Mikes guide to build a Derby Car to stock rules.
First and foremost you need a car.
How do you pick a car? If you think any old car will do, think again.
The best car to use is mostly a personal preference though. But most will agree 70’s cars (Old Iron) are your best bet, hands down.
Don’t get in a big hurry to buy a car. Start looking early in the season. When you find one, do your research before you buy. Some good places to find information on almost any car are wecrash.com and nwdemoderby.com. There are many other helpful sites. Just check out the Derby Forums tab.
How much you pay for your car really depends on how much your willing to spend. Some people spend $1000 or more. Not me though. Personally I have never spent more than $300 but I’m willing to spend $400.
Okay, so you took your time, did your research and found yourself a car. Now it's time to strip it. Remove all of the interior including the dashboard. When removing the dash be careful not to unplug vital wires. Your car won’t start when something’s are unplugged. It’s best to start the car after you unplug connectors or cut wires.
Remove all of the windows, lights, molding, pot metal, door handles, emblems, bumper covers and trim.
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After its stripped I like to get the fuel system and battery box out of the way before I weld up the doors.
Car with manual fuel pump: Disconnect and remove the original gas tank from the car. Inside the car, where the back seat used to be, mount a 5 gallon steel gas tank securely to the floorboard. (Use a steel boat gas tank, a Jeep can or go to M&M boys demo products and purchase one of theirs.) Depending on the car this will vary, but you will need about 20’ of 5/8” fuel line. Run two lines (one for the feed and one for the return) along the floorboard through a hole in the fire wall to the pump on the side of the engine block. Disconnect the original lines, determine which is the feed and which is the return and attach the new lines. Make sure all your fuel lines are securely fastened to sustain impact.
Car with submersed automatic fuel pump: On these cars the fuel pump is located inside the original gas tank. Some will bypass this by using an aftermarket fuel pump (high pressure if EFI). If you want to use the original fuel pump you will need to cut a hole in the top of the 5 gallon boat tank or Jeep can and get creative. M&M Boys Demo Products has a tank with a hole on top and an adapter plate for universal mounting (Highly recommended).After you have your tank situation figured out, mount it in the car where the back seat used to be. Depending on the car this will vary, but you will need about 20’ of 5/8” fuel line. Run two lines (one for the feed and one for the return) along the floorboard through a hole in the fire wall to the carburetor or injector. Determine which is the feed and which is the return and attach the new lines. Make sure all your fuel lines are securely fastened to sustain impact. (Toggle switch for aftermarket fuel pump must be within reach of Fire and Safety Crews)
Your car might have a fuel pump inertia switch which cuts off the fuel pump upon impact. This needs to be removed or bypassed.
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You can use an old steel tool box, or using 1/8” steel plate, bend yourself up a box that will house your battery or two batteries and mount it to the floorboard on the passenger side. (M&M Boys Demo Products also have a wide variety of battery boxes.) Remove your battery from the engine compartment and place it in the box. Trace the battery cables back to their origin. The positive cable will be connected to the back of your starter and the negative cable will be attached to the engine block. Reroute them through the firewall on the passenger side. The negative cable can be relocated if not attached to the back of the engine block. Extensions may be necessary. Now, reconnect the battery, through a piece of rubber over it and secure it.
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Alright, the cars all striped, your fuel systems complete and you’ve relocated the battery. Now you’re ready to start welding up the doors. Don’t know how to Weld? Well. You better find some one who can or you’ll have to Chain and go (not recommended).
There are several different techniques used for welding up the doors. I prefer to use 5/16” rod to fill the gaps between the doors. In my opinion, welding the window frames solid is unnecessary and a waist of wire. I use (3) ¼” plates 1-1/2” wide 4” long and weld them at the top of the door frame to the to the body in 3 locations. Believe it or not, but some people simply use duct tape. The rest of the door should be welded solid on the out side only.
Other good materials to use as filler are Rebar, the steel straps from the original gas tank, 1/4” plate 1-1/2 wide, all-thread 3/8-16, and for some of the closer fills, you can use nails, and scraps you pulled from your door mechanism.
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Now let’s go take care of those bumpers. If your bumper ends protrude past the side of your car or look like they may act as hooks cut them back or bend them in.
Most likely your car has factory 5mph bumpers. If not then this doesn’t pertain to you.
Starting in the early 70’s cars were equipped with these 5mph bumpers, which is basically your bumper attached to large shock absorbers. This next step is not required its just recommended. Remove the nut of the back of the shock. Your bumper should now slide off with the shocks attached. Cut off the push rod at the base (Note: if using a torch to cut with, the shocks are filled with oil. Be prepared for a fire). Now put the bumper back on the car. With the push rod cut off, the bumper should fit very close to the core support. Now weld the bumper to the brackets and the brackets to the car (solid). Do not weld the bumper directly to the car. Repeat the process to the other bumper.
Whether or not you do this, you should run two chains around your bumper through the body. This will keep the bumper from falling off and getting hung up under the car.
So, we’re done with the bumper, but while your there, measure from the bottom of the bumper to the ground. If you’re less than 18” you might want to get some height. Here are some ways you can raise your car.
You can stuff the shocks. This can only be done to the rear shocks. Jack up the back of the car getting the tires off the ground. Soak some old shop rags in water and stuff them in the upper part of the shock using a screw driver until it’s full. Pack them down by lowering and raising the car several times. Repeat if you’re not at your desired height. (Remember not to exceed 18”).
If your car has torsion bars crank them up. If it has springs you can pick up some spreaders or spacers at your local automotive store. If it’s got leaf springs you can re-hang the shackles by drilling and bolting through the frame. There are other ways to raise your car.
Since you’re already under the car stuffing your shocks, run chain around your axel to the frame on both sides.
Time to work on the trunk. Now, were going to chain it down but first I want to tuck it. Why you ask? Well it’s quite simple actually. There are two reasons that I know of. First of all during the derby the trunk lid tends to bend up and impair your vision. Tucking will keep the lid inside the trunk and allow the trunk to pack in a lot better. Again this is not a requirement it’s only a recommendation.
Remove the trunk lid measure from the trunks rain gutters to the floor of the trunk. This distance is where you will bend the lid. On the inside of the lid, measure from the end of the lid and draw a line from one side to the other. Then cut the bracing out about a 1-1/2” along your line. After that it should easily fold over. Now measure the width of the rain gutters. This is how much material you need to remove from both sides of the lid you just folded in. Some people cut out the rain gutter instead but in my opinion, I think that only compromises the structural integrity. Now you’re ready to put the lid back on and chain it down. Cut holes through the trunk and the floor for the chains. Piece of cake!
The Hood: You need to cut a 10” hole over your carburetor. This is to allow access to fire crew. You can chain or bolt the hood, either way it needs to be in four locations. Two along the side toward the front and the other two along the side toward the back. Personally I prefer bolts. I use ½”all-thread, drill through the hood and weld the all-thread to the fender wells and the core support.
If the front portion of the hood hangs over the front of the car you can bend it down the same way we tucked the trunk. This will act as a shield for your radiator. If the hood doesn’t hang over but you would like to bend it, you can remove the hood from the hinges and slide it forward, make your marks, flip it, cut it and bend it. (Not recommended if chaining)
Additional holes will be cut in the hood if diverting the exhaust.
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Exhaust system: Most commonly the exhaust is diverted through the hood. There are many ways of doing this and it varies per car. If this is what you want, your best bet would be to go to wecrash.com to find out how to make headers or find a place to buy them.
Diverting the exhaust through the hood not only looks cool but it diverts the heat away from the engine and transmission.
If you choose to leave the exhaust under the car, it is a must that you cut it back to a bare minimum of half its original length, to prevent it from getting pinched off and killing your engine.
Windshield braces: Two windshield braces are required for driver safety. When properly installed they will prevent a flying hood or tire from striking the driver. Measure from the top of the window frame to the bottom. Cut you material to that length and weld them in place. This is also allowed in the area of the former back window.
There is a lot of different material that can be used for window bracing, such as: ¼” flat stock, 1”x1” angle, 1” pipe / conduit, old leaf springs, ect…
Impact Cage: Get yourself some good steel. 2”x6”x1/4” Rec.tube, I-beams, or C-Channel. This is for your safety so don’t F-around!
Measure from the front of the front door to 12” behind the driver seat. Cut your material at that measurement twice. Weld to the doors inside the cab, at an angle so the front cross bar will clear the steering column and the back cross bar is 4” below the window frame. Measure the distance between the two side bars. That is the length to cut you cross bars. The rear cross bar cannot be more than 6” behind the seat.
A frame around your gas tank is permitted for protection as long as it is not attached to the car. The gas tank protection is to be welded to the rear cross bar.
Just about finished, but there’s still some things you need to consider. For instance; switches. You can run your car with just the key but if you drop your key out there or your ignition fails, you’re screwed. (Check out our Switch Box under the Products tab.)
If you go with switches, make sure you disengage the locking steering column. Some people do this simply by turning the key on and duct taping it in place. Personally I prefer to disassemble it entirely and throw away the key. But that’s just me.
Shifters: Column shifters are known for failing out in the arena. The linkage winds up just breaking apart.
It’s easy to make yourself a floor shifter. First determine where your linkage attaches to your transmission and detach it. Now cut a hole in the floor board directly above it. Get a piece of 3/8” rod, bend it to a preferred shape and length, and weld a loop at the end to be attached to the transmission. To attach, use a bolt with a nyloc nut and don’t tighten it down all the way or it won’t work. It needs to be able to pivot.
You’ll need to make a support bracket to hold it in place. From park shift to reverse. Now, place a clamp on the rod at the back of your bracket to block out park and your good to go. (You can see pictures and different examples at wecrash.com)
For non-Ford drivers, your distributor is very close to your firewall. You might want to consider cutting a hole in the firewall directly behind the distributor so if the nose starts going up, the distributor will have room.
Tires: If you use the stock passenger tires, they most likely won’t last long. Find yourself some good 700’s (7.00-15LT) Trailer tires. These are the best.
If you can’t find 700’s settle for LT275/75/R15. or LT235/75/R15 or similar.
Look for LT or ST series these are light truck and trailer tires and are 4 to 6 ply.
Good place to look is your local Pick and Pull wrecking yards.
Remember; you can only use mud and snow (M+S) tires on the non-driving axel.
If you wish to have more clearance for your tires you can cut away your fenders, up to 6” around your tire. I normally cut out the inner finder well directly behind the rear tires.
Do not use stock or custom aluminum alloy rims. They will most certainly break.
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Dimpling and notching the frame: This is done to assist in the upward motion of the trunk as it packs.
Notching: Cut a small v 1” to 2” on top of the frame between the rear bumper and the humps.
Dimpling: Apply heat using a torch to the top of the frame between the humps and rear bumper. When it is red hot, hit it with a heavy hitting hammer until you have a 1” to 2” dimple.
Locking the rear axel: Your car most likely has a limited slip differential. This type of rear end only turn’s one or the other wheel if one has less contact with the ground than the other.
Locking turns both wheels regardless. You can turn your limited slip to a locker by removing the back plate and welding the spider gears together. Do not attempt this unless you’re absolutely sure of what you doing.
So, you’re pretty much done at this point. All you got to do now is paint it. Be sure your numbers are large and legible. You can paint them on or use vinyl. Check out our Vinyl Lettering Packages under the Products tab.
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Alright, so good luck on your build, and feel free to e-mail your questions or concerns to firstname.lastname@example.org
Build That Derby Car!
Full Size or Compacts? This seems to be an ongoing argument amongst derby drivers.
Some Full Size drivers consider the Compacts to be just a half time show. They also assume that compacts are easier to build and are more of an entry level or elementary stage of Demolition Derby.
I must stand in defense for the Compact driver. I myself drive both, and think neither one to be the lesser. I can somewhat agree on the compacts being a good entry level stage, only because the car count is usually lower and the hits don’t ring your bell quite as much.
I started out in the compacts. My first car was an 87 Buick Sky Hawk. I didn’t know how to build a derby car. I just grabbed the rules and followed them one step at a time. There was no wecrash back then, I was on my own. It was a stock derby and the rules were the same for the Minis and the Full Size. Meaning the build would have been no different if I was to build a New Port instead. So I built the car with some help from Larry and Myles. Took it to the derby and took 1st out of 9 cars. There were 30 cars in the V8 class, so I probably would not have fared as well.
I love the V8’s. There’s nothing like the sound coming from 8 pipes out the hood. Taking and delivering hits, backed by the power of a V8, and the weight and mass of the old iron is surreal. But if you’re on a tight budget the minis are probably your best bet. My New Yorker cost me about $1100 when finished. The last car I built was a 1984 Volvo. Total dollars spent on car and build was $500. I built that car exactly the same as I would have built a Full Size. The comparison of building either one is the same to me. One is not easier than the other. In fact sometimes I find some Minis to be more of a challenge with all the computer BS and EFI.
The bottom line is we are all Demolition Derby Drivers regardless of what we choose to take out into the arena. Rather than devoting your time to prove one type is better than the other, why don’t you try focusing some of that energy on more important things? Like promoting the sport, increasing car counts by encouraging new blood, and getting out there and putting on a good show for the fans so they will come back for more. If you don’t fill the stands the promoters will find something else to promote. And if the driver count continues to drop more shows will get canceled. So, with that said, derby drivers of all types get into that arena and give em Hell.