Teach me about rotary swaps

I admit it, I have become curious about magic spinning triangles. It's been stirring every since I saw battered beat half to death RX-7s NEVER BREAK at Lemons year after year after year. I swore up and down that pistons were the only answer, but now it may be time to explore other opportunities. These questions are intended to help me understand the ins and outs of swapping a rotary into a non street-car with very little dollar investment.

What does 12a mean?

What does 13b mean?

Which were good engines?

Which were swappable?

Which were carbureted?

How many spark plugs do they have? When do they fire?

How many fuel injectors? When do they inject?

Is it possible to swap a Renesis without a Mazda engineer handy?

Transmission options?

What does 12a mean?

What does 13b mean?

Which were good engines?
6-port 13B's are very popular, I like 12a's because of the low cost to buy, however there are not as many re-build parts available

Which were swappable?
All are swapable, the 12a's and carbed 13b's are easier because the ignitors are right on the Dizzy resulting in a true 2 wire engine (give it fuel, Bat +, Bat -, and your running). Later ones have Fuel injection so they are more complicated however they are realatively easy to swap.

Which were carbureted?
All 12a's (except the JDM 12aT and Older 13b's (pre-RX-7) )

How many spark plugs do they have? When do they fire? 4 2 per rotar, various times. The leading ones fire 15ish degrees before the trailing ones, however many people will have both fire at once with no ill effects.

How many fuel injectors? When do they inject? Not sure.

Is it possible to swap a Renesis without a Mazda engineer handy? Yes it's just like a early one however to retain the stock ECU you need quite a bit of wireing (imobilizer, key, etc)

Transmission options? Any stock rotary trans. I think people make bellhousing adapters for VW/Porsche type transaxles.

tuna55 wrote: I admit it, I have become curious about magic spinning triangles. It's been stirring every since I saw battered beat half to death RX-7s NEVER BREAK at Lemons year after year after year. I swore up and down that pistons were the only answer, but now it may be time to explore other opportunities. These questions are intended to help me understand the ins and outs of swapping a rotary into a non street-car with very little dollar investment. What does 12a mean? What does 13b mean? Which were good engines? Which were swappable? Which were carbureted? How many spark plugs do they have? When do they fire? How many fuel injectors? When do they inject? Is it possible to swap a Renesis without a Mazda engineer handy? Transmission options?

I have done asked myself the same questions and here are MY results for what I can find, YMMVC.

12a and 13b are displacement in tenths of a L and the letter seems to be like a version designation.

Good engines seem to be the ones that run and don't smoke, a lot.

They all are swappable, but some have better end uses then others.

Dunno on carbs.

2 plugs per rotor, leading and trailing.

1 injector per rotor. Injects just prior to plug firing. Since there is only three "cycles" to make a rotary work: intake, combustion, and exhaust.

You'd have to ask an engineer, but again, anything is possible with money. Lots of money.

I have seen you can mod a 20b bell to fit onto a Ford C4. You can spend big bucks and Freddy Brown can procure you a bellhousing to mate to their AOD trans. Also Quicktime makes a few bellhousings for the 13b to fit Liberty and G-Force clutchless 5 spds. Besides just using the stock Mazda parts.

HTH, Brian

I'm a +1 to this.

The article in the current issue about the chevy power plants was concise and very helpful. Would be a good template for detailing power plant swaps from a single marque in the future, kind of a semi-recurring article like the "learn me x car" ones.

If you look past the poor gas mileage, expensive apex seals, the need to rev it to the moon(a benefit to some) and the polarizing love it or hate it exhaust note what you are left with is that a 13b still weighs in around 300lbs and puts out ~145hp stock. That is not impressive at all.

When I was looking into swaps for my car the rotary kept coming up but it never seemed worth it. The ratios never added up, dollar to horsepower, horespower to weight. A 6 gal gas tank with a motor that might get 18mpg? It wasn't for me.

The appeal of a rotary is that it doesn't work that well on the street. They NEED to be beat on to run properly and last.

Which is why they work so well in racing. The Mazda 4-rotor LeMans car was banned for a reason. You guys saw the Grand Am/Rolex RX8s when they first come out, and they were INSANELY fast.

From talking with Tuna, he's looking at it for Lemons. And it makes sense. You can get them for peanuts, they make more power (and likely weigh less) than what he's using now. They're simple, and as long as you keep them cool, and keep oil in them, they'll run that race without breaking a sweat.

The weight i admit isn't impressive. What IS impressive is WHERE the weight is placed. There are numerous mazda engines that make MORE power and weigh LESS than a rotary, but they're more complicated, might be more finicky, and the weight is higher. A KLZE weighs about the same as a dressed rotary, and makes 200hp. An FE3 weighs about the same, is an i4, and makes up to 170, depending on which version.

I don't think he's looking at this from an outright power/fuel consumption standpoint.

In reply to 92CelicaHalfTrac:

Exactly.

In reply to ditchdigger:

The appeal is that these things never break while racing. 145 hp is 45 more than we're making now. A huge gain. Likely that gain will come with increased reliability, not the opposite, and the swap, if easily carbed, is pretty easy, not to mention the weight distribution benefits, which are multiple.

Plus, as bad as Apex seals must be (never even seen one) try finding a rod bearing for a Volvo B20 in kershaw.

In reply to bluej:

Good idea here.

What does 12a mean?
Each rotor is 120mm in width

What does 13b mean?
Each rotor is 130 mm in width (so it is pure capacity)

Which were good engines?
13B 4 port carbed was awesome but old school
20B is a 3 rotor and makes prodigious power Turbos make power but lose some reliability

Which were swappable?

All of them

Which were carbureted?

All 12a were carbed, early 13B 4 port, 10a were carbed

How many spark plugs do they have? When do they fire?

4 plugs two per housing they fire in sequence to better burn the mix

How many fuel injectors? When do they inject?
Adjustable and variable

Is it possible to swap a Renesis without a Mazda engineer handy?

Possible yes, easy no.

Transmission options?

any but the Mazdas are decently strong and feel good

IMHO

I had a 13B 4 port bridgeported RX3 with a 929 5 speed and an alfa third member.....and it was AWESOME

Ranger50 wrote: 1 injector per rotor. Injects just prior to plug firing. Since there is only three "cycles" to make a rotary work: intake, combustion, and exhaust.

"It depends". Both my FC Turbo II and my FD had two injectors per rotor.

OK, what's up with ports? How many is good? Are more better? How much better? For Lemons, would you port them? I have read a bit and there are tons of different porting jobs out there. Is it a "grab a dremel and a paper template and go to town" type job, or is it a "precision mill with ball end" type of thing? Is it something most people just leave the hell alone?

Oh, and just to clarify, we're talking non-turbo

tuna55 wrote: OK, what's up with ports? How many is good? Are more better? How much better? For Lemons, would you port them? I have read a bit and there are tons of different porting jobs out there. Is it a "grab a dremel and a paper template and go to town" type job, or is it a "precision mill with ball end" type of thing? Is it something most people just leave the hell alone?

For Lemons, it'd be grab a dremel and a paper template. HUGE gains to be made with porting, and porting makes them sound awesome.

Ranger50 wrote: 1 injector per rotor. Injects just prior to plug firing. Since there is only three "cycles" to make a rotary work: intake, combustion, and exhaust.

Incorrect a rotary is a four stroke engine and has a compression cycle

Ports are the intake opening into the housing, enlarging them and even crossing the seals is what is called porting, not unlike porting a head to increase flow

Note: earlier engines have their intake via the end plates and the porting takes place there, however newer engines are peripheral ported meaning through the housing

Do use a lightweight car for the swap as they make low torque at low rpm making it difficult to get a fast heavy rotary vehicle

OK, so does it matter how many ports it has to begin with? Is a 4 port 13B going to make 2/3 the power of a 6 port 13B?

Is a 12A going to make 12/13ths the power of a 13B?

aussiesmg wrote: Do use a lightweight car for the swap as they make low torque at low rpm making it difficult to get a fast heavy rotary vehicle

I understand that much, keep in mind this is road course racing, so not much low RPM here. I am getting the idea that this is why rotaries suck on the street and it's also why they amaze at the track.

Bridgeported RX4

http://www.youtube.com/watch?v=rKmK-paBLcE

tuna55 wrote: OK, so does it matter how many ports it has to begin with? Is a 4 port 13B going to make 2/3 the power of a 6 port 13B? Is a 12A going to make 12/13ths the power of a 13B?

13b is a 13b so no more power and they are the same capacity, ports relate to the cooling of the engine. The 4 ports respond better to old school porting.

12a is lighter and can potentially make around 280hp in full race trim NA, the 13b can reach as much as 320hp. More is not realistic in a 1300cc engine NA

aussiesmg wrote: Bridgeported RX4 http://www.youtube.com/watch?v=rKmK-paBLcE

Also there are street ports, this ports, those ports, bridgeports (ironically not done with a Bridgeport mill), what ports make sense?

aussiesmg wrote:

tuna55 wrote: OK, so does it matter how many ports it has to begin with? Is a 4 port 13B going to make 2/3 the power of a 6 port 13B? Is a 12A going to make 12/13ths the power of a 13B?

13b is a 13b so no more power and they are the same capacity, ports relate to the cooling of the engine. The 4 ports respond better to old school porting. 12a is lighter and can potentially make around 280hp in full race trim NA, the 13b can reach as much as 320hp. More is not realistic in a 1300cc engine NA

OK, how much power can they make with a iffy header and a tiny bit of carb work and porting? How much is the weight difference?

If you take a 13B six port and wire the secondary ports open all the time, you get a really good high RPM engine that runs on pump gas and will last a long, long time.

All 1986 and later rotary engines are fuel injected. If I recall correctly, the 1984-1985 13B engines that were in the GSL-SE cars were also fuel injected. All 12A engines were carbed.

There are two injectors per rotor, at least on the later engines. The secondaries don't open until later RPMs, though.

The 1986-1988 13Bs had mechanical fuel injection. I've never seen one break. The later 13Bs had electronic fuel injection, and I've seen them break quite a bit. You can premix just like a 2 stroke engine to take this out of the equation, though.

The engine mounting points for the 12As and 1984-85 13Bs are different from the later engines.

There is an adapter to put a T5 onto a rotary engine. I forget who makes it, though.

I have used stock and ported rotary engined cars on the street, one did 55K in one year, trouble free.

I did use the 2nd gen ignition upgrade, RB exhaust, Mikuni carb and rats nest removal....but the engine was stock and when pulled was running fine with 180K on it. I also premixed proper 2 stroke oil.

92CelicaHalfTrac wrote: The appeal of a rotary is that it doesn't work that well on the street. They NEED to be beat on to run properly and last.

tuna55 wrote: OK, how much power can they make with a iffy header and a tiny bit of carb work and porting? How much is the weight difference?

Depending upon the engines strength, stock 12a made 115 hp when new, with the mods I had it made around 150hp which was a nice street car but not world beating. A 4 port 13b with similar mods should be around 165hp, but they are getting hard to find. 13b 6 port should be similar but keep the fuel injection.

porting is very subjective and depends a lot upon experience, a street or extend port is a moderate improvement on stock, monster port is a large street port, bridgeport becomes 2 ports as they cross the apex seal line leaving a bridge, a J port is radical and best left to those with a lot of experience as it really pushes the limits of the bridge.

Bridgeports etc are rough running and not very street friendly. If you want to keep it for street use I recommend going to an extend port