount bolt to the trans tunnel walls?
Correct. It's simple, light, and works great. I'll be going with a little 5 speed in my blue car eventually.
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Old 04-24-2017, 05:59 PM
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Hmmm. Did you pull that picture or am I going crazy.
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