An RX-8 is just a long Miata. (RX-8 Turbo MZR Autocross car)

AWSX1686 (Forum Supporter) said:

In reply to johnvitamvas :

Nice! The serpentine belt looked funny at the end there. Probably normal, just caught on camera in a way it could be seen. 

The front engine cover has provisions for a center idler pulley (for a different belt-routing altogether) but after seeing that on the dyno I'm thinking about turning a custom pulley to use that idler location. It would split up the span from the upper tensioner to the main pulley and would likely eliminate all that belt slap.

Having said that, it ran like this all year and I never saw any damage to the belt, so I suspect it's probably OK.

johnvitamvas said:

This looks great. I see you have labelled the input ports as F and R. Does that just correspond to the port on the MC that you are taking it from, or are the lines actually split front and rear? (Ie, you could put a prop valve on the rear line like an early miata)

In reply to tran :

That just represents the ports on the master. The Rx8 uses diagonal brake circuits like most modern cars. A prop valve won't work but it's also not needed.

In reply to johnvitamvas :

Thanks for the info. How have you found the proportioning? Does the EBD counter any pad compound changes you make or do you still have to tune the bias with pads and rotor sizing?

In reply to tran :

I'm running EBC Blues all around and the bias seems fine. One of the best parts of the RX-8 is the stock braking system.

Thanks for the info!

This is legendary. Since l learnt about the chassis stiffness, suspension setup and engine position of the RX8 I have wanted to make one my DD. Ultimate mechanical chassis. 

Would I be right in saying that a stock NC subframe and 2.0/2.5 duratec should match the stock rx8 bellhousing with some custom mounts to get the position correct?

Nice meeting you yesterday John. The car looks great!

timoc33 said:

This is legendary. Since l learnt about the chassis stiffness, suspension setup and engine position of the RX8 I have wanted to make one my DD. Ultimate mechanical chassis. 

Would I be right in saying that a stock NC subframe and 2.0/2.5 duratec should match the stock rx8 bellhousing with some custom mounts to get the position correct?

No, sorry, the duratec/mzr 4cylinder engines have a different bell housing pattern than the rotary engines. Think nc Miata or ranger/b-series manual transmissions for stock rwd options that bolt to the 2.0/2.3/2.5.

An NC transmission would have the best chance of being made to work with the PPF. Some fabrication is almost guaranteed to be necessary.

AWSX1686 (Forum Supporter) said:

Nice meeting you yesterday John. The car looks great!

It was nice to meet you as well! The looks of the car need some work since I cut the fenders for 12" wheels :) It looks really silly with the rain setup. But I was really pleased with how easy the car was to drive in very slippery conditions.

Unfortunately, while the NC Subframe bolts up to the RX-8 unibody, if you were to install an NC subframe with the factory NC engine location, the engine winds up about four inches inside the car and requires the firewall to be cut out. Since this isn't allowed in Street Mod (and lots of time trials classes), I moved the engine four inches forward relative to an NC installation. This makes it not feasiable to use the NC gearbox and power plant frame. But the NC gearbox isn't really strong enough for the power level and the power plant frame isn't compatible with / isn't needed with the Ford 8.8 rear end.

There is someone in the UK that is making an adapter to allow the use of the RX-8 gearbox with a Duratec, so that's an option for anyone wanting to do this swap but for whom the FD gearbox isn't a good option.

Impressive, and thank you for taking the time to share it all with us. 

Small update. I actually drove the car at an event! It was super wet and cold, so I ran the PS4S tires. They are phenomenal in the wet. The car was a total Bob Costascat. I just unplugged the boost controller so it ran on the spring, and it was one of the most friendly cars I've ever driven in the wet. One of the courseworkers liked the sounds the car made, so she recorded a video on her cell phone

https://www.youtube.com/embed/wPcL_ZAUCKc?wmode=opaque

The only thing I really didn't like was the brake feel. I plumbed the car with -3AN braided PTFE hose when I moved the ABS pump to behind the driver's seat, and the brake feel was really terrible. I got all the air out of it but it still felt like stepping on a sponge. So as much as it pained me to do it, I ended up completely re-plumbing the car with copper-nickel brake lines. Definitely not the most fun job, but it was pretty satisfying to learn a new skill and I only had to re-make one flare out of all of them to ameliorate a leak. Brake feel is fantastic now, just like stock. So I'm happy with that. The copper-nickel stuff is super easy to work with. I could have done a better job making pretty bends, though
 

I had planned to do the December Dixie event in the car, but I can't travel without quarantining for two weeks so that's out. I may try to get to one of the upcoming trackcross events at Summit point in December just to shake down the car a little more in the hopes of doing the Dixie and Charlotte National events in '21.

A couple minor updates.

First of all, this happened:



Suffice it to say it's challenging to register a car like this in Maryland. In five years, when the car is 20 years old, I have options, but for now this works.

Going back to last year, when I ditched the FD RX-7 gearbox and went to the 4-speed, I needed to clearance the unibody a little. Part of the internal mechanism for the shifter wanted to occupy the same space as the trans tunnel sheet metal. So I did the rational thing and cut a rectangular hole just big enough to fit the gearbox. There was really no way to close it back up from the bottom, so I put it off. You can get a sense for it in the image below. It was about a 3" x 4" rectangle and it opened up the underside of the car to the interior.



Given that I'm off work for two weeks I bit the bullet and tackled this. That meant removing the entire dashboard. Super super not fun.

The tricky part is there are multiple layers and varying thicknesses of sheet metal forming the unibody. As viewed from the interior, the top layer is about 16-gauge, pretty thick. The next layer down is also roughly 16-gauge. Then there is a bottom layer of roughly 22 gauge, so very thin. The approach I took was to cut the opening into a circular shape on the sides, clean up the squared-off ends, and form two curved pieces of 16-guage to bridge the top and bottom layers. That's in the picture below. It took a long time because I don't really have any metal forming tools, so it was just all manual bending by hand. That bridged the top and "middle" 16-gauge layers of the unibody and made everything strong again. I then just folded up the 22-gauge bottom layer and tacked it into place. Hard to describe but it turned out okay. Welding sheet metal is a little tricky and I'm not a welder.



So that fixed the sides, I then made a "cap" of 16-gauge and welded that in. The welds on the leading side look abysmal but they're actually well-penetrated, I just didn't take a lot of time to make them look pretty.



So, that project done, next I updated my gearbox mount. This is version 2. Version 1 was made from .080" wall, 1x2 rectangular tubing. I was worried it wouldn't be strong enough and it wasn't. After the dyno session it had a bit of a bend in it. I decided to scrap it and make a new one out of 0.120" wall, 1x3 tubing. This one came out really nice.



Last step here is to reinforce the center section which was cut out for bolt access by adding a couple of pieces of angle steel, then prime and paint it.

Now that the car is registered I can take it out on the road and work on some of the areas of the tune that are hard to hit on the dyno. Side benefit is the car is a riot on the street, although it's geared a little bit too short.

Good gravy, this thing is fun.

https://www.youtube.com/watch?v=HMtPDjrEhjE

In reply to johnvitamvas :

Ooh yeah! It seems to be fairly well settled, yet changes direction promptly. Not to mention the power :)

I haven't gotten around to sorting through my runs from Spring Nationals but Sam did and posted them on the youtubez. Sam finished 2nd in SSM at both events (obviously this is not an SSM car but Sam is Sam)

Here's his best from Friday (day one of the first Tour): https://youtu.be/Rf-c7QZtgs4

Here's his 2nd best from Saturday. Camera died for his final run which was a bit quicker: https://youtu.be/AKb4Qefa3nY

Here's his best from the second day of the second tour. First day was raining: https://youtu.be/YuwAzin6NtM

The car ran flawlessly the entire time and we beat the tar out of it. I think I'd be happier with a clutch diff (vs. the helical we have in there) but we were able to eventually make the helical work okay. We had pretty bad inside-rear wheelspin exiting corners the first couple days. Ended up changing a bunch of stuff on the chassis to make it work better and what helped the most was swapping to 85/140 conventional gear oil in the rear end. Not perfect but better.

Which helical diff do you?  I have a Truetrac, but I don't have enough experience on it yet.

Hey Paul.

It's a TrueTrac. The instructions clearly state to not use synthetic fluid and I guess I missed that, I had Redline Shockproof in it. I don't know if that was the issue or if it was something else, but we had tons of inside-rear wheelspin. I've had the diff in the car since I built it, and never had problems before, but I think the car just wasn't working well in 2019 and it didn't expose the issue until we had it sorted. Now that it's generating meaningful mechanical grip and weight transfer, it's spinning up a lot.

The rear suspension has tons of droop and I've got a heavy-rate helper spring on each coilover out back. We also pulled a lot of rebound damping out of the back. We tried disconnecting the rear bar and it helped but the car didn't pivot as well like that. The 85/140 helped a lot but it still isn't perfect.

I ordered a Giken for the 8.8 but they are backordered until next year so I think I have to live with the helical for now. I think long term I'll end up running the Giken for autocross and I'll keep the TrueTrac for track stuff. That will let me have a second assembled 8.8 with taller gears that are more suitable for track work.

Jon Lugod worked some of his magic before he left OS Giken and managed to get me a unit for the RX-8. I scrambled to swap it in and get some heat cycles on it before the Toledo Pro and I'm super glad I did, because it made a huge difference in the performance of the car. Much easier to drive than it had been with the helical diff and it puts down power a lot better. I added some rear spring to get rid of a low-speed push I had been fighting and that worked out as well.

More refinement to the traction control, flat-shift and launch control made launches a piece of cake as well and the 1.9x 60' times reflect that. I'm super happy with the car and really looking forward to Nationals now.

https://www.youtube.com/watch?v=F06XKJTGgN4

Wow that thing is a beast.  Nice work!

Wow. That's the first Autocross video I've ever watched where the car looks....fast. Nice work, looks like a ton of fun.

Hello this is my first post on GRM forums. I'm a forum lurker for a long time but I have never before felt the urge to post anything so I'm sorry to wake this thread from the dead but I'm feeling that one vital (for me) detail is missing from the build description. .

@johnvitamvas :

I really admire your build and since you have so much knowledge about RX8 - MZR swap i thought I'd try to ask for more info regarding the detail that bothers me.

I have read some more threads on other forums where you'd answered questions related to this swap but I have never found a direct answer.

That's enough courtesy, let's get to the point:

 At the beginning (post 11/26/19 12:40 p.m.) there is a picture of the engine sitting in the engine bay with what I assume are your custom engine mounts you described earlier. At this point there is no mention about the V8-roadsters subframe yet (or I have missed it). There is also no mention about any custom oil sump either (or I have missed that too). Does that mean that using the NC miata subframe one could position the MZR block inside the RX8 chassis  without NC miata subframe modification, and using a generic oil sump AND only cutting through RX8 cowl (that piece of sheet metal under the windshield)? In other words: is it possible to put an MZR engine in the RX8 engine bay using NC subframe, one of the OEM oil sumps and cutting the cowl but not the firewall with just custom engine mounts?

The reason behind my question is of course my plan to build an RX8 for myself. 

I have read this thread a couple of times and i know that using any stock transmission (mx5 5 or 6 speed) with the above mentioned engine position would put the shifter in an unusable position (far to close to the engine bay) but I also know that a hybrid could be made out of a NC miata and RX8 transmission that puts the shifter further to the back of the car. If that is not enough there are multiple ways to extend the shifter position. I have run a metalworking shop for almost 10 years creating parts for sport-oriented cars (drag, drift, dirt) and such operation doesn't scare me. With those 10 years behind my belt I have also made many aquaintances that would help me along this operation I have planned. 

The question I'm asking is actually the "edge" that is keeping me from pulling the trigger.

Whatever your answer, thanks for sharing this wonderful build with the public. Much appreciated !!!

Cheers

In reply to IgorW :

Hi Igor,

Sorry for the slow response, but I haven't been keeping up with this thread. The car is almost unrecognizable at this point from the photos here.

The short answer is no, you can't bolt an MZR (2.0, 2.5 or anything else) into an RX-8 just by cutting the windshield cowl and making custom engine mounts. The long answer is below:

I abandoned the V8 Roadsters tubular subframe after it destroyed itself mid-autocross in 2023. One of the control arm mounts ripped out. I'm now using a stock NC Miata subframe.The stock NC oil pan won't work - it doesn't clear the subframe and steering rack. That results from two things. One, the NC engine is leaned over towards the passenger side of the car, which makes the subframe and rack interference worse. Two, the front of the NC oil pan is too deep.

Both the factory Ford Ranger (with the Duratec motor) and the Ecoboost Mustang have oil pans which will clear the rack and subframe. However, neither is a suitable design for a vehicle that sees high g-loading. The Ecoboost oil pan caused oil starvation problems particuarly on heavy braking.

Ultimately, I bought an oil pan from Esslinger Engineering. It has appropriate baffling inside it to prevent oil starvation in cornering and hard braking. Two downsides. One, it is very pricey. Two, I still had to notch it to clear the driver's side of the steering rack. Really, just the upper bolt interfered. I shaved the bolt head down, but I still needed to notch and re-weld the corner of the pan. 

At this point, I have a Ford 6R80 automatic transmission with a custom torque converter in the car. It's greatly improved the axle life during ProSolo launches and the gearing is better for autocross and time trial use as compared to the GForce 4-speed I previously had. 

Finally, I ended up putting my engine mount brackets in CAD so I could build myself some spares. If you end up wanting a pair of them, let me know! You can e-mail me at johnvitamvas at gmail dot com. Would be happy to answer any other questions you have. 

V/R,

JV