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Our Locost (Note: We wrote the following back in July of 2011, just as we were about to embark on our Locost build. Over the two-and-a-half-year course of the project we had to make way more design decisions and compromises than we ever imagined back then, and as a result our Locost isn't exactly as described below. But we're keeping this page as we originally wrote it, as a reminder to us of just how much we learned in the process of building a car from scratch.) A Locost built from M.G. parts. British chassis, British running gear. Sounds like a natural. If you’re a product of the seventies and a sports car nut, you’ve probably ridden in, driven, or owned an M.G. We owned several. We autocrossed them, raced them, and took them apart and rebuilt them. By today’s standards they were a simple, no-frills sports car. They might’ve been slightly underpowered, but take away 1000 pounds and suddenly you’ve got a very fast car. We’ve spent a great deal of time over the past few years working out many of the details of this build, but probably not all of them. Considering that we're trying to stay as true as possible to a book build, there shouldn’t be a lot of details to work out, but the book isn’t entirely clear on everything, and we’ll also be incorporating a few changes for an MGB donor. We’ve outlined some of our design details below. The Frame Changes to the book frame include our version of the Aussie mods (see below) and the front suspension pickups. The radiator mount is a little different, as is the handbrake, and the steering rack mount will vary slightly from the book as well. We’ll also be adding a roll bar, one that’s tall enough to pass any broomstick test, and also tall enough to make the car more visible in traffic. Materials All the 1" square steel tubing we're using was purchased online. It’s designated A36, which is 1018 mild steel with a minimum yield strength of 36K psi. We're replacing the 3/4" square tubing in the transmission tunnel with 1"x1/2" rectangular tubing, which weighs the same as the 3/4" tubing, but is stiffer in the stressed direction. It also fits the rest of the chassis tubes better, narrows the tunnel by half an inch—critical for fitting the MGB gearbox—and looks better to boot. Aussie Mods The book frame gets a lot of criticism for its perceived lack of torsional rigidity. The idea behind the Aussie mods was to significantly increase frame stiffness without adding much weight. Our version will increase frame stiffness, but maybe won’t save as much weight. We're adding cross-wise rails under the seats, a cross tube to the nose piece, and maybe extra tubes in the engine compartment. Aussie mods suggest we're also supposed to remove a couple of tubes, but we honestly can’t figure out which ones. Front Suspension The MGB suspension is based on a design that originated before the big WWII. So it’s tried and true. It does have a few shortcomings, though. It’s rather heavy for unsprung bits, and because it doesn’t use any ball joints, it doesn’t allow for caster adjustment. In fact the caster has to be incorporated in the suspension pickups. An MGB runs 7 degrees of caster, which is generally considered by the MGB community a bit too much. The Locost book specifies 5 to 5-1/2 degrees, so we're shooting for 5. For this to happen, the suspension pickups have to be rotated 5 degrees, as viewed from the side of the car. This raises the front pickups about 1/2"-3/4" from the book, which lowers the front end half that amount. Which is excellent. With lower A-arms flat (parallel to the ground), the roll center will sit about 3" above the ground, and with the steering rack 5" above the bottom of the frame bump steer will be minimal. Track will be 52-1/4". All suspension mountings will use the standard Spitfire/Herald "metalastic" bushings on the inboard end, and spherical rod ends outboard, except for the outer front A-arms which use the standard MGB trunion bushing setup. The angle of the springs as viewed from the front is 30 degrees, static length between shock mounts is 11-1/4 inches. We calculated spring rates using an online spreadsheet referenced on Kinetic Vehicles website, and found the front motion ratio was really low (0.48), and that 400# springs are needed to keep from using up all the suspension travel in droop. On the plus side, this setup yields a natural frequency of 1.75 Hz, which should be fairly comfortable. We’d like to incorporate a sway bar into the front suspension. Because of the rearward placement of the drivetrain, not to mention the driver, the front roll couple could end up on the low side. An even bigger problem is the disparity in spring rates, which have to be stiffer than optimal in back because of limited travel. The stock MGB sway bar may be adequate, but I think we’ll be looking for something bigger. Rear suspension This is all book, a five-link setup with four parallel trailing arms and a Panhard rod. And I wish my spell-checker knew what a Panhard rod was. We're using the later MGB axle which is slightly lighter and has straight axle tubes, making the bracket attachment fairly simple. Spring rates in back will be 180# with a motion ratio of 0.76. Distance between shock mounts is 11-1/4 inches, with only 2 inches of travel. Natural frequency is 2.11 CPS, which isn’t optimal but should work okay with 1.75 in front. Rear track will be 52", accomplished by adding 1-1/4" wheel adapters to the stock rear hubs. Power train Starting out with the faithful old M.G. B-series engine, a 1.8 liter OHV cast iron behemoth putting out just over 100 hp at the flywheel. This engine was designed to work well with 94 octane leaded gas. Many MGB heads have been converted to hardened steel valves that let you run unleaded. Worst case scenario are the lead substitute additives that you throw into the tank at each fill-up. Pre-68 engines have no emissions controls. Later engines have a few fittings on the head for EGR and the like, however even the latest of the dual-carb engines, from 1974, can be backdated to produce the same power as a ’67. Stock heads can be ported and polished for an additional 10-15 hp. We’d like to see 100 hp at the rear wheels, more than that would of course be a bonus. The M.G. transmission is a nice well-spaced 4-speed. The early model is the smallest, but it’s what we used to call a "crash-bottom" box, having no synchro on first gear. Not a major handicap. The all-synchro box is slightly larger and so will confiscate some space from the driver’s footwell, which was of course the passenger’s footwell in the original configuration. There’s also an overdrive gearbox, but it’s too big, too heavy, and too lame to consider. Mounting the engine is straightforward if you have an engine available. A couple of steel tubes topped by plates on either side will do the trick. Mounting the transmission will be a little problematic, and the details on this have yet to be worked out. It’s pretty essential to have the engine and gearbox on hand before welding the G-tubes and the center H-tubes. Electrical system Not looking forward to this. Although the electrical system in an early MGB is really simple by today’s standards, wiring is wiring, and you can’t see electricity. Unless the wiring harness from the donor car is in truly outstanding condition, we're likely to shell out $475 for a new one from Moss Motors. Locost batteries are normally mounted on the rear shelf of the engine bay, and there’s no reason not to do this. Putting the fuse box there also makes almost everything a little easier, except maybe changing fuses. One of the beauties of the MGB electrical system is that it’s practically digital. You either have voltage or you don’t. No measuring output currents or resistances. No threshold voltages. No relays. It’s 12 volts all around, or 14 in the charging system, which is 12 for all intents and purposes if you round down. A small light bulb with a pair of alligator clips tells you everything you need to know. Cooling system All standard MGB hardware, with the addition of a catch tank, which on an MGB was the ground. I don’t know if some kind of universal overflow tank will work the way it does in actual cars to keep the radiator full, but we’ll see. I don’t like the radiator mounts in the book. They just don’t look good. We’ll do something similar, just better looking. We were planning to mount the radiator straight up, but after looking up the dimensions of the standard Locost nose cone, I can see why it’s leaned backwards. It actually lays at about the same angle as the nose tubes. It would be nice to be able to add coolant without removing the nose cone, since adding coolant is a regular affair with an M.G. We could cut some kind of access hole like the oil filler on a Cessna, but I think we’ll wait. It’s something we could do some time after the car is built. Fuel system Not messing around with this, just buying a fuel cell from Summit Racing. Matching up the sender might be a problem, although I’ve seen instructions online for getting the 240 ohm M.G. gauge to work with a standard 90 ohm sender. But that’s more electrical stuff. Exhaust This could be fun or it could be a PITA. We're planning to start with an MGB manifold flange and build a 3-into-1 header from there. The only other known example of an MGB Locost kept the stock manifold and built a 2-into-1 downpipe that bolted on to the bottom of the manifold. Not only does this look weird, but the stock header is a cast iron unit that weighs a good 40 pounds. The reason the header is 3-into-1 and not 4-into-1 is that the MGB exhaust ports for cylinders 2 and 3 are siamesed into a single outlet in the middle. This is not considered to be a problem since cylinders 2 and 3 fire a full rotation apart, and so they use the port on a time-share basis. No attempt will be made to achieve any kind of optimal tuning with the custom header, but a rough attempt will be made to keep the tubes all about the same length. Body Three words: British Racing Green. The rest is inconsequential. We're not big fans of the bare aluminum look, and I like to paint, and we have all the gear for it. We’ll paint the car with the fenders off, attach the rears with black piping and the front with chrome-head bolts. But the car has to be green. Down the road we would look at some kind of yellow vinyl striping, you know, just to make the car stand out a little. We're planning to get the cowl (a.k.a. scuttle), nose cone, and windshield from Kinetic Vehicles in Oregon. The cowl and nose cone are both fiberglass. I expect the hood (a.k.a. bonnet) to be the main challenge to our bodyworking skills. After getting it to fit on all sides, a big opening needs to be cut in it for the MGB valve cover, which will stick up about an inch. Then some kind of bulge needs to be attached, to cover the hole. This will probably be made of fiberglass. We could try to make it out of aluminum if we had access to an English wheel. And we had any experience with an English wheel. Interior We’d like the driver’s seat to be adjustable, but I personally like the appearance of the Lotus-type bench seat. I'm hoping we'll be able to figure out a way to do both. The dashboard design is critically important, because after the coachwork, it’s the most distinctive feature of the car. My favorite dashboard layout was the one in my 1980 RX-7. It featured a large tach in the middle, and other gauges of little or no importance off to the side. If we could find a 2" Smith speedometer to match the MGB’s fuel, water, and oil pressure gauges, that would be perfect. I always liked the look of a long row of toggle switches. Flip on the fuel, gauges, coolant fan, ignition – then hit the starter button. That’s cool. Add to that switches for all the lights, and maybe a few more just for looks. Problem is, we now know toggle switches are deadly dangerous, and must be replaced with rocker switches. I think we’ll include a radio. Most Locosts don’t, and by "most" I mean all, because you can’t hear the thing anyway. But a car is a convenient location for a radio at those times when you’re just idling along in traffic, or wrenching on the car under a big shade tree. We don’t need anything fancy or hi-fidelity. If we can hear the ballgame we're good. |
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