The molds were sold this weekend; the new owners will be building a couple of track cars for themselves and selling shells. They’ll be providing me with an e-mail address for anyone who’s interested. With the molds gone it frees up space, both in the backyard and in the rafters, which is already filled with Midlana’s fenders and nosecone and whatever other stuff will fit.
Rear suspension design is progressing and it looks like A-arms will fit with pushrod suspension. That won’t be for certain until everything is mocked-up on the table.
Using a detailed spreadsheet the current weight estimate is around 1500lbs. I’m trying hard to be honest and objective with all component weights but it’s hard to not miss something. On-hand parts have been weighed so they’re known quantities, except for the engine. That’ll have to wait until the table is built and I borrow my brother’s engine hoist and scales. For now I’m assuming 450lbs, same as the H22A1 in Kimini. Midlana’s engine, an Acura K24A2, will have an aluminum flywheel added which will save weight, though the turbo will add it right back on again.
The spreadsheet also calculates weight distribution, 64% rear. I’d prefer 60% but if that’s what it ends up being, oh well. Currently, the fuel tank is placed laterally behind the seats – it’s dead space otherwise. It puts the tank right at the CG and keeps PMOI low, all good things. I think I’m going to make my own tank this time instead of using a fuelcell, mostly for cost reasons. Because the tank will be confined behind a bulkhead, and protected laterally by the engine and wheels, I’m taking the calculated risk that fuel won’t end up in the cockpit. That’s my choice, though builders will have a choice of either making their own or buying a ready-made fuelcell.
Received the oh-so-cool but expensive Tilton bottom-pivot brake assembly. Still waiting on the shocks, and while they aren’t really “needed” for a while, they’ll serve as a nice psychological push forward. Also, the seats should be showing up in the next few weeks. Once that happens everything will be present to push forward, which means I’ll be itching to get parts on a table. And that means moving Kimini out of the garage one way or another.
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.
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.
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.
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.
The front suspension pickup points have been chosen, and next is working out the pushrod and shock setup. I’d like to make the shocks a feature, visible from outside, but it’ll be a challenge to miss the driver’s feet, steering shaft, pedals, master cylinders, radiator ducting, etc, etc. Checking brake master assembly clearence though, shows there won’t be any choice but to use a bottom-pivot assembly. There’s simply not enough vertical space for an overhung type, even with remote cylinders. One perk of a floor or firewall mount is that I don’t have to snake the steering shaft through the pedals, or avoid putting the shocks there.
At the Cars and Coffee event were two really cool cars. One was an original Cobra, not that big a deal around here, but this one had a polished aluminum body, just like chrome and very impressive. The other was what appeared to be an unrestored Toyota 2000GT. I never thought I’d get a chance to see one in person; they’re just beautiful cars, very elegant. It’s a shame they were never imported; they could have outsold Datsun’s Z car but I think they were too expensive. A real shame. Interestingly, it was parked next to a Ferrari Daytona, allegedly the inspiration for its styling.
The network problem was an intermittent router, which was a real pain to figure out. A number of times I tried bypassing it to see if it was the problem, but it had apparently already messed with the computers, so it appeared that the modem was bad, or that the problem was with the ISP. Anyhow, a new router fixed everything, and it’s all running much faster than ever before. I think the old SMC router was going bad over a long period of time. Linksys stuff rocks, plug it in, turn it on, and it just works, no drivers, no settings to mess with – nice.
The readers have spoken; the front suspension shall be push-rod. I won’t know how the rear suspension will lay out until I get to that part of the design. I suspect it’ll have to be push-rod, too, due to the deep wheels. Even though most builders will use narrower wheels than what I’m using, I have to design it to work with the widest wheels that the design will accommodate.
Ordered a set of fenders from www.kineticvehicles.com which are needed during mockup of the rear part of the chassis, nevermind that I’ll need them eventually anyway.
Oh, and it looks like I found a buyer for… no, not the car, but the molds. They would have gone with the car, but the lack of car offers meant I was happy to find a buyer for them. It’s just as well; had they left with the car, they would have essentially been given away for free.
After thinking it over and hearing from readers I’ve decided to stick with Miata rear uprights. As several people pointed out, I’m supposed to be designing an easy-to-build, simple car, not something where all sorts of different donor parts are needed and custom parts fabricated. Okay, lesson learned.
Speaking of features on the car, I have a reader question: Do you want push-rod suspension or traditional outboard suspension? Push-rod suspension: looks sexy, good stock travel. Cons: heavier, more complicated, takes up space inside the chassis, takes longer to build, more expensive. Outboard suspension: simple to build, easy, cheap. Cons: not great shock travel. Your choice, pick your poison!
My brother just started driving his Super Stalker, even though it’s not complete (hood’s not painted, no fenders or mirrors, etc). He said, “First gear is useless… second gear is useless, third gear is, oh crap!” I guess he’s impressed.
Forgot to mention that I took Kimini up to the “Cars and Coffee” event. This has turned into a huge deal, with hundreds of cars and spectators. Nearly everyone’s there by 7am and gone by 9am(!) which is cool because it leaves you with practically the entire day for other things. As cars start leaving, a crowd gathers at the exit, cameras in hand, to watch and listen as some exotic machinery leaves. In fact, there was a Ferrari 250GT there, or something that was so close to an original it had people all excited. Anyhow, I don’t post pictures any more because there are 100s of people who do so now. All you have to do is Google “Car and Coffee 3/1/08”.
In other news, I’m closing in on the front wheel geometry. Because I’m making the front track wider than the usual Locost, it presents the opportunity to use an unmodified Miata steering rack. People have a lot of trepidation about modifying steering racks, so this both simplifies and speeds up construction. Moving links around and juggling the wheelbase made it all work out, so unless something nasty shows up, this iteration looks promising.
The second set of rear uprights arrived, setting a new record in poor packing. Styrofoam peanuts don’t protect 40lbs suspension parts, so they punched a hole in the box, which arrived half empty of peanuts, I’m sure UPS appreciated that. I’d be upset if they were broken, but thankfully suspension uprights are darn tough. So, portions of these may be used instead of the Miata rear uprights. As much as I look at the Miata parts I just can’t figure out how to make a clean, easily adjustable rear suspension with them. While the alternative design requires fabricating custom uprights, the bolt-on spindles don’t require making precision bearing cups. (This adheres to my goal of making the car producible without requiring a lathe.) I’m curious what people think though, about making suspension uprights if it is an improvement over using the stock Mazda parts. Of course the question becomes, “How much better would it be? Is it worth the extra work?” I hope to answer that soon. It’s the eternal compromise, do I use parts which are just “okay”, or require extra work to make it much better? It’s a thin line between doing it right and getting it done.
Been working hard on the front suspension design which is testing my nerves – just like 12 years ago. Since I’m using Mazda Miata front uprights, I wondered what kind of numbers Mazda used. The internet revealed the stock suspension points, and even if they aren’t exact, the Miata’s setup is very interesting! What I find fascinating is how Mazda doesn’t follow the commonly held notion about keeping the roll-center stationary, not even close. But if it’s examined using force application points, figuring that the outboard tire carries most of the load, then it works. Of course, the reality is that it (the car) works just fine, as Miata owners will attest. So it’s very interesting how Mazda’s setup violates the so-called stationary roll-center rule… very interesting indeed. So, good, this means I press on with my suspension design and hopefully have some good numbers this week. Once the front suspension is done I can start working my way aft.