Real Talk: Rotary Swap

[simontibbett]

All the BS aside of the people who say it's insanely hard, anyone ever really tried it? I was talking about it the other night and had researched it a while back, but haven't actually took my motor out and mocked a 13B in there.

HAS ANYONE REALLY attempted it or know someone personally who has? Everyone seems to think this swap cost over 10k, I am speaking 13B, carbed, THAT'S IT, no boost, nothing else. Stock Miata tranny. I hear you can use them, I don't know how. Depending on mounting do you HAVE to cut the firewall and tranny tunnel? Do you HAVE to do this and that that this guy says you HAVE to do www.rotarymiata.com.

I think they just don't want rotary Miatas so common so came up with a special club to scare people away lol.

Long story short, 1.6 is no good, rotary I can get for as much as McDonalds, could be fun.

If you DON'T have real experience with this swap, then I don't need to hear it's 10k, it's impossible, it's a lot of work, etc.

[Jack-MX5ATLanta.com]

Tyler picked up a 13B with the intention of carbs like you. I think you use the tranny from the rx7 but use the rear end of the Miata. The only major fabrication from what I heard are the motor mounts. It doesn't seem too hard to be honest but then again you'ld expect more if that was the case.

[wildfire0310]

Stock Miata tranny. I hear you can use them, I don't know how.
I think they just don't want rotary Miatas so common so came up with a special club to scare people away lol.



Ok so I am going to be really nice to your right now. Since I done something really really close

You can use a stock miata tranmission or the stock rx7. Either one, The biggest difference when all said and done with be how new the tranmission is and the 5th gear. 1-3 are close enough between the two tranmission not to matter and 4 gear is the same 1:1 ratio.

Ok here is how it work.

rx7 FC3s N/A tanny and Miata 5sp are both M-type and the core gear box is interchangeable. The difference comes(other then the gear ratios) is that the bell housing and tailshafts are different.

Now you can swap the bell housing and tail housing round with little work(most of the work is putting the miata tail housing on the rx7 gear box as there is a nice counter weight. Which either has to be removed or shave down the inside of the tail housing(which is what I did)

Now the biggest issue. I talked to a guy at MazCare when I did my swap and he said he had done Miata gearbox in an Rx-7 and said something about having to use the rx7 input shaft due to lenght. I want to say the miata one was to long(but i can't remember to T since it didn't effect me).

So if you wanted to use a Miata tranny with a rotory you would need.

Rx7 motor
Rx7 flywheel
Rx7 clutch
Rx7 bellhousing
Rx7 throwbearing
Rx7 pivot
Rx7 Slave(not 100% on this one)
Miata tranny
Maybe the input shaft from the rx7 the miata tranny.


Before any one ask:

---I am running an rx7 hybrid tranny in my miata now and have for about 5-10K miles with no real issue. Hence how I know all about this

---NO YOU CAN NOT USE AN R-TYPE TRANSMISSION to make a hybrid

Hopefully that helps

[metalman]

rotary I can get for as much as McDonalds,

That fact alone should tell you something. :lol:

[simontibbett]

Ok thanks for the help! I will look more into it. I'd like to keep it simple.

As for the motor being cheap, I have friends who race rotaries and aren't scared to help people for the low low :) lol.

[Jack-MX5ATLanta.com]

I don't think the Apex seal problem is too bad with the NA one's either, it's just a matter of keeping the oil topped up which is fine for an enthusiast but not so good for the casual customer, which I suspect is where the bad rep came from.

[wildfire0310]

I don't think the Apex seal problem is too bad with the NA one's either, it's just a matter of keeping the oil topped up which is fine for an enthusiast but not so good for the casual customer, which I suspect is where the bad rep came from.

It depends on how old the motor is. I know after about 100K the apex start to go, grained it tends to one seal mildly.

But to add my 2cent... Why would go through all the work to put just an stock-ish N/A rotory in the car.

You can have the same power from just a 1.8 with basic bolt-on for much less work.

Not trying to say don't do it but atleast boost it or port the motor or something. IIRC the stock power for a FC3S S4 motor was 127 whp.

[Jack-MX5ATLanta.com]

I thought that when carb'd up you could get some decent power from them? Either way, it would be a good idea to rebuild the motor if you're serious about it. If you're gonna get it for cheap it's worth making sure it's in decent nick.

[simontibbett]

Well that would be a possibility down the road, but I just love the powerband, sound, look, etc lol of a rotary. My friends basically stock 13B with intake and exhaust, and a few free mods will pull car lengths from a 1.8.

He pre mixes everytime he fills up too lol.

[Jack-MX5ATLanta.com]

I feel you there. Although I'm in a bit of a love hate relationship with the sound.

[wildfire0310]

Trust me there are a few of us that are rotary nuts. Blame my buddy for owning two FC's and for me owning a DSM. I drove his cars as much as I drove mine own.

I will own an FC or FD one day.

I am just saying time/money for each you could do a simple 1.8 with a shaved head and I/H/E and keep up with most simple FC. Now boost or brigde-port the Rotary and talk about a mean evil little rotary.

[simontibbett]

True, time isn't a problem. If I can do this swap for around the same price as a regular 1.8 then I will do it. I have welder and tons of other tools. Plus like I said endless supply to anything rotary.

[Roadster]

You've already got the PNP, Thimon. A bit of boost on the 1.6 seems like a much more effective route than trying to cobble together a rotary, unless you're just wanting to tinker with something. It doesn't seem worth the trouble for something less reliable. I know they can make a lot of power per liter, but....unless it's a really ridiculous power gain, like a 5.0 or LS swap, I can't see the point in messing up the good things the Miata drivetrain has going for it.

It'd be cool to see it done, at any rate.

[metalman]

You've already got the PNP, Thimon. A bit of boost on the 1.6 seems like a much more effective route than trying to cobble together a rotary, unless you're just wanting to tinker with something. It doesn't seem worth the trouble for something less reliable. I know they can make a lot of power per liter, but....unless it's a really ridiculous power gain, like a 5.0 or LS swap, I can't see the point in messing up the good things the Miata drivetrain has going for it.



That pretty much sums it up. And, when coupled with costs/aggravations of swaps in general is why more of these are not done....and when done usually utilize something other then carbs and 'antique' technology. ;)

[Acesanugal]

You can't beat the smooth power delivery of an N/A 13b. You just can't. True, in stock form they don't make a whole lot of power. When new it was only 146bhp. The thing about it is that the swap would be a cool project and the outcome would probably be worth it. The perfect engine in the perfect chassis. How can you top that?

But don't take my word, I'm partial...

[redrumracer]

as long as you have a welder and a way to cut the metal i dont think it would be that hard or costly.

[Roadster]

as long as you have a welder and a way to cut the metal i dont think it would be that hard or costly.

I'll build a low-budget lunar lander while I'm at it. :facepalm: :lol:.

[jesseealexander]

^^ lol

[redrumracer]

I'll build a low-budget lunar lander while I'm at it. :facepalm: :lol:.

lol go for it, id be willing to bet a low budget swap would be more successful than your lunar lander.

but you have to go lower than what nasa put up there since they choose the lowest bidder

[Doppelgänger]

your best bet would be to get a S5 89-91 N/A engine since it starts with higher compression and 160 bhp and maybe even find a used RB carb setup.

[Roadster]

lol go for it, id be willing to bet a low budget swap would be more successful than your lunar lander.

but you have to go lower than what nasa put up there since they choose the lowest bidder

The point is, anybody that says "all you need is a welder and some metal to do a swap" must have never attempted one. It's just not that simple; unless it's a 240, or a traditional old school American car where there are no major engine bay constraints and the mounts are nearly universal, or in the ball park enough that a little sheet steel will bridge the gap. Going from fuel injection to carb would probably be simpler than going from carbureted to fuel injected, but the gains in this case just don't seem to justify the amount of trouble it would be, that's all I'm saying. This is very similar to the SR20 swap thread that occurred a while back...

[N3v]

I know that rotaries require a modified subframe. it has to be modified to be lower to the ground so the dimensions of the rotary will fit. Then you have to either come up with a creative way to keep the ppf or fab a transmission and third diff mount.

N/A a rotary shouldn't tear up the stock rear end too badly, but it'd need a custom driveshaft. I would also recommend a bridge port, if you're gonna do all this other work anyway.

[simontibbett]

I know that rotaries require a modified subframe. it has to be modified to be lower to the ground so the dimensions of the rotary will fit. Then you have to either come up with a creative way to keep the ppf or fab a transmission and third diff mount.

N/A a rotary shouldn't tear up the stock rear end too badly, but it'd need a custom driveshaft. I would also recommend a bridge port, if you're gonna do all this other work anyway.

You can use stock Miata drivetrain.

[redrumracer]

The point is, anybody that says "all you need is a welder and some metal to do a swap" must have never attempted one. It's just not that simple; unless it's a 240, or a traditional old school American car where there are no major engine bay constraints and the mounts are nearly universal, or in the ball park enough that a little sheet steel will bridge the gap. Going from fuel injection to carb would probably be simpler than going from carbureted to fuel injected, but the gains in this case just don't seem to justify the amount of trouble it would be, that's all I'm saying. This is very similar to the SR20 swap thread that occurred a while back...

i have done a motor swap before and if he is going to carb then getting the motor actually sitting in the engine bay isnt that hard nor is anything else really that hard when going to a carb set up. the hardest part would be the drivetrain.

[jesseealexander]

i say put in e30 drivetrain and fab a third mount... **** rotaries.

[N3v]

You can use stock Miata drivetrain.

i've never heard of that approach, but thats cool. I think it wouldn't be too hard then to leave everything in place except the engine and front subframe, then bolt the 13b up to the tranny, then see what would need to be done to keep it there.

[Roadster]

Psh, E30. He needs an RB26DETTTTTTTT. Yes, octurbo.

[redrumracer]

Psh, E30. He needs an RB26DETTTTTTTT. Yes, octurbo.

i 2nd his idea of an rb26detttttttt, minus 7 turbo's. well 6 instead since you autocross so the boost doesnt hit at once.

[jesseealexander]

neither simon nor tommy autocross much sir... lol

[simontibbett]

Yeah I didn't autocross once this season. lol

[redrumracer]

ok autocross, roadrace, what ever YOU guys call it.

[simontibbett]

BIGGG difference between the two ;)

[redrumracer]

BIGGG difference between the two ;)

for yall, for me its all the same, just a bunch of turns

[simontibbett]

for yall, for me its all the same, just a bunch of turns

LOLOL that is sig worthy right there!

Big parking lot with slow turns and cones, or large purpose built road course with 100+mph turns and straights, etc. Def. the same thing. hahahaahhaahah

[Roadster]

Let's throw rally and hillclimbs in there, too. That way there are only two kinds of auto racing: drag, and....that turning stuff. :lol:

[simontibbett]

Let's throw rally and hillclimbs in there, too. That way there are only two kinds of auto racing: drag, and....that turning stuff. :lol:

There we go.

[redrumracer]

Let's throw rally and hillclimbs in there, too. That way there are only two kinds of auto racing: drag, and....that turning stuff. :lol:

hey that sums it up, thanks.

[silver280zx]

wow, this is a pretty long thread now. Ya a friend of mine is giving me a 13b na motor and tranny. The motor makes 160hp on the stock fi setup. I know a few people who play around with rotories or that have in the past, and they were saying with a bridge port na 13b, and a 50mm 2 barrel weber carb, you can make around 280-300hp na. Hes was saying the only real downside to one of those is that the gas milage will suffer a bit. The great thing about them is that when you carb the motor, they pretty much dont have anything on them and look like a tin can. They are about as simple as a 2 stroke engine too.
http://www.arios.info/demo/img/003.jpg

[Jack-MX5ATLanta.com]

I find that kind of gain on an old rotary motor hard to believe, otherwise wouldn't everyone be running with one?

[wildfire0310]

I find that kind of gain on an old rotary motor hard to believe, otherwise wouldn't everyone be running with one?

I am not sure the gains are that high but the reason rotarys are not as big is that the gas mile just sucks. And old buddy Austin had a TII for awhile. It was nicely modded and was easily putting down 300 with plenty to go. The sideeffect. If you rolled into the boost you could physical watch the gas gauage start to go down. We went for a run down 400 one late night and he just rolled into the boost and held it for a good little distance and I watched the gauge drop a whole quarter of a tank:jawdrop::jawdrop:

He figured it out that he got something like 5-6 mpg at full boost:jawdrop: Now he **** was running on the rich side but 8-9mpg at full boost was the best he was ever going to get.

[simontibbett]

Yeah you can make really good power especially for NA with a rotary. Gas mileage does suck though, even NA.

[Jack-MX5ATLanta.com]

I am not sure the gains are that high but the reason rotarys are not as big is that the gas mile just sucks. And old buddy Austin had a TII for awhile. It was nicely modded and was easily putting down 300 with plenty to go. The sideeffect. If you rolled into the boost you could physical watch the gas gauage start to go down. We went for a run down 400 one late night and he just rolled into the boost and held it for a good little distance and I watched the gauge drop a whole quarter of a tank:jawdrop::jawdrop:

He figured it out that he got something like 5-6 mpg at full boost:jawdrop: Now he **** was running on the rich side but 8-9mpg at full boost was the best he was ever going to get.

Wow :?:

Time for a bigger tank at that point. That's ridiculous.

[wildfire0310]

Wow :?:

Time for a bigger tank at that point. That's ridiculous.


IIRC, the cars mpg were

no-boost 17-19 mpg hwy
mild boost(around 5psi) 10-12
full boost 5-6 mpg

[FE3tMX5]

...He figured it out that he got something like 5-6 mpg at full boost:jawdrop: Now he **** was running on the rich side but 8-9mpg at full boost was the best he was ever going to get.

That doesn't sound that unreasonable for boost. We figured a 1.6 ITA Miata at 8mpg on a good day for Rd. Atl. That's just a massaged stock engine.

[simontibbett]

That doesn't sound that unreasonable for boost. We figured a 1.6 ITA Miata at 8mpg on a good day for Rd. Atl. That's just a massaged stock engine.

Idk about that low...

[wildfire0310]

That doesn't sound that unreasonable for boost. We figured a 1.6 ITA Miata at 8mpg on a good day for Rd. Atl. That's just a massaged stock engine.

IDK, that just seem stupid high. Either why, it sucks when it your DD street car:cry::cry:. I remember him b***hing cause he would have to fill up each day due to his drive to MazMart(back when he worked there) would use up over half a tank one way. BTW he lived in Flowery Branch.

[FE3tMX5]

Idk about that low...

The miata or the rx? And we're talking about mileage under full boost right? Not mixed.

[simontibbett]

The miata or the rx? And we're talking about mileage under full boost right? Not mixed.

The Miata, I believe the RX-7 my friends NA FC gets horrible mileage lol.

[silver280zx]

How horrible is horrible? My Z when it was cammed got 15mpg city and it was an L6 Na

[FE3tMX5]

It was measured for 07 ARRC enduro pitstops during the prior sprint. No guessing, known for a fact. This was a mild 1.6 making 113.9 rwhp on well set up 93 Miata. The longer you stay in it, the more fuel you use. :D

[Doppelgänger]

Single-digit mpg is pretty standard when standing on the throttle. Maybe if Austin would have learned to not drive fast everywhere he went, he'd not have a reason to b!tch about gas. I know Paul had told me on a few occasions that Austin would brag about how fast he got to work or got home the evening before. I have a good bit of power under my foot too, and I do use it... but not ALL of the time.

[wildfire0310]

It was measured for 07 ARRC enduro pitstops during the prior sprint. No guessing, known for a fact. This was a mild 1.6 making 113.9 rwhp on well set up 93 Miata. The longer you stay in it, the more fuel you use. :D

Yea I could see track car getting that kinda of mpg, as your normally 100% or 75% throttle or your on the brakes.

How horrible is horrible? My Z when it was cammed got 15mpg city and it was an L6 Na

Well your still in the teens so not that bad.

[wildfire0310]

Single-digit mpg is pretty standard when standing on the throttle. Maybe if Austin would have learned to not drive fast everywhere he went, he'd not have a reason to b!tch about gas. I know Paul had told me on a few occasions that Austin would brag about how fast he got to work or got home the evening before. I have a good bit of power under my foot too, and I do use it... but not ALL of the time.


Yea well Austin wasn't always the brightest. That was an amazing car and if he could have stayed off the gas some he could have kept from getting tickets and won't have had to sell that car.

[simontibbett]

Eh I guess.

Hey though, new age TDI Cup cars make like 30mpg in racing conditions ;)

[FE3tMX5]

The problem is the OE ecu- closed loop with foot to the floor. So no matter what changes you've made to the car, the ecu is going to run the map that Mazda decided was the ideal fit for longevity and emissions- not for performance.