Datsun 510 Rally Beater: Part 2

In the introduction to "Project Rally Madness" in the March issue, we did something a little unusual. We suggested you not follow our lead.

Don't take that the wrong way, though. We didn't tell you not to try rallying, which is turning out to be the most fun you can have on wheels, we warned you not to build your first rally car yourself. All the personal blood, sweat and tears that go into building a car tend to make you drive a little too conservatively. Besides, functional used rally cars can be had for only a few thousand dollars--usually less than it costs to do it yourself.

The next bit of advice we gave was not to use the car we were using (a 1971 Datsun 510) because it's too old, too rare and increasingly too difficult to find parts for. Instead, we suggested the far more common and therefore far more disposable Toyota Corolla GT-S or first-generation Mazda RX-7.

Of course, just like everybody else, we're ignoring our advice. The car was already there, many critical parts (like the drivetrain) were taking up space in the garage, and because we vowed to keep the car a beater, we felt pretty confident we could keep the price down and the emotional connection low.

Sure.

In the last installment, we pulled the drivetrain out from under the workbench, plopped it into the car, and managed to pump it from 77 to a still-laughable 95 hp at the wheels.

Given our modest goals, that's plenty of power for now. Far more important is putting together a suspension system that can handle on the rough, bumpy terrain of a rally.

A good rally suspension is a very different animal from a good street or track suspension. First, and most obviously, it needs to provide enough ground clearance to tiptoe over all the rocks, ruts and broken rally car pieces you might encounter. How high that is depends on where you're going to race. East Coast rallies tend to be relatively smooth, consisting mostly of well-graded gravel roads. You still need enough ride height to soak up jumps and drive out of ditches, but it's not uncommon to see East Coast rally cars at stock ride height or even slightly lower. If you are planning on racing in the Southwest, however, you can expect to race on roads made up of grapefruit-sized rocks and lined with ones the size of watermelons.

Fear of these big rocks may tempt you to jack the suspension to monster truck heights. This isn't a good idea either. Besides raising the center of gravity, which hinders handling and increases the odds of a rollover, raising a rally car too far can leave it with too little droop travel. The suspension should have enough droop to keep from topping out the suspension on minor whoop-de-doos, and should be articulated enough to keep all four wheels in contact with the ground when the road is uneven.

Keeping the suspension well articulated means avoiding large anti-roll bars when at all possible. If you can get away with using just the stock anti-roll bars (or bar, in our case) that will also save a few dollars.

Bushings
Another issue to think about is compliance. While we normally seek to eliminate uneccesary compliance in street and road race suspensions, driving in the dirt is a different world. The handling precision we seek with polyurethane bushings, heim joints and other compliance-killing road racing tricks simply isn't possible when your tires are sliding across a surface of dirt, rocks, tree limbs and all of nature's glory. Far more important than geometrical precision is isolating the suspension and the chassis from unnecessary shock and premature wear. While this is seldom an issue on the street, no matter what kind of beater you're working on, it wasn't designed for the kind of abuse a rally will give it. Preserving the mechanical integrity of the suspension mounting points is worth a slight loss of precision, in our eyes.

It was for this reason, as well as our fundamental cheapness, that we decided to stick with the stock rubber bushings in most of the suspension. The one exception is the front (and only) anti-roll bar bushings, which we replaced with Energy Suspension bushings (part number 9.95122 and 9.8105 if you are looking for them). The anti-roll bar is not in a position to transmit shock to the chassis, so we can take advantage of polyurethane's superior durability there.

Springs
Finding springs stiff enough and tall enough for rallying can be a challenge if you are planning to compete in a production class that requires stock spring perches. Since the bigger-than-stock engine (1.8 liters, vs. 1.6) and non-stock carburetion (dual Hitatchi SUs from the Japan-only SSS 510) have already forced us to run in an open class, we are allowed to use coilovers, opening up a world of possible spring rates from Eibach's race spring catalog. We cut the stock spring perch off and installed a Ground Control threaded collar over our strut tube. Ground Control's threads are quite coarse, offering added strength and making them easier to clean. The perch can be clamped on the collar to lock it in place. This method also effectively seals the threads when clamped, and allows the threads to be extra loose when making adjustments--a real benefit when they're dirty.

OK, so coilovers allow you to run any spring rate you want, but where do you start? In general, you want something significantly stiffer than the stock spring, but softer than a road race spring. Of course, the quickest, easiest and often most effective way to determine the right spring rates is to find someone with the same car who is doing really well and ask them what they use. Despite the fact you will soon be their competition, we have found that most rallyists are surprisingly friendly and open about how their cars are put together. In our case, we simply called Nissan Motorsports and asked them what they used in the 510s that won the East African Safari rally 30 years ago. To our amazement and theirs, they were able to find all the specs on those springs.

The 510's stock front springs are a marshmallowy 85 lb/in, while the Safari springs were 150 lb/in. in the rear, a motion ratio of greater than 2:1 means spring rates must be much higher: Stock springs are about 320 lb/in, while the Safari springs are an incredible 519 lb/in.

Since the front perch is adjustable, the free height of the spring isn't critical; our only concern was that the spring have as much travel as the strut. With the strut out of the car, we had measured an amazing 8 inches between full extension and full compression, so the difference between the free height and the point at which the coils bind had to be at least as long. Luckily, Eibach's race spring catalog lists critical information like free height and compressed height on all its race springs. We ended up with a 12-inch front spring.

The 510's rear spring sits in the middle of the rear semi-trailing arm, completely separate from the shock absorber (which is mounted at the end of the arm). This makes using a race spring more complicated, since it isn't designed to accommodate race-style flat spring perches. The rear suspension can be converted to coilover, and the spring mounted on the shock, but this complicates the procedure, since the shock mounts must be reinforced to support the car, and the spring rate must be different to account for the shock's lower motion ratio. After much head scratching, Johnathan Spiegel from the Progress Group came up with the bit of inspiration that only later seemed an obvious answer. Cut a race spring.

The stock 510 rear spring is wound flat on top, but has an open coil on the bottom. We could duplicate this by cutting the flat coil off one end of an Eibach race spring. Since the Safari spring was 11.2 inches, 3-inches in diameter, and 519 lb/in, we took a 12-inch, 3-inch diameter, 500 lb/in Eibach race spring and cut it to the same height.

Cutting coils off a spring, of course, increases the spring rate, so we did a little math to see what we had done. The formula to determine the spring rate of a coil spring is:

This requires a lot more information than we wanted to dig up, but since we wanted to compare our 500 lb/in spring before and after cutting, we can make things a little easier. We know the wire diameter, the elastic shear modulus of the material, and the overall diameter of the spring are not going to change, so we can group them all together and call them Jim. This gives us a much simpler formula:

Since we knew the spring rate was 500 lb/in before we cut it, and we counted 7.75 active coils (the coils ground flat at both ends don't actually bend when the spring is compressed, so they are not active), we did a little algebra and learned that Jim = 3,875. After cutting, we had what looked like seven coils, but the bottom spring seat on the 510 is tapered to match the open coil, so the first few inches of wire is stationary on the spring perch and won't be active. Installed, it looked more like 6.8 coils. Jim (3,875) divided by 6.8 coils gives us 570 lb/in., which overshoots our 519 lb/in target by a little bit, but not enough to worry about. Compared with the alternative of custom winding springs, being 50 lb/in too stiff is nothing.

Dampers
Shocks, to a rally car, are more critical than springs, bushings, ride height or any other suspension component short of the tires themselves. It is the shocks that must take the constant pounding of rocks, ruts and bumps, and turn them into a smooth, fluid motion. The shocks must take that ill-advised 2-foot jump at 70 mph next to a cliff, absorb the impact and give you the control you need to come out looking like a hero. It's no surprise, then, that you will need shocks designed specifically for rallying.

Good luck.

In our case, 510 rally shocks haven't been made for more than a decade. If you are faced with a similar dilemma, look for a car of similar weight and layout that does have rally shocks. If, like us, you have struts on at least one end of the car, plan on using a strut insert; a complete replacement strut from another car probably won't fit, but inserts are fairly universal. On the rear, our car uses fairly conventional shock absorber shape that can cross over (physically, at least) to a lot of other cars.

Again, asking around is the best way to find out what kind of shock will work for your beater. We were getting close to figuring out how to make a Toyota rally shock fit our car when we stumbled across a lost set of Tokico Prodra G rally shocks for the 510. Once upon a time, Tokico was a big name in rally circles and it made some damn good rally shocks. The Prodra line was discontinued years ago, and there are none left, so it was quite a surprise when we stumbled upon this set. Until we wear them out, our shock needs are taken care of.

Skidplate
Like it or not, a skidplate will inevitably be part of your suspension. Racing over rocks means countless opportunities to ram a rock through your oil pan, into your crank pulley, or through your gas tank. If you don't protect the bottom of your car, odds are you will break something. More than just durability, though, a good skidplate will actually make you faster, as you can pound over rocky terrain with one less worry to slow you down. How complex your skidplate needs to be depends on your car, but for the 510, it was remarkably easy. We wanted our skidplate to wrap all around the front of the car to prevent it from snagging on the ground if we nosed in off a jump. (We've seen this happen more than once.) Looking around for easy mounting points, we found that there were three bolt holes in the bottom of the front crossmemeber and two in the front of the bumper (for the license plate) that looked like they could take the load. Mocking up the skidplate out of cardboard allowed us to determine the simplest shape that would fit and protect the engine compartment adequately. We found a sheet of 1/4-inch thick 2024 aluminum at the local metal supply shop for $50, and with some help from our friends at the Progress group, we put the two necessary bends in it to make a perfect skidplate. 2024 aluminum is very soft, so it bends easily. Unfortunately, a soft material will also bend more easily on the rocks. 5052 is also a good choice if your bending brake is not super strong. 6061 is probably the most common alloy, and one of the strongest for this application, but bending 6061 is tricky and it can sometimes crack if asked to bend too far.

Wheels and Tires
Rallying is no different than any other form of motorsports when it comes to tires. As with all things automotive, the tires are the most important part of the handling equation. Everybody knows this, but if you can persuade yourself to forget this fact, you can save a lot of money. You see, those with big budgets and the desire to win will get rid of their rally tires when they still have about half their normal tread. That's where cheapskates like us come in. Where a new, 14-inch Michelin rally tire costs around $130 and a 14-inch Silverstone rally tire costs around $110, used 14-inch tires trade hands for $20 to $40 depending on wear and how many holes are in the sidewall.

Holes in the sidewall? You bet! Just because your wheel and tire are designed to be tubeless doesn't mean you can't put an innertube in there. We managed to get several good tires with sidewall punctures and revive them with tubes. This is something you can only do with rally tires, as they are built so tough that a little hole here or there does little to their overall integrity (other than that little air holding bit). Don't even think about putting tubes in a street or road race tire! Finding a tire shop that has innertubes and knows how to install them can be difficult, but we found that used tire dealers are typically the most cavalier about doing things that other tire shops might be afraid to do.

For our tire supply needs, we buddied up to Jay Streets, a Northern California rallyist who is so serious about rallying that he casts off enough half-shredded Silverstones to keep our 510 well treaded for a season. (He is also serious enough that were it not for a big crash late in the season, he may well have taken his Corolla GT-S to a Group 2 national championship in his first year of rallying.)

Wheels have the potential to be a huge expense as well, since you will need all your tires mounted and ready to go if you plan to change any during a rally. If you only run relatively short rallies, six wheels might be enough, but if you are really serious, 10 wheels and tires might be a wise investment. That gives you two full sets (so you can separate your used tires into evenly worn sets) and two spares. This is where the junkyard comes in handy. For the Corolla GT-S, Streets has found the seven-spoke, 14 x 6-inch Mitsubishi Starion wheels are virtually indestructable. For a Mazda RX-7, unfortunately, there is little in the junknyard that will fit, except for stock Mazda wheels. For our purposes, we found the hideously unattractive (and therefore strangely appealing) four-spoke 280ZX wheels fit perfectly, are abundant, and, despite our best efforts, seem impossible to bend. Along the way to this discovery, we did try a six-spoke 280ZX wheel from a similar vintage car that looked much better, but found them to be far too delicate. Their two-piece construction results in a weak, unsupported rim and after about an hour of pounding around in the dirt, each wheel was bent in at least three places.

If you are experimenting with junkyard wheels, be sure to try them on the front and back of your car. We have found many wheels that fit the rear of the 510, but few that fit over the large 280ZX spindle that we installed when upgrading to 280ZX brakes (more on that in the next installment).

Safety Equipment
Safety equipment is boring. Things that make your car faster and things that make it handle better are always more fun than things that make you survive a crash better.

Until you have a moment.

My moment came during an early test drive on our local network of powerline maintenance roads. All it took was one early apex and one properly shaped dirt bank and my priorities shifted instantly. One moment it was all about timing, speed, drit and glory, the next moment it was all about keeping the vinyl top off the ground. A slightly early turn-in resulted in the inside wheels climbing a bank, catapulting the car onto two wheels. Putting the wheels back on the ground required steering toward a sheer cliff. I stopped about a foot short of the cliff, but post-incident inspection of the tire marks revealed we had traveled about 20 feet on two wheels. And that, boys and girls, is why you want a roll cage as soon as you think your car might become a rally car.

The transition from yard art to play car to rally car actually took about eight months, so our cage did not go together in the most efficient or effective manner. In the waning weeks of the play car stage, we contacted Autopower and were pleased to learn that it still offered cages for the 510. Since we were trying to work on the cheap, we ordered up a bolt-in, six-point cage so we wouldn't have to pay to have it welded together. Autopower's bolt-in cage consists of a four-point rear hoop, two extensions that follow the top of the window line and the A-pillar before dropping to the floor just in front of the dash, two door intrusion bars and a bar across the top of the windshield. The rear hoop has attachment points for shoulder harnesses for both driver and navigator.

The different parts of the cage butted against each other and connected with a sleeve that, in turn, is held in with bolts that pass through each bar. These bolt holes are not pre-drilled, allowing you the installation flexibility needed to make the cage fit properly. Drilling these holes is a surprising amount of work, however. After drilling all 64 holes through the cage's .120-inch thick mild steel, plus 20 holes through the car, we have this advice to give: Buy the most expensive drill bit you can find. After drilling about 20 holes with a cheap Russian drill bit, we finally bought a $12 titanium drill bit that could do the same job in one third the time. It is also wise to use some WD-40 (or actual cutting oil if you can find it) to cool the bit while you are drilling. In the end, the cage fit very well and all the drilling took about one full day.

While bolt-in cages are legal, a belated look at the SCCA rulebook revealed that corner gussets had to be welded to a few locations on the cage. So, while we had managed to avoid going to the welder so far, some welding is inevitable. While having the gussets installed at a local rally shop, we also had the cage mounting points welded to the car, making our bolt-in a weld-in after all. After all this welding, it seems to make more sense to start with Autopower's weld-in cage. This will ultimately make a stronger, safer cage and would trade off your hard work with a drill for a welder's hard work with fire.

While at Autopower, we also picked up a set of five-point harnesses. Autopower offers both cam-lock and latch-and-link style harnesses, but with a rally car, cam-lock is really the only option. Latch-and-link harnesses are cumbersome to put on, and with on-the-clock tire changes a fairly common occurance, you have to be able to put the harnesses on in a hurry. When mounting racing harnesses, the mounting points must be chosen wisely to ensure proper function of the belts. The lap belt is easily attached to the stock mounting points, but the shoulder harnesses need to be mounted to the roll cage directly behind the driver and navigator seats. The SCCA is very specific about how the harness is routed, so check the rulebook (or the photo here) before mounting your harnesses.

Now that we have a roll cage, we need a helmet! Crashing in a roll-cage equipped car without a helmet is often more dangerous than not having the cage in the first place. Simple fact: roll cages are harder than your head. In addition to adding roll bar padding to any part of the cage that our heads, shoulders or hands might hit, its now time to get the right safety gear on the occupants of our beater rally car. As usual, we turned to Racer Wholesale for reasonably priced safety gear. Full face helmets are not required, and novice navigators often find open face helmets more convenient in the event of unexpected gastronomic reversal (it happens).

On the other hand, if you like your face and want to keep it, a full face helmet is a must. Be wary of motorcycle helmets; they are not legal for competition use in a rally car! Inside the helmet there should be a Snell certification starting with either M (motorcycle) or SA (special application). Motorcycle helmets are typically designed to dissipate a single impact, while SA helmets can take the repeated hits common in a rally-style mutiple roll. The G-Force GF950 helmet is SA2000 rated (the number indicates the year of the specification--SCCA currently requires SA90 or newer) and has a removable, washable liner. This is important not only for the sake of cleanliness, but to make installing the microphone and speakers for your intercom much easier.

You will also need at least a two-layer Nomex(R) driving suit and you will probably want Nomex(R) gloves and shoes as well. The SCCA requires a suit rated SFI3.2A/1 or higher, and requires flame-resistant underwear if the suit is not at least three layers thick and rated SFI3.2A/5 or higher. A custom-fit driving suit is always the way to go, but if you're building a beater rally car, you probably can't afford one. If you need the cash for the car, the off-the-shelf G-Force GF525 that we used meets the SFI3.2A/5 rating, allowing you to forgo the extra layer of underwear on hotter events, and costs about $325. Racer Wholesale is known to have sales where the suits get as low as $199, so check the Web site often. Off the shelf driving suits, naturally, are built for people of average proportions. Although six sizes are available, as a tall, skinny, white guy, my suit is still pretty baggy. Consolation can be found in the service area where all the rallyists in 10-year-old suits look like their clothes were painted on. With room to grow, I'll be looking good in 10 years!

With the helmet, driving suit, shoes and gloves, personal safety gear from Racer Wholesale adds up to about $660--and a little bit more if you race where it's cool enough to survive with another layer of Nomex(R) underwear.

Next Time
It seems like we should be done. We have an engine, suspension, tires and safety equipment, and we have been pounding on the car fairly regularly. The roll cage has made a huge improvement in chassis rigidity, which is something you really notice on rocky roads. The suspension absorbs even the most ill-advised jumps with ease, and the safety equipment makes us feel like real rally drivers. So what's left?

We still have laughably small brakes, no lights, questionable wiring, no rally computer, no intercoms and probably about a thousand other little things we have forgotten to deal with. Next time, we'll see if we can't actually get to a real rally.

To remove the stock spring perch, we carefully cut away the weld with an air powered cutoff wheel. You must be careful here to avoid cutting into the strut tube itself.	After grinding away the old weld material, we slid the Ground Control threaded collar into place to establish the right location for the collar's seating ring. Then we had to find someone with a welder...	Finding a spring with an open coil on one end, 11.2 inches of free length, and 519 lb/in spring rate proved too difficult, so we made our own from an Eibach Race Spring and a cutoff wheel.
Fully assembled, the coilover assembly looked way too high tech for our beater. Luckily, a little bit of dirt goes a long way toward making things look right again. For bump stops, we removed the stock, 30-year-old rubber snubbers and replaced them with modern bump stops pilfered from the junk pile at the Progress Group.	Like it or not, a skidplate eventually becomes part of your suspension. We bent up this simple skidplate from $50 worth of 2024 aluminum plate. It helps to know someone with a bending brake.	For wheels, we used 280ZX wheels from the junkyard. They are only $20 each, and are virtually indestructable. Tires are used Silverstone rally tires bought from someone far more intent on victory than we are. Price: $20 to $40 each, depending on the number of punctures.
After the first "moment" a bolt-in Autopower roll cage did much to ease nerves and to improve chassis rigidity. As you can see here, the cage is held together with sleeves that are bolted to the main structural tubes. To ensure a proper fit in the car, the holes are not pre-drilled, so be prepared to spend some quality time making holes. Our advice: get the most expensive drill bit you can find.	Once we decided to actually compete with our rally car, we had to make the cage legal. That meant adding some strengthening gussets in certain parts of the cage, and, for our own peace of mind, welding the cage to the car. As you can see, the footprint of the cage is rather small, so a good roll could push the cage through the floor. To prevent this, the cage was welded to the rocker panel as well.	The harnesses are from Autopower. In rallying, you often have to put on your harnesses while on the clock, so the cam lock system that allows you to latch one belt at a time is a big advantage.