|The MGA With An Attitude
AUTOCROSS PREPARATION-- PP-102
Yes this is about performance enhancement. One of the nice side effects of autocrossing is that it will help you become a better and safer driver, but the honest goal is to ultimately get your car to go from here to there a little faster. This involves both driver skill and vehicle preparation. The driving skills will come with seat time, but first you have to get your car on the course, so lets get on with the basic vehicle preparation stuff first. About face!
If you're just getting started, stay in Stock class for a while to get some practice, and learn all about rules and classifications. Get a copy of the rule book for whatever organization you want to run with, and be careful not to overstep the bounds of whatever class in which you choose to compete. Stock class allows any front sway bar, wheels of any material as long as you retain the original dimensions, and any DOT approved tire (has a minimal tread not slicks) including sticky road racing tires. You can do pretty much anything you want with air cleaner elements, even removing them, as long as you don't remove the housings. You can do anything you like with the exhaust system as long as it doesn't bust the sound meters, except you have to retain the original exhaust manifold. For cars 1975 or newer you would have to retain the catalytic converter, which pretty much renders an MGB non-competitive, so forget about running a rubber bumper MGB in Stock class. If your car originally had a points type distributor, you can use any points type distributor (Mallory dual points with no vacuum for instance). If your car originally had electronic ignition, then you can use any electronic ignition unit (but cannot revert to standard points).
The first requirement is to have safe car, meaning nothing loose in or on the car, the battery securely fastened down, nothing going to fall apart, good throttle return springs, no missing lug nuts, no more that one loose or missing spoke in wire wheels, working brakes and steering, and a seat belt. These are things that will be checked during tech inspection before your call will be allowed on the course. You will also be required to wear a safety helmet. There will likely be requirements for a particularly recent vintage of helmet, so check with the event sponsoring organization on these specs. Some loaner helmets may be available, but you would be well advised to buy your own helmet if you intend to continue this activity beyond the first few events. You will most likely be required to have a valid driver's license from your state of residence, and maybe also show proof of auto liability insurance as required by your state of residence. In some cases you may also be required to have proof of medical insurance and/or to be a registered member of a particular competition organization that provides some minimum level of insurance.
You can have any steering wheel within 1" of the original diameter. You can use any valving in the original shock absorbers, any brake lining material, any brake fluid, any type of oil in the drive train, any pump grade gasoline (not racing fuel). Nitrous Oxide injection or any form of pressurized air intake is not allowed in Stock class. You can have all the "fuzzy dice" you like. That means pretty much any accessory device that does not materially affect the performance of the car. This includes a G-meter, but not telemetry. You have to run a full body assembly and full interior as stock. You can remove the spare tire, and anything else on the car that was originally intended to be easy lift out. If your model of MG had the factory option of the "erectable" top, then you can lift that off and leave it at the curb as well. If the heater was listed as an extra cost option, or the car could be purchased new without a heater, you could remove the entire heater assembly and leave it home. You can always remove air conditioning parts unless they were standard equipment on every car produced. You can also run with just a few gallons of fuel in the tank, so you drop about 50 pounds just by not filling the tank on race day.
You can make any adjustments within the range of the original factory equipment. So you can adjust tire pressure and toe-in to your heart's desire, but you can't change caster or camber (it's not adjustable). You can install a trailer hitch, as long as it serves no other purpose (like chassis stiffening or intentional weight redistribution). You can have quite an assortment of safety features in Stock class. You can install a roll bar or even a full roll cage, as long as it's bolted in and not welded to the chassis (even if it does incidentally do a lot of chassis stiffening). You could have an on-board multi-point fire extinguisher system, or any type of battery cut-off switch. If your car was not equipped with shoulder harness from the factory (prior to 1968), then you would not be allowed to use shoulder harness unless you install a roll bar. If you install a roll bar (not required but recommended) you can use any seat belts you like, even 5 or 6 point safety harness. Otherwise, if it isn't specifically mentioned in the rule book, it has to remain stock, as delivered from the factory. I'm still waiting for someone to protest my large walnut shift knob as being a "performance accessory" (and they could be right, as that was my intention).
Exceptions to the rules: If your car originally had two batteries, technically you have to retain two batteries for Stock or Street prepared class, as switching to a single battery can be considered weight reduction or weight redistribution, which is a Prepared class option. However, considering the vintage of the car, most local clubs will allow the single battery in Stock class, as the original twin 6's are pure crap and the new 12's are cheap, and you drive it on the street daily. As with the battery change, with a local club you may well be allowed to use urethane bushings or the MGB GT V8 bushings in the lower a-arms. The original soft rubber bushings are so bad that they deteriorate to nothing in a couple of seasons, so you have a good argument to say that upgraded bushings are a legitimate period accessory as commonly installed by the dealer, even though it was not a factory option. Or just don't bother to mention it, and probably no one will ever notice. For the most part nobody cares about such minor things, until you start regularly spanking everyone at the events, and then your direct class competitors might start looking a little closer. When someone finally files a protest (if ever), then you can decide if you want to revert to pure stock or graduate into the next class. It's real easy to get booted out of Stock class. A lousy Weber downdraft carburetor or wide wheels will do it.
One of the first performance parts you will likely want to add to your car (or change) may be a large front anti-sway bar (commonly referred to as "swaybar"). SCCA (and a lot of other competition organizations) will call it "free". This means they will allow the use of any front anti-sway bar in Stock class, and with good reason. Here you are about to get a very basic lesson in vehicle dynamics.
<DYNAMICS-101> Nearly every street use production automobile ever produced has built in understeer (commonly referred to as "push" in the steering). This means that if you enter a corner too fast the front tires will lose grip with the pavement before the rear tires will, and the car will drift to the outside of the curve. The natural tendency then for a driver is to lift off the throttle and maybe apply the brakes (hopefully without locking up the wheels). The resulting deceleration will transfer some weight forward to load the front wheels more and to unload the rear wheels a bit. With this weight transfer, the front tires will grip a little better and the rear tires will grip a little less. This combined with a decreasing speed will allow the front end to hook up and pull into the turn so you don't run off the road. This is all quite natural for the driver, and a safe way to build street going cars. Unfortunately this is not the fastest way to get around a corner.
The flip side of this equation is called oversteer. In that case when you enter a corner too fast the rear tires will let loose before the front tires, and the tail end of the car will start to drift out. In mild cases, initially this may come to a point of equilibrium where the tail hangs out a little farther than the front end, and you find yourself steering slightly to opposite lock to keep the front tires pointed in the right direction down the road. This is often accompanied by some tire squealing with a bit of side slip as the tires dissipate some energy in the form of heat, and the car slows down a bit to a safer and more stable speed. That's the optimistic view. But if you're going too fast, or in the middle of this maneuver you suddenly lift your foot off of the throttle and maybe take a quick stab at the brakes (as is the natural human tendency), then the resulting forward weight transfer from deceleration will increase the oversteer condition, and the tail may let loose and fly while the front end continues down the normal intended path. The end result then is to find yourself traveling backwards or doing a complete uncontrolled loop, also definitely not the fastest way around a corner, and of course not very safe either.
For a road racing car wanting the fastest way around a corner you would like the steering to be very nearly neutral, having neither understeer nor oversteer. This allows the front and rear tires to develop maximum lateral grip at the same time, and you can go merrily around the corner at maximum speed. For an autocross car the speeds are somewhat slower and the transitions from straight line travel to tight turns can happen a lot quicker. In this case you might actually want a bit of oversteer to help with initial turn-in at the entrance to a turn. </DYNAMICS-101>
The point is that standard production type understeer is not a desirable trait for a competition car, so you would like to have some "legal" means to adjust this particular handling characteristic. This is why the addition or change of the front swaybar is allowed in Stock class. It is one of the most effective ways of changing the steering characteristics. Just how and why this works is left for another tech session, but for now it is sufficient to say that adding or increasing the diameter of the front swaybar (up to a point) will improve the steering response, give the front tires a better grip, and allow your car to go around a corner a little faster. In the process of getting the hang of how this works and learning to tune it properly to take best advantage of it, you will also have to train yourself to drive accordingly and not do something stupid or impulsive that would cause an accident.
Then you drive. And you drive some more, .... and you drive some more. With increasing seat time you should naturally gain speed and reduce lap time. Treat this endeavor like school, as you have to learn things. Keep your eyes and ears open, pay attention to business, and apply the things you learn as you acquire new skills and knowledge. In any class with Solo-II you should quickly realize that there is some advantage to having a small car. Other things being equal, a narrow car will go through a slalom quicker, so MGs in particular can be competitive and a lot of fun to run in Stock class. If you think it might be nice to actually win sometimes, then driver skill and finesse is paramount, and there is no substitute for seat time. Given the very specific class that your car runs in, this is not a horsepower race. You should expect to place near last for the first several events you enter. The skill and speed come more naturally with practice (and study so pay attention). Maybe about the time you wear out your first set of street tires you'll be ready for a new set of those sticky racing tires. But be aware that other organizations may have different rules for tires, some assigning "points", or some maybe not allowing race tires in Stock class. Pay attention to the folks who are winning in their class, especially the folks who are winning in YOUR class. Stay close by, ask questions, make a (mild) nuisance of yourself. Take a winner to lunch and pick up the tab, keep the conversation on the right subject, and keep your ears and mind open. A LBC can be quite competitive in Stock class once the driver has enough experience. There are very few "secrets" to this sport, but there is a lot to learn.
If you like bolt on performance parts, you may like to try Street Prepared class with SCCA. This allows nearly anything that can be bolted on without cutting or welding and without removing the cylinder head (no hot cam). Any intake and carbs, any exhaust headers and pipes (even toss the catalytic converter), and any suspension height change, negative camber a-arms, any springs, sway bars, transverse links that can be bolted on. In theory you could even install a rear subframe with independent rear suspension, as long as it attaches to the original leaf spring mounting points. Also any size wheels and DOT approved tires (anything with a tread pattern, not slicks), as long as they don't bump or rub anywhere (includes road racing tires), but you cannot flare the fenders. Ventilated disk brakes with 4-piston calipers and carbon pads are popular. Posi-traction and gear ratio changes are allowed. Pressurized air induction is not allowed. Updating or backdating of engines is allowed as a complete unit, so here you could install a 1961 spec 1622-MK-II engine in your MGA 1500, or you could install a complete 1967 spec MGB engine (with no emissions equipment) in your 1976 MGB (but not in an MGA). A roll bar is not required, but highly recommended. You will not be allowed to use a shoulder harness (except stock style) in an open car unless you install a roll bar first.
Be aware that Street Prepared class has to run about 3-1/2 seconds faster in a 60 second lap to be competitive. That puts your 4-cylinder LBC right up there with a factory stock Porsche 911 (at least an early one), or a stock late model Mazda Miata, but it ain't easy. You can do a lot with wider wheels, suspension and brakes, but you will find you car wanting for another 50 horsepower or so, and that's not easy to get with just intake and exhaust changes. This stuff may sound appealing, but if you want to be competitive in this class you will have to spend some money. If you just install exhaust headers and get stuck in this class without the benefit of other allowed equipment, you probably lose.
The next step up is Prepared class, where the prep rules are very similar to vintage racing. You can do almost any internal engine modification with the original block and head (including a hot cam and pistons). Nearly any intake and exhaust is allowed except that you have to use the original carburetor bodies (I think) and may be restricted on the maximum size of valves. Nearly any suspension mods are allowed including fabricating custom parts. Lightening is allowed, so strip out the interior and all the lights and glass (except the windshield which can be shortened), ditch the bumpers, and lose a few hundred pounds of dead weight. A racing seat, slick tires and flared plastic fenders are also allowed, but by this time the car is definitely not street legal, so figure in the cost of a trailer and tow vehicle, and the cost of another more stock LBC to drive on the street. This class requires a roll bar, and you will need to cut another 2-1/2 seconds off the lap time to earn the trophy. If you haven't had a close look at a vintage racer, make a point to go see one. This is not something you would want to do to a daily driver. The first caution about the rules applies here. If you just install a warm cam you're in Prepared class, and instantly non-competitive.
And if you're still crazier than all this, you can try Modified class and really cook your checkbook. Here anything goes, including engine transplants. Heck, you can even build any kind of car of your own choosing completely from scratch. The only determining factors for your racing class are engine displacement and gross weight. Take off another 4 to 6 seconds, depending on the class you end up in, and find a new insurance agent. Pressurized induction just kicks it up a class similar to having a larger displacement engine. Open wheels and wings of any size are allowed. Sanity is optional.
If you're serious about any of this, give a hoot and maybe we'll do lunch. I did mention obscene amounts of fun on the opening page.
1958 MGA with an attitude