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Old 11-12-2008, 02:11 PM   #1
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Default gear question, also 5spd bell housign compatible with 6spd?

Ok, so i'm in the process of doing a rotary swap and i know that is not your guys thing but the people on miata.net were just not giving me the info i needed.

so i'm goign to be dropping a 13b-re (the twin turbo rx7 engine) into my miata and i have a few questions regarding the trans.

a) what are the capacities, i hear the 250hp is the max but haven't heard a torque spec. the engine is 255hp and 232 ft lbs. and we be drivien at full race paces. (i have a 94 5spd by the way and it's a 91 miata)

b) if the trans can not handle the power, i know that rx7 owners swap miata gearing into their trans's for track uses. will this work putting in rx7 gearing into a miata trans?

c) does the 6 spd from the 99+ miata's share a bell housing with the 5spd from the 90-97 trans? also wat is the 6spd capacities?

i'd really like to get ahold of this info and have done a ton of research but am turning no results, maybe i'm looking in the wrong places but any help available is wonderful.
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Old 11-12-2008, 09:46 PM   #2
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You want a 6spd if your planning on making over 300whp and tracking it. Bolt pattern between the 6 and 5 spd is the same but you'll need an adapter plate to fit it to your 13b. Search for turbo II swaps should give you some more info.
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Old 11-12-2008, 10:28 PM   #3
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If you can't find the answers to those questions, give up on the 13b swap.
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Old 11-13-2008, 12:58 AM   #4
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As far as what I can tell from searching there is no adapter plate for the Miata trans, however, the 5spd from a NA shares the same essential lay out as the rx7 trans up to at least 93' to swap a 13b onto a Miata in the regards of putting the power down is supposedly as simple as doing some machine work on the input shaft to the trans and swapping the Miata "bell housing" for the rx7 housing. I have no reason to think that is wrong but the 13b-re rotary I want to swap puts out more power than the NA trans can handle. So I was thinking I have never fussed around with the NB 6 spd, but if the "bell housing" is identical to the one on the NA, and it could handle the power then perhaps I can put the 6spd in and then I do not have to to any of the special modifications that go along with beefing up an NA trans or adapting the rx7 trans.

If the NA 5 spd "bell housing" is the same as the NB 6 spd (and I mean the same not the same bolt patterns on the engine side) then I will go through with the swap cause come on how sick would that be to have a 6spd rotary Miata, maybe it is sacrilegious in terms of the 4 banger gods but it will be an awesome project with an amazing result.

I'm also a competent mechanic, as I have just finished a replica lotus 11 built from the ground up, so doing this swap should not be difficult, I just need this last bit of information.

again thanks for your time.
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Old 11-13-2008, 01:03 AM   #5
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Quote:
Originally Posted by Savington View Post
If you can't find the answers to those questions, give up on the 13b swap.
Agreed.

Oh, by the way, the 6 speed and 5 one is the same **** . LA TRANSMISSION 6 VITESSES C'EST LA MÊME CHOSE!
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Old 11-13-2008, 01:24 AM   #6
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So what exactly is the difference between the 6 and the 5 that makes people say the 6 is stronger (heard it hear the miata.net).
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Old 11-13-2008, 01:28 AM   #7
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I don't want to say ****, but I think that the gears are cryo treated or something. There is some sort of treatment that makes them stronger.
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Old 11-13-2008, 01:34 AM   #8
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Well I guess I'm putting a 6spd in then.
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Old 11-13-2008, 09:08 AM   #9
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It's a totally different trans internally. It's not about gear treatment. The 6 speed probably weighs 20 lbs more than a 5 speed.

Frank
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Old 11-13-2008, 09:22 AM   #10
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There is a difference in the starter mounting on a six speed. Not insurmountable, but take it into account.
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Old 11-13-2008, 09:27 AM   #11
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I thought the 6 speed case was also stronger than the 5 speed, eliminating case-flex under high load conditions.

on a side note: needs more pics of said swap
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Old 11-13-2008, 10:14 AM   #12
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I just did this sway. I did order the new backing plate from mazdaspeed (cheap) and sprung for a starter so I could use all three bolts. Need to cut one connector off the 5 speed and move it to the six and sway the mechanical speedo. All in all, very easy mod.
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Old 11-13-2008, 01:16 PM   #13
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The imporatant thing though is whether or not the 6spd NB bellhousing is the same as the 5spd NA bellhousing, because I'm bolting it up to a 13b engine. On the NA you can swap the bellhousings with the 13b one from an rx7 which is key to the swap. I'd use the NA trans but it if I bolt the 13b-re twin turbo rotary engine i'm gettign to that trans it will litter the land scape with internals.
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Old 11-13-2008, 04:29 PM   #14
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Seriously, ditch the 13B-REW swap idea. You don't know nearly enough about these cars to even start to attempt it. Have you even looked into steering racks or firewall modifications yet?

The 5 to 6 swap is very well documented on M.net. If you can't search and see whether the bellhousings are the same or not, you are in for a long rough road and nobody here is going to hold your hand as you stumble down it.
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Old 11-13-2008, 06:22 PM   #15
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Sorry gonna do it. I know enough about general tech and about English sports cars that I'm confident with my mechanical ability to do it.

Just finished building a Lotus 11 replica from scratch (not a kit), and have been working on cars for about 10 years solid. Just don't know the miata to well yet, haven't had it that long. So far your the only person that hasn't been of some help. But regardless I have my info and will go ahead with the swap.

Thanks to those who have been a help though.
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Old 11-13-2008, 07:06 PM   #16
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Please read that before Sav starts to use instults!

Rotary Miata FAQ!
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Old 11-13-2008, 11:27 PM   #17
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I've had that page bookmarked for a couple months now and it was what gave me the idea in the first place. That project utilized a turbo II trans which has clearance issues so a fair amount of firewall modification needs to be done as well as the transmissions tunnel needs to be raised, but after doing some research on the no pistons forum I learned that you can get around this by utilizing the Miata trans and swap the NA bell housing for an rx7 housing (supposedly one of the few interchangeable parts between type 2 and type 3 Mazda transmissions before 94), this bell housing swap allows a 13b to be installed after some machine work to the input shaft of the trans. Down side is there needs to be a custom oil pan to make this work due to the engine being mounted lower in the engine compartment. Luckily I have a dry sump canister and pump sitting in my garage that I'm going to use to get around this clearance issue with a very shallow sump. Now the person who did this before utilizing a 13b on Miata trans had the N/A 13b which was not pushing the upper limit of the Miata trans capacity. I want to install a 13b-re which is putting out 232 ft. lbs. so I needed to know what I could do to make the miata trans more durable (swapping in rx7 gearing if possible), or what Miata trans could be swapped in to avoid this problem. I learned that the 6spd supposedly had more power handling ability so I realized if I could swap the bell housings from the rx7 trans to a NB trans then this is the route to take. That is why I asked those 3 at the start of this thread, but now I have my answer so as soon as I have enough cash together to do this swap I'm going to.
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Old 11-13-2008, 11:54 PM   #18
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I am fairly certain the motor interferes with minor chassis parts (i.e. the steering rack). But moving those and maintaining correct suspension geometry should be a snap, right?

And let me guess - you're doing a 13B because it's light and compact, right?
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Old 11-14-2008, 02:08 AM   #19
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If you swap the front cover to the 1st gen 12a or early 2nd gen 13b you gain the mounting point you need, then it is building a cross member to attach to. If you do not have a power steering rack, there is no issues, with interface. I don't have a power assist rack so I do not have this problem.

Swapping to a 13b-re because it has the power output I am looking for it, short of swapping a 1.8 it is one of the most direct swaps, I'll have a better base to do further tuning then the 1.6 or 1.8 can offer, and simply I'm familiar with the 13b design, used to own a turbo II rx7 so I know the engine.

I'm pretty amazed though that you keep trying to validate your point. The forum is here to ask questions, I had 3 pointed questions, I know this forum has a lot of knowledge to tap so I thought I would. I know the answer is probably buried in another forum, maybe even this one, but I had a specific question that I was having a hard time finding info on.

Anyways, your input is appreciated negative or positive, cause I'm sure you have a vast amount of knowledge. On that note I wish you good luck with your tuning, cause reading your signature sounds like you have a nice setup, and you have a nice looking car.
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Old 11-14-2008, 02:54 AM   #20
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Quote:
Originally Posted by swerv_on View Post
If you swap the front cover to the 1st gen 12a or early 2nd gen 13b you gain the mounting point you need, then it is building a cross member to attach to. If you do not have a power steering rack, there is no issues, with interface. I don't have a power assist rack so I do not have this problem.
Fair enough.

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Originally Posted by swerv_on View Post
Swapping to a 13b-re because it has the power output I am looking for it, short of swapping a 1.8 it is one of the most direct swaps, I'll have a better base to do further tuning then the 1.6 or 1.8 can offer, and simply I'm familiar with the 13b design, used to own a turbo II rx7 so I know the engine.
It most definitely isn't one of the most direct swaps. The 302 is well-documented and fits easily, and even the LS1 is becoming more and more common as time goes on. The 13B has been done, but it is (IMO) one of the more difficult swaps out there.

Quote:
Originally Posted by swerv_on View Post
I'm pretty amazed though that you keep trying to validate your point. The forum is here to ask questions, I had 3 pointed questions, I know this forum has a lot of knowledge to tap so I thought I would. I know the answer is probably buried in another forum, maybe even this one, but I had a specific question that I was having a hard time finding info on.
The thing is that they aren't really buried. A quick search for 6-speed swap would have turned up that the transmissions swap with ease; the only complications are a bit of wiring and one starter bolt which doesn't line up. The bellhousing patterns themselves are the same.

Quote:
Originally Posted by swerv_on View Post
Anyways, your input is appreciated negative or positive, cause I'm sure you have a vast amount of knowledge. On that note I wish you good luck with your tuning, cause reading your signature sounds like you have a nice setup, and you have a nice looking car.
Thanks. I'd love to see pictures of your Lotus replica. I'm harsh because the questions you ask are easy to find answers to, and while you sound knowledgable and experienced, I think you're in for quite a surprise in the difficulty of the swap.

I generally don't like 13B swaps for a number of reasons. The motor itself is terrifically heavy; an LS1 swap would weigh about as much and provide a much better baseline for a lot of power. I also despise the 13BREW powerband specifically; my dad owned a '95 Rx7 for 6 years and the motor made NO power below 4000rpm, and it really only pulled to 6800 or so.

Anyway, I wish you luck with your project.
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