I'm getting a FB tomorrow if all goes well (trading my NA FC for an '83 with a rebuilt motor & a bunch of other stuff done).

I've been pondering/researching various motor options for it. I'm going to keep the stock motor in it for a bit, but I have a spare set of end irons that could be used for a bit of fun, and eventually I'll be doing a massive engine change, going FI, etc.

The car is going to be mostly a weekend car. I plan to autocross it a good bit, hopefully run some HPDE events or open track days (eventually), etc. However, I'd also like to have a motor that I can take on road trips if desired - it doesn't need to be the best behaved motor, but if I'm taking a 200 mile trip with a passenger, I'd prefer to get there without them offering to walk back. My FC put about 140-150 to the wheels (dynoed at 140, then added some other stuff), and that's fine for a DD, but I'd prefer something a good bit more powerful.

I'm also not opposed at all to fender flares if needed to help get the power to the ground with gobs of sticky rubber. FBs look damn good with flares IMO.

I'm mostly used to 13B engine stuff, and the 12As are a bit different, due to their spinning ability. The answer to "How do I make power in my FC?" is universally "Turbo." I'm hoping to get a few other options here.

So far, I've got the following thoughts on each of the major motor types I'm considering:

Stock 12A motor - this is what it comes with.
Pros: It's in the car, fairly fuel efficient, decent powerband.
Cons: It's stock, and just doesn't make insane power.

Ported, possibly bridgeported 12A
Pros: Significantly more power - it looks like a good bridgeported 12A can make 170+ to the wheels based on the dyno tables. Also, I have the parts for this laying around. And, from what I hear, fuel economy isn't *too* terrible with a street port or bridgeport - reports?
Cons: Reduced fuel economy, really. And I don't think it'll be awful. I've got the parts and would just need a soft seal set to do this. As long as it's somewhat streetable and doesn't consume fuel at an insane rate, I'm most likely going to do this and use it like this for a while. Winter project and all.

Onto the longer-term options:
Peripheral ported 12A
Pros: Insane power, I've seen reports of nearly 300 to the wheels. Simple, elegant, "pure."
Cons: Fuel consumption on the highway - I can't imagine it's particularly good. Also, I don't enjoy driving cars that have to be flogged hard to get out of their own way - the 1st gen S2000 drove me nuts because it didn't make power until 7000 RPM. And I suspect a PP is going to be similar.

S5 NA motor, ported
Pros: Darn good fuel economy, 200 to the wheels is doable based on what FC guys have done. Also, a very usable powerband - this would be a great autocross motor, at least for "fun" purposes (I don't compete in classes, so throwing myself into harsh classes doesn't bother me).
Cons: A very practical, all-around motor. Somewhat boring option.

13B Turbo, built
Pros: A metric ton of power - pretty much as much as I'd want. What can the FB chassis hold sanely? Good fuel economy as well, at least on the highway.
Cons: Expensive - I'd need to do a full drivetrain swap (T2 tranny, LSD, etc). I'd also need all the turbo parts, turbo, intercooler, etc. Trivial to get "too much" power for autocross/etc.


So, what do people think? I'm pretty sure I've seen all these options done at various points, and usually I see threads on how they're done, but I haven't seen a lot of driving impressions on the various motors.

Thanks!

-=Russ=-

 

20b N/A with a mild peripheral port. That or 4 rotor N/A.

 

12a BP, or since you car thinking of throwing in a 13b, Bridgeport that. PP will be harsh if done "correctly", but can be pretty streetable. It is either one or the other, insane NA power, or very good power but also semi=alright in street traffic.

I would much rather have the BP, the sound of it is

Also, the rear end can hold on to about 200-225whp before braking. And this is taking care of it, like any rear end should be.

 

i would say 12bp, or a big SP or BP 4port 13b. i have a huge SP 4port 13b with -se rotating assy/housings with old school endplates and it is great. lots of power down low(well compared to a stock 12a) and the top end is great.


isaac

 

Unfortunately, I'm not *that* rich or insane. :-)

I'll definitely see how the 12A BP runs. That may hold me for a while. Anyone got suggestions on templates for that? :-) I've not kept track of where everything sits on the 12A 4 port irons.

-=Russ=-

 

I have a S4 13BT in my GSL-SE and absolutely love it. Problem with auto-x is that the motor swap puts it in a class that without extensive mods, the car won't be competitive. If you just want to auto-x for fun, then its a different story. With a chassis that has nearly 300k miles and a worn suspension with stock SE rims and street tires, I still bested the times of a C4 vette and an STi. While the swap can be costly, it is not overly difficult. Good luck.

 

I'm at the same cross roads. I'm thinking of going with a 1/2 Bridge 13b. I want to be able to beat on the engine and not worry about heat and detonation, or hours of tuning.

 

what about a 4port 13b. IIRC good low end torque and streetportable to get you mid-upper 200. Throw on a carb and exhaust from racingbeat, et voila!
Not only that, but you could use the irons from your present 12a; you're a fc guy so I'd assume you could pick yourself up some nice used 13b housings and rotors for pretty cheap; Combine the two and you have one of those there H setups that mazdatrix charges 3k for.
.02

 

Do you just have someone mill the irons for the coolant seals? It's in the realm of possibility, at least. Why does a 4 port 13B make so much more power than a 6 port 13B? The generally accepted limit of a street ported 6 port is somewhere right around or slightly north of 200 to the wheels, it seems.

-=Russ=-

 

I'm not sure about those numbers, in fact, on could say IMNRC.

 

12a irons will NOT mate 13b housings unless they are from an oldschool 4 port 13b (REPU/RX4/RX5), without machine work. The 84+ 13b engines have the water seal grooves in the side plates, instead of in the rotor housings like the 12a.

Turbo irons are 4 port, but not sure if the will work with NA housings.

If you take out the sleeves why would the 6 port be any less capable? Easier to 1/2 bridge at least, no?

 

Incorrect, the 84-85 Se engines are compatiable. The 86^ are different.

 

My bad. I thought the SE was same as 86+ 6 port.

 

Question. What benefit would using 12a irons have over SE?

The reason I ask is because I have an SE motor in my garage, and I'm pulling my 12a to replace it. Wondering if a mix match would be any better seeing as how I have all the parts.

 

benifet would be making a 4 port instead of a 6port se..^^^ as disscused above.

 

I believe you can also port a 4 ported motor more than a 6, unless you go all out and fill in the 5th and 6th ports.

 

So, driving it with the stock ported 12A, I think I'm less in need of a massive engine now. Didn't realize just how light these are.

I'm looking now at a bridgeport, probably half bridge, with the primaries opened up a bit & the secondaries opened up decently. I'd probably need a different carb for it, and something with the exhaust, but that should get me into a very enjoyable range of power.

-=Russ=-

 

So SE13b with 12a 4port irons is my best bet?

Can an rx8 rotating assembly be used with that? Higher compression, ect...

 

If I'm going with a half bridge on the 12A, should I be looking at opening the exhaust ports as well, or will I be fine with the stock ports? Also, what will I be looking at in terms of intake manifolds & carbs? I'm fairly sure the stock setup won't flow enough to keep that motor fed.

-=Russ=-

 

Exhaust ports are very important they need to reflect the intake ports to make the best power, I want to go the 13b 4port w/half bridge as well, right now I have a large sp (I made my own template) in a 12a, that I built, fuel consumption is a bit much for the daily driver that it is but it kicks the **** out of the 1/2 bridge (had cermet b housing which were probably gone after about 2k km, 3sq ' of flaking at least when dissasembled )that I bought, But i think I got riped as the guy dissapeared as I was inquiring about warranty at under 10k km in 6 months, I want to find a reasonable condition 84/85 13b motor and touch up the 1/2 bridge a bit of my 12 a irons, but Right now I have more than broke the bank on my current setup. weber IDA 48 and racingbeat sp exhaust syst. ,msd, elec fan completely clean eng bay. its fast and responsive even down low I keep up with my buddys 383 camaro.