Long Term Build: My 91 Rotary Miata
 

Well, I sold my Turbo'd Rx7 last week and already the void is setting in.. I have been kicking around the idea of putting a rotary in my beloved Miata autocross car for about the last 10 years or so.. I haven't really been emotionally attached to any of my Rx-7's since my first (1983 that I sold back in 1999 due to frustration). So since then I have run through 29 Rx-7's.. I always sell them and then always buy another..

This cycle has to stop. My miata used to be my fathers (bought it from him last year) and we have spent the last 12 years or so autocrossing it together as father son bonding time, just like the time we spent building my first rx7 as a teenager.. The miata has been on track duty since late 1998-early 1999 and the 1.6L is starting to get a little old and is ready to be put out to pasture.

In comes the rotary.... I do not have a solid plan yet, but know I will be going 13B with a GSLSE front cover and a custom motormount bar that will attach to the chassis infront of the steering rack. Either using a gslse oil pan or the moroso.For now I am just pouring over all the build threads and finding the stuff I like and don't and modifying the plan around that.

I haven't decided if I am going to go EFI turbo, blowthrough turbo, N/A carb'd or what, but those details don't matter much to me right now. I am going to retain the miata rear diff, trans mount, etc and will most likely use the rx7 turbo transmission as my little miata tranny is pretty noisy after all the abuse. This will require a custom driveshaft.

As for timeline? Well I do not want any downtime from the track this year and the success of this project hinges on a few time related factors. I am currently building a new house with a larger garage so I will have adequate space to complete the project. I hope to finish the car over the winter season in a 3 month build marathon. This will include a full paintjob on the little red miata.

Ultimately I hope to have all the parts collected by November when the season ends and have it back together running and painted in time to start the next season. If I do not have everything in hand in time then it will be pushed back another year, as I could not stand to sit out a season. Hence the "long term" project title.

This thread will be updated with info as I have it to share, I also plan to document each step unlike everyone else who builds these, almost all the threads go "im building a miata with a rotary, insert picture of rotary engine, then BAM engine in car with no pictures or measurements of mounts, cuts in the firewall etc... For those that know me on here or in person, this project will come to fruition.. And it will be a step by step make it seem easy to all build thread.

Hopefully last shots under piston power... See you guys around November..

https://www.rx7club.com/attachment.p...1&d=1336926118
https://www.rx7club.com/attachment.p...1&d=1336926118
https://www.rx7club.com/attachment.p...1&d=1336926118
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neat. i considered a rotary miata recently, in CA the legal swaps are an 89-92 NA engine into an 90-92 miata, or the 93-95 Rx7 into the same year miata.

if you're going NA, you should keep the miata trans and just rebuild it, its got the nicest gear ratios.
for the diff you can stay miata, but you'll want the 94-05 diff/axles they are the same size as the Rx7 NA parts, so they are totally fine, the 90-93 diff is from the 323GTX, so its teeny...

IMO the miata is so light that even a stock S5 NA engine, with the miata gears and a 4.3 rear end (its stock in some miatas) would be really really fun!

i've driven some turbo miata's and 230hp is scary, and my friends 340hp miata is just retarded.

Luckily in TN we have no inspection (emmisions testing but no visual).

I have posted a WTB thread for the various parts needed to get going.. My thought is N/A carb'd to get me going and if I feel the need to really screw the car up I would look at turbo later.

Probably going to run a flipped redrilled GSLse pan to clear up some of the clearance issues.

i haven't really looked too hard at how to mount a rotary, it sorta looks like the FC and the miata mounts are in the same place, its just the miata is a teeny bit narrower... the other thing is that the exhaust and the brake and fuel lines are swapped on the miata vs the Rx7, so that might be "interesting"

the cool part though is that the miata is fun with 116hp, so really even 150 is like 50% more, you don't need a ton of motor...

http://www.youtube.com/watch?v=45f3xjLqflE

video does not convey how terrifying the car is @340rwhp, and its not just fast, but the center of rotation is actually behind you, so its actually scary!

+1 on Everyone else's swap being built by gnomes in the middle of the night.
Finally, a thread worthy of the *suscribe* feature!


That 340hp miata is ENTERING straights at the top of fourth gear. An NA engine with functioning aux ports and vdi would be a lot of fun in a miata. Don't see a turbo setup being really useful on an autocross. Sure would be fun though! Looking forward to this build.

I am pretty excited about the swap. Trying to collect parts. Hopefully they will hurry up with my new house so I can get in a garage worth working in.

I want to bounce a few ideas off you guys.. The SCCA season has been extended into December this year so I have a little more time to do research and development.. My ultimate goal will be to build a basic swap kit that wont break the bank. After seemingly years of research it seems that there are 2 types of swaps I have seen (with very little info included in the builds..

TYPE 1- Rigged backyard build, hackjob, lots of cutting, ghetto welding... Not your average DIY project for average Joe..

TYPE 2- Professional looking job using blank tubular subframe, custom welded mounts, not a bolt in deal, not financially possible for most people...

I have been trying to bridge the gap in these two types with my planning. I have come up with an elegant/affordable solution but wanted to discuss the idea with you and get some feedback.

The biggest struggles with a budget drop in build are making the oil pan fit over the OEM Mx5 crossmember, fabbing motor mounts, hacking the pan and routing exhaust.. My proposed solution to the tubular subframe, or hacking the OEM frame and oil pan is the following:

Create a solid steel spacer for the entire front crossmember to drop it down approximately 1 1/2 inches to allow clearance for the oil pan over the subframe, room for the exhaust to run down over to the drivers side. The choice could then be made to use the stock 2nd Gen motor mounts, REW mounts, or a custom 1st gen front cover mounting system.

This only leads me to wonder what this option would possibly do to the suspension setup? My car is a track driven car and the suspension is very well balanced.. I would need to lower the suspension to compensate for the 1 1/2 lift.

Open to your suggestions, this option would drastically lower the cost of swapping a miata to a 13b powerplant. Could be done (spacers, motor mounts, hardened hardware) all in for about the same cost as ONLY the tubular front end would cost...

Let me know what you think. I am having the CAD files done right now for the spacer plates.

I'm certainly no expert but I would think you would be asking for trouble alterting the suspension geometry to that degree. But I know nearly nothing about that so if it works well awesome! And cheap too.

I don't know your situation but with a bit of welding some of aftermarket tubular subframes made for V8 swaps would be damn near a drop in affair. Prices in the 700 range sound fair to me and may be the route I'll be taking with my 95 NA, unless Lucky 7 Racing comes out with something before I'm ready.

Lucky 7 racing has intentions of producing either a subframe ready to bolt in and up to a 13b or adapting the mounts on the factory subframe on an exchange basis. You could toss Fris a PM and see if they have any updates.

Either way good luck on your endeavors.

Matt

I'm with Lizo...the v8 subframe kits are very reasonable and prob would come close to giving you all you need to do a rotary swap in a miata. 700 or so dollars is not too much to ask when you dont want a hacked back yard looking job and it is certainly cheaper than a custom one off. Good luck with it. Cant wait to see which direction you take.

Where are you guys finding $700 tubular k members... All the places I am seeing them they are over $1000 with shipping.

While the complete kits are going for thousands, you can get just the subframe for the engine a good bit cheaper...I wasnt factoring in shipping. I also just took some pics of a friend's project. It is a (or gonna be) a v8 miata. He is opting to mod the original subframe to accept the new motor. I took some pics but cant post because I am at work. We made a jig to hold the subframe, cut out the middle and bought some square tubing from summit. Intensions are to clear all the "bulky" sections from the subframe so as to give extra clearance for headers etc...in your case (I believe) you just need to clear the 13b oil pan. This option would give you all the clearance you needed and then some since the 13b is quite a bit smaller than a v8. With a little grinding and fresh paint, it wouldn't really look like a backyard hack job either. I will post up pics tonight so you have a better idea of what I am talking about.

I would love to see some pictures. Thanks

Glad this project is still on!

Flyin miata makes a tubular bolt-in subframe for their v8 swap kits.
Flyin' Miata : Engine conversions : V8 conversions : V8 Roadsters LSx engine installation kit

Subframe is available separately and they happen to include rotary in their description.
Flyin' Miata : Engine conversions : V8 conversions : V8 Roadster front subframe, no mounts

Personally, I would much frefer the bolt-in tubular subframe than a cut and welded stock one.

I have looked at the tubular front subs, but I am really hoping to find a good way to adjust the mounting of the front subframe to eliminate the need for a $750 fronk k member.. I am not going to hack up my OEM k member I know that..

My thought was if I can get the engine in there and am happy with the result I may be able to offer them to the general population for a reasonable price.. Or at least share the method. That way people without fabbing skills or $1500 + just to spend on the mounting method could swap thier Miata.

This is how the e30 guys are shoehorning the M62 V8 motors in the M3 cars..

http://www.e30club.ru/gfx/upload/m60_16.jpg
http://www.e30club.ru/gfx/upload/m60_13.jpg

Anyone else have any thoughts on the spacer idea.

I'm not a fan of the spacer because it changes suspension and steering linkage geometry. Yes, you can fix it with custom end links, offset bushings, etc. But that's just going to be more of the "guess and check" type of modification that irritates me, personally.

Back when I was looking into doing a monster miata, there were some people that had really clean, modified stock subframes. Problem was that it was their 4th or 5th attempt at doing it. First timers didn't fare as well. With your short, 3 month schedule, I still think the best way to go is starting from a tested base like flyin' miata's tubular version that already has the mounting figured out. Fab your engine mounts and go from there onto trans mounting, driveshaft, exhaust, paint prep.

I am going to use the stock rx7 transmission with the Miata tail section bolted to it, so the trans will bolt to the PPF. I have adjustable Racing beat endlinks already so I wasnt worried about that..

I may buy a tubular cross member if I have to.. I am definetly not cutting up the stock K member.

Interested to see how the spacer idea turns out. Good idea using the miata tailshaft housing and PPF.

I forgot that both suspension a-arms are both mounted to the subframe, so they should articulate the same using spacers. Worst case, you have to get some adjustable A-arms and a bumpsteer kit to get the travel/feel back to where it should be. Should still be way ahead compared to buying the tubular subframe.

Keep up the good work and thanks for sharing!

Why would you do a rotary? Just courios. It seems like a lot of work with little pay off with only an a extra 50 hp

Why is the sky blue? Why are boobs good? How does a posi rear work?.... It just does..

In all seriousness.. This is a rotary forum, I am a lifer.. I wouldn't care if it added 0 HP.. Its all about the engine..

Same reason I am planning a RE5 project that involves putting sportbike swingarm, and front forks on a slow rotary 70's motorcycle.. Cause rotary..

I am not worried about HP at all on the Miata, that car is all about handling. I would like the extra revs in the autox car, and I am always already only 3 seconds off the leader with my 178k mile sleepy 1.6L.

Back from the dead... Well in never died to me.. I have collected a tom of parts and am still in the R&D stage of the mounting.. I am modifying a front crossmember after all. Just picked it up today. I will be using an rx7 N/A transmission with the miata tail shaft housing on it.

I am going to keep the stock oil pan and either lower the steering rack 1.5 inches or space the subframe. I am in the process of building a jig for the subframe so I can cut and weld it without it flexing..

glad you are still with this project! I recently picked up a 90 miata that I think will be getting the rotary treatment...here is the pic I promised from before

http://imageshack.us/a/img706/5172/brd9.jpg

Yeah, funny! I have seen similar pictures and plan to do a similar version. I will be cutting, boxing and trimming but don't think that mine will be completely in half..

https://www.rx7club.com/attachment.p...1&d=1379249283
https://www.rx7club.com/attachment.p...1&d=1379249283