Bench Racing: Rules of Thumb
"Every additional point of compression ratio will deliver four-percent more power." "You need to burn a half-of-pound of gasoline every hour to make one horsepower." "An 11-degree drop in air temperature will deliver a one-percent increase in power." "Each additional psi of boost pressure will deliver a five to seven percent increase in power." "Ten extra degrees of cam duration will raise the peak power point by 500 rpm." Maybe you have heard some of these "rules of thumb", maybe you have not heard these yet. When a group of enthusiasts start talking about going fast and what it is going to take to go faster, chances are the rules of thumb will surface in the discussion.

The Value of Thumbs
Thumbs allow our species to function at a level of dexterity not found anywhere else in nature. Rules of thumb while not always 100-percent accurate, often show or explain a performance trend. With regards to the aforementioned rules of thumb, higher compression ratios, lower intake temperatures and higher boost pressures generate more power; it takes more fuel to make more power and longer-duration cams make power at higher rpms. These are all verifiable trends.

The Dyno Results
In this test, we compared a set of Skunk Stage II camshafts to a pair of Civic Type-R cams fitted in a B18C5 Type-R Integra engine. According to the rule of thumb regarding cam duration, the longer duration Skunk Stage II cams should have produced peak power at about 1000 rpm above the Civic Type-R cams (as the duration of the larger Skung Stage II cams is about 20 to 25 degrees more than the Type-R cams). In practice, the Type-R cams peaked at 7500rpm while the Skunk Stage II cams peaked at 8400rpm. While not exact, this rule of thumb proved to be a pretty good guess.