So I want to make a hybrid-5speed...
01-16-11, 11:56 AM
#1
MG Midget /w 12a
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So I want to make a hybrid-5speed...
My 12a 5speed 2nd speed synco is starting to go. Looks like a hybrid Miata/RX-7 transmission would be good choice for replacment. I always hated how far 2nd and 3rd are.
So, where should I get a QUALITY used Miata transmision? I hear it has to be a transmission from a 1800cc Miata.
So, where should I get a QUALITY used Miata transmision? I hear it has to be a transmission from a 1800cc Miata.
01-16-11, 12:49 PM
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Pagefaulted,
You can use any year Miata trasmission. They are all pretty much the same with some internal changes made over the years but will all transplant into an RX7 case. Don't forget you have to machine the input shaft though. Also, if you are tracking the car, use a truck 5th gear which is much lower than the Miata or RX7 5th gear.
You can use any year Miata trasmission. They are all pretty much the same with some internal changes made over the years but will all transplant into an RX7 case. Don't forget you have to machine the input shaft though. Also, if you are tracking the car, use a truck 5th gear which is much lower than the Miata or RX7 5th gear.
01-16-11, 04:47 PM
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Miata input shaft splines needs to be milled about 3/8" back to clear the end of the e-shaft.
http://mazdatrix.com/faq/miatainputshaft.htm
http://mazdatrix.com/faq/miatainputshaft.htm
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01-17-11, 08:43 AM
#9
I know there are lots of Miata guys running turbo's and well over 250 rwhp and don;t hear about them going through trannys too often. I think there is a misnomer in the strength/weakness of the trannys in our cars, since most everybody that builds an RX7, builds it for drag racing. Drag racing launches are known to be extremely brutal on driveline components, especially when you're launching at over 8k rpms and making more than 3 times the stock horsepower levels. It doesn't matter what tranny you put in, if you abuse it, it will fail.
01-17-11, 12:52 PM
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High HP, sticky tires, and high RPM launches will destroy parts, end of story. Doesn't matter what they are, their lifespan is greatly reduced with this kind of treatment.
Mazda sells a racing gearset for the Miata or 81-91 NA RX7. The main gearset is all the same, you just buy the input shaft to match your application (RX7 or Miata). I assume the difference is just the overall length, as mentioned in the mazdatrix article I linked earlier.
Mazda sells a racing gearset for the Miata or 81-91 NA RX7. The main gearset is all the same, you just buy the input shaft to match your application (RX7 or Miata). I assume the difference is just the overall length, as mentioned in the mazdatrix article I linked earlier.
01-17-11, 05:04 PM
#11
Gear is very important on cars with very small powerbands. (our cars) It is hard to beat stock gearing. What little research I did the newer they got the higher the gear ratios got. I am currently using a 81-83 trans which has lower gearing the the gslse than trans. I works great for my combination. Do your research. Our you can make your car a dog
01-17-11, 07:25 PM
#12
I have been using a miata tranny for years (before anyone else in the RX7 club). It is true that the miata's input shaft is longer. Although it is recommended to be machined, it is not required. I just chopped it; therefore, no need to worry about the pesky pilot bearing. This idea came to mind from a local tranny shop so we started messing around with extra parts and junkyard miata tranny (a dime a dozen at local jnkyard). It a good tranny/strong tranny, but if you go turbo, use the stronger turbo II tranny (these trannies are built for the purpose). Stay off FD tranny, they are not as strong as TII.
01-17-11, 08:05 PM
#13
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High HP, sticky tires, and high RPM launches will destroy parts, end of story. Doesn't matter what they are, their lifespan is greatly reduced with this kind of treatment.
Mazda sells a racing gearset for the Miata or 81-91 NA RX7. The main gearset is all the same, you just buy the input shaft to match your application (RX7 or Miata). I assume the difference is just the overall length, as mentioned in the mazdatrix article I linked earlier.
Mazda sells a racing gearset for the Miata or 81-91 NA RX7. The main gearset is all the same, you just buy the input shaft to match your application (RX7 or Miata). I assume the difference is just the overall length, as mentioned in the mazdatrix article I linked earlier.
its a 340RWHP car too, so its kind of insane
01-17-11, 09:29 PM
#15
The advantage that the Miata gear set offers that the gear ratios are closer together. From a racing aspect a miata gear set offers a useable 2nd gear for slow corners. The stock RX7 trans 2nd gear ratio does not.
My IT car had a 4.88 rear end and was setup to use only 3rd and 4th on the tracks in the midwest. This was done because 3rd and 4th are closely spaced so the engine stays in its power band on the track. A 5.12 is also a good gear because it makes 5th useable. To use a stock RX7 2nd gear on a race track you would need to run a 4.10 or a 3.90. However, this doesn't work as well because the gap between 2nd and 3rd is too wide.
For the most part running a 4.88 works fine because it is possible to maintain decent momentum with an RX7 that handles good. But there are always at least one corner that would work better if I had a gear that was slightly lower than 3rd.
When you start messing with a ported engine it is harder keep the engine in its power band with a wide ratio box. A close ratio box is a necessity.
As far as toughness the Miata boxes are holding up well in racing conditions. In fact they seem to work better than the Mazda Comp boxes. About the only thing that is more bullet proof is the Jerico NASCAR boxes that a couple of the guys I know have been using.
My IT car had a 4.88 rear end and was setup to use only 3rd and 4th on the tracks in the midwest. This was done because 3rd and 4th are closely spaced so the engine stays in its power band on the track. A 5.12 is also a good gear because it makes 5th useable. To use a stock RX7 2nd gear on a race track you would need to run a 4.10 or a 3.90. However, this doesn't work as well because the gap between 2nd and 3rd is too wide.
For the most part running a 4.88 works fine because it is possible to maintain decent momentum with an RX7 that handles good. But there are always at least one corner that would work better if I had a gear that was slightly lower than 3rd.
When you start messing with a ported engine it is harder keep the engine in its power band with a wide ratio box. A close ratio box is a necessity.
As far as toughness the Miata boxes are holding up well in racing conditions. In fact they seem to work better than the Mazda Comp boxes. About the only thing that is more bullet proof is the Jerico NASCAR boxes that a couple of the guys I know have been using.
01-17-11, 10:36 PM
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01-17-11, 10:42 PM
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he's got plenty of video... http://www.youtube.com/watch?v=4Bp4L..._order&list=UL
he's had plenty of trouble keeping it cool, and keeping the head on the block
01-18-11, 11:39 AM
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I have been using a miata tranny for years (before anyone else in the RX7 club). It is true that the miata's input shaft is longer. Although it is recommended to be machined, it is not required. I just chopped it; therefore, no need to worry about the pesky pilot bearing. This idea came to mind from a local tranny shop so we started messing around with extra parts and junkyard miata tranny (a dime a dozen at local jnkyard). It a good tranny/strong tranny, but if you go turbo, use the stronger turbo II tranny (these trannies are built for the purpose). Stay off FD tranny, they are not as strong as TII.
Hard on both the engine and trans.
01-18-11, 02:01 PM
#22
he's got plenty of video... http://www.youtube.com/watch?v=4Bp4L..._order&list=UL
he's had plenty of trouble keeping it cool, and keeping the head on the block
he's had plenty of trouble keeping it cool, and keeping the head on the block
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