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M20 RX8 6 Speed Adaptor Plates

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    M20 RX8 6 Speed Adaptor Plates

    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 the average person can't do.
    Attached Files

    #2
    Attached are the gear ratios
    Attached Files

    Comment


      #3
      What kind of power do these things hold up to? I've heard good things about the shift feel, but as far as I'm aware they're pretty weak transmissions.
      2000 A4 1.8TQ | 1988 325is | 1976 280Z | 1953 CJ3B

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        #4
        RX8 transmission is the same as the s15 silvia box im pretty sure (AZ6 aisin). plenty of people quite very high powered sr20 turbos through them.

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          #5
          Yeah, I was looking at them recently, and I'm pretty sure you're right. They were used in the RX8, MX5 and S15, and I think maybe one other car. Some people say the S2000 trans is based on it, but it's kind of inconclusive.
          2000 A4 1.8TQ | 1988 325is | 1976 280Z | 1953 CJ3B

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            #6
            I'm no expert on the torque they will handle. I don't track it and dont know anyone who does, as usual if you Google it you will get a full range of opinions from people without first hand knowledge! They were designed for average torque high revving engines. I think they will be fine for any N/A m20 engines (mine is a 3.2l stroker) doing very spirited street driving, i think anyone running this on a big turbo motor doing 1/4 mile starts would be taking a risk but that would be up to them, it may stand up to it depending on your set up. I believe the S2 tranny will take more torque than the S1 it is certainly bigger and heavier.

            The transmissions mentioned above by others may all be the same in the main aspects but the bell housing and input shafts and ratios are not (or may not be) the same as far as I am aware. I have been told that an MX5 tranny would not bolt up to the plate I have made because the pattern is different. Also the input shaft is different length etc.

            I think this transmission is more akin to a G265 with an additional OD gear. I'm not sure what close ratio tranny options are out there for the M20 aside from the early G245 and what performance trannys people run behind their M20s. AFAIK the 265 was never available for the M20 and the CR G245 costs a fortune... both lack an OD gear... i guess this is just a new and different option (G265 ratios attached)
            Attached Files
            Last edited by knapmann; 09-12-2019, 09:57 AM.

            Comment


              #7
              Originally posted by rturbo 930 View Post
              Yeah, I was looking at them recently, and I'm pretty sure you're right. They were used in the RX8, MX5 and S15, and I think maybe one other car. Some people say the S2000 trans is based on it, but it's kind of inconclusive.
              The s2000 transmission has different dna; has an additional gear reduction tail section. Same company makes the 997 Porsche gearbox also but they are not related The rx8 gearbox is very cheap and plentiful; perhaps it would be better applied to a k24 engine or similar where something weird is needed anyways. The zf6 and g420 and other 6 speed options that bolt to the m20 are quite good in application. honestly the rx8 unit would not be an upgrade compared to the zf 6 and Getrag 6 but it may be more available depending on geographic location The g265 is an outdated relic. Nobody uses it in a e30 unless with a very specific application in mind G260 5mt that comes in the e30 originally is very good with stock final drive 373 and overdrive 5; It really doesn’t need changing if the engine is healthy
              OBD1 M54/M52TU swap as a M50b25

              Z4 non powered steering rack fits e30



              Euro e46 2005/6 320d 6mt gearbox into E30 with M20 hardy and beck 1985 327s engine

              Comment


                #8
                Originally posted by Wanganstyle View Post
                The s2000 transmission has different dna; has an additional gear reduction tail section. Same company makes the 997 Porsche gearbox also but they are not related The rx8 gearbox is very cheap and plentiful; perhaps it would be better applied to a k24 engine or similar where something weird is needed anyways. The zf6 and g420 and other 6 speed options that bolt to the m20 are quite good in application. honestly the rx8 unit would not be an upgrade compared to the zf 6 and Getrag 6 but it may be more available depending on geographic location The g265 is an outdated relic. Nobody uses it in a e30 unless with a very specific application in mind G260 5mt that comes in the e30 originally is very good with stock final drive 373 and overdrive 5; It really doesn’t need changing if the engine is healthy
                It depends what you want in application, you say the RX8 unit is not an upgrade over the G420 and ZF6, but as I pointed out above the G420 and ZF6 are nothing like as close ratio as the Mazda transmission and in no way comparable to the ratios of the period BMW close ratio G245 and G265 transmissions. They simply are not CR units.

                G420
                1st 4.227
                2nd 2.528
                3rd 1.669
                4th 1.226
                5th 1.000
                6th 0.828

                ZF6
                1st 4.350
                2nd 2.496
                3rd 1.665
                4th 1.234
                5th 1.000
                6th 0.851

                Comment


                  #9
                  Originally posted by knapmann View Post
                  It depends what you want in application, you say the RX8 unit is not an upgrade over the G420 and ZF6, but as I pointed out above the G420 and ZF6 are nothing like as close ratio as the Mazda transmission and in no way comparable to the ratios of the period BMW close ratio G245 and G265 transmissions. They simply are not CR units. G420 1st 4.227 2nd 2.528 3rd 1.669 4th 1.226 5th 1.000 6th 0.828 ZF6 1st 4.350 2nd 2.496 3rd 1.665 4th 1.234 5th 1.000 6th 0.851
                  Close ratio or not it doesn’t matter; all the g260 and zf6 and Zf5 work wonderfully on track. Works great on race track. Have you actually race track tested either? Have you ever been on a circuit? My Local clients have been winning national championships with the zf5 speed since 2014. Nobody is complaining about the ratios being not close enough If you wanted something actually stupid close ratio why not use a s2000 f20c gearbox?
                  OBD1 M54/M52TU swap as a M50b25

                  Z4 non powered steering rack fits e30



                  Euro e46 2005/6 320d 6mt gearbox into E30 with M20 hardy and beck 1985 327s engine

                  Comment


                    #10
                    Originally posted by Wanganstyle View Post
                    Close ratio or not it doesn’t matter; all the g260 and zf6 and Zf5 work wonderfully on track. Works great on race track. Have you actually race track tested either? Have you ever been on a circuit? My Local clients have been winning national championships with the zf5 speed since 2014. Nobody is complaining about the ratios being not close enough If you wanted something actually stupid close ratio why not use a s2000 f20c gearbox?
                    The RX8 transmission has the same ratios as an S2000 transmission once you factor out the reduction gearing.... You seem quite focused on how this would perform on track, as I have said above, I am not advocating its use on track particularly or behind really powerful engines which I assume these track cars will have. I think this is a good option for fast street cars as I have used it for. Im sure there is a reason why BMW sold CR transmissions for the M10 and M20 engines in the 70s and 80s, and you cannot deny that there is demand for them and they cost a lot of money and are expensive to rebuild. The downside is their lack of OD gear. This is a solution to these issues.

                    Comment


                      #11
                      Originally posted by knapmann View Post

                      The RX8 transmission has the same ratios as an S2000 transmission once you factor out the reduction gearing.... You seem quite focused on how this would perform on track, as I have said above, I am not advocating its use on track particularly or behind really powerful engines which I assume these track cars will have. I think this is a good option for fast street cars as I have used it for. Im sure there is a reason why BMW sold CR transmissions for the M10 and M20 engines in the 70s and 80s, and you cannot deny that there is demand for them and they cost a lot of money and are expensive to rebuild. The downside is their lack of OD gear. This is a solution to these issues.
                      everything ZF/getrag is expensive to rebuild. entirely another level to modify and upgrade


                      the CR items are ok for road cars with different engine configurations and final drive configurations than usa; euro only bits.
                      the factory e30 gearbox and setup matches the M20 engine perfectly; the RX8 is for a 9500rpm rotary NA; Ive had my fair share of FC, FD in the past and love rotary engines; the personality is completely different.


                      if you want to know what some E30 M3 DTM grp A cars were using:
                      it was not a "cr" off the shelf unit. A few have these have been built stateside; the cost is immense and its not that easy to mess with.


                      G265 with long 1st for standing starts, 2/3/4/5 close





                      OBD1 M54/M52TU swap as a M50b25

                      Z4 non powered steering rack fits e30



                      Euro e46 2005/6 320d 6mt gearbox into E30 with M20 hardy and beck 1985 327s engine

                      Comment

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