[blykins]

In and of themselves, the Thumpr cams are not inherently evil....

They cross the line when they are paired up with engines that need to produce vacuum for accessories, or in situations where there is an emissions testing program.

The way that they work is that they have a very large duration split, usually 14 degrees or so. That's combined with a pretty tight LSA...usually 107. They do well in a raw street strip engine because a tight LSA generally produces a bit more torque. The lobe designs are also on the lazy side, so they're going to be easy on parts and quiet. However, that tight LSA and that large duration split is going to create a huge amount of overlap. That overlap is what makes the sound, but it also insures that both valves are going to be open at the same time for a longer period. That can facilitate reversion which can cause problems of its own.

If you have to have an evil sound, I suppose they fit the bill. However, IMO, there are better choices for a street cam, especially when you're pushing power brakes, worried about gas mileage (hahaha), or have to go through stringent emissions testing.