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dollraves
dollraves Reader
3/23/13 11:05 a.m.
wbjones wrote: welcome back to the forum ... we've been missing you

You may regret saying that by the end of this project! ;)

dollraves
dollraves Reader
3/23/13 1:24 p.m.
dollraves wrote: Okay, have some pics of the RX7 and Miata trannies with their tails off. First pic: RX7 on left, Miata on right 90 RX7 vs 91 Miata tranny Second pic, opposite side: Miata on left, RX7 on left NA Miata vs S5 RX7 tranny The gear boxes appear to be the same - the RX7 has an extra milled spot or two. The shaft appears to be the same (rough measuring). The RX7 tail fits to the Miata gearbox without a problem, but the Miata tail bumps into the counterweight (?). Anyone think I would I berkeley anything up by pulling the counterweight off the RX7 shaft to put the Miata tail on there? -doll

I plan on chucking the widget on the RX7 shaft and fitting the Miata tail over it unless someone weighs in with why this would be a Very Bad Idea. :D

MrJoshua
MrJoshua PowerDork
3/23/13 2:34 p.m.

Is it solid metal? If so, my guess is it is some kind of vibration dampener that helps the transmission live longer at the higher rpm range of a rotary. Even if it is I doubt it will matter much unless you endurance race the car.

Overall-I would clearance the crap out of the front subframe while it is in the car and weld in reinforcements. Then I would put the mazda engine and trans where I wanted them. Then I would fab up a trans mount and diff nose mount and lose the powerplant frame. It is probably going to be in the way when it comes time to do the exhaust anyway.

Curmudgeon
Curmudgeon MegaDork
3/23/13 2:52 p.m.

Welcome back! Been wondering where you were.

I have been into a few RX7 gearboxes (most recently the 1990 version in the Jensenator) and have never seen that whatever it is before. I'd say you should be safe in removing it. Mr Joshua speaks truth as well, the PPF might create some problems. IIRC its main reason for being is to sharpen the throttle response. No, really.

Also, if you need to, it's easy to move the shifter position forward.

Brett_Murphy
Brett_Murphy GRM+ Memberand SuperDork
3/23/13 11:39 p.m.

Didn't I hear that putting a 12a transmission tail on a 13b non-turbo transmission gets a better something or something or other? A road racing friend was telling me that was a "cheat" the IT guys used to try. I forget why.

(edit) There was something to do with a B2000 5 speed transmission tail, too. I think that was for re-positioning the shifter, though. That is probably what Dr. Hess was talking about.

dollraves
dollraves Reader
3/24/13 10:43 p.m.

In reply to Brett_Murphy:

No idea. I don't have a 12a transmission, though, so moot point at the moment.

I was hoping to put the Miata tail on the 13b transmission in the hopes that I don't have to fabricate the transmission mount; if I can use the existing mount, that's one less thing I have to do. But I can see Mr. Joshua's point about just removing that and fabbing a mount. I'll play with it and post pictures tomorrow or Tuesday.

wvumtnbkr
wvumtnbkr GRM+ Memberand HalfDork
3/25/13 7:59 a.m.

Thread jack!

I have a 12a trans sitting in my garage. I also have a busted s4 NA trans in my garage. Is there a way to combine them to make a good spare out of the two? Is it as simple as swapping tailshafts?

Thanks yall!

Rob R.

dollraves
dollraves Reader
3/25/13 8:53 a.m.
wvumtnbkr wrote: Thread jack! I have a 12a trans sitting in my garage. I also have a busted s4 NA trans in my garage. Is there a way to combine them to make a good spare out of the two? Is it as simple as swapping tailshafts? Thanks yall! Rob R.

If they're sitting in your garage, take them apart and try to swap them...and start your own thread about it. :P

GameboyRMH
GameboyRMH GRM+ Memberand UltimaDork
3/25/13 9:44 a.m.
SVreX wrote: Start with the stock RX7 ECU and fuel injection. Then switch to megasquirt.

This - it's the easier, cheaper AND better option. A carb swap will be expensive, it's just like doing a carb to EFI swap but in reverse, and then a big Weber will make gas disappear for no reason and leave you with less tunability than even stock EFI.

wvumtnbkr
wvumtnbkr GRM+ Memberand HalfDork
3/25/13 9:44 a.m.

Ha!

Touche!

Just thought we could get all of the S4, S5, miata, 12a, trans swap knowledge in one place.

P.S. I have never seen one of those large round "counterweights" on an RX7 trans before either.

Rob R.

wvumtnbkr
wvumtnbkr GRM+ Memberand HalfDork
3/25/13 9:46 a.m.

I still have a question about megasquirt.

Has anybody figured out how to get it to run the unique spark system of a rotary?

Why go megasquirt anyway? What is the benefit?

Thanks,

Rob R.

GameboyRMH
GameboyRMH GRM+ Memberand UltimaDork
3/25/13 9:57 a.m.
wvumtnbkr wrote: I still have a question about megasquirt. Has anybody figured out how to get it to run the unique spark system of a rotary? Why go megasquirt anyway? What is the benefit? Thanks, Rob R.

It can be done with mods to the MS2, the MS3 can do it right out of the box (see this thread: http://www.rx7club.com/megasquirt-forum-153/step-step-ms3x-installation-fd3s-tt-988332/ )

Megasquirt gives you huge tunability options, it's a standalone ECU that can do almost anything you can imagine (not just in terms of customizing fuel maps but think spark control, boost control, flex fuel, changing the engine sensor types...), vs. a carb where fuel delivery is mechanically determined, and you basically only have the options of changing jets and adjusting mixture.

fidelity101
fidelity101 HalfDork
3/25/13 10:34 a.m.
Brett_Murphy wrote: Didn't I hear that putting a 12a transmission tail on a 13b non-turbo transmission gets a better something or something or other? A road racing friend was telling me that was a "cheat" the IT guys used to try. I forget why. (edit) There was something to do with a B2000 5 speed transmission tail, too. I think that was for re-positioning the shifter, though. That is probably what Dr. Hess was talking about.

What you do is run a 1st gen 13b trans in an NA FC and you get .1 in gearing reduction across 1st, 2nd, 3rd.

In comparison to a stock NA FC transmission. I did this setup on mine for a while, worked great!

wvumtnbkr
wvumtnbkr GRM+ Memberand HalfDork
3/25/13 10:47 a.m.

In reply to GameboyRMH:

What is the benefit of megasquirt vs. an Rtek 2.x? Is how I should have stated the question.

Thanks,

Rob R.

DaveEstey
DaveEstey SuperDork
3/25/13 11:56 a.m.
fidelity101 wrote:
Brett_Murphy wrote: Didn't I hear that putting a 12a transmission tail on a 13b non-turbo transmission gets a better something or something or other? A road racing friend was telling me that was a "cheat" the IT guys used to try. I forget why. (edit) There was something to do with a B2000 5 speed transmission tail, too. I think that was for re-positioning the shifter, though. That is probably what Dr. Hess was talking about.
What you do is run a 1st gen 13b trans in an NA FC and you get .1 in gearing reduction across 1st, 2nd, 3rd. In comparison to a stock NA FC transmission. I did this setup on mine for a while, worked great!

^^This. I plan on switching my First gen 13B tranny into my car after the spring events.

GameboyRMH
GameboyRMH GRM+ Memberand UltimaDork
3/25/13 1:52 p.m.
wvumtnbkr wrote: In reply to GameboyRMH: What is the benefit of megasquirt vs. an Rtek 2.x? Is how I should have stated the question. Thanks, Rob R.

I can't find a spec list for the Rtek 2, depends on what it has, but the MS' strong points are flexibility and the feature/price ratio. Most other ECUs with a similar set of features are vastly more expensive.

wvumtnbkr
wvumtnbkr GRM+ Memberand HalfDork
3/25/13 2:34 p.m.

http://www.pocketlogger.com/index.php?pid=rtek7&tab=feat&stage=2&ecu=S5NA

Here is what I found. These can be found used for around $200.00

I realize it is not as tuneable, but for a relatively stock S5 NA rotary, I would think you wouldn't need any more than this.

Just a thought for future development of the RX-5 or miata-7.

GameboyRMH
GameboyRMH GRM+ Memberand UltimaDork
3/25/13 2:51 p.m.

A used Rtek might be a better deal in this case specifically, yeah. It has the really important features and should be easier to set up, being engine-specific.

SVreX
SVreX MegaDork
3/27/13 10:18 p.m.

My suggestion of the MS was not just about the car. It was about Doll's specific situation.

1- The money isn't really the issue. She has both cash and space in the budget.

2- There is a LOT of MS knowledge on this board and among her friends.

3- DIY Autotune (MadScientistMatt) can walk her through the programing.

4- It offers her a lot of future flexibility and expandability. She can drop a stock ECU in her Challenge car, expand to a plug-n-play MS with a pre-packed map, learn from Matt and others how to improve it over time, then later swap it for a unit she builds herself and upload the maps she has created (if she is REALLY tight looking for Challenge budget dollars). This is 4-5 years worth of growth for her.

I have no opposition to an Rtek, and there is a good chance it is a better option for some people. I just don't think it is the best idea for her, considering the learning curves and available support among her friends.

mistanfo
mistanfo SuperDork
3/27/13 11:35 p.m.

Concerning the MS, I seem to recall them doing an RX7 in the GRM tent a few years ago at the Mitty, and I believe it was running b he end of the weekend.

SVreX
SVreX MegaDork
3/27/13 11:56 p.m.

^Yep^. That was MadScientistMatt with his head under the hood.

fidelity101
fidelity101 HalfDork
3/28/13 8:44 a.m.

In reply to DaveEstey:

It worked great! the NA Aluminum flywheel is a lb lighter than the turbo one too. However, I wore out some of the gear syncros. Never had an issue of it blowing gear teeth apart but then again I never made a whole lot of power.

wvumtnbkr
wvumtnbkr GRM+ Memberand HalfDork
4/1/13 9:43 a.m.

When you took the tailshaft off of either transmission, was there a rollpin holding the shift lever in place?

If so, how did you get it out?

I am taking apart an S4 trans to rebuild. I have never had one with a roll pin. They have all been bolted.

Thanks,

Rob R.

Ashyukun
Ashyukun Reader
4/2/13 10:10 a.m.

A few things, since I'm just now seeing this...

Premixing is definitely the way to go for a project like this IMO. I did it for 6 years on a normal street RX-7 that was driven about 40% of my time and I never had any issues with it other than funny looks when I dumped 2-stroke oil down the gas filler at the gas station. On a Challenge car? It seems like a no-brainer. Simply things under the hood so there's less that can go wrong and kill the engine, and if any of the lines are already broken then it's an even easier choice. You will need to make sure the ECU doesn't put the engine into limp mode though if you remove the OMP completely...

As to why they never put the 13B into the Miata in the first place? Story I always heard around the RX-7 boards was that doing so had been the original plan, I heard that the early Miatas you could almost just bolt up the engine to their transmission and the engine mounts matched up- but that the Miata with the 13B absolutely SPANKED the RX-7 due to its lighter weight, and they didn't want the smaller, less expensive Miata outperforming their larger, more expensive offering and canibalizing the sales of the RX-7 to racers/enthusiasts.

Looking forward to seeing this at the Challenge this year, I do love me some magic doritos (though ironically I just sold the 13B I'd been holding on to). I dream of finding a wrecked RX-8 in a salvage yard and having a 13B-MSP to use either when the D's PRV eventually dies or in another project.

wvumtnbkr
wvumtnbkr GRM+ Memberand Dork
4/2/13 10:53 a.m.

S5 stock EFI system will put the car into limp mode without the OMP connected.

Some people just wire it to the fender and leave it electrically connected when they run pre-mix.

Rob R.

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