An M.G. Locost Build

Our Locost
Last updated February 16, 2014

(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 youíre a product of the seventies and a sports car nut, youíve 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 todayís standards they were a simple, no-frills sports car. They mightíve been slightly underpowered, but take away 1000 pounds and suddenly youíve got a very fast car.

Weíve 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 shouldnít be a lot of details to work out, but the book isnít entirely clear on everything, and weíll also be incorporating a few changes for an MGB donor. Weíve 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. Weíll also be adding a roll bar, one thatís 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. Itís 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 inchócritical for fitting the MGB gearboxóand 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 wonít 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 canít figure out which ones.

Front Suspension

The MGB suspension is based on a design that originated before the big WWII. So itís tried and true. It does have a few shortcomings, though. Itís rather heavy for unsprung bits, and because it doesnít use any ball joints, it doesnít 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.

Weíd 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 weíll 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 isnít 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 í67. Stock heads can be ported and polished for an additional 10-15 hp. Weíd 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 itís 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 driverís footwell, which was of course the passengerís footwell in the original configuration. Thereís also an overdrive gearbox, but itís 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. Itís 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 todayís standards, wiring is wiring, and you canít 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 thereís 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 itís practically digital. You either have voltage or you donít. No measuring output currents or resistances. No threshold voltages. No relays. Itís 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 donít know if some kind of universal overflow tank will work the way it does in actual cars to keep the radiator full, but weíll see.

I donít like the radiator mounts in the book. They just donít look good. Weíll 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 itís 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 weíll wait. Itís 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 Iíve seen instructions online for getting the 240 ohm M.G. gauge to work with a standard 90 ohm sender. But thatís 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. Weíll 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

Weíd like the driverís 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, itís 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 MGBís 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 Ė then hit the starter button. Thatís 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 weíll include a radio. Most Locosts donít, and by "most" I mean all, because you canít hear the thing anyway. But a car is a convenient location for a radio at those times when youíre just idling along in traffic, or wrenching on the car under a big shade tree. We donít need anything fancy or hi-fidelity. If we can hear the ballgame we're good.

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