[DML] "Horsepower" In The Neverending Performance Debate

["content22207" <brobertson@xxxxxxxxxxxx>]

In the current performance debate the word "horsepower" is starting to
be tossed around. A refresher primer may be necessary:

There is no such measurement as horsepower. Horsepower is a
*CALCULATION*, made from other measurements. For example, there is no
such thing as a "horsepower gauge." There are gauges that measure is
calculative components, but horsepower itself does not independently
exist.

HP = Torque x RPM / 5252

Torque and RPM are the measurable components of the HP calculation.
Gauges exist to measure each.

BTW: There's a historical explanation to that obscure formula. In the
1800's a fellow named Watt wanted to sell steam pumps to raise water
from coal mines. That job was already being performed by horse driven
pumps (horses were harnessed to big horizontal wheels, walked in
circles, and the motion was tranfered to vertical pumps). He needed a
calculation that would allow mine owners to compare his engines to the
horses they already were using. Watt measured how much weight an
average horse could raise vertically in one minute. That weight &
height translates into the 5252 (its a factor of 1, so the formula
holds for however much torque or however many RPM's are measured).

What does all this mean? First, owners need to divest themselves of
images of horses harnessed to the front of their little silver cars
like a Conestoga wagon. That's the popular image: 130 HP equals the
power of 130 pulling horses. Nothing could be further from the truth.
There are 400 HP semi tractors that pull 70,000 lbs of weight with
relative ease, and there are 400 HP sportscars that can't pull a
U-Haul. Same 400 HP rating, so obviously the horse drawn image doesn't
work.

It all boils down to torque (sometimes called "bottom end power") and
RPM's ("top end power"?). An engine that produces a tremendous amount
of rotational force, but does so at low RPM's, will have a
surprisingly low HP calculation. An engine that produces relatively
little rotational force, but spins very quickly, will have a
deceptively high HP calculation.

In our sportscar example: Hitched to a semi trailer, the little car
would either stall the engine, burn up the clutch at point of release,
or boil the transmission fluid (if it were an automatic), before it
budged the trailer. The sportscar doesn't produce any usable power
until its engine is spinning very quickly. At idle it's very weak.

By contrast, the semi tractor produces a tremendous amount of power
from idle forward. But its engine does not rev very high at all
(semi's spend most of their life in the 1,200-1,500 RPM range). Hence
its HP calculation is a fairly low number.

Of course transmissions also affect the transfer of power to driving
wheels (semi's have up to 18 gears), but the HP principle remains.

Again, what does all this mean? Second, DeLorean owners need not hang
heads in total shame over our paltry 130 HP rating. The PRV produces
more torque than many higher reving engines with corresponding higher
HP numbers. Until those engines reach their higher RPM's, we have more
usable power. If they fail to reach those RPM's (under load, going
uphill, etc), they never will match our power.

Could the PRV produce even more torque or RPM's? Of course. The
easiest way to bump up torque is higher compression or forced
induction. RPM's are harder to modify since they are largely
determined by internal engine components such as camshafts and
crankshafts. Which brings up a good point: "Red line" is not the point
at which an engine is producing its maximum power. Rather, the red
line is the point at which an engine is producing no more power.
Basically the valves are starting to float. Maximum power is actually
reached prior to the red line (ever notice how HP calculation graphs
peak, then start to drop off?). Noise level continues to increase, but
usable power is declining.

The big picture? DeLorean owners need to decide what performance
targets they are trying to reach. If they want a more powerful engine,
compression and induction are the avenues they need to explore.
Modifying ignition may help marginally, but the gains are nothing
compared to super or turbocharging. However, if "performance" means
reliability, consistent operation in a variety of atmospheric
conditions, maximum fuel burn, etc, modifying ignition *IS* a viable
avenue. I personally chase the latter targets (why in the world
otherwise would I modify ignition on humongous 7.5 liter low reving
Lincoln engines! They certainly aren't going to change into race
engines from ignition alone).

Food for thought in the neverending performance debate.

Bill Robertson
#5939



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