On the Dyno: Do horsepower figures lie?????

[Reynaldo K Tong <reynaldo@xxxxxxxxxx>]

BMW Digesters:

On the day of the Hurricane Georges came to Miami, FL I restricted =
myself from using my computer because something might happen when =
lightning strikes. I was restricted to using my cell phone (thank you =
Lithium Ion battery) and reading my magazines. Man, I never knew I had =
these kinds of magazines until I went to our storage room. I never knew =
I had 12 kinds of magazines and easily over 12 issues of each kind.

Oh well, to the good stuff, I found this article funny and decided to =
share it with you guys / gals:

On the Dyno: Do horsepower figures lie?

Factory horsepower numbers are generally considered the last word in =
automotive data charts. As far as we know, it's been decades since any =
manufacturer purposely inflated a power rating. In fact, we've surmised =
that certain car makers are underrating their motors for various =
political reasons. The tip-off is performance that's better than the =
power - to - weight ratios and gearing/aerodynamics factors would =
suggest.

But as any mechanical engineer will tell you, it's unlikely every copy =
of an engine (all Viper's V-10's for example) will put out the same =
level of power. Slight variations in manufacturing tolerances, differing =
fuel quality, and even the weather on a given day can alter the =
real-world power output by several percentage points.

Ever new car sold in the I.S. is rated in "SAE net" horsepower figures, =
the Society of Automotive Engineers' formula for checking power at the =
flywheel. In real-world terms, however, these numbers are generally 15 =
to 20 percent higher than what actually reaches the drive wheels, due to =
parasitic loss from the drive-line components.

To check the drive-wheel output of our Top Gun competitors (Corvette =
ZR-1, Viper RT/10, Lotus Espirit Turbo, RX-7 Turbo, 911 Turbo 3.6, Supra =
Twin-Turbo), we put each car on the rollers at Bob Jennings Dyno Shop in =
Sepuvelda, California. To our surprise, only the ZR-1's dyno number =
showed a drop in output versus its SAE net horsepower number. The Viper =
could possibly have exceeded its rated 400 horsepower, but that's the =
maximum this dyno is capable of measuring. All the other cars either =
equaled or beat their horsepower ratings. So, is this a conspiracy or =
just optimal conditions on the day of our test? Word from on of our =
deep-cover operatives confirms that certain motors are underrated by the =
factory to avoid raising the ire of insurance companies or other =
fun-hating factions.=20

So, do us a favor and keep this information to yourself.

Vehicle					Factory horsepower		Horsepower at flywheel

Corvette ZR-1			405@5800				395@6000
Dodge Viper RT/10		400@4600				400@5500
Lotus Espirit Turbo		264@6500				275@6800
Mazda RX-7			255@6500				255@6600
Porsche 911 Turbo 3.6	355@5500				360@6000
Toyota Supra Turbo		320@5600				320@6000

Motor Trend / August 1993


Wow... look at those horsepower at wheels. And to think you need to add =
15 to 20 percent more. Geesh..

I think the only way to measure TRUE horsepower is to take your engine =
from you car chasis and mount on a table, and they stick a lot of tubes =
to each end of the exhaust manifold, electronic wire every where you can =
stick to a electrical line to. I saw something like this on some fancy =
magazine or brochure (can't either remember AC-Schintzer or Racing =
Dynamics).=20

Now my question is that are they using those factory wheels? Check out =
my figures:

1st set up:	RS Akimoto Intake, AA Chip (413kh), Magna Flow w/2.25, 15" =
wheels
2nd set up:	K&N Insert filter, AA Chip (413kh1), Magna Flow w/2.5", 15" =
wheels
3rd set up:	AA Intake / Chip (413akh), M3 exhaust w/ 3", 17 M3 wheels.

The numbers are as follows:

1st set up:		170 hp / 164 tq at wheels, averaged (3 runs)
2nd set up:		180 hp / 172 tq at wheels, averaged (4 runs)
3rd set up:		160 hp / 153 tq at wheels, averaged (4 runs)

If you are wondering, yes, I kepted my catalytic and resonator intact =
because I have seen and heard a 318i with M3 everything you can think of =
except the muffler, he told me he took of the cat and resognator and =
kept the original exhaust and it sounded like crap.

I decided to keep it on the 3rd set up because I'm not going to drive my =
car to 6400 rpm just to get "180 hp" at wheels. I know my car is =
semi-fast, but who do I need to prove it to? You? I don't think so, and =
anyways, Hialeah and Metro-Dade Police Department are getting more =
strict about "testing" how fast your car can go. Anyways I have to be on =
the 3rd setup because I sold my 15" wheels. So kinda screwed there... :)

- --
Reynaldo Tong
93 325! (I got a paint job, and they accidently turned the 325i to 325!)
BMWCCA #150169
Everglades Chapter
reynaldo@domain.elided

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