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Ron Stygar Carl Buckland Dale Beuning Forums Help
Date: Thu, 4 Jan 1996 08:41:12 -0500 From: read_at_engr05.comsys.rockwell.com (Pete Read) To: jrallen_at_halcyon.com Subject: Performance Testing Methods John Allen asked about a standardized method for estimating the horsepower/torque effects of various engine modifications.
He mentioned both Bowling's Highway Dynamometer program (Web
Page http://devserve.cebaf.gov/~bowling/auto.html) and the
Metric Mechanic 60-80 in 3rd/4th/5th gear method.
After checking them both out, either method seems fine, but
Metric Mechanic (MM) gets my vote. The MM 60-80 mph test is
much simpler to do and the results are easier to grasp.
Here's a brief explanation of each.
Bowling's Highway Dyno program provides a corrected
horsepower and torque readout. Car acceleration is found by
running wide open throttle, in the highest gear possible,
through the entire engine rpm range without shifting.
Elapsed time is recorded at even mph increments (e.g. in 3rd
gear, every 10 mph from 30-90 mph). Then the times are
entered with specific car information (gear ratios, weight,
engine displacement, etc.), and environmental conditions.
Just for fun, I interpolated Evan Evan's 3rd gear 60-80 mph
M5 test figures to plug in some numbers (stock 3.96 versus
Dinan 3.60 seconds). Assuming constant acceleration, I
divided the 60-80 mph time values into four equal parts.
Note this test should be done over a wider rpm range and the
time between speeds needs to be measured, not estimated.
Time Speed
Dinan
Next the following inputs:
Gear Ratio 1.35 (3rd gear)
Front Area 20 sq ft (default)
The results were: Stock,(Dinan)
MPH RPM Road Hp Flywheel Hp Corrected Hp
The MM test measures 60-80 mph acceleration times in 3rd, 4th, and 5th gears. On a level road in 3rd gear, start at 55 mph and floor the throttle. Start the stopwatch at 60 mph and stop it at 80 mph to measure the elapsed 60-80 mph time. Repeat the test for 4th and 5th gears. You end up with three numbers (60-80 mph time for 3rd, 4th, 5th) that give a good feel for performance across the useable power range.
Evan's before and after tests (3rd 3.96/3.60 sec, 4th
5.13/5.30 sec) indicate that the Dinan chip increases
maximum power, but seems to decrease mid-range power. The
MM 3rd gear (max power) test correlates well with 0-60 mph
and quarter mile times. Evan's 0-60 mph times dropped from
7.00 to 6.52 seconds, again indicating a maximum power gain.
Here's what increases and decreases power. Increase Power Change --------- ------------ Elevation decrease Temperature decrease Pressure increase Rel Humidity decrease Elevation seems to be the most important factor. Temperature is somewhat less important, but significant. The elevation rule of thumb is a 1% loss for each 100 meter (328 ft) increase. People in mile-high Denver have 16% less power than people at sea level. Cool outside air temperature helps, but it's heated above ambient temp in the intake passages.
So I'd suggest reporting any significant elevation and the
air temperature for 60-80 mph tests.
The Metric Mechanic method produces three numbers. The 3rd gear time correlates well with car magazine 0-60 mph times many people (like me) memorize. The test is easy on your car and repeatable because there's no wheel spin or redline shifting. It's possible to find each test number discretely, in less than 10 seconds, on most highways. So remember, in 3rd gear, if it goes from 60-80 mph in four seconds it's a real M5, but if it takes five seconds, it's only a 535i. Regards,
Pete Read |
