Pinging project truck requires tinkering

Dear Car Talk: I have a project truck. It’s a 1979 Ford F-100 with a 300-cubic-inch inline six-cylinder engine. Before I had it bored out to 30/1000s, it didn’t ping. Now, using the recommended spark plugs, it starts pinging under very light load as soon as it warms up. I am assuming that’s because of the increased compression ratio, which is causing a higher cylinder temperature. Everything else — timing, carbon buildup, fuel mixture — seems fine. I haven’t checked the exhaust gas recirculation (EGR) yet, though. So, am I right about higher compression and higher temps leading to pinging? I have been unable to find cooler spark plugs that will fit. Could I run a cooler thermostat instead?

— Don

Good thing this is a project truck, Don, because I project you’ll by tinkering with this for a long time. Here’s the problem: We all know that the original engine was durable, but underpowered. Or, as we say in the business, with no disrespect meant to our canine friends, that six-cylinder engine was a dog.

Most people who bought the truck with that engine wished they had opted for the V-8. But instead of making your “project” replacing this engine with a V-8, you tried to increase its power. So you increased the size of the cylinders, and then I’m guessing you decided to replace the pistons with some differently shaped Mount Kilimanjaro ones that would generate more power. In doing so, you increased the compression ratio. And that’s probably why it’s pinging.

You should check the EGR valve and make sure it’s working properly. Unfortunately, there are no cooler spark plugs or thermostats that will resolve this.

If the EGR is working correctly, then you have two options. Since you appear to have money to burn on this truck, Don, one option is to spend an extra 50 cents a gallon on 93 octane fuel, and see how much that helps. Alternatively, you can try to retard the timing. But that’s going to have to be done through trial and error.

If you’re lucky, you’ll be able to set it so the pinging stops, and you’ll have almost as much power as you had before you re-bored the engine and installed those stupid pistons. Or you could just let it ping. And when the pinging melts your new pistons, put in a V-8 instead. Good luck, Don.

Movie ‘strobe’ effect tricks the eye

Dear Car Talk: Why is it that sometimes, when you see a car in a movie, the car is moving forward but its wheels are rotating backward?

— Stan

Good question, Stan. It has to do with the “frame rate” of movie film. Imagine you’re in a room that’s pitch black. And there’s a single car wheel in the room at the end of an axle, so you can spin it. Now imagine you start spinning the wheel, and you turn on a strobe light.

Now let’s say the speed of the wheel is matched to the speed of the light. So every time the light flashes on, the wheel has made one rotation. Since you only see the wheel in the same position each time, the strobe light would fool you into thinking the wheel is not moving at all!

Now let’s say the wheel is turning a little slower than the speed of the strobe light.

So the wheel makes a little less than one full rotation between flashes. Each time the light flashed on, the wheel would appear to be slightly “behind.”

That would effectively trick your eye into thinking the wheel was going backward, even though it’s going forward, just more slowly. Movies work kind of like that strobe light.

Most film is shot at a rate of 24 frames per second. Normally, that’s fast enough so your eye doesn’t notice that it’s seeing 24 individual pictures every second. What you see is smooth motion. But when you get something that’s moving quickly, like the spokes of a car wheel, you can get that “strobe” effect.