Gearbox options/experiences
03-09-2014, 04:37 PM
#101
Seems like a x-link is in order
https://www.miataturbo.net/suspensio...es-dust-75506/
Nismo gearset in the 6speed might only need work in both ends to work, but how much more it will hold is anyones guess.
A cheap, durable box with good ratios will not magically surface, the ones available are already in use in some track car close to you..
https://www.miataturbo.net/suspensio...es-dust-75506/
Nismo gearset in the 6speed might only need work in both ends to work, but how much more it will hold is anyones guess.
A cheap, durable box with good ratios will not magically surface, the ones available are already in use in some track car close to you..
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03-09-2014, 06:06 PM
#104
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Rx8 box is the same as the Miata box except for the 4th gear, bbundy is trying one IIRC
Quaife T9 boxes have a max power rating of 250hp
T5 has the wrong ratios
S15 is the same box as the Miata with different ratios
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03-09-2014, 06:50 PM
#108
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Im not sure how you can say FC/FD ratios are junk. Unless youre just talking about 5th being long, which is not always a bad thing.
Add 500 rpm to your redline and an FD box is going to shift just like an NB box, only with a longer 5th gear.
Add 500 rpm to your redline and an FD box is going to shift just like an NB box, only with a longer 5th gear.
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03-09-2014, 07:03 PM
#109
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They're junk.
Let's put this thread back on track. There are a few really important things when picking transmission ratios, and top speed capability is not even in the top 3.
Gear Ratios:
First things first, we need to have four usable track ratios. 2nd gear in a 5-speed is too short (more on that below), but 3rd gear in the 6-speed is usable. With the 6-speed, you end up with less RPM drop between ratios and the ability to carry a lower gear should the need arise. This isn't doable with a 5-speed - there's one correct gear and that's just how it is (and sometimes you're caught between gears). Less rev drop means more net power output over time and never being caught between gears. The end result is that 6-speed cars are faster on track than 5-speed cars by 0.75-1.0sec on a 2-minute course. IMO, 4 ratios are required.
The placement of those four ratios is just as important as having them. Place one too low and it may as well not exist. Place one too high and you compromise the split between the other three, or end up with a high gear that you can't pull. The lowest of the four ratios needs to be something in the 6.0:1 range, so with a 3.63 rear end, that's a 1.65:1. A high-horsepower Miata can't use 2nd gear in a 5-speed (1.888:1) but 3rd in a 6-speed (1.645) is just tall enough to be usable exiting tight corners, so that's the benchmark. This is less a speed-in-gear issue and more of a pure traction issue, so raising the redline doesn't work. Any gear numerically higher than 6.0:1 can be considered unusable/nonexistent on track.
Once you've placed the first ratio, the goal is to aim for no more than a 25% difference per ratio, and less than that as you go faster. That's far enough apart to make each gear worth having, but close enough to provide an option for the occasional corner that's "between" gears. If you're spinning 7k+ through a corner, it's almost always better to drop into the next gear, and you want the revs in that next gear to be 5600rpm (20%), not 4900rpm (30%).
The factory 6-speed pretty much follows this. It has gear drops are ~24%, 20%, 16%, a usable low ratio, and decent straight-line speed for most tracks (although to be honest, that problem can be sorted with more valve spring and more RPM for the few times it's needed). Any aftermarket option needs to maintain those characteristics, IMO - I'm not keen spending $4-5k on a gearbox option only to go slower on track.
Gear Ratios:
First things first, we need to have four usable track ratios. 2nd gear in a 5-speed is too short (more on that below), but 3rd gear in the 6-speed is usable. With the 6-speed, you end up with less RPM drop between ratios and the ability to carry a lower gear should the need arise. This isn't doable with a 5-speed - there's one correct gear and that's just how it is (and sometimes you're caught between gears). Less rev drop means more net power output over time and never being caught between gears. The end result is that 6-speed cars are faster on track than 5-speed cars by 0.75-1.0sec on a 2-minute course. IMO, 4 ratios are required.
The placement of those four ratios is just as important as having them. Place one too low and it may as well not exist. Place one too high and you compromise the split between the other three, or end up with a high gear that you can't pull. The lowest of the four ratios needs to be something in the 6.0:1 range, so with a 3.63 rear end, that's a 1.65:1. A high-horsepower Miata can't use 2nd gear in a 5-speed (1.888:1) but 3rd in a 6-speed (1.645) is just tall enough to be usable exiting tight corners, so that's the benchmark. This is less a speed-in-gear issue and more of a pure traction issue, so raising the redline doesn't work. Any gear numerically higher than 6.0:1 can be considered unusable/nonexistent on track.
Once you've placed the first ratio, the goal is to aim for no more than a 25% difference per ratio, and less than that as you go faster. That's far enough apart to make each gear worth having, but close enough to provide an option for the occasional corner that's "between" gears. If you're spinning 7k+ through a corner, it's almost always better to drop into the next gear, and you want the revs in that next gear to be 5600rpm (20%), not 4900rpm (30%).
The factory 6-speed pretty much follows this. It has gear drops are ~24%, 20%, 16%, a usable low ratio, and decent straight-line speed for most tracks (although to be honest, that problem can be sorted with more valve spring and more RPM for the few times it's needed). Any aftermarket option needs to maintain those characteristics, IMO - I'm not keen spending $4-5k on a gearbox option only to go slower on track.
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03-09-2014, 11:33 PM
#110
Given that much thought has been put into this and cheap easily installed substitute seems to be lacking we seem to be stuck with developing the box we have? It has been stated that getting custom gears made for the 6 speed is prohibitive. However, it seems as though there are getting to be enough people regularly exceeding the limits of the 6 speed that it might be worth it and possible to do a group buy. Probably going be the only way to get relatively easy install, "ideal" ratios. There are probably enough people frustrated enough with this to consider contributing something to the develop costs in addition to buying a set. I would be up to a point. Not sure if anything could be done as far as offsetting the costs of rebuilding the transmission.
Just doesnt seem like a problem that is going to go away.
Would we need an entire gear set or just 1/2-4 etc.
The rest of the box seems up to higher power levels
obviously not everyone agrees on ratios etc but..
just thinking it would be cheaper to help pay for the development of a product than buy somthing like a Jericho and need new driveshaft, PPF solutions etc
Just doesnt seem like a problem that is going to go away.
Would we need an entire gear set or just 1/2-4 etc.
The rest of the box seems up to higher power levels
obviously not everyone agrees on ratios etc but..
just thinking it would be cheaper to help pay for the development of a product than buy somthing like a Jericho and need new driveshaft, PPF solutions etc
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03-10-2014, 01:09 AM
#112
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E92 M3?
Per BMW Gear Ratios - E36 / E46 / E90 / E91 / E92 / E93 / E85 / E86 / E83 / E82 / E88 it's
4.06, 2.4, 1.58, 1.19, 1.0, 0.87
(it's labelled 'manual', so I'm assuming that's the stick, not the dual clutch flappy paddle box)
It sounds like 3-6 might fit your criteria, slightly taller 3rd than a Miata 6-speed, and slightly shorter 6th, dropping 25%, 16%, and 13%. Google suggests they might be available for $1200-$1500 or so. I have no idea how heavy they are or if they'd have a prayer of fitting in a Miata tranny tunnel.
--Ian
Per BMW Gear Ratios - E36 / E46 / E90 / E91 / E92 / E93 / E85 / E86 / E83 / E82 / E88 it's
4.06, 2.4, 1.58, 1.19, 1.0, 0.87
(it's labelled 'manual', so I'm assuming that's the stick, not the dual clutch flappy paddle box)
It sounds like 3-6 might fit your criteria, slightly taller 3rd than a Miata 6-speed, and slightly shorter 6th, dropping 25%, 16%, and 13%. Google suggests they might be available for $1200-$1500 or so. I have no idea how heavy they are or if they'd have a prayer of fitting in a Miata tranny tunnel.
--Ian
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03-10-2014, 07:41 AM
#116
Getrag 420G (e.g. M3 E46)
4.32, 2.54, 1.62, 1.23, 1.00, 0.83
0.00, 41%, 36%, 24%, 19%, 17%
$2k+ on ebay, plus modding. No spare parts available... New box to get syncros...
But although the M3 are running a little different powerband, just ask the racers you can get hold of. One of my firens have toasted a number of 6sp in his E36M3 and are now going to a 5sp with custom gears instead.
I don't remember the exact gearboxes he have used but there might not be a low hanging fruit in the Beemer camp either.
4.32, 2.54, 1.62, 1.23, 1.00, 0.83
0.00, 41%, 36%, 24%, 19%, 17%
$2k+ on ebay, plus modding. No spare parts available... New box to get syncros...
But although the M3 are running a little different powerband, just ask the racers you can get hold of. One of my firens have toasted a number of 6sp in his E36M3 and are now going to a 5sp with custom gears instead.
I don't remember the exact gearboxes he have used but there might not be a low hanging fruit in the Beemer camp either.
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03-10-2014, 09:38 AM
#120
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