Metric Mechanic - Performance Testing Procedures

The 60-80 Test Described

Whenever I talk to a potential customer about an engine, they always want to know

• The Horsepower of the engine
• The 0-60 times
• Quarter mile elapse speed and time.

Based on one or more of these three factors, he or she envisions how fast their car will accelerate. These figures should reflect acceleration, but in reality many times they do not. This brought us to develop a new form of testing that we believe is the most honest way of rating acceleration - the 60-80 mph test.

I'll begin by explaining the error factors that come into play with more traditional testing methods.

Horsepower Ratings
Measuring horsepower by the automotive industry has been as follows:

DIN HP (Deutsche Industry Norm)
To the Germans, this unit of horsepower measurement is referred to as DIN.

SAE Gross HP (Society of Automotive Engineers)
Before the mid 70's, gross horsepower figures were used in the United States. Gross HP is measured from engines run with open exhaust, unrestricted intake and no accessories such as fan, alternator, water pump, etc. Driven by the engine, this figure is usually about 13% higher than DIN HP.

SAE Net HP (Society of Automotive Engineers)
Net HP figures are a more realistic representation of an installed engine's actual power output. These figures take into account the effects of air filter, exhaust and accessories. Net figures are usually about 4% lower than DIN.

Misleading HP Figures
Depending on which HP measurement method you use, there's a 17% variation. For example, an early Bavaria was rated at 192 HP (Gross) and a 535i was rated at 185 HP (Net). The Bavaria also has about a 10% weight and gearing advantage. But, when it comes to acceleration, the 535i will definitely beat a Bavaria even though by all indicators it shouldn't.

Another good example is the BMW M3 and the Ford Probe (Turbo). The M3 is rated at 192 HP (Net) and the Probe is only 145 HP (Net). Both cars are geared and weigh about the same. So, here's a 47 HP difference but their acceleration is identical. With acceleration, what really counts is how much torque can be applied to the rear wheels versus vehicle weight. For a further explanation, read the article on Axle Torque to Vehicle Weight Ratios in this catalog.

By now it should be obvious that a stopwatch, not necessarily a dynometer is a better tool for measuring a car's acceleration. Remember that your final goal in buying a more powerful engine is to gain acceleration - it's that simple!

Traditional Methods for Measuring Acceleration
In the past the traditional method for measuring acceleration has been 0 - 60 mph or 1/4 mile speed and elapsed time. The problem with this type of test is that you are starting from a dead stop, so how well you launch the car can play a big factor when timing. Driver skill, reaction time, sticky tires, wheel spin, limited slip, gearing weight transfer, added weight, road surface, etc., can all be factors when leaving the starting line. Shifting technique and shift points can create error factors once the car is in motion. We wanted to come up with a testing procedure that could eliminate as many errors as possible.