22 Mar 2008

Checked out my brother’s nearly-completed Super Stalker. All that’s needed is paint, installing the fenders and painting the engine cover. He’s been driving it a few weeks now so first he took me for a ride, then let me drive, then I let him drive Kimini.

Driving observations:
His car has TONS of low-end power thanks to the supercharger, the problem is getting it to the ground. The long wheelbase and steering rack results in a rate about half of mine, and I may have the same issue with Midlana. A slower ratio is better for the street, though I’m curious what he’ll think about it on-track. Probably the biggest difference though is ride quality. He went on a road that has two bumps in it, one upward and another downward. His seats have less padding than mine, but when we hit those bumps, it was a real harsh blow to the backside, enough to make you clamp your teeth together when approaching it. The wind whipping around the windshield wasn’t as bad as I had previously experienced in a Caterham. He said that’s probably because he made the windshield both 2″ wider and taller. The exhaust sound is pretty loud, obviously due to its proximity to our ears, but made worse by the low frequency nature of the V6. At a certain speed and engine load, it all resonates, like someone feeding 100Hz into your headphones and cranking the volume way up. He said it’s loud even with earplugs because they don’t filter out low frequencies well. He may try pointing the exhaust tips differently to see what happens. Oh, and now that I’ve driven both a high and low-pivot pedal setup, I’m not concerned about the differences. Yes, the brake pedal arc does lift your shoe off the floor, but it simply isn’t a big deal. After a couple minutes I didn’t even notice the difference.

His observations of Kimini were that it was much more refined, much quieter, and that the steering was much more sensitive. When he drove over the same two bumps he couldn’t believe the difference. That’s the day-to-day consequence of high unsprung weight and little suspension travel. Examining the rear suspension showed that it has only about 1.5″ of compression travel so he may try relocating the shocks to free up some travel (allowing softer springs and shocks.) He’s also looking into stiffening the shocks and swapping in stiffer springs.

No we didn’t drag-race. We both agreed that the two cars are very different animals and we both respect the other’s car enough that there’s nothing to prove – each has its strengths. I think his is faster in a straight line, but only if he can get the power down. In the curves, who knows. There’s no way to properly compare the two outside of a racetrace. Having driven his car, I can’t understand why anyone would want more power. First and second are useless if you hammer it, and third is a dicey proposition if it’s not pointed straight or if the road’s not smooth. All more power does is make more smoke, so he’s getting wider and stickier tires to help cure that.

21 Mar 2008

The front push-rod design went smoothly thanks to the Mitchell software. The design freedom of pushrod suspension is great since it allows achieving all the goals: placement, accessibility, aesthetics, and the target spring rate.

Ordered double-adjustable QA1 shocks with 6″ travel, identical units being used at all four corners. Also ordered the uber-cool Tilton
pedal set, never mind the price. Next will be the rear suspension design, starting with carefully measuring the Miata rear upright.

A long-term background exercise has been the chassis side treatment – how to make it clean, elegant, simple, yet functional. I should mention that while the car started out as a “mid-engine Seven” visually, it has diverged somewhat over time. All the various parts require small changes to the initial body shape; the end result is that the finished product will have its own unique identity – good.

17 Mar 2008

A hanging pedal assembly isn’t going to fit – nuts. It shouldn’t have surprised me; the hoodline is pretty low, and some (most?) Locosts use bottom-pivot assemblies, so what did I expect? Guess I’ll just have to deal with the different feel. Tilton has a very nice floor-mount assembly that includes clutch, dual brake plus balance bar, and throttle pedal, but it’s expensive. While they can be built from scratch, pedals are kind of, um, super critical. I think I’ll pass on designing them for safety reasons and go store-bought. If builders want to make their own, the Gibbs book already shows how. Buying one saves time and lets me get on with the design, and there’ll be enough room that builders can decide which way they want to go.

This means I have a new Tilton pedal assembly for sale, part number 72-620. It’s a steel, two pedal, three cylinder assembly, with the master cylinders pointing toward the driver. It does NOT include balance bar or master cylinders. It sells new for $234 through Taylor Race Engineering, but I can’t expect full price so I’m asking $175 plus shipping. It’ll head to Ebay this weekend if no one grabs it.

Regarding the shocks, I’ve decided to go with QA1 double-adjustables, about $260-$290 each. Like much of the design, builders can choose whatever shocks they want as long as they’re the same length and use the same spring rate. Between the expense of the shocks, pedal assembly, and my brother having bought corner scales that I need to pay half of, I’ll have to pick and choose what to get first.