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Some getting-started questions for a Miata donor
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Author:  tlippy01 [ June 9, 2019, 5:49 pm ]
Post subject:  Some getting-started questions for a Miata donor
Hi everyone, apologies in advance if this gets long, I'm hoping to start a build this summer, and wanted to ask for some advice. I have a donor '94 Miata (1.8L, 5-speed, Torsen LSD) and want to use as much of it as possible to build something as similar as possible to a standard 7 (at 5' 8" and 150 lbs I don't need a lot of space). I have a good TIG welder and source of cold-rolled steel, and most importantly, a father with lots of expertise who's eager to help. The basic plan is to buy ~150' of 1" square and ~50' of .75" round cold-rolled 16ga A500 (the ".75 for bracing), pre-chopped into 6' lengths for my truck. I have one of those cheap steel king-sized bed frames, thought I'd throw a sheet of 3/4" ply on that for tack-welding the frame, then finish things with the "rotisserie" approach I've seen around here.

My first question is, given this donor car and goal, is there a particular build log here that would be a particularly great example to carefully work through? There are so many that it's hard to decide where to focus, particularly as a newcomer.

My second question: I have a CAD file marked as "book chassis", but can't remember where I found it...can anyone point me to one that's a known fit for the '94 Miata donor? I'd like to make use of the Miata subframe, and like I mentioned, aim for a series 1 or 2 in appearance (wouldn't say no to keeping space for potential turbo, but not at all essential!)

Third, when welding the frame, would it be useful to have already pulled the miata engine/transmission, so they can be swung into place for verifying all the mount points etc? I guess this is somewhat related to my second question: if I have a model that's a verified fit for a '94 Miata I'd be glad to just follow it scrupulously, but if there's less certainty I might want to be checking as I go.

Thanks for any pointers or advice on these or anything else!

-Tom

PS: I've attached the CAD chassis file I mentioned in case it's useful, but I'm like 75% sure I found them through these forums anyway.
Author:  GonzoRacer [ June 10, 2019, 7:12 am ]
Post subject:  Re: Some getting-started questions for a Miata donor
Hi Tom-
I can't really say which build log you should use as a "template" for your build. I can, however, think of one in particular that would be pretty much useless for ya... Unless you like sausage, bad jokes and green paint. :mrgreen:

When we were building the chassis for the Slotus, James had an extra 5.0 Ford block that we used to test fit the motor mounts and the bell housing/clutch spacing, etc. I would recommend having the Miata engine/trans available for the same testing. Even if your drawings are perfect, test fitting the actual piece will catch errors like, "Ooopsie, the plan must have said FIVE and THREE sixteenths, not THREE and FIVE sixteenths, huh?"

YMMV, My .02, IMHO, etc, etc.
Good luck with your build!
:cheers:
JDK
Author:  ngpmike [ June 10, 2019, 2:08 pm ]
Post subject:  Re: Some getting-started questions for a Miata donor
Welcome to the forum! Now that the niceties are over, I'll give my usual scolding. "Location is a good thing to give in case someone local to you is willing to lend a hand, or give advice".

While technically not a part of the Forum files, you might take a look at http://cheapsportscar.net/. This is Kieth Tanners blog about his "Book frame, Miata powered Locost" build. Kieth built his from a Miata specific kit, but there are lots good pics and info.

Quote:
I have a good TIG welder and source of cold-rolled steel, and most importantly, a father with lots of expertise who's eager to help
Those are some great resources to have, and your basic plan sounds good.

There are quite a few Miata based builds on here, so the "Search" function is your friend.

Good Luck, and keep us posted! :cheers:
Author:  Want2race [ June 10, 2019, 3:12 pm ]
Post subject:  Re: Some getting-started questions for a Miata donor
I think the miata was a good donor but ultimately I wasn't very satisfied with the end result.

My blog has a few posts. It has been thinned out a bit but might help- exportedafrican.com

I have a bunch of miata parts that fit book chassis dimensions if interested. Think I have the headers, thinned wiring, driveshaft and a few other parts..
Author:  RoyzMG [ June 10, 2019, 5:29 pm ]
Post subject:  Re: Some getting-started questions for a Miata donor
Tom-
There are two sets of plans that might help you if you plan to use the Miata running gear in a "book" size Locost. One is from the Saturn Sports Car (SSC) Miata 5 site as shown below:

http://www.roadster-builders.co.uk/viewtopic.php?t=674

These PDF plans and details may not be downloadable, if not I have a copy of Rev. 3 I can send you. Send me a PM is necessary.

The other would be what is known as the Vodou Auto Kits plans which should be available, just do a search of this site. if you can't find them I again can send you a recent copy.

I never used these plans but instead modified the McSorley 442e plans to accept a Mazda train and for my second Locost, the Honda S2000 drive train. I'm sure you'll find people on this site that have used either plans and could help you out.

In answer to your other questions, I would recommend building a little more substantial build table and then you can use it to tack weld the chassis and also "roll" the chassis in 90 degree fashion for finish welds. You can also use the table to trial fit the engine and tranny, and differential.

I'm not sure this helps but let me now if you need anything else.
Good luck with your build and welcome to the site.
Cheers,
Roy
Author:  nick47 [ June 10, 2019, 7:45 pm ]
Post subject:  Re: Some getting-started questions for a Miata donor
Many of the Miata builds I've seen used a larger than book-sized frame. Keith Tanner (cheapsportscar.net) did use a book frame, and his website (and book) are good resources, once you have the frame built (he bought his). The book frame is plenty big enough for you, marginal for the Miata engine, but you can make it fit.

A book frame is light enough that a rotisserie is overkill, IMO. You want a nice flat surface to tack together the bottom frame tubes, everything else is just added on as you go.

I wouldn't try too hard to incorporate the Miata subframes. A DIY suspension using Miata spindles will be lighter, simpler, and more fun to build. An excellent supplier of Locost A-arms for Miata spindles is Kinetic Vehicles in Oregon.

Always a great idea to duplicate a known, working example as closely as you can, but not always possible. Just keep asking questions.
Author:  tlippy01 [ June 10, 2019, 8:36 pm ]
Post subject:  Re: Some getting-started questions for a Miata donor
Thanks everyone! I managed to find all the guides mentioned, looks like some great reading material.
Author:  JackMcCornack [ June 11, 2019, 4:46 pm ]
Post subject:  Re: Some getting-started questions for a Miata donor
nick47 wrote:
I wouldn't try too hard to incorporate the Miata subframes.
I am in full agreement re the front subframe. There is no question that the front subframe is a heavy clunky ugly ill-fitting unpolishable piece of poop on a Locost. It's also many inches wider than the front of the Locost chassis, and includes engine mounts where you don't want them. That's the reason it's so heavy; it serves purposes unneeded on a Locost, like stiffening the front of the Miata unibody and holding the engine up.
nick47 wrote:
A DIY suspension using Miata spindles will be lighter, simpler, and more fun to build.
A point Nick makes (re the front suspension) that is non-intuitive is, on the front, building your own A-arms is considerably simpler than attempting to splice in the Miata front subframe. The only advantages to that subframe are a) you won't have to shorten your steering rack, and b) it came free with your donor car.
nick47 wrote:
An excellent supplier of Locost A-arms for Miata spindles is Kinetic Vehicles in Oregon.
Nick is right, said Jack, blushing modestly (see http://kineticvehicles.com/ControlArms.html). Light, strong, and only slightly weird looking.

But the rear suspension is a different story, in my opinion. It's a complete package as it sits, its only tasks are rear suspension tasks (supporting the diff, providing and positioning the control arms), it plugs into the chassis with six bolts and a brake line fitting, and the geometry is right as delivered. And since it's covered by body and fenders, it doesn't detract from the classic sevenish lines of a Locost.
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