redlightrich

iTrader: (1)

Hello, I have been searching, and I become more and more confused. I will start with a simple and basic question.

Will the SA's 12a 5 speed bolt up to a 13b without any drama?

I ask as a 13b may be in the cars future.

Next, I am trying to get the power to a more reasonable level. I love the car, but feel it lacks power. My MX5 weighs 2400lbs, and motor is rated at 170 HP. It is not fast, but it is ok. It falls into the driving a slow car fast category. It is just enough to be fun.

My SA weighs about 2200 lbs, so if I could get the SA's power to near 155 HP and gear it similarly to my MX5, it should have similar fun factor. I am not opposed to more power, but I don't need a high power motor here. Like I said, just enough to be fun.

I have been all over this in my mind. The things I want above all are:

excellent reliability
ease of maintenance
more power
MUST STAY ROTARY

I am not opposed to adding stand alone and fuel injection
I am not opposed to adding turbo if done with fuel injection

So basically, I am committing to adding fuel injection ( for the reliability and ease of tuning factor)

Should I just go to 13b? Or can I make fuel injection and my required power work reliably with the 12a? My current 12a is low miles and runs fairly well ( it does have a bog at 2500 rpm probably due to carb, but I wont worry about that now)
I don't want to waste money, but I can afford to do the job properly. I will buy reasonably priced items, and put it together. I will not buy any 4000 dollar kits. I find that part of the fun of ownership is working on the car, so a kit sort of takes that away.

So I guess my question boils down to can I fuel inject and turbo my 12a ( low boost) reliably, if my power goals are as stated, or will the motor not hold up well. By low boost, I mean near 7 lbs or so.

My hope was I could use the FI manifold and some other items from a 13b, and bolt them to the 12a, and buy a 12a single turbo exhaust manifold, and plumbing would be fairly easy.

I wish I could easily find the JDM 12a turbo set up, but we know that wont happen.

I will appreciate any experienced help that you can offer. As you can see, I am leaning towards making the 12a work, being it is already there, and a good one.

Thank you

Rich

KansasCityREPU

iTrader: (9)

To inject a 12A, you must do a lot of design work and nothing is a direct bolt-on. If you did design a 12A injection system, by the time you're done you could have went another route and got more HP.

With this said, I believe the best solution is to go with a S4 turbo. You'll need a GSL-SE 13b from cover and oil pan.

DreamInRotary

iTrader: (49)

Check out my YouTube channel or one of my builds for an in-depth look at what an S4 13bt swap entails. It's worth it in the end!

j9fd3s

iTrader: (3)

i prefer the NA setup myself, and having been around, i've seen and done a few different approaches.

for the transmission, the 13B does bolt up to the transmission, in fact the engine/transmission pattern is the same from 74-2012, so pretty much anything works with anything, although you need the right flywheel/clutch.

in fact for gearing the miata gearset plops right into the Rx7 case. the diff ratios too, so you have 3.9, 4.1, 4.3, 4.4 and 4.77 as bolt ins.

155Whp is very realistic, and this gives lots of options, not sure if that is easier or harder.

the 12A will do it, but it will need a street port, full exhaust, and at least a modded stock carb, or more likely an aftermarket.

if you wanted something more modern, the 13B from the later Rx7, FC, is a pretty easy swap, and with headers, ecu, and stock everything else it'll do exactly 155rwhp, and with a small street port and some tweaks, there is this: https://www.rx7club.com/time-slips-d...-port-1006884/

if you wanted something really modern, the Rx8 engine can be used. its around 170-180rwhp, but it would be easy to smog, and doesn't need a full exhaust, although it does need a fancy ecu, as it has a multi stage intake.

DreamInRotary

iTrader: (49)

This requires the wiring harness you so aptly avoid though

I know what you mean though, the EFI wiring harness can be a nightmare for most people. Even though I've done it twice now it's still a bit of a hassle and very time consuming.

j9fd3s

iTrader: (3)

if you bought an aftermarket ecu, it would come with something easier than the factory harness. i've done factory harness its a LOT of work

diabolical1

iTrader: (3)

for EFI, a 13B would be easiest, but I must admit seeing someone willing to run a 12A with fuel injection intrigues me a great deal. there are a handful of ways you could do it. I can't say which would be best for you, but if it's a discussion you'd want to explore, count me in.

Jeff20B

iTrader: (13)

You can't go wrong with a hogged out Nikki and a 74 ported 12A. 155HP should be easy and super reliable.

redlightrich

iTrader: (1)

Thanks for all the terrific replies. I am afraid of the hogged out Nikki approach, as I want something as reliable as an anvil. I realize I may be speaking from a ignorant standpoint, but my thought was if I substantially modify the stock carb, somewhere there will be a trade off that I will not want.

I would have went 74 port and worked a Holley ( I know Holley carbs real well from my Mopar days) but I have read page upon page of warnings in where all say run from the Holley carb! My guess is that the rotary engine has a substantially different intake track flow than a piston motor, because I can tune a Holley real nice on a boinger.

I keep hearing about the 74 port, which seems like a sane approach. I have always wanted to crack open a rotary, so maybe this is the start. I considered the RB full exhaust, and with the 74 port I should be close, but I am still at a loss for the induction. I was hoping to hear that the 13b intake would bolt up, then I would source a fuel pump, properly sized injectors and a Power FC.

I want to keep a choke, I want smooth and repeatable idle, good transition and good WOT.
What are my carb choices for this?

If I could find a Tll, I may consider that, then buy a GSL-SE front cover, oil pan and pick up. The issue is finding a motor worth rebuilding ( I would not take a used motor and drop it in).

Keep the ideas coming. I start the tranny conversion this week from auto to manual!!!!

Jeff20B

iTrader: (13)

Tough call. You have experience with a Holley so maybe a Holley on a rotary is an ok choice for you. Then again, the Nikki is so reliable it is what Mazda installed on these engines in the first place. If that isn't reliable, I don't know what is. That's why recommended a hogged out Nikki because you get the power of a Holley with the reliability of a stock carb, all rolled up in one neat package.

Can I let you in on something? When I did a hogged Nikki on my 74 ported 13B with 12A irons, it had more power than a friend's EFI 6 port swapped into his car. They're both 84 FBs and both had access to my RB full exhaust (tried it in one car, then swapped it to the other, then back again for testing). My car was just so much more powerful and drove smoother than EFI.

The only drawback of one of the mods I did to my Nikki was to get rid of the choke flap for slightly more air flow, and because I was going to go turbo on it, and I needed to block off the holes the flap's shaft rode in.

This did not affect the engine's ability to cold start at all. All it did was make it harder to keep it running after it starts because you would have to keep your foot on the pedal. I did keep the fast idle linkage, so I can set the **** to about 2k where the Nikki is supposed to cold idle and that takes care of that, but I don't often do it. I just keep it running with my foot. You don't need to worry about this with EFI.

I would never swap EFI into another FB. As for a Holley, maybe, if conditions call for it, but the Nikki is my number one top choice.

j9fd3s

iTrader: (3)

the difference between the 12A and 13B is the length, so intakes and exhausts don't interchange.

the 74 port is nice because its really mild, so it works very well with mufflers and stuff. going bigger you start to make trade offs, like loosing low end and such.

after having done various efi's and carbs, i think if the car came with a carb, i would leave it carb. it takes a while to dial the carb in, but once you do they work really well. swapping to efi is a lot of work.

t_g_farrell

iTrader: (1)

Look at my mods. I get 134 HP at the wheels and that was measured before the RB SP exhaust,
FAT Nikki, and TFIDFIS ignition setup was added. At the time it was measured I had a
stock ignition, RB Dellorto DHLA 48 intake, and the RE single pipe exhaust system.

Doing the math for, say 12% loss, 134whpx1.12 = 150bhp at the flywheel conservatively.
I think with all the mods I now have that has increased a bit and is probably very close to
your desired 155bhp goal.

Jeff20B

iTrader: (13)

Mazda claims the stock S4 NA was rated at 146HP at 6500. This is on a stock cast iron exhaust manifold and a 2.5" exhaust with a cat. If you swap this engine into an FB chassis so the RB full exhaust can be used, we can assume the power will go up by at least 11HP. Why only 11? Because the stock FC exhaust is already at 2.5". If we compare this with the stock GSL-SE exhaust, which was only 2" with three cats, you get an advertised 21HP improvement with the full RB exhaust.

So now we can assume the S4 NA in my friend's car was making around 157HP borrowing my full RB exhaust. Comparing apples to similar kinds of apples using the same exhaust in the same year chassis, my car with the 74 ported 4port 13B with a hogged Nikki, seemed to make more HP. So because it was enough to feel, I'm going to assume it was over 160HP. By how much over, I don't know. All I know is when you'd open the secondaries, it had impressive power basically wanting to break them loose in gear on dry road going straight (not cheating by going around a corner and punching it or reving it and dumping the clutch) but the primaries were impressive too with good amounts of tip-in, kinda similar to EFI. So maybe more like 170HP max? I don't know. But what I do know is this is a winning combination and should be able to produce 155HP on a 12A, if not slightly more.

I'm looking forward to proving this. I have plans on throwing a 74 ported 12A together later this year. It will get nitrided Y irons, decent housings (hard to find these days), hogged out Nikki, similar intake manifold to what's on my 13B, so an old school one like from a '79 or maybe older. And of course the RB full exhaust and direct fire (DLIDFIS is all I use because it works). 155HP is the goal.

j9fd3s

iTrader: (3)

in my incomplete dyno library we have a few things.

a pro7 car, which was a stock 12A, with the stock exhaust manifold, but they let you do the fat nikki mods, they would generally dyno around 112-116Rwhp. adding a header brings it to 125rwhp, and ITA.

the alternative pro7 setup was to use the euro market N210 rotor housings, which had 10 degrees later exhaust closing, and they add about 10hp. other than that i have no info on ported setups, as they weren't legal in ITA/Pro7

Paul Yaw, did a lot of carburetor development, as he was running pro7/ITA, and the most he was ever able to do, was 155 at the flywheel

the 86-88 FC non turbos do about 116-122 rwhp stock. just making everything functional, and doing the exhaust they will do about 140rwhp. full headers and an intake, and its doing 145-150, add a tunable ecu and you're doing 155rwhp. like the thread i linked, a little porting, and smoothing, and there is a bunch more hp, 180 is pretty easy.

a stock S4 turbo engine will also do 155rwhp, but since its a turbo, even just uncorking it, puts you in the 210rwhp area. from there the sky is the limit, although it is a challenge to separate the BS from the non BS. most interesting one i have seen recently is a full bridge 6 port with a T88 turbo, 631ps.

other ports to consider is just a traditional 4 port 13B, with a street port, and proper carb it should easily be in the 160-170hp range, and run forever. the larger ports start to show the limits of the stock drivetrain, there was a guy who built a Peripheral port 13B and it dynoed at like 310hp at the flywheel, but the T2 drivetrain takes 80hp to spin so it only did like 225rwhp...

and just for reference we're racing a 2001 miata this year, and we've got i/h/e/ecu and depending on the dyno (one dynojet said 147, the other said 137...) it does 137-147hp

t_g_farrell

iTrader: (1)

I should load a good iphone dyno app on my wifes phone and see what it comes up with. I hear they
can be fairly accurate and a lot cheaper than actual dyno time

j9fd3s

iTrader: (3)

i wish we could do that, but after the nationals at the end of the month, they are going to weigh us and then throw it on the dyno. and the dyno they are going to put us on was 3% higher than the other dynojet, and then another 5-6% higher than the mustang dyno we tuned the car on.

a phone app, is much less wasted time!

redlightrich

iTrader: (1)

Ok, I am getting convinced to try the Nikki carb method. I am hearing too many positive comments about the Nikki to ignore it. That being said, I will try to hunt up a stock Nikki to modify. I would prefer to leave my original stock one as a safety net. Seeing as so many say good things about a modded Nikki, I should pay attention. This also allows me to keep the stock intake manifold as a bonus!!

I hear Jeff talk about the 74 port, which seems to be the route I would want to go. I am not a HP freak, I really prefer torque, but seeing as that wont happen on my 12a, I will spin the engine when I have more HP to spin it for.I exclude a bridgeport because it seems like it will not suit my intended use. And although sometimes I love to make noise, I wouldn't want to do it all the time.

Is the 74 porting something I should send out, or can a skilled amateur do it by buying port template? I have a fair amount of skill, and I have all the grinding equipment I would need to port. I do not have a lapping table or rotary broach or anything else to machine the irons. So maybe porting myself will be a false economy?

I am buying the RB full exhaust, so perhaps the ports, exhaust, and carb mods will get me close to my goals. I have converted it to an FB dizzy already, so at least I will have more accurate timing than with points.

Any thoughts about the air pump? If I am changing the exhaust, and modding the carb, is there any good reason to try and adapt it to work? I would think it is taking away hp just driving it. Would I free up any power by tossing it? The mechanical fan is a reliable safety measure, so I may leave that there instead of an electric fan.

Thank you all for helping. It saves me from continual trial and error!!!

Rich

t_g_farrell

iTrader: (1)

Unless you need to pass emissions, toss that air pump and go with dual pulley on the
alternator and run 2 belts or it will squeal like a pig when you rev it.

Jeff20B

iTrader: (13)

Lapping is obsolete. Don't do it. At this point only idiots and crooked shops do it. If the irons are worn beyond spec they need to be replaced with good used ones. I'm sure yours will be fine to reuse.

Porting is the best thing you can do. No one makes a 74 spec template. You have to make one yourself out of construction paper. Any 74-75 or 87+ turbo end iron will have the size and shape you're looking for. Only port up. Don't go down to match the lower area of the 87+ as Mazda redid this area but it shouldn't be transferred to older irons.

You can try a single belt for a while. See if it squeals.