The signs of spring are unmistakable: flowers are blooming, basketballs are bouncing in the playoffs, and race car exhausts are booming. Racers are shaking off their winter doldrums, and race cars are coming out of hibernation in unheated garages and shops. But before you rev up for the new season, it’s essential to clean the cobwebs out of both your brain cells and your race car.
Racers have a tendency to focus on high-tech equipment, but this is the time of year to pay attention to the basics. Even the most sophisticated computers operate on a very simple binary system: they reduce the universe to ones and zeroes, to “Off” and “On.” A computer can tell you the driveshaft rpm at every millisecond during a run, but it can’t tell you why your engine is popping and banging at the top of low gear. That’s something you’re going to have to figure out using your analog human brain.
Race cars are like athletes: they lose their edge when they’re inactive. They get rusty, both literally and figuratively. There is an example sitting just outside my office door. When Bruce Allen and I parked our Reher-Morrison Pro Stock Firebird at the end of last season, it had just qualified in the No. 1 spot in Houston and advanced to the semi-final round in Pomona. Ten weeks later at a test session in Tucson, the car would hardly go down the track!
We poured fresh gas in the fuel cell and then watched it leak out through a seal in the fuel pump that had hardened over the winter. When we tried to make a pass, the engine misfired like an old lawn mower. It took a full day’s work just to get back to where we were when we unloaded the car last November.
When an engine isn’t running right, I go back to the old “Combustion Triangle” we studied in auto shop. The three sides of the triangle are air, fuel, and spark – and you need all three to support combustion. If the engine won’t run, it’s up to you to figure out which element is missing.
Air supply is straightforward in a race car. Unless the hood scoop configuration is really awful or the isolator plate is missing, it’s relatively easy to give an engine all of the oxygen it needs. (You did remember to take the plug out of the hood scoop opening, didn’t you?)
The vast majority of engine problems are caused by the fuel and ignition systems. These troubles can be difficult to diagnose because the causes are seldom obvious. For example, the fuel pump may produce adequate pressure and volume, but a fuel line can have a “flapper” – a loose piece of lining or a deteriorated hose – that shuts off the flow of gasoline intermittently. A fitting may have been installed improperly, creating a restriction in the line. The hose on the suction side of the fuel pump can collapse and cut off the gas supply just when the engine needs maximum flow. We all have shiny braided-steel lines on our race cars – but do we really know whether the rubber underneath the braids is in good condition unless we inspect it regularly?
A carburetor that has been idle (pardon the pun) over the winter may have passages that are clogged with gum and deposits. Alcohol is especially tough on carbs; I’ve seen metering blocks with passages that were eaten out or blocked entirely by methanol corrosion. If the damage isn’t visible, you could waste weeks trying to find the problem.
Any debris in the fuel system will eventually end up in the carburetor. Usually you’ll find junk in the needles and seats, but occasionally it can work its way into the circuits. I’ve found pieces of fuel cell foam in jet blocks – how on earth did it get there? I don’t know, but it sure did mess up the fuel curve!
We strain every drop of gasoline that goes into our Pro Stock through a fine screen. I also recommend using a filter to keep contaminants out of the fuel system. But just because you have a filter, don’t automatically assume that it’s in good condition. A filter element that’s been exposed to moisture or excessive humidity can starve an engine for fuel.
Electrical problems can be tricky to diagnose. Attention to detail is essential. In a previous column, I pointed out the pitfalls of assuming that things are as they seem. Don’t assume that the terminals and connections are good – check their resistance with an ohmmeter. Did you paint your car this winter? If so, does the post for the ground strap have paint on it? Get out your stiff wire brush and scrub every electrical connection until it sparkles!
Crank trigger ignitions are wonderfully accurate, but they can also be extremely temperamental. It is absolutely crucial to shield and isolate the crank trigger sensor wires. These systems are highly susceptible to interference from other electrical devices. I’ve seen engine misfires cured by turning off an electric water pump or fan; that’s a clear case of electronic interference. Never bundle the crank trigger wires with the wires for other circuits; the current drawn by an electric motor can disrupt the signal from the crank sensor. In one extreme instance, I witnessed an engine running without a trigger wheel! It didn’t run very well, but the interference from the electrical accessories was strong enough to trigger the ignition box.
A compression tester is another essential tool in your diagnostic kit. An old-fashioned compression test isn’t as “high tech” as a leakdown test, but I believe that it provides more useful information. A leakdown test essentially tells you how big the piston ring end gaps are. If you took the top compression rings out of an engine, the tapered face second rings would still produce excellent leakdown numbers – but they wouldn’t seal the cylinders very effectively under actual operating conditions. Heck, if you want zero leakdown, you could install rubber O-rings on the pistons!
In the real world, cylinder pressure is what makes power. If you’ve pinched a top ring, for example, a compression test will spotlight the problem instantly, while a leakdown test usually won’t. When you perform a compression test, all of the cylinders should produce similar readings. The numbers on the gauge are irrelevant; the indicated pressure depends on the battery’s voltage, the static compression ratio, the camshaft timing, and other factors. It is very important that the compression readings be consistent among all of cylinders. It’s unlikely that you’ll have eight bad holes; you can usually isolate the problem quickly to one or two cylinders.
We live in an age that worships high technology, but the principles of combustion have been known since an inventive cave man first discovered how to make fire with flints and tinder. The technology of racing has advanced considerably since then, but the basics of air, fuel, and spark still apply.