yuba Posted January 3, 2022 Share Posted January 3, 2022 (edited) Hi, kinda curious here. I have a Subaru BRZ, 3rd and 4th gear are made out of cheese and the current transmission options are as follows: 1. PPG gearset ($8k), helical cut with synchros 2. PAR gearset, straight cut 1-4th gear with synchros, helical cut 5-6 with synchros 3. CD009, requires cutting out the stock transmission mounts and welding new ones in. Not legal The current rules say: 6.1.3 Transmissions Sequential, paddle shift/semi-automatic, and dog-ring/straight-cut gears (i.e. non-synchromesh) transmissions are permitted, but will be assessed via the “Adjusted Weight/Power Ratio” formula regardless of whether they are OEM or not. All automatic transmissions with six (6) or more gears will be assessed with a Modification Factor in ST3-4. Given the text "i.e non-synchromesh" does this mean the mod factor does not apply to straight cut gears that are synchromesh? Thank you Edited January 3, 2022 by yuba Quote Link to comment Share on other sites More sharing options...
National Staff Greg G. Posted January 16, 2022 National Staff Share Posted January 16, 2022 On 1/3/2022 at 3:08 PM, yuba said: Hi, kinda curious here. I have a Subaru BRZ, 3rd and 4th gear are made out of cheese and the current transmission options are as follows: 1. PPG gearset ($8k), helical cut with synchros 2. PAR gearset, straight cut 1-4th gear with synchros, helical cut 5-6 with synchros 3. CD009, requires cutting out the stock transmission mounts and welding new ones in. Not legal The current rules say: 6.1.3 Transmissions Sequential, paddle shift/semi-automatic, and dog-ring/straight-cut gears (i.e. non-synchromesh) transmissions are permitted, but will be assessed via the “Adjusted Weight/Power Ratio” formula regardless of whether they are OEM or not. All automatic transmissions with six (6) or more gears will be assessed with a Modification Factor in ST3-4. Given the text "i.e non-synchromesh" does this mean the mod factor does not apply to straight cut gears that are synchromesh? Thank you Correct, the dog-ring/straight-cut gears mod factor is for "dog box" shifting with no clutch and no need to synchro the gears. Now, if a transmission is found that is "technically" synchromesh but somehow can non-clutch up and downshift as fast as a non-synchro dog box, we would reassess the rule, at least in regard to that transmission. In general, straight cut gears in a synchromesh transmission do not provide a big shift time advantage, but may provide some better longevity. Also, I'm not sure what the CD009 would actually entail, but your blanket statement about modifying transmission mounts is not correct: The following are permitted exceptions to 6.2.1 above: 1e) Modifications of non-subframe/non-suspension cross-members (other than the rear frame cross beam), transmission mounts, differential mounts, and radiator core supports are permitted. Quote Link to comment Share on other sites More sharing options...
yuba Posted January 16, 2022 Author Share Posted January 16, 2022 (edited) 1 hour ago, Greg G. said: Correct, the dog-ring/straight-cut gears mod factor is for "dog box" shifting with no clutch and no need to synchro the gears. Now, if a transmission is found that is "technically" synchromesh but somehow can non-clutch up and downshift as fast as a non-synchro dog box, we would reassess the rule, at least in regard to that transmission. In general, straight cut gears in a synchromesh transmission do not provide a big shift time advantage, but may provide some better longevity. Also, I'm not sure what the CD009 would actually entail, but your blanket statement about modifying transmission mounts is not correct: The following are permitted exceptions to 6.2.1 above: 1e) Modifications of non-subframe/non-suspension cross-members (other than the rear frame cross beam), transmission mounts, differential mounts, and radiator core supports are permitted. Interesting, thank you! By modifying transmission mount I mean that the brackets on the body of the car that the stock transmission mount bolts on to need to be cut out and new ones welded in. Edited January 16, 2022 by yuba Quote Link to comment Share on other sites More sharing options...
National Staff Greg G. Posted January 17, 2022 National Staff Share Posted January 17, 2022 2 hours ago, yuba said: Interesting, thank you! By modifying transmission mount I mean that the brackets on the body of the car that the stock transmission mount bolts on to need to be cut out and new ones welded in. Modification of those transmission mounts appears to be permittedModification of those transmission mounts appears to be permitted Quote Link to comment Share on other sites More sharing options...
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