RX7 fd3s transmission in MX5
01-25-2008, 02:11 PM
#1
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RX7 fd3s transmission in MX5
Because I have many answers about this modification, I decided to open a topic for this.
Well
The miata transmission is very nice, but can't handle safely more than 250 WHP.
At stock situations or at light turbo setups you 'll not deal with problems, but with 300+ WHP the 2th or 3th gear sometimes will gone
So there are two solutions
1)exotic stuff gears (os giken, quaife etc) but very expensive
2)adaptate transmission from another car, more inexpensive from the first solution but very difficult to do a perfect job.
So I put a turbo trans model "R" from RX7 fd3s (93-95).
It was from the beginning a difficult modification but the engineer succeed in this 100%.
The gear lever is exactly in the same position like the stock, and the "sense" of changing gears maybe is better than a stock transmission miata.
The 1-2-3d gears are a little shorter than stock gear ratio
The 4th is the same 1:1 ratio
And the 5th is much longer than stock ratio!! And this is very nice for a 380+ hp turbo miata!
The modification based to a new housing between the block and the RX7 transmission. We modificated the miata housing (bellhousing? ) and connect to its end, the end of the RX7 housing.It was a very difficult job because it had to be perfect at straight line with the stock one.
You will see at the fotos what exactly we have do because my english are not so good to explain exactly what I want to tell.
The driveshaft was cut and modificated to match to the RX7 transmission.
Well
The miata transmission is very nice, but can't handle safely more than 250 WHP.
At stock situations or at light turbo setups you 'll not deal with problems, but with 300+ WHP the 2th or 3th gear sometimes will gone
So there are two solutions
1)exotic stuff gears (os giken, quaife etc) but very expensive
2)adaptate transmission from another car, more inexpensive from the first solution but very difficult to do a perfect job.
So I put a turbo trans model "R" from RX7 fd3s (93-95).
It was from the beginning a difficult modification but the engineer succeed in this 100%.
The gear lever is exactly in the same position like the stock, and the "sense" of changing gears maybe is better than a stock transmission miata.
The 1-2-3d gears are a little shorter than stock gear ratio
The 4th is the same 1:1 ratio
And the 5th is much longer than stock ratio!! And this is very nice for a 380+ hp turbo miata!
The modification based to a new housing between the block and the RX7 transmission. We modificated the miata housing (bellhousing? ) and connect to its end, the end of the RX7 housing.It was a very difficult job because it had to be perfect at straight line with the stock one.
You will see at the fotos what exactly we have do because my english are not so good to explain exactly what I want to tell.
The driveshaft was cut and modificated to match to the RX7 transmission.
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01-25-2008, 04:47 PM
#6
Technically the issue with the plates is you usually can't take advantage of all the bolts/holes originally designed to be used with the trans or block. What bigt did is stronger (weld job dependent) solution. That said, the adapter plates seem to hold us power as anybody has thrown at them. I'm still undecided on my approach.
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01-25-2008, 05:26 PM
#8
Technically the issue with the plates is you usually can't take advantage of all the bolts/holes originally designed to be used with the trans or block. What bigt did is stronger (weld job dependent) solution. That said, the adapter plates seem to hold us power as anybody has thrown at them. I'm still undecided on my approach.
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01-25-2008, 07:51 PM
#13
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Τhere is no problem with the weldings, the job that have been done is very accurate, and don't forget that the stresses in these points are not so much because tha car is a RWD and not a FWD that they have much more stress at the transmission housings
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01-25-2008, 08:09 PM
#14
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I hope that you understand right the modification.
The RX7 transmission is not like miata trans, it is 2 pieces, the front housing, and the trans. The miata trans, is one piece.
The front side of the miata trans has been cut, and weld to the end of THE FRONT HOUSING OF RX7 TRANS. So the new "custom" housing came and seat to the RX7 trans like the stock RX7 front housing, using the stock bolts etc.
I used a stock 1.8 bp flywheel with a custom 6-pad clutchkit.
The center of the disk has been modified because miata's trans and rx7's trans has another frame in the center shaft.
The RX7 transmission is not like miata trans, it is 2 pieces, the front housing, and the trans. The miata trans, is one piece.
The front side of the miata trans has been cut, and weld to the end of THE FRONT HOUSING OF RX7 TRANS. So the new "custom" housing came and seat to the RX7 trans like the stock RX7 front housing, using the stock bolts etc.
I used a stock 1.8 bp flywheel with a custom 6-pad clutchkit.
The center of the disk has been modified because miata's trans and rx7's trans has another frame in the center shaft.
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01-25-2008, 08:33 PM
#15
When you welded the cut miata bellhousing to the FD transmission bellhousing, were you able to bolt the bellhousing back on as if it was stock?
Another question you might be able to answer. On the TII transmission the bellhousing also bolts on in the same fasion as the FD does. Are the TII and FD trannies the same length? IE, if you did this cut-n-weld mod to a TII tranny, would it sit in the correct location?
Another question you might be able to answer. On the TII transmission the bellhousing also bolts on in the same fasion as the FD does. Are the TII and FD trannies the same length? IE, if you did this cut-n-weld mod to a TII tranny, would it sit in the correct location?
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01-25-2008, 09:18 PM
#17
bigT, your last post is more confusing.
I've got two of the S3 R trans and they're four sections: tail, intermediate, the gearbox and bell housing. As I understand it, the Miata bell housing is welding to the part of the S3 housing that bolts to the front of the gear box. That's what it looks like in the photos. Essentially the mounting of the S3 box is cut out to form a plate to weld the Miata housing too.
mouse- the rx7 shaft is shorter. Using the 1" aluminum adapter plate, there's roughly 1/2" spline penetration to the clutch hub with a miata set up.
I was hoping to build an OE bolt up solution without having to do gear swaps for my FE. My assumption was that input shafts were the same across all R trans - for the 929, rx7 TII, truck/ute and bongo van. They're not. The van and truck get the longest, the rx7 is in the middle with the 929 (going to the v6) the shortest. Here's pic of a TII gear box bolted up to a van bellhousing - that added an extra 7/8" inch of space over the TII housing. Problem with the truck/van trans is the sucky gearing. I'll probably end up doing similar to bigT - using the bell that bolts up to my block, sectioned to fit the TII shaft. May cost, but once you've got it, it's done and can just move over to the next box if needed.
I've got two of the S3 R trans and they're four sections: tail, intermediate, the gearbox and bell housing. As I understand it, the Miata bell housing is welding to the part of the S3 housing that bolts to the front of the gear box. That's what it looks like in the photos. Essentially the mounting of the S3 box is cut out to form a plate to weld the Miata housing too.
mouse- the rx7 shaft is shorter. Using the 1" aluminum adapter plate, there's roughly 1/2" spline penetration to the clutch hub with a miata set up.
I was hoping to build an OE bolt up solution without having to do gear swaps for my FE. My assumption was that input shafts were the same across all R trans - for the 929, rx7 TII, truck/ute and bongo van. They're not. The van and truck get the longest, the rx7 is in the middle with the 929 (going to the v6) the shortest. Here's pic of a TII gear box bolted up to a van bellhousing - that added an extra 7/8" inch of space over the TII housing. Problem with the truck/van trans is the sucky gearing. I'll probably end up doing similar to bigT - using the bell that bolts up to my block, sectioned to fit the TII shaft. May cost, but once you've got it, it's done and can just move over to the next box if needed.
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01-25-2008, 09:25 PM
#18
Adapter plates could be far more an easy way to go than welding. Also it has been used for decades in the beetle world, where the engine don't even have mounts and just hang from the transmission with no fails or so. People stuff EJ20T and 13B there with no problems.
http://www.kennedyeng.com/
May be some thing can be done with Kennedy but will cost probably 400 and more
http://www.kennedyeng.com/
May be some thing can be done with Kennedy but will cost probably 400 and more
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01-25-2008, 09:40 PM
#20
bigT, your last post is more confusing.
I've got two of the S3 R trans and they're four sections: tail, intermediate, the gearbox and bell housing. As I understand it, the Miata bell housing is welding to the part of the S3 housing that bolts to the front of the gear box. That's what it looks like in the photos. Essentially the mounting of the S3 box is cut out to form a plate to weld the Miata housing too.
mouse- the rx7 shaft is shorter. Using the 1" aluminum adapter plate, there's roughly 1/2" spline penetration to the clutch hub with a miata set up.
I was hoping to build an OE bolt up solution without having to do gear swaps for my FE. My assumption was that input shafts were the same across all R trans - for the 929, rx7 TII, truck/ute and bongo van. They're not. The van and truck get the longest, the rx7 is in the middle with the 929 (going to the v6) the shortest. Here's pic of a TII gear box bolted up to a van bellhousing - that added an extra 7/8" inch of space over the TII housing. Problem with the truck/van trans is the sucky gearing. I'll probably end up doing similar to bigT - using the bell that bolts up to my block, sectioned to fit the TII shaft. May cost, but once you've got it, it's done and can just move over to the next box if needed.
I've got two of the S3 R trans and they're four sections: tail, intermediate, the gearbox and bell housing. As I understand it, the Miata bell housing is welding to the part of the S3 housing that bolts to the front of the gear box. That's what it looks like in the photos. Essentially the mounting of the S3 box is cut out to form a plate to weld the Miata housing too.
mouse- the rx7 shaft is shorter. Using the 1" aluminum adapter plate, there's roughly 1/2" spline penetration to the clutch hub with a miata set up.
I was hoping to build an OE bolt up solution without having to do gear swaps for my FE. My assumption was that input shafts were the same across all R trans - for the 929, rx7 TII, truck/ute and bongo van. They're not. The van and truck get the longest, the rx7 is in the middle with the 929 (going to the v6) the shortest. Here's pic of a TII gear box bolted up to a van bellhousing - that added an extra 7/8" inch of space over the TII housing. Problem with the truck/van trans is the sucky gearing. I'll probably end up doing similar to bigT - using the bell that bolts up to my block, sectioned to fit the TII shaft. May cost, but once you've got it, it's done and can just move over to the next box if needed.
Ok now I'm a little confused. So if you go bigturbo's route, do you have to change input shafts, or are the differences in length negligible?
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