Daffy's SE

[Magpie]

I'm following as well. However I would go for something like https://www.par-engineering.com/product-category/gearsets/?filter_car-make=mazda

[Okibi]

A couple of people are running these https://shop.quaife.co.uk/mazda-mx5-mia ... fe-gearkit

[greenMachine]

Those gear sets are interesting, but I am not sure they are the answer for truly high power. One theory is that the problem is as much the case flexing as the gears not being up to the job. Stronger gears will last longer, but how much longer before the case flex kills them too? The Usians on MTnet don't seem to place a lot of confidence in either the Quaife (think some have broken them) or PAR (nobody on MTnet tried them) options. IIRC CT used a Nissan box which had the case strengthened, and that seemed to work for him, but I am not sure what his numbers were.

The KMiata BMW solution seems to be a total answer, though it is early days. I am sure they are breakable too, but it seems astronomic power levels are required. I look forward to learning from the brave pioneer who goes down this path here, especially on the extent of 'plug and play', and budget required.

Of course the other solution is a slush box ...

[Magpie]

As Daffy and I discussed there are internal modifications made to the S15 box which can be duplicated on the MX5 6 speed. However, Daffy is putting some serious torque through his 6 speed and maybe strengthening, shot peening etc may not be sufficient and in the end a lot of money to spend on a guess.

The car could be returned to manage the torque delivery, however will this prevent a repeat?

Buying some other Aisin boxes (S15, Lexus, RX etc) to see if there are interchangeable parts is not cheap and there is no guarantee of a result.

Therefore the BMW sounds the best long term solution.

[ManiacLachy]

I think for a fun street car that just has way too much power, the KMiata BMW trans solution is the ticket. If you were racing then probably an up-rated gear set, or sequential box would be good. Or the auto if you were all about drag racing. But shifting a manual is part of the appeal of a street car, and the BMW will hold it down.

Also, swapping out the diff to a lower ratio Getrag will give you longer gearing and a quieter highway cruise, plus a higher top speed when you wring it out - he's got the power so to enjoy a longer gearing.

When I've done searches I could never find the right BMW 6-speed for sale. I wonder how widely available they are here? And I'm curious to the total cost of the conversion. Shipping the parts from the US, plus the woeful state of the dollar right now isn't favourable.

[JBT]

When I've done searches I could never find the right BMW 6-speed for sale. I wonder how widely available they are here?

Availability in Oz is a big problem. Most non-IIIM E46 models here are auto or 5 speed manual and most IIIMs were auto or SMG.
I don't think the IIIM 6 speed manuals of that era are compatible with this conversion anyway - if I understood Daffy correctly.
I had an E46 325ti (the hatch) with 6 speed manual. It was, for the Aust market, a fairly rare car and rare transmission but that is probably the transmission needed. None of that model were sold in USA. More likely to be available in Europe.

[ManiacLachy]

Thanks JBT, that's been my observation as well. Which is a real shame. Personally, I'd want the 6-speed for the overdrive gear. From my reading the 5 speed has the same ratios as the 6 speed, with the 6 simply having an overdrive, they both have 5th as the 1:1.

I wonder how much it would cost to get a bunch of gearboxes in a shipping container? Who am I kidding, I've got other hurdles to deal with before I come to this. A better turbo and a built engine, by which point I'll be in the poor house.

I can't wait to see what Daffy does.

[manga_blue]

I keep hearing that gearbox case flex is an issue. I just wonder if someone with a bit of spare time on his hands has tried welding a web of external bracing all around the exterior of the case? There's room for it.

[93_Clubman]

Phil, there was some talk about it a while back but not sure if it was done. Might have been Lou or Dann or maybe CT.

[Daffy]

Thanks for the feedback so far everyone, I was going to quote some replies but there would be too many for one post!
So this IS going to happen, I’ve crunched some numbers, inclusive of if we have to source a BMW GS6-37BZ box in the USA (the average price there for one in good condition is USD $700-1000 where in Oz so far I’ve seen hovering around the AUD $1500-2000k mark, the difference seems would cover import cost.)
So at this point I’m looking at a 7 to 8k AUD outlay. Mechanic Daz has already looked at ways to tweak the set up for ease of future repairs/box in box out and clutch repairs, but more about that when we get to that point.
I spoke with the fella repairing the SE box, he tells me that apart from the damage to the reverse idler and lay shaft everything else is fine, so with the replacement parts, I’ll have a quality rebuilt SE 6 speed as a backup.
The Kmiata kit thus far has not reported back with any flex issues in their V8 roadster applications.
Still a lot more to work out, so more details to come everyone.


https://kmiata.com/blogs/news/miata-to- ... -for-order

[JBT]

if we have to source a BMW GS6-37BZ box

Aaaah, that was fitted to very few E46 models - just the 325ti like I had and the 330.
More likely to get one from a wrecked E87 hatch but very few being parted out.
Unfortunately, most E60 and E90 six cylinder cars sold here were auto and you don't see many E85 (Z4) manual wrecks.
Check out the BMW 1 Series Australia and the BMW Sales And Spares (AUS ONLY) FB groups. You might get lucky Daffy.

[greenMachine]

Good news on the SE box!

Have you looked at sourcing a box from Europe? I believe that there are BMW importers operating on similar principles as the MX5 importers, and they may be able to source one for you. At least you would have an alternative, and a price comparison.

[Daffy]

Good news on the SE box!

Have you looked at sourcing a box from Europe? I believe that there are BMW importers operating on similar principles as the MX5 importers, and they may be able to source one for you. At least you would have an alternative, and a price comparison.

Already doing some research into that too greenMachine, still crunching some figures

if we have to source a BMW GS6-37BZ box

Aaaah, that was fitted to very few E46 models - just the 325ti like I had and the 330.
More likely to get one from a wrecked E87 hatch but very few being parted out.
Unfortunately, most E60 and E90 six cylinder cars sold here were auto and you don't see many E85 (Z4) manual wrecks.
Check out the BMW 1 Series Australia and the BMW Sales And Spares (AUS ONLY) FB groups. You might get lucky Daffy.

Thanks again for the further links JBT, I’ll touch base with you again soon enough!

[SKYHI]

Good news on the SE box. Hopefully I won't need to go down the same path re the gearbox upgrade, but will be very interesting to see how it all goes.

[manga_blue]

Good news on the SE box!

Have you looked at sourcing a box from Europe? I believe that there are BMW importers operating on similar principles as the MX5 importers, and they may be able to source one for you. At least you would have an alternative, and a price comparison.

Just for further info if it helps... I've owned and self-serviced a few Mercedes over the years and I've sourced a lot of parts from Europe, including places like Poland, Latvia, Lithuana, as well as Germany and the UK. Seller service and postage has always been really, really good, even from those smaller states. In my experience they've been a lot easier to deal with than the yanks, as well as being far cheaper.