On Sat, 18 Mar 2006 01:32:13 +0000, Mark Rand
wrote:

On Fri, 17 Mar 2006 23:31:11 +0000, Andy Dingley
wrote:

On Thu, 16 Mar 2006 03:13:05 +0000 (UTC), Christopher Tidy
wrote:

But what about a car? Is the 130 hp or whatever maximum engine power the
manufacturer quotes a continuous or an intermittent rating?

Continuous, but at a constant rpm which is unrealistic for anything
except motorway cruising. It's done by measuring on a dyno, either an
engine dyno or a rolling road.

It's usually quoted at some ridiculous rpm limit too, fairly close to
the redline. Long stroke engines with small valves will have failry
flat curves (i.e. torque is approximately constant with speed), highly
tuned engines (motorbikes) have "peaky" torque curves, so max power only
happens when you rev hard.

But most cars are driven with insufficient use of the gearbox. Whereas on a
bike the gearbox is a natural extension of the driving style. So the engine
types work for their intended uses.

Particularly when most American iron today turns less than 2000 RPM at
the legal speed limit in top gear. Where it's producing something like
75 HP at full load, or more likely closer to 35 or 40HP at cruise.

The engines, in most cases, ARE capable op putting out 80% power for
hours on end at the rated RPM though - which IS rather incredible. A
smallblock 8 cranking 6000 RPM for several hours at a time - with
virtually the same geometry a sicties or seventies engine had trouble
staying together at 4000 for a few minutes, or 6000 for 1/4 mile.


Mark Rand
RTFM

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