Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

Hi all,

So this is the first build thread I've done, and will be slowly updating as things happen. It may be slow at times but I plan to complete the build this year.. We'll see.

The BUILD:
This build started as a spit-balling, dreaming idea of a homebuilt Ariel Atom-esque car with my father. The idea goes something like;
-KL series motor.
-MX3 transaxle.
-Unaltered Miata front subframe (in Exocet fashion).
-Modified Miata rear subframe to house engine and transaxle.
-Tube chassis and single centred seat connecting front and rear.
-80" Wheelbase.

It was a bit of a crazy idea, but out of curiousity I made a parts list with prices, and guestimated I could build it for a not too terrible price.

Then I decided I was going to do it.

So I bought a Mazda 626 Cronos for its KLDE and wiring harness. It had over 200,000 km, but I paid $200 for a running car. Less than I estimated for the engine.

Attachment 234313

And pulled the motor.:fael:

Attachment 234314

And the harness too.

Then after talking with another local Miata racer, I scored this 2001 rolling chassis.

Attachment 234315
Attachment 234316

Along the way I also bought used MX3 transaxle, axles, clutch, flywheel and pressure plate.

This afternoon I am heading to a friend and cage builder of mine to discuss and begin building the chassis. I have a truck load of subframes, an engine, trans, etc..

Early prediction is the engine and trans will not work with the rear subframe no matter how much modification. It will likely mean custom control arms to mount around the drivetrain, or infront or behind.

I'm slowly trying to turn this day dream into a reality. ;)

I've debated with myself what wheelbase the chassis will be built on. I believe I can fit it all into 80", which would be great for things like AutoX events, but make it a handful if I were to do something like a lapping day on track. Miata stock is something like 89.4", I'm considering possibly something in between the two..

Definitely wanna see this happen!

This sounds like an awesome project. I'll be following this one.

Are you planning on getting this registered somehow or just a track toy?

This is a one day project of mine. Good luck and I'm looking forward to seeing how it goes. 80" puts it at about the same dimensions as the Palatov D1/D4 (dp vehicle home) which seems to work pretty well for him. Longer would probably be aerodynamically better if you were doing body panels.

If it's a track car have you thought about a proper transaxle? These cars don't have a lot of power and are gearing sensitive on track. If I drop a BP into a midengined car I'd want a Hewland Mk9 or something behind it, where I could get exactly the gearing I want.

I have no idea what is going on here, but I'm subbing for win and awesome. Good luck man!

Thanks.

Not likely to register for the road, from what I've heard it can be pretty difficult to do in Ontario.

Very cool link. Thanks for that. I love that they're towing it with a Fiat 500. :giggle: I'll read up on his blog about his experience with ~80" wheel base My only concern is that on track it will be even more difficult to control in the event of the rear end loosing traction. But we'll see.

It is a track toy. Though the gearing isn't ideal, part of my goal with this project is to keep thing as inexpensive as possibly, and briefly looking at the gearbox for sale used, it'd be beyond my price range. I'm hoping that the KL at ~160hp (when new) and a guestimated weight between 1200-1400# with make up for the poor ratios.

Any questions ask away! Thanks though, likely going to need it! :party:

If you're building a custom frame with the engine in back why use the front sub frame. Seems you're adding weight and complexity for little value. If you want the geometry, why not fab up a couple brackets and copy the subframe geometry? It's also good, but not fantastic (see people messing with parts to get to the camber an SM7 or similar actually wants, offset hubs, etc).

The Hewlands are pricier, just threw it out as an option. It's also more or less based on a 4spd VW Beetle transmission (which is also and option). I'm assuming that if I get to build one that I'll only get to do so once, so my goal will be to get the nice stuff, even if it adds to the cost.

I'd be interested to see how the weight distribution plays out.

Thanks for your take on this, helps put ideas in my head. Using the front subframe will definitely add weight over tubular, though to me it cuts down of complexity, as everything Miata will work with it. The geometry isn't perfect but it's known to work well and I don't have the know-how to build a better design one. It also cuts down on budget to use stock parts.

The main reason (and part of what sparked this whole project) I'm choosing to use the Mazda MX3 front hubs are the same as Miata rear hubs. This idea was what put me into the perspective of transverse V6 in a Miata rear subframe. Using no custom transaxles or CV shafts, the drivline will mate to Miata rear uprights.

Not saying there aren't better, more track oriented ways to go about something like this, but I'm aim to have the car running for the price of some midengine transaxles.

I think it's definitely going to be rearward heavy. Spring rates will obviously be a long shot from typical Miata numbers, as well as ideal shock valving.

The weight balance brings up another topic I've debated of tire sizing. Due to being RWD and rear heavy, I believe a staggered tire choice will probably be required. Ideas? Sizes?

I'm not (necessarily) saying to not use the subframe's geometry. I'd just copy it with brackets on the frame you're already building instead of bolting in the sheet metal stuff. Use the stock control arms, hubs, everything, the just bolt to a lighter assembly.

Definitely an option. My buddy aiding in the chassis build should have a final plan after we work out some detail later this week, that's likely something we'll discuss.

Hi everyone,

Small update for anyone following.

Chassis builder worked on some designs, material arrives tomorrow.

Attachment 234308
Attachment 234309
Attachment 234310
Attachment 234311
Attachment 234312

These are still tentative and will have some updates. But this is the basic idea and shape it will likely follow.

That looks insanely small. Is the engine sitting right over the rear axle?

It is. The rear end may need to be extended slightly, but it's not far off.

The rear bank on the V6 is leans over top of the drive axle like, the the front leans toward the front on the car. But it does make for a fairly compact system.

I'd take a long hard look at that before hacking up a bunch of good steel. Looks like a passable roll cage in a marginal frame.

The front of that looks really, really soft. Maybe the subframe will stiffen it up enough, but I suspect the whole thing will just flex around your front cross member. Also, the scale's wacky. Are your feet going to be inside the entire cage with a dash member that's missing? If not that thing's no where near safe to drive. That roll bar may not meet SCCA/NASA spec without a diagonal. Could be wrong, but I think it's a requirement.

Thanks Pat.

I believe the front end will be stiff enough, as you say, the front subframe will box in the front end tubing. I agree there will need to be some tubing added there, though.

There should definitely be a diagonal added to the main hoop. There's a few things that will be added to a final design. This is the basic layout, though.

What a fun looking project to build. Good luck with it.

Thanks. Should be fun when done.

Hi everyone,

Another update with a new design. This is about V3.. Or so. It's become much more tailored to its purpose, and more specific.


Attachment 234304
Attachment 234305
Attachment 234306
Attachment 234307


Still tweaking minor things, but it's getting closer.

This looks a lot better than the other version.

Thanks, like I said, it's transforming into something closer to the final idea.

So I did this yesterday.

Attachment 234302
Attachment 234303

Small update. Slowly making progress. Starts to get you an idea for the size of it.

Attachment 234300

Attachment 234301

Opinions welcomed. :D

nice, I'm glad to see this is making steady progress. I really want to see the end result.

Thanks, I'm looking forward to it too.

Another update. Looking much more car like now. Can see how the front end is coming together.

Attachment 234298

Attachment 234299

Opinions welcomed. :makeout:

What is the purpose of the hoop within the front subframe? Will it be connected at the front end to the subframe?

It will be connected. As well as that's the rough location of drivers feet amd pedal assembly. So there a little extra protection and mounting surface there.

Another update. This one is getting to be exciting.

https://www.miataturbo.net/attachmen...ine=1429483872

https://www.miataturbo.net/attachmen...ine=1429483872

https://www.miataturbo.net/attachmen...ine=1429483872

I love the update but what is the weight distribution going to end up as. There doesn't seem to be much in the front to offset the weight of that engine.

There isn't, unfortunately it will be quite rear heavy. I'm considering moving as much as I can up towards the front, ie. Battery, possibly fuel, anything else.

Update. More bracing added. Shock towers starting to come together. Its clearer now how its going to look different than many Locost and similar build which often use inboard suspension.

https://www.miataturbo.net/attachmen...ine=1430050365

https://www.miataturbo.net/attachmen...ine=1430050365

https://www.miataturbo.net/attachmen...ine=1430050365

:party:

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

Couple of pics of the updated shock towers under construction.

The last towers locations posted weren't exactly in an ideal location, as I'm looking to replicate the stock Miata tower locations.

https://www.miataturbo.net/attachmen...ine=1430354811

https://www.miataturbo.net/attachmen...ine=1430354811

Just a mock up with the engine in and rear section started. Suspension work next.

https://www.miataturbo.net/attachmen...ine=1432039263

This is crazy, in a good way. Props deserved for just going for it.

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

Thanks. Definitely not the first time its been called crazy, won't be the last.

I'm hoping I can get it out for at least one autocross or HPDE this year.

Looking good.

How do you install/remove the engine with it caged in like that?

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

It's stuck for ever. :p

You can vaguely see tube clamps at each end of the upper tubes. Similar to these :

http://www.pirate4x4.com/news/wp-con.../07/180095.jpg

I saw that but then for some reason assumed they were both slip in joints and was like... how is that going to come apart.

Cool project.

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

These should work well. I believe 949 was using these on one of their cars door bars to allow customers easier in and out for ride along. Pretty cool units.

<p>Collecting suspoension parts. Picked up a set of these yesterday. MSM Bilsteins in for the DIY coilover set up.</p><p><img src="http://cimg6.ibsrv.net/gimg/www.miataturbo.net-vbulletin/1480x2000/80-cdnn0xa_15b4fbafdb33e7e63e936748bb816d430322afca.j pg" title="" />And a tentative cart of things to go with it.</p><p><img src="https://cimg5.ibsrv.net/gimg/www.miataturbo.net-vbulletin/673x586/80-cart_9b3b13437007402fa3106f9dff40e224923ddc6e.png" title="" />&nbsp;</p><p>Any one have input on Summit Racing springs? They're inexpensive, and that's part of the the purpose of this build. Look like a worthwhile option.</p>

<p>ive never bought srpings from them, but i found thier house brand stuiff is always pretty high quality for the price. of course they are just rebrading, but ive noticed they are usually name brands. example: i bough an FPR from them for half the price of the holley. i recieved a holley in a summt box. i wouldnt doubt the springs are made by moog, or afco. if you call and ask, they usually divulge the details.&nbsp;</p><p>&nbsp;</p><p>car looks great so far! but&nbsp;i hope you dont include that raised bar that went in the middle in the roll structure in V3 rendering. it looks goofy and doesnt look strong.</p>

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

Hi Sean, lol. <br /><br />That's good to hear, and inline with everything else I've heard about Summits branded products. <br /><br />That third bar was never my plan, lol. its been replaced by a corner to corner diagonal. <br /><br />Thanks for the input!

<p></p><p>&nbsp;</p><p>hi mike, that should be much better, both in form and function. maybe even an X with slightly smaller tubing?</p>

<p></p><p>&nbsp;</p><p>I think one diagonal should be plenty. Try to keep weight away from up top.</p>

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

This project is still alive! ..though slowed some. That happens when a hobbyist chassis builder gets busy with work.. But there's an update on some progress. <br /><br />Rear suspension is coming, upper arm has been relocated to a rearward mount with a modified (butchered) stock upper arm. What would have been the rear arm mount is now the front, with the front section cut off and moved the rear. A plate boxing will connect the two. <br /><br />http://imgur.com/a/wCRcf

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

Hello, back again. <br /><br />Major update. The chassis for the most part is done. It sits on its own wheels. And it sits with TONS of ground clearance. <br /><br />The shock tower location were matched to OEM location, and the car currently sits on OEM spring and shock. The front shocks are at full extension, and the rears are only compressed ~3/4" or so. I haven't scaled the car yet, but its very light. <br /><br />Attachment 234292<br /><br />Attachment 234293<br /><br />Attachment 234294<br /><br />Attachment 234295<br /><br />Attachment 234296<br /><br />Attachment 234297<br /><br />It will be home soon, where the real car work begins.. Hopefully more frequent updates moving forward!

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

Scaled the frame and engine this morning. It weighs in at 1200# as you see it in the previous posts. Heavier than I had hoped for, but we'll make it work. <br /><br />Started doing some planning. Still need to pull the pedal asset and steering column from the 2001. Test fitted the stock rad from the 626 (large, heavy) and stock rad from a 1999 Miata. I think I'll be using the smaller light Miata rad. <br /><br />Attachment 234291<br /><br />Over the next week or so I plan to gather the pedal and column, mount the seat in an approximate location to begin pedal and steering wheel mounts.

Meh, I would put radiator further back and set up so the rad is mostly even with or behind you and the hot air goes away from you. But that's just my idea.

Miata Based, Mid Engine, Single Seat Tube Chassis Build
 

I hear you. That was my original plan as well. But moving it up will help in offsetting the weight of the motor over the rear axle, in an effort to balance the car more. <br /><br />I'll do some ducting to dump the hot air towards the rear control arm and axle area.

Subbed!

Any updates? I know this thread is OLD - but any progress?