Question - It ain't genetic, so what is it? My daughter and I both have manual transmission cars, but she is a confirmed "late shifter," and I am an equally confirmed "early shifter." She goes into fourth gear at about 2,500 rpm, while I go into fourth at about 1,500.
I taught her to drive about 30 years ago. She married a guy who is a late shifter. So please tell me who is being more engine-considerate, and how you account for this difference between us. - JasonRAY: Well, Jason, just be glad that she isn't like my brother. He's completely "shiftless"!
TOM: I don't think either one of you is being inconsiderate to your engine, Jason. The truth is, by shifting earlier, all you're doing is trading off some acceleration for some fuel economy. Based on your description, neither one of you could be described as a bona fide "motor wrecker."
RAY: Shifting up at 2,500 rpm, as your daughter does, is well within the acceptable range of engine speeds. In fact, most manufacturers probably would recommend shifting somewhere between 2,000 and 3,500 rpm. So we can't criticize her at all.
TOM: If she were constantly shifing at 4,500 rpm, then she'd be subjecting the engine and clutch to some excessive wear and tear. But she's nowhere close to that.
RAY: And your earlier shifting is mostly fine, too, and even saves you some gasoline. But believe it or not, you're actually in more danger of being "engine-inconsiderate" than she is. While shifting at 1,500 is fine on flat roads under moderate acceleration, you have to be careful not to shift too early, or you'll "lug the engine."
TOM: That doesn't mean you get out and drag the engine around with a rope. Lugging is when you force the car to try to accelerate in too high a gear (at too low an rpm). That causes the engine to strain and overheat. The telltale sign of lugging is when the engine bucks, pings or knocks.
RAY: If you ever notice any of those symptoms, then you need to take a driving lesson from your daughter and learn to shift a little later, Jason.
TOM: And how do we explain you being an early shifter and your daughter being a late shifter? The answer is simple, Jason. It is a genetic trait. But the genetics lab at MIT recently determined that it skips a generation. Which means that your father was probably a helluva lead foot!
Question - I have an '81 Chevy Caprice, and it backfires. What do I have to do to correct this problem? - Lawrence
RAY: Get a '91 Chevy Caprice.
TOM: Most of the backfiring I've seen on these cars is the type that occurs under the hood, rather than out the tailpipe. So I'm going to assume that's what you've got.
RAY: And it's usually caused by one of two things - either bad ignition timing (which is often the result of a worn-out timing chain) or, more likely, a weak accelerator pump in the carburetor.
TOM: When the accelerator pump is really weak, the fuel mixture becomes so lean that the flame in the cylinder propogates too quickly . . . so quickly that some of it sneaks out the open intake valve. And that popping sound you're hearing is that part of the combustion that's taking place in the intake manifold.
RAY: So check the timing, Lawrence, and if it's OK, then a new accelerator pump or a carburetor rebuild might be in order.