10 Jul 2008

Most steering racks are measured in “inches per turn”, the amount the rack moves with one revolution of the steering wheel, yet no one seems to know what the Miata rack speed is. So finally getting around to it, the Miata’s various hydraulic lines were removed and the rack cranked to one end. Backing it off by exactly one turn showed the speed to be 1.77″, a surprisingly fast rack for a modern car. (Kimini’s Triumph Spitfire rack is about 1.8″/turn.) That’s a good thing because there was a concern that my “sports car” might turn as slow as a Lincoln, you know, about 10 turns lock-to-lock. (A bit of an exaggeration, but not by much. We rented a Lincoln for a trip once and the brakes, seats… and steering were terrible.) Anyhow, it means Midlana will have fairly quick steering – as intended. Also, the rack appears to be in good condition, with no slop in the assembly.

8 Jul 2008

The sawhorses supporting the table are rated for a combined load of 2400 lbs, so “technically” there’s nothing to worry about. However, the rating is apparently a laboratory-tested value using a static vertical load. However, if it’s a real-world load that is sometimes bumped side-to-side – like a car project – the wobbly, spindly legs don’t endear much confidence. After a reader mentioned a builder’s table collapsing, it pushed me to add two 4 x 4 legs with cross-bracing at the heavy end of the table now before things get heavier. Better safe than sorry.

I can already tell that making the table 60″ x 120″ wasn’t a luxury; any smaller and too much of the chassis would hang off the edges. I thought (for what, a day?) that maybe a 4 x 8 ft table would have worked – nope. While the wheelbase is 96″, the overall length of the car is about 11 feet; good thing I didn’t cut corners. BTW, one good sign of how stiff the screwed-and-glued table assembly is, was when the drivetrain was sat on it. Not one pop, creak or crackle. Good.

Speaking of getting the engine on the table, I turned the crank several revolutions with a wrench. It was reassuring to feel the compression in each cylinder – no sudden clunks or scraping sounds. Another concern averted.

As a fun side project, the selection of turbochargers is narrowing down. I’m fully aware that a turbo isn’t a requirement, much less needing it now, but at least once, I’d like to own a powerful rear-wheel-drive turbo car. I realize a turbo can make a car slower at the autocross, and potentially only a little faster at trackday events, but you know, I don’t care. This car’s all about having fun. I’m not building an F1 car, trying to win an SCCA national championship, or even a local autocross event. It’s for fun. I might even buy the turbo early as motivation, an awesome component to serve as a goal, to provide a suitable platform worthy of its inclusion.

6 Jul 2008

A busy weekend. Saturday the table was finished, attaching the remaining panels and lifting the heavy *cough* bastard *cough* onto the sawhorses. Borrowed the engine hoist and scales from my brother so I could answer a question that’s been bugging me for a long time: what are the drivetrain component weights? I expected it to be about the same as the Honda H22A1 I used in Kimini, or about 475 lbs. This engine’s basically the same, in fact it’s a bit larger, 2.4 liters instead of 2.2, so it seemed fair to expect about the same.

So what does a Honda K24A1 weigh? Engine + exhaust manifold + alternator + starter = 283 lbs. This does not include the flywheel or clutch (I have neither), nor engine mounts. The 5-speed transmission weighs 87 lbs + 10 lbs for the intermediate shaft, for a total of 381 lbs. Figure 8 lbs for an aluminum flywheel and maybe 15 lbs for the clutch. As far as I can remember, these are the same parts included when the H22A1 was weighed. So the grand total is 403 lbs, which is pretty awesome, a lot lighter than the H22. Of course neither total includes the engine mounts and axles but I’m pretty happy. It nicely lowers the weight by ~70 lbs and moves the CG further forward, now at an estimated 40/60 front/rear. I’m happy.

On the floor alongside the table is the bundle of wood that will become the mockup. I’ll buy some plywood to make 90 degree “bends” for the cage, but things are moving along. I included a sketch (preliminary) as a teaser so you can get a feel where things are headed :). The last shot was after I turned off all but one of the lights, the first parts of the puzzle on the table, awaiting their buddies to become something pretty cool.