kaseysdad14

Hi everyone. I'm new to the 7 forum but have been around the 8 one. I need some 7 help. I'm trying get a plan together to put a rotary into a triumph spit fire. Going to put a narrowed miata subframe in front and back. Space is really a big deal for fitting the motor. A lot of guys go 12A NA. I would like to go fuel injected and also be able to add a turbo later. Also, the 13b TT engines are easy to find. Which engine is most reliable, and can be turboed? How much of a power drop am I looking at going NA on the 13b TT? Looking at about 750 kg car, if I can find a way to get 250 horsepower that puts me at a 1:3 power/weight ratio.

diabolical1

iTrader: (3)

most reliable is too relative a term, but i'll give my thoughts at this point in time. they'll both be dead reliable in N/A situations as long as there is some semblance of general maintenance. 12As also seemed to just keep going. someone should make a t-shirt that says something like, "12A: no chrome, no problem."

that said ... forget the 12A! the 13B has one advantage that no 12A ever can and that advantage is time. it evolved. it became purpose-built and it survived into the 21st century. many 12A parts are NLA and the stock-piles of used stuff are being hoarded (at least, I try ... and there are many that are richer and more fortunate than me that have the same mind). 13Bs can be built in a variety of flavors. you have choices.

you can turbo a 12A, no problem. you can obviously do the same to a 13B and Mazda saw it fit to do so for decades. Mazda also did so with the 12A, but that's an ever rarer animal, so note it's existence and move on. if you start with a factory 13B turbo block, you're golden.

i'll answer this bit of your post like this ...

the likely scenario with an N/A setup, you'll be limited to about 200 HP or so without going with some kind of race-type porting. more can be achieved with streetporting, aftermarket intake systems and such, but you'll have to WORK for it. most choose to use high compression (9.7) though. i have heard stories of people achieving similar with the stock 9.0s, but i can't think of one to cite off the top of my head right now. turbocharging on the 9.7s can be done and i don't see it being an issue if you only want 250, if you choose that route. obviously, if you leave it with the stock 9.0s, then you can turbo and get 250 AND MORE.

you mentioned you hang out on the Rx-8 board, so i should also mention your other option. if you're still in the air about going turbo later on, you could go for an MSP engine. it might not net you 250, but it should get you further than an N/A REW block without significantly more hassle. if you're decided on the turbo at at some point, stick with the REW.

Evil Aviator

Don't get a 12A. The parts are too difficult to find nowadays, and the 13B has more potential anyway.

I don't think a non-turbo 13B from an RX-7 is such a great idea for you either. While a non-turbo 13B can be turbocharged, its high-compression rotors are not optimal for this, and neither are its exhaust port baffles, as well as a few other minor issues. If you are OK with a 200hp non-turbo engine and you want to keep it that way, then I think it would be a great choice due to its operating cost & reliability. However, if you want a turbo engine, then get a turbo engine. If you decide to just use a non-turbo engine, the 1989-92 engines have the highest compression, lightest rotors, and highest rpm redline of the RX-7 engines. The RENESIS engine from the RX-8 may be a good choice too, so be sure to check in the other forum to see what they think.
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Most of the cheap used 13B engines are "J-spec" Japanese engines (13BT, 13B-RE, or 13B-REW), which are all turbocharged. They have different engine mount placement, so that may be a factor in your build. The 13BT and 13B-RE have about 200hp in stock form, but they can be modified for 250hp very easily. The 13B-RE has 255hp stock. For your application, I think that all of them will have similar reliability.

If it makes any difference, the 1988 and earlier engines have a mechanical oil metering pump (OMP), while the later engines have an electrical pump that needs to be controlled by an advanced engine management system. If you plan on deleting the OMP and running pre-mix oil in the fuel, then this is a moot point.

These engines literally breathe fire, so you will need a serious radiator and thick exhaust piping that is not near anything that will melt or catch on fire (including parking on top of leaves or dry grass). Additionally, you will need muffler(s) that are rotary-engine friendly, such as those from Racing Beat, Apexi, GReddy, HKS, or Rotary Performance (Bonez).

Which engine management system are you going to use?

kaseysdad14

I don't have my plan all worked out. I've got my 8 with the 13b-msp. I guess what I meant to say was I want to go turbo but the plumbing will be a trick as I'm not exactly sure how much room I have in the hood. (7 inches narrower than a miata). Basically what im looking for is an engine i can turbo but wont require it til I can figure it out. Plus most JDM engines come lacking the turbo. I'm well aware of the exhaust temps all rotaries push out.

I haven't got to the management system yet. I'm open for suggestions.

On the rx7 omps how much are they adjusted by throttle and rpms? I know that it adjusts on the 8. I plan on adding a sohn adapter to pump 2 stroke oil in and lightly premixing to accommodate the lack of a third oil nozzle. I'm going to run 2 stroke in this engine, just not sure if I'll premix or feed the OMP.

I've read about some people using the msp irons with the rew housings. The msps don't get complete ignition due to a rich area close to the trailing edge that the rews just fling out the exhaust port. Thoughts?

Now here's where I'm going to sound stupid. The 12a and 13b have the same housing dimensions with the exception of width. Is the compression adjusted using a different rotor or a different e-shaft or how?

lduley

iTrader: (1)

The e-shaft has nothing to do with compression on a rotary, if it did, the rotary wouldn't run

Since the housings are different widths, using 12a rotors in 13b housings would never work.

The way the compression differs on a rotary is the size/depth of the pocket on each rotor face.

Also, if you want to run the motor, but than goto turbo, it will be a big headache. You'll have to change the intakes, completely redo your engine managment system, chanhe the injectors etc. If your gonna put the motor in a different car, do it right, do it once and save your brain cells, beer, and $$$$

diabolical1

iTrader: (3)

okay. simple. get an REW block, build it (if needed) and run it without the turbo. they will power the car just fine.

who will be installing and tuning it when the time comes?

i have no idea about the details on exactly how the electronic MOPs work. what i can say is adapting a front cover that uses the mechanical MOP should be no big deal if needed. also, premixing is fine.

also, the pre-MSP rotaries didn't seem to display the same kind of weird wear that the S1 MSP did. they did just fine with one nozzle centered in the rotor housing (some had additional nozzles upstream in the manifolds, too, though). there would be no NEED for you to run both, but ultimately, it's your decision.

i honestly don't know if i follow what you're saying here. even if the peritrochoids are slightly different between the MSP and REW rotor housings (and i have no idea if there are or aren't), the ignition pattern you're describing shouldn't change.

are you just saying if you went MSP that you'd want to run additional peripheral exhausts simply to cut down on some of the caked up carbon in the MSP exhaust ports over the long term?

as said above, the compression is just a function of the rotor recesses - shallow vs. deep. the e-shaft has no bearing on it.

diabolical1

iTrader: (3)

simply not true. the only thing he'd need is a header/manifold and the exhaust. the OEM intake, ignition and fuel systems will work just fine with an aftermarket EMS. you add the turbo and associated parts and plumbing later, then retune. the only thing that may dictate a setup other than stock would be the physical space he has and i figure since it's a custom project from the get-go, then it's a moot point anyway. by the very nature of the project, he has to MAKE things fit.

RXSpeed16

iTrader: (41)

The idea of MSP irons and rew (or any pre-MSP) housings would get you 5 total exhaust ports. It's been done, but is not common. I'm not sure exactly how that specific combination would work in terms of bolt pattern/port location for intake and exhaust, but it could be made to fit.

All peripheral exhausts housings (pre-MSP) exhibit the "rich pocket at the trailing corner" behavior. This a concern for emissions purposes and has no effect on performance.

I remember trying to test fit a bare 13B in an NA miata subframe. It was very tight. I can't imagine trying to fit it with the REW's twin turbo's. Also the mounting is different between 1st gen 13B, 2nd gen 13B and a 3rd gen REW is different, so you can give yourself a head start by picking the right engine.

kaseysdad14

I forgot about the pocket on the rotor. I knew that the rotor would have to match the housing depth and that the apex locations on the rotors needed to maintain proper spacing.

So from the word go I'm going to have space problems. I'm definitely not going 13b-rew with the twin turbos. They almost double the width of the engine. If I go turbo its going to be a single mounted somewhere unconventional, with a plumbing nightmare for sure. One the bright side with the engine mounted I get 3 sides of access. Its really just a if I want to do it I can, not a I'm going to do it.

I'm thinking 13b-rew with no turbo. I've seen things about the haltech and apexi systems? Any opinions there. I need to find somewhere to tune it in too. I'm in Knoxville about 4 hours from Atlanta, I'm sure there's someone around who can tune it in. Trying to cross bridges when I get there. Car, engine and trans, diff, suspension, management. Got at least a year before I'm there.

diabolical1

iTrader: (3)

fair enough. as i said, you can run the engine N/A without issue - a few little ports to plug or re-route, but that's about it. a healthy REW block will make good power.

for your EMS, there's no issue tackling it at a later time, but the link i was trying to make before is that you need to sort out who will be working with it first, then choose. i suppose you could choose and then find someone, but that may or may not lead to a situation lacking practicality or convenience (like having to drive/ship the car hours away for initial install and tune, then working out how future tweaks would be made as well - that sort of thing.) basically, the common advice get you're pretty much guaranteed to have local, reliable support for.

kaseysdad14

So i keep doing research and I wanted to see if anyone had some input on some other parts.

I'm planning on finding a 94+ Miata torsen rear diff and swapping in the front 7" ring and pinoin gear off a Kia Sportage to get a 4.778 final gear. It will make the car revvy, but this is a fun car and I don't care.

Flipping around the trans between one of the 7 gear boxes and the 6 speed off the 8. I know its weaker but again we aren't talking about a 600 HP monster.

Finally, I'm thinking the apexi system for engine management.

Let me know what you think about anything

RXSpeed16

iTrader: (41)

Just my opinion, but:
If you're staying NA, I'd highly suggest the 89-91 NA intake system. It really improves the drivability of non-turbo engines. The best part is that the control system is all stock. Which means it is cheap and has a giant manual to help you troubleshoot.

Upgrades:
-Light steel flywheel or aluminum flywheel
-The 6-speed is a fine if the shifter lines up. It just needs a turbo flywheel, starter, clutch, and some sort of slave cylinder.

Once you get the swap running, then you can worry about ems upgrades and diff swaps. I'd suggest getting it running on stock power and then deciding where to go from there.

kaseysdad14

The problem is the stock rear diff can handle about 90 HP. On top of that the swing axle on the rear end makes it wildly unpredictable. So if there's a new motor, it will need a rear diff soon there after. I just thought I'd change the diff and set up an independent rear suspension in one step.

kaseysdad14

Dropping the turbo off the motor and still running the stock ecu should make it run like crap right?