Not all racecar drivers are mechanics. Some drivers have to be shown where the door handle on the driver’s door is just to get inside a car. In NASA, out of necessity, a lot of us are drivers and mechanics. Just because you are a racecar driver who wrenches on your own car, that doesn’t mean you’re actually a good mechanic. Most of us know just enough to get by, and occasionally we take things apart that we don’t know how to fix. That means we have to promise some of our good friends lots of free beer to come over to fix what we started. In all of this mechanical mayhem, oftentimes parts get swapped, things are moved from one project car to another, and when all is said and done, sometimes we really don’t know what is on our car. As racers, we just know the car runs and if it runs fast, that is all we care about.
Where things get tricky is at big races, like the NASA Championships, where contingency money and national titles are on the line. At these events, cars need to be legal for their class. Racing at this high-level, cars are scrutinized to a much tougher precision and cars need to be within their rule specifications. If they are not, people get disqualified, trophies change hands and contingency checks bounce out of your checking account.
It is better to show up at the NASA Championships with a completely legal car, one you can depend on to keep you from being disqualified. To ensure your cobbled-together car that you thrashed on for an entire regional season is legal is to actually know what is currently on your car. For instance, are the camshafts you are running in your engine correct? You may think they are, but unless you measure them yourself, you won’t know for sure. Not only are you checking for legality, but you are also checking for the best performance. Maybe your cams are the wrong ones, smaller, worn or less than optimal. Maybe that is why you get passed on the straight all the time, or lose a few positions at the start?
Cams are essentially the mechanical brains of an engine. They are the devices that tell the distributor which cylinder to fire, which valves to open, to close, when, and for how long. Cams are extremely important. How important? Try running an engine without them. It doesn’t work. On our Honda Challenge car, we decided it was important to measure our cams and ensure we had the most optimal legal stock part in the car for following the class rules — in Honda Challenge 4, cams must be stock — and also to make sure our cams were as optimal as possible.
The “lift” of a cam is what determines how far a valve will open inside the cylinder, and how much air and fuel get into that cylinder. Since engines are just big air pumps, the more air, the better for efficiency and performance. To measure lift on a cam, all you will need is a digital caliper and some math.
Yes, there is a little bit of math involved here, but don’t get scared. You don’t need to remember any trigonometry, just some simple subtraction — your phone will do that for you. For the first value you will need, measure the smallest diameter on the cam, the circular part, which is called the base circle. Once you have that measurement, write it down. Before using your digital calipers, make sure you close them all the way and then zero them out.
The next value you will need is the largest diameter on the cam, the lobe part, which is called the base circle and lobe lift. Write that measurement down. Here comes the math. Now simply subtract the base circle number from the base circle and lobe lift number. What you are left with is the lobe lift portion. This measurement is the lift of your cam. This is how far it is opening your valves.
So, now what? Well, now you need to do your research. Is your lift correct? Is it correct with manufacturer specifications for that particular model of vehicle? Do you have another set of cams that might be better? Find out.
Since we are regulated to stock cams in Honda Challenge 4, the trick is to find the best legal stock cams that exist for a B18 engine. Where do you do that? At the wrecking yard! Grab your tools and your digital calipers and go on a scavenger hunt for the stock cams that give you five thousandths more valve lift than the worn-out ones currently in your racecar. I found a pair that set me back a whopping 50 bucks.
Measuring cam lift is not a complicated process. Grab some digital calipers, measure the smallest and largest diameters on the cam, subtract the two numbers and you have your lift measurement. Now head out the garage and impress your neighbor with your new vast engine knowledge.