On Wed, 25 Jun 1997 03:21:23 +0000 "Scott Gardner" <gardner@lwcomm.com>
writes:
> Can anyone tell me what the changes have been in the last
>hundred
>years that allow a constantly increasing output from a given-size
>engine? I'm not interested in turbocharging or supercharging in this
>discussion. I read about 500 cubic-inch Cadillac engines from
>thirty years ago putting out 145 horsepower, which is the same power
>as my 82 trans-am put out in a 305 c.i., and is about the same
>power some modern cars put out from a 1.8 or 2.0 liter four cylinder.
>Other than four-valve engines and overhead cams, what has been the
>big technology gain that has allowed the big increase in hp/liter? I
>guess this also begs the question "How has fuel flow/hp decreased so
>much in the same amount of time?" I know I've beaten this example to
>death, but my '86 Jetta had a 1.8L in-line four, 8.0:1 CR, with two
>valves per cylinder, just like my 'B', but put out 102 hp at the
>tires versus 95 or so at the flywheel in a 'B', and got about 35-39
>mpg in city driving. The only difference I can think of is the fact
>that it was fuel injected (mechanical FI, though, no
>computer-controlled EFI), and that it had an overhead cam. I can't
>remember what the Jetta weighed, but it certainly wasn't LESS than
>the 'B'.
> I'm kind of amazed that we've been able to steadily wring more
>and
>more specific power out of engine designs that haven't changed
>radically in almost 100 years. Show a modern engine to someone from
>1920, and after you got past the plumbing on top, he'd recognize most
>of the parts.
>Scott
>
>Scott Gardner
>gardner@lwcomm.com
>www.lwcomm.com/~gardner
One big factor is engine speed. A basic rule of engine tuning is that if
you can induce and engine to peak at a higher RPM, the HP will be
greater. If you look at the engines speeds of powerplants in the 20's &
30's, you wont find the HP listed at 5000 RPM or so. Instead, its
something like 1700 or 2000.
The engine speeds have increased as a direct result of technological
improvements in everything from metalurgy to cam design, to whatever else
you care to throw in. It probalby isn' one specific change that has
accounted for an increas, but a synergistic (SP) combination of it all.
Rick Morrison
72 MGBGT
74 Midget
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