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Curmudgeon SuperDork
5/28/11 7:12 a.m.

This is a project I've thought about for some time!

Building a custom left engine mount is easy to do, the right not so much. The stock RX7 mounts are at best 'floppy', I dislike them so I used polyurethane 'tee' bushings from Energy Suspension to make my mounts. I can get you pics of how mine were done if you need ideas.

If you need more flexibility of engine position than the whole stock Miata powerplant frame thing gives you, the RX7 shifter can be moved forward up to 4" easily and I think the Miata's can as well. The Miata PPF can also be easily shortened as needed. I'd dtry to scoot the engine back so the front pulley is in line with the front axle centerline, that shoud be pretty easy without a lot of firewall pounding. The only thing which might get in the way is the clutch slave cylinder/clutch fork.

I have used two of the Racing Beat header kits, they are reasonably priced and work well. The best thing is they include 2" OD .120 wall tubing, the 16 gauge stuff in the cheap aftermarket headers can burn through QUICK. You really don't want rotary exhaust blasting into the engine compartment! The stock RX7 manifold is heavy and it strangles the engine, there's an easy 20 HP in a set of headers even if the primary tube length is not ideal (it's best between 24 and 27 inches).

About easy and low budget engine management: MS etc is certainly doable, but here's the easy way: use a S4 ECU with a S4 front cover and mechanical oil metering pump. The S4 front cover is an easy swap. The only mod you have to do is grind or cut away about 3/8" of a water pump stud boss on the S5 water pump housing, otherwise the whole thing is a bolt on deal, you can even use the S5 oil injection lines. A word of caution: be VERY careful of the eccentric shaft thrust bearing! It's a needle bearing with .0015 of end play and can easily be knocked out of position if you aren't careful. The best way to do this is with the front of the motor tilted up and the flywheel wedged forward so the eccentic shaft can't slide toward the back of the motor. If the transmission is still on the engine, you can use the clutch mechanism to wedge it forward and I've done it in the car by using a 2x4 between the seat and the clutch pedal. Then remove the pulley adapter from the eccentic shaft and remove the front cover, etc.

While you are at it, there is a temperature controlled thermostatic 'pellet' which keeps oil from being sprayed inside the rotors until the oil temp gets high enough. Those things fail in the closed position, causing the rotors to get too hot inside and roasting the oil control O rings, leading to oil consumption which must be experienced to be believed. Atkins Rotary has a blockoff kit, or you can stack 3 8mm ID lockwashers on the shaft of the stock one when you reinstall the eccentric shaft bolt, this does the same thing.

The wiring diagrams etc for both management systems are easily found on line and I happen to have a spare S4 ECU. The S5 'inline' air flow meter is compatible with the S4 ECU, that's what is on my car now. Otherwise, the only sensor you would need to replace is the throttle position sensor (use an S4 piece, you have to make a simple flat metal bracket); the air, coolant temp, etc sensors are the same from S4 to S5. The S5 TPS's are much sought after (hint, hint: budget recoupment!). I made a cable to operate my OMP, using bicycle brake cable casing and wire. If you go this route, add a compression spring at the OMP so that when the OMP is wide open, the spring allows the throttle to open a bit further without bending anything. I can shoot you a pic showing how I did mine if you need it.

The '6 port' actuators run off of the exhaust air injection pump and do make a noticeable HP difference at higher RPM, so you need to leave that in place. Or, you can use an RPM activated switch and one of those cheapo air pumps for a standalone setup (that's what's on the Jensenator at the moment). The weird thing about them is they run off of PRESSURE, not VACUUM. Atkins Rotary has 6 port valves which are shaped for better air flow and again these make a noticeable difference at high RPM. They are something like $70 for a set.

The S5 thermostat housing is plastic and they are known to break. I used a FB metal one, redrilled the two original holes and welded a tab on for the 3rd bolt hole. Took a load off my mind! Don't run the engine without a thermostat, the 'internal bypass' will prevent coolant from getting to the radiator and make it overheat. Rotaries do NOT like overheating! You can also use a S4 water pump housing, this will give you an aluminum thermostat housing with a high 'fill point' but it may not clear the Miata hood.

dyintorace SuperDork
5/28/11 7:52 a.m.
Curmudgeon wrote: About easy and low budget engine management: MS etc is certainly doable, but here's the easy way: use a S4 ECU with a S4 front cover and mechanical oil metering pump.

I happen to have what I think is an S4 ECU. It's labeled "N326". It could be had for the price of shipping.

Curmudgeon SuperDork
5/28/11 1:11 p.m.

I think N326 is an S4. My spare S4 is labeled N3Y6, my S5 ECU's label is partly illegible but it has a 'N3 space space 1' on it.

dollraves Reader
5/31/11 4:01 p.m.

Holy cow, Curmudgeon. You may just a free trip to the Republic of California with that write-up. ;)

Thanks for all the great info!

92CelicaHalfTrac SuperDork
5/31/11 4:10 p.m.

Unless i missed something, what's the advantage of the S4 ECU over the S5 ecu in this case?

Curmudgeon SuperDork
6/4/11 5:54 a.m.

dollraves: I'm single now.

92celica: the S5 has an electronic oil metering pump which is great while it's working but it's a bit twitchy. The OMP can be working just fine but if the ECU thinks it has a problem it throws the system into 'limp mode'; turns off the leading ignition and cuts the fuel pressure. This is very disconcerting in the middle of an autocross run or etc. If you try to use the S5 ECU and disconnect the electronic OMP it goes into limp mode immediately. The S4 uses a mechanical OMP which, while it will use more oil than the electronic setup, won't put the ECU into limp mode.

Megasquirt is an option as well, it's been done before. To my addled brain, when doing a swap on a budget and on time constraints it's just simpler to use an S4 ECU since Mazda's already done all the programming for you.

vdubinsd New Reader
6/4/11 8:57 a.m.
dollraves wrote: In reply to Brett_Murphy: Let's just say...there are ways around everything, even in CA. If I register my vehicle in a low-population county, I only have to smog it the first time I register (i.e., register first, then swap engine!). Fortunately for me, I have friends in low places. ;)

Dont know if you are anywhere down here south (san diego/orange county) area or not but....

I have been pulled over and forced to open the hood - city cop knew 81 VW Rabbits did not come with huge intercoolers.Tow truck came, tickets issued for every equipment violation including "removal of federal emission equipment (cat converter) and "modified emission equipment". $1650 after court costs and good luck getting registered after that.

I have seen mobile emission testing stations (mandatory drive by exhaust sniffer) set up 1/2 mile away after autocross events. I have been in quite a few situations where vehicles were "checked for emissions" after seeing a lowered car on nice wheels and not finding anything else wrong. And if you say "no, i will not open my hood and you cant make me" will end up with your car on a tow truck anyway, trust me seen it happen.

I am 100% behind modifiying your car, and my car doesnt exactly pass emissions, but gotta be smart if daily driven....if there is a police car behind you at a stoplight and you have a catless exhaust running megasquirt and the cop's eyes start watering from your exhaust guess what will happen.

Running the S4 control module and having underlying mods will give you a good tune out the gate, and if you run a nice high flow cat, you should not have any problems-if the Miata is a 90 also, might even be able to get it to actually pass........

kellym New Reader
6/4/11 9:56 a.m.

If you need some help with the swap let me know, I'm up the penninsula in Menlo Park


dollraves Reader
6/22/11 4:39 p.m.

Did the garage warming thing this past weekend... thanks to Capt Slow and a couple of Mopar guys for coming by Friday night and helping me roll the RX7 into the garage, drink beer, and commence with lazya$$ couch sitting. :D Some GTX guys came by on Sunday and helped with the initial deconstruction of the RX-7!

GRMer racinginc215 has graciously offered to buy much all of the blue interior - you'll have to fight him for it. The hood and hatch are currently on CL (http://sfbay.craigslist.org/sby/pts/2456189780.html - yell at me if it looks like I've priced them too high). PM me if there's anything in particular (other than the engine, of course) that you might be interested in. :D

A quick shot of my happy little jewel: My 13B

I've never had an engine so clean. I'm sure the judges are hoping I can keep it that clean. ;)

I'm booked solid the next four weekends (SIGH), but the garage will be open most evenings during the week, should anyone want to help with the destruction. I'm hoping to pull the engine and have the car out of the garage in 3 weeks flat, despite my lack of weekends.

Javelin SuperDork
6/22/11 5:40 p.m.

Thanks for the updates! Following this one with great interest.

dollraves Reader
6/22/11 5:45 p.m.

Thanks, Javelin. I know a lot of folks are all "what? you haven't even BEGUN to build!" But, as a novice, I want input all along the way, and I want OTHER novices to feel like they can do this.

It'll be the little Rotary Miata that the GRM boards built! ;)

In other news, there's a rumor that, since they're comparable years, I can take the titles for the Miata and for the RX-7 to the DMV and tell them I'm doing the engine swap. They'll re-title the Miata as an RX-7 for smog purposes. Wish me luck!

belteshazzar SuperDork
6/22/11 6:36 p.m.

i love

this build

yamaha Reader
6/22/11 7:02 p.m.

Well, I approve of this lunacy, so that means its 3 paul approved ;)

Curmudgeon SuperDork
6/22/11 9:19 p.m.

Mmmm... fresh rotary.... mmmm.

racer_ace Reader
6/23/11 1:36 a.m.

In reply to dollraves: Nice! From the picture it looks like the intake pipe that routes over the fan shroud was not on the car... If you do have it and are willing to sell it please let me know.



dollraves Reader
6/23/11 11:31 a.m.
racer_ace wrote: In reply to dollraves: Nice! From the picture it looks like the intake pipe that routes over the fan shroud was not on the car... If you do have it and are willing to sell it please let me know. Thanks, Ray

There's a box of bits & pieces I haven't gone through yet, Ray. Got a shot of the intake pipe so I can sight-match?

Capt Slow
Capt Slow Dork
6/23/11 2:12 p.m.

So exactly how much time do you have until the challenge? Do you have a go/no-go date picked out?

Curmudgeon SuperDork
6/23/11 2:14 p.m.

You really want style points? Adapt the RX7 5 lug brakes to the MeOtter.

dollraves Reader
6/23/11 4:26 p.m.
Capt Slow wrote: So exactly how much time do you have until the challenge? Do you have a go/no-go date picked out?

We did last year's GTX in six or seven weeks, and even then, we went 2 weeks over schedule (mostly due to brake failure). Granted, we literally had boxes of parts and had to piece that car back together. We probably worked 10-12 hours a day on the weekends, with another 12 hours scattered over the course of the week. (Edit: There were were 5-6 guys who rotated through to help me out, so I wasn't all alone in that)

I'm more worried about finances and vacation time at this point. This has been an expensive year, and I burned a lot of vacation time on the hooterectomy. My go/no-go date is September 17th, as that will give me time to buy air plane tickets to see family (I can work remotely if I'm not busy driving a car...)

This is a pretty well documented build, so I'm not forging any new territory, just doing it for under $2k. If I can part out the cars sufficiently and don't have to spend a lot, I might even be able to do it for under $1k. I'd like to spend a little more time on the cosmetics of the car this year, as I've never done that before.

Curmudgeon wrote: You really want style points? Adapt the RX7 5 lug brakes to the MeOtter.

Heh, I like that idea. I LOT. I'd love to keep the RX7 wheels, too! And...great mines think alike! I've been calling the silver '91 "My Otter." We, um, won't discuss the name of my former '95. cough

dollraves Reader
7/14/11 2:16 p.m.

Oof. This is looking more and more like a $2012 entry...trying to get the Miata sorted out and registered.

Right now, there's a major metal-on-metal grind and the tunnel that runs between the seats gets stupid hot after 20 miles; once, smoke (or maybe steam? it rained that day, very damp in car) came up from under the shifter boot. Oddly, though, the grind is significantly muted when there's a passenger in the car - still there, just much quieter. Shifting gears is a bit notchy, and fifth just pops back into neutral if you can get it into fifth at all.

Fortunately, there's a guy in Martinez looking to trade me a working Miata tranny for the RX7 tranny. I know what I'll be doing this weekend.

Karl La Follette
Karl La Follette Dork
7/14/11 3:01 p.m.

Dollraves you can run on our team MGExploder in last years RX7eruption . Eruption never lived up to its potential because of tire issues <<< we just spun em >>> and ignitors where crapping out on top end of the drags .. And this offer is open to any challenge entrants that have trouble with a crapped out entry . i still have the sentravalanche mitsuwatanabee available . Sorry triumph stag entry nope keep that for myself after we tore the stock rear end out from doing burnouts .

Capt Slow
Capt Slow Dork
9/8/11 3:55 p.m.

So are you going to make it to $2011 ? updates? need help?

dollraves Reader
9/10/11 11:41 p.m.

Nope, definitely a $2012 car. Might not make GRM at all - major work roll out on 10/31 that may sink me. :(

I would love help! The engine bay is mostly cleared out and I'm just trying to figure out how to pull the engine now. Let me know when you can work me into your schedule, Cap'n!

The metal-on-metal grind in the Miata is the diff - it's complete toast. I'm thinking of pulling the back end out of the RX7 and getting the stub axles machined down to fit the Miata. Pure foolishness, I'm told, but I would love the hubs & rims off the RX7, and besides, I have it, so it would just be the cost of machining, figuring out how to pull the front hubs over (getting tips on this one from a Monster Miata guy), and figuring out the suspension. Minor details, really.

Oh, and I gave up on trying to make the silver into my DD and just bought a red '91 Miata Thursday from Paul at Rotorsport. Because they're small - I need two! Well, mostly I need a reliable DD that isn't my poor old GTX.

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