M20 RX8 6 speed adaptor plates

[knapmann]

Hello all. I thought I would post this here in case it of interest to people. Attached below are pictures of my M20 engine and Mazda RX8 6 speed transmission combination that I have made using an adaptor plate I designed. It is installed in my '02 and runs great. The idea of this was to replicate the gearing of the early getrag 245 /265 close ratio and the over drive transmissions in one transmission. The ratios of the Mazda tranny are basically a CR 5 speed with an OD 6th gear on top. I thought these ratios were much better than using a later M5x 6 speed which has a much wider spread of ratios designed for big torque and cruising over attacking corners as well as the issues of the engine angle differences making the M5x transmissions mount on an angle when mated to an M20. I have the facility to reproduce these adaptor plates if anyone is interested in buying one.

I will add that it isn't simply a case of bolting these things together using the plate, there is a bit of machining involved that would need subbing out and a bit of measuring and thought but it's nothing a normal man in a garage can't do.

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[knapmann]

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[DanThe]

Looks like a good alternative to an expensive S50 box, how does the shifter line up for an E30?

[Gavt]

And it looks about 1.5 times longer than the standard. What prop shaft is used. Does it mount to existing body mounts or does that need fabricating aswell.

[steve_k]

following this out of interest.

[knapmann]

Looks like a good alternative to an expensive S50 box, how does the shifter line up for an E30?

The box is 735mm from bellhousing face to shifter. I dont know how this compares to a std e30 box... in my '02 it moves the shifter back around 50mm. I suspect it will be either the same or less than this in an e30. If someone could measure an E30 M20 box from bell housing to shifter that would be good to know.

[knapmann]

And it looks about 1.5 times longer than the standard. What prop shaft is used. Does it mount to existing body mounts or does that need fabricating aswell.

You use the rx8 front UJ and spline fitment and e30 rear UJ with a straight shaft. No centre bearing.

I assume you would need to fabricate something. I don't own an E30 so I don't know what tunnel mods if any would be needed. I suspect just custom mounts

[martauto]

Could you tell me how thick the adaptor plate is please and what threads you are using ?

Cheers Mart.

[knapmann]

Could you tell me how thick the adaptor plate is please and what threads you are using ?

Cheers Mart.

It's 8mm thick. The box mounts with 6x M12 bolts. 4 of the six bolting points can be beefed up but welding M12 nuts onto the plates to give 20mm of thread. I'm not sure if this is really necessary but no harm in doing so.

[martauto]

Could you tell me how thick the adaptor plate is please and what threads you are using ?

Cheers Mart.

It's 8mm thick. The box mounts with 6x M12 bolts. 4 of the six bolting points can be beefed up but welding M12 nuts onto the plates to give 20mm of thread. I'm not sure if this is really necessary but no harm in doing so.

I think that is the way to go , 8mm is a little bit too low but I can see why you cant use a bigger section. Any chance of a bit of stainless ? 316 etc ?

Mart.

[knapmann]

Could you tell me how thick the adaptor plate is please and what threads you are using ?

Cheers Mart.

It's 8mm thick. The box mounts with 6x M12 bolts. 4 of the six bolting points can be beefed up by welding M12 nuts onto the plates to give 20mm of thread. I'm not sure if this is really necessary but no harm in doing so.

I think that is the way to go , 8mm is a little bit too low but I can see why you cant use a bigger section. Any chance of a bit of stainless ? 316 etc ?

Mart.

Personally I think 8mm with nuts as well is more than enough, the plate only sees torsional forces, of course it depends what the engine torque is like but it would have to be pretty mega to cause an issue with an 8mm plate and 6x M12 bolts. I would have to see if I could get 316 made but obviously this would be more expensive etc.

[martauto]

The four bolts with nuts are like you say more than enough but do the others take the same load ?
By the way, dont let folk kid you about the cost of 316 etc, it`s a cheep stainless but very good also.
Mart.

[MarkpW]

PM sent Re M10 adaptor plate.