Squarefour's Miata Based +442
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Author:  squarefour [ September 6, 2005, 6:28 pm ]
Post subject:  Squarefour's Miata Based +442

I like this new format, so I am inspired to contribute.

As a log, this is a little late (I have put about 500 miles on it), but the car isn't quite done (rear fenders are still in the mail).

In the beginning (just over a year ago):

I recreated some McSorley (442) dwgs in Autocad and had a guy at work plot them out 1:1. I then simply cut tube to fit the drawings, clamped them down to the MDF and tacked together. It was like making a balsa model airplane, only with an angle grinder instead of an xacto.


As you can see, I spent a lot of time coming up with a fancy clamping system:)

Author:  squarefour [ September 6, 2005, 7:00 pm ]
Post subject:  more...

All three "levels" tacked together. Sat perfectly flat on the floor. I was shocked.


Still didn't have a good welder, so borrowed a really nice one from a buddy. Only had it for the weekend, so put in a grueling 15 hours of solid welding in one weekend. I was balancing the welding (weld joint on one side, then the other), so half that time was spent flipping the frame back and forth. I also used wet rags 6" away from the welds to remove heat.

Frame STILL sat flat on the floor.

On to the tunnel:

I kinda built it around the pedals and seats.


Shoulda left a tad more clearance around the seats.
One of the reasons I went with 442 is the pesky input offset with the RX7 axle. I knew the tunnel was going to have to be a little big.

But the width of the RX7 axle is marginal (for tire clearance) with a 442, so I "deviated from the book" to make the trailing arm front mounts flush with the frame sides.


Author:  squarefour [ September 6, 2005, 7:12 pm ]
Post subject: 

Yada, yada, yada...


Note the new garage, moving in the middle of the project was one of the two big time-wasters.

Author:  squarefour [ September 6, 2005, 7:32 pm ]
Post subject: 

The most-dreaded task was upon me: engine wiring harness.

Pulled the harness from the donor Miata. No pics, you know what that looks like: Ugly.

Dragged the big snake over to the 7 and plugged in all the engine connectors and ECU, and jumpered a coupla things at the ignition switch plug.

Voila, engine started.

So then ensued a long process involving many iterations of this:

-Cut wires that aren't connected to anything.
-Make sure engine still runs.

Ended up with a vastly slimmed-down snake:

Author:  squarefour [ September 6, 2005, 7:38 pm ]
Post subject: 

Fun Pic:

This is how I got 375lb springs, that are an inch longer than the coilover, onto the coilover. This crazy idea courtesy some guy in UK. It was fun watching the zips slowly stretch as I was fumbling the spring into place and tightening the preload nut.


Author:  squarefour [ September 6, 2005, 8:00 pm ]
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Fully driveable at this point, if a bit windy, it is off to the local highway Patrol office to have a VIN plate attached.


Author:  the JoKeR [ September 6, 2005, 9:31 pm ]
Post subject: 

Very nice! That spring compression method is pretty interesting! :shock: It'd be fun to take a torch to it and slowly burn the ties off until the thing pops!

Who's pedal assembly are you using and where did you source your rear suspension links? I'm starting to put together a list of suppliers for myself and like the looks of those.

Author:  chetcpo [ September 7, 2005, 9:15 am ]
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So are you using all Miata drivetrain except for an RX-7 rear end? What about the steering rack, front spindles, etc.? Congrats on your project nearing completion, looks terrific!

Author:  Dave [ September 7, 2005, 12:41 pm ]
Post subject: 

Looks great! You've got a lot done in a year! :shock:

Author:  squarefour [ September 7, 2005, 12:43 pm ]
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Thanks but I haven't gotten to the ugly part of the saga yet.

Meanwhile here are all of the specs I could think of:

Mazda MX5 (’93) donor (engine, trans, front brakes/uprights)
Mazda RX7 ’81-’85 GSL live axle (3.9, LS, disc brakes)
Mazda RX7 axle shafts & rotors redrilled for 4x100
McSorley +442 frame, enlarged trans tunnel
GTS widetrack wishbones, lowers angled at BJ for MX5 upright and reinforced
MX5 upright top hole retapered for book-type TRE, lower Maxi BJ fits with no mod
MX5 upright steer hole drilled for 5/8 stud rod end (FK JMX10-T-YX) on top
Coleman Racing rack/pinion, 12:1, 18.5” c/c, rod ends BOTH ends of tie rods
Standard premade 5/8 steering tie rods (Al) from Speedway I think
Coleman steering 48spline ujoints/shafting to a Borgeson double-D telescoping shaft
GTS nosecone (standard width) & ft wings, Caterham series 2 rr wings
Honda Del Sol radiator (dual core for DOHC VTEC) small, good for 160hp min
MK coilovers
Trailing arms:
5/8 premade tie rods (Steel)
Speedway 5/8 urethane RE @ axle (1/2” not available)
FK RSMX7T RE with 1/2-5/8 thd inserts (need to maximise tire clearance)

Kirkey ProStreet drag racing seats (cheaper, lighter, easier to exit than RR version)
Tilton floor mount dual pedal assy, Wilwood remote res MCs
Speedway floor mount throttle, chopped for clearance, mounted on wedge bracket
AIM Mychron XG Log electronic dash in AIM Kart steering wheel, on Speedway disconnect
For Track:
Rays CE28n 14x6 wheels (28mm off ft, 22mm off rr), Victoracer V700 195-55/185-60
Normal use:
cheesy donor car 14” wheels and 185-70/195-70 tires (I live on a dirt road)

some links:

http://www.speedwaymotors.com/xq/aspx/d ... roduct.htm

http://www.hrpworld.com/index.cfm?form_ ... m_cat_id=0

http://www.colemanracing.com/catalog/in ... ath=2_1380

Author:  squarefour [ September 7, 2005, 1:03 pm ]
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Sent this pic to the Farm to get insurance.


Old Ducati muffler I had lying around. Noticed it fit perfectly AFTER I spent money on other stuff.

Cobra hoop roll bar I had done.

AIM Mychon in a kart steering wheel. It is the only instrumentation.

The scuttle-less construction. There will be a firewall in there eventually.


I miss those pretty yellow gel-coat rear fenders...

The plan was to drive it around for a while in pretty much this state, and check it out thoroughly before disassembling again for paint and skin.

Author:  squarefour [ September 7, 2005, 1:36 pm ]
Post subject: 

Anyway, onto the ugly part:

Two days after the previous pic was taken, it looked like this:


My guess is a weld spark went into the seat foam, smoldered for a while, then erupted. All I know is, I welded a Dzus plate onto the dash bar, went in the house for lunch, heard noises, car was in flames.

The plastic fuel cell held up pretty well, otherwise I'd have lost the garage:

The good news:

I still have my house.
Frame is OK.
Axle OK.
Everything forward of the seats OK (except the Mychron and brake res).
I was gonna have to dissassemble it anyway for paint/skin.

Author:  squarefour [ September 7, 2005, 1:59 pm ]
Post subject: 

So I collected myself, tore the car apart, painted and plated stuff, ordered new seats, fenders, coilovers, Mychron, brake res's, lights, ebrake, etc.

I also ordered fancy wheels and an aluminum flywheel just to cheer myself up.

Put on the skin:

Fabbed ANOTHER chassis wiring harness and put the whole thing back together.

The new fenders and coilovers from UK never arrived and are presumed lost. Luckily the burned coilovers, with new springs and rubber parts, seem to be working fine. I went ahead and ordered Caterham fenders from Colorado and they should get here tomorrow.

Like I said, I've put about 500 miles on it since reassembly. I blew the clutch slave on the third outing, and bent the lower wishbones on the fourth (rough roads, too much bottoming out?). Straightened them out and put on a lot of gusseting.

I just spent an unreasonable amount of time (~30hrs) fabbing the front cycle fender mounts.

I find myself a little superstitious about taking pictures now, but I'll try to get over that once the rear fenders are painted/mounted.

That's it, this log is up to date.

Author:  Dave [ September 7, 2005, 3:01 pm ]
Post subject: 


that fire would have been horrible! There was a guy building a Robin Hood in Europe that burned down in a similar fashion - he lost the whole thing and his garage. Good to see you're rebuilding though. Best of luck this time around.

Author:  the JoKeR [ September 7, 2005, 3:25 pm ]
Post subject: 

I never saw that plot twist coming. :shock: Glad to hear the damage was as limited as it was - it could obviously have been much more serious.

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