KMiata Swap – Suspension

It’s time. It’s finally here. With the Chasing the Dragon Hill Climb complete (and successful beyond my wildest dreams, making the fastest pass by a Miata ever), it’s time to put the bigger, lighter Honda motor in the race car.

Unfortunately however, things got off to a rocky start. Prior to the Hill Climb I started test fitting things to the V8Roadsters subframe and all was not well.

The first bit of prep was to get the steering rack on the subframe. So as to not lose the NB rack bolts I figured I’d put the bolts into the threaded holes in the subframe for safe keeping.
3 out of 4 had powder coat completely boogering the bolt holes. Adding to the fun, the thread pitch of those holes is M12x1.25mm, which is the one M12 tap I don’t actually have in stock.
A quick Amazon shopping trip and a couple days later, the tap comes in.
After chasing the threads in the good bolt hole and 2 of the 3 bad ones, I realize 1 of the engine mount brackets completely blocks access to the 4th. Improvise and overcome right?

Turns out, a 5/16″ 12-point socket makes a good-enough narrow access tap wrench for an M12 tap.

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That’s not great, but a pretty small issue all things considered.
Then a friend (thanks Nick!) who has experience with V8R subframes suggested I check the rest of the holes, and that’s when the big problems started. I could not get the upper control arm bolts through the bores at all.

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I went as far as creating a custom tool with some rod and sand paper to grind the powdercoat out of the bores, thinking it was a similar issue to the steering rack bolts, but no, the bore was shaped like a banana. I still don’t know if it was overheated when it was welded to the frame or what, but it wasn’t great. And given that it left the shop like that, their QC wasn’t exactly giving me warm-fuzzies either.

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To KMiata’s credit, they handled getting a new one shipped out and return shipping for the bad one to V8Roadsters to ‘investigate’. Once we determined just how bad the problem was, I had a new one in hand a few days later.

And check it out: bolts that go in without any hammering or clearance! What a concept!

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Next it was time to get the steering rack prepared. Because of tight clearance to the oil pan (…a recurring theme…), all the hydraulic fittings on the steering rack housing had to be cut off. I used a 3/16″ rivet and some JBweld to seal the holes.

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Next I discovered that Mazda changed the design of their inner tie rod lock washers. The old style washers sat on the OD of the tie rod’s threads, so it was flat between the rack and the tie rod. The newer style lock washers have a shoulder that goes on the over OD of the rack. That prevents my steering rack limiters from seating all the way at the ends of the rack, taking another 3/8″ or so of travel out of the rack.

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I corrected that by throwing the limiters in the lathe to put a counter-bore in the ID to clear the washer on 1 side, but still ride nice and snug on the rack:

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Time to start disassembling the car:

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Given that I’m going to have to install and pull the drivetrain several times over the course of the coming build, I also wanted to remove the upper radiator support (which doesn’t actually support the radiator in an NA Miata), and make the front bumper bar into a bolt-on piece. As you can see, the engine and transmission will come out of the car practically straight:

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A little bit of cutting and welding later, and the front bar bolts to the chassis legs:

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It’s so much easier pulling the whole thing as a unit:

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With the rack put back together, I could finally put the subframe in the car. Unfortunately there’s evidence that my car has been in a minor front-ender, which appears to have slightly tweaked the subframe pickup points. Because of that, I had to pat my head and rub my tummy and figure out which order the bolts wanted to go in so that all the holes actually lined up, but once I figured out which hole was the furthest out and started there, it all bolted in.

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I found a couple of bad ball joints during disassembly, so I called Mazda Motorsports and re-loaded the parts cannon to get good parts on board, but once that was done, everything bolted up nice and easy (including the steering rack)

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Next, on to the KMiata specific engine mods.

Electric Power Steering Conversion – Part 4

HAHAHAHAHAHAAAAA!
Man, it’s so good. The adjustments are pretty darn sensitive. We spent the first 6 or so runs dialing out a little bit at a time until we got to the point where the previous spot was better and dialed it back up that notch.
Video won’t show much, but being able to make fine adjustments was a nice change of pace… it went from having to be muscled around the course to finally being able to have soft hands on the wheel.

All in all: if your class allows it, or if you’ve got a street car without PS, this is a great bit of kit 😀

Video:

Electric Power Steering Conversion – Part 2

Continued from Part 1.

With the column completed, I could get it mounted in the car. Woohoo, it fits! And SOMEHOW, the steering wheel spline size is the same for both the GM and stock columns. My quick release bolted right on.

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While tiedown straps are nice and simple, they’re not exactly sturdy enough for keeping a steering column in place, so it’s time to break out the cutting and welding tools.

The Miata and GM column mounts are not parallel, so it took a little creativity to get everything lined up correctly. After a little bit of measuring, I realized I could cut the shapes I needed out of a drop of 2″ square tube. Everything looks parallel in the picture, but there’s about a 1/4″ slope on 1 side of each bracket to fix the difference in angle between the stock pickup and the GM mount.

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The stock column mounting-plate made a good datum & base to fabricate from. The brackets are bolted to the GM break-away tabs as they would in the donor vehicle, retaining all of the safety features built in to the new column.

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I added a couple gussets to stiffen things up, as there will be a fair deal of torque put on this mount during competition.

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I hacked the lower mounts off of the sacrificial column, and used the stock firewall mount points as the basis for the new lower mounts. The left-side mount was by far the most difficult. It took quite a bit of jiggery-pokery to get all of the angles correct so that there was ample clearance for the brake pedal.

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There was far more room to work with on the right-hand side.

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I’d been working with the motor disconnected, as it is big and heavy, and would make things far more difficult in this stage. The time has come to put it back on. Plenty of clearance in the footwell.

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Also, check it! I can get about 1″ of tilt on the column (nearly the full stroke in the mounts)! I was fairly convinced that the tilt wouldn’t work with my install, but here we are. Finally, an NA Miata with the oft-advertised but never before actually seen tilting steering column!

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The tilting column adjuster handle is VERY much in the way when climbing around the column getting in and out of the car, so that needed to be modified to tuck it out of the way:

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I also went ahead and installed a smaller steering wheel. I went from a ~14″ / 350mm wheel to a 11″ / 280mm wheel. This effectively reduces the arc length that the driver’s hands need to travel to put in the same steering angle by about 25%.

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With all of the hardware complete, I could get a start on the electrics. I ran and terminated all of the large-gauge wires that carry power to the motor (that are connected directly to the battery with a 60 amp fuse in line), and started modifying the switch panel to accept the potentiometer. I should be able to put the controller in there as well, to keep it out of the box, and tap into a couple of spare pins in the harness going out of the box to run the controller output to the motor, making for a nice, clean install.

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Continued on Part 3

Electric Power Steering Conversion – Part 1

UPDATE: Now that this is done, and has been a huge success, I want to put a quick guide & parts list right up top for reference. This is if you take the DIY route. EPowerSteering.com also sells full ready-to-run (just fabricate mounts for your car) kits:

Compatible Steering Columns:
02 – 07 Saturn Vue
05 – 07 Chevrolet Equinox
03 – 06 Saturn Ion (only in steering column with metal ECU case!!)
Pontiac Torrent

EPS Controller
Steering Column Adapter (requires cannibalizing stock Miata column)
Dust boot (to keep water from running down into the sensors)
Fuse holder
60A Fuse (get a spare, just in case!)

When you order the controller, put a note in that you would like a 10K potentiometer adjuster. Per EPowerSteering.com, the adjustment range on the 10K is much more appropriate for smaller cars. I can attest that with the standard 100K that they ship with, my adjuster hovers around “nearly off”, and the 10K pot will give finer granularity in the lower ranges of adjustment.

If I have one complaint about the race car it’s that the steering wheel is fairly brutal on the driver. With aero and 9″ slicks going through a Manual rack there’s a ton of feedback. Too much feedback. And because of how heavy it is even with the Manual rack (again, 9″ slicks), I haven’t even wanted to run a depowered PS rack.

Of course, power steering would fix this, but it’s heavy, often messy when they boil over, and saps power from the engine. I already don’t have nearly enough power, so that’s out.

However, I found out recently about a GM electric steering column that’s been seeing heavy use in Rally and other offroad racing disciplines, along with a company that sells a controller that spoofs the CanBus signal, and allows you to adjust the amount of steering assist. I’ve been toying with the idea for a while now, but an autox buddy had one installed in his Ecotec powered Lotus 7 clone and frigging loves it. With some direct experience and some research in the bag, the time came to start building.

So here’s the plan:
-Snag a steering column & controller
-Fabricate mounts and an intermediate “adapter” to go between the end of the GM rack and the input of the Miata’s intermediate shaft. I want to keep it as bolt-in as possible in case something breaks and I need to swap stock parts in.
-De-Power and refurb the PS rack I’ve had sitting on the shelf for ages now waiting for its moment to shine. With the power steering, adding in the faster rack would be good. I’m going to pair this with a smaller steering wheel to lower the distance my hands will need to travel on the wheel for a given angle of input.
-Add steering rack travel limiters to prevent the 15x10s rubbing on the sway-bar in paddock / grid / during big spins.

The steering column in question is out of the Saturn Vue & Chevy Equinox, and is a little over 3″ shorter than the stock NA steering column. I went to the local Pull A Part and snagged one out of the yard, along with the full wiring harness. The nice thing about this column is that they’re built for far heavier cars than what I’m putting it into, so it should be plenty. This system has seen extensive use in the offroad racing community, and I’ve seen them installed in things between ride-on lawnmowers and Unimogs. It appears to be insanely versatile.

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To get everything lined up in the right place took a lot of careful measurement. It doesn’t need to be micron-perfect, but within 1/8″ or so is the goal.

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The mounts are within an inch or so of where the Miata’s mounts are, so I’ll be able to use the stock upper mounts points (using a modified stock column mount), and will need to re-engineer the lower mounts. The plan is to weld brackets onto a stock upper column mount, and cut the lower mounts off of a sacrificial stock column.

Overall, the GM column is about 3″ shorter than the stock Miata column. This is a good thing as it will allow me to get the steering wheel in a stock location without having to modify the intermediate shaft that runs between the column and rack.

After disassembling the sacrificial stock Miata steering column, I discovered, much to my amazement, that the lower section (where it bolts to the intermediate shaft) is 3/4″ diameter. And just about every aftermarket steering component out there is 3/4″. Due to that size being ubiquitous, EPowerSteering.com sells a 16mm spline to 3/4″ shaft adapter.  I’ll use that and a section of the stock steering column to build a small adapter that will spline / bolt onto the bottom of the GM column, and spline / bolt into the stock intermediate shaft.

I took the parts to a buddy’s shop where we cut the stock steering column down to length, and TIG welded the parts together. It could have been MIGed, but with the threads and fine splines, I wanted to avoid spatter at all costs.

After it was welded, I drilled and tapped through the adapter and spline stub to run a bolt to serve as a failsafe in the event the weld breaks, as that weld essentially is a single-point-of-failure in the steering system.

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With the column setup complete, it was time to start fabbing the mounts in the car.

Continued in Part 2