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On Aug 31, 7:47 am, wrote:
On Thu, 30 Aug 2007 20:54:58 -0700, rw
wrote:





wrote:
On Thu, 30 Aug 2007 19:50:07 -0700, rw
wrote:

wrote:

On Thu, 30 Aug 2007 14:43:41 -0700, rw
wrote:

wrote:

If the car in question runs without combustion issues on "regular," the
only thing one ____might____ get from using a slightly higher octane
rating is marginally quicker acceleration of the car and a
proportionally higher acceleration of cash outflow...

Fuel mileage will be different.

I can run my Subaru Turbo Outback just fine on regular (premium is
recommended), but the mileage (miles/gal) is less. As close as I can
tell, it's just about as economical to run it with premium, but if a
rider thoughtfully filled it with regular I wouldn't mind one bit.

Good lord - an Outback has a turbo'ed V8?!?! Either I'm wrong about
what I think the Outback is, size-wise, or the pistons must be the size
of US half-dollars. But IAC, you shouldn't see a noticeable MPG
difference, all other factors equal

So who am I going to believe? You or my own eyes? Especially considering
that you're nearly always wrong about everything.

I really don't care what you believe, but if you believe that the
"octane rating" is a measure of "power," you're wrong.

I know perfectly well what an octane rating is. It's true that using
premium gasoline in a car designed for regular is a waste of money. What
you seem not to understand is that turbocharged engines (and in
particular the one in my car) are designed for premium gasoline, and
they do not run as efficiently on regular gasoline.

Unless the design is poor, turbocharged engines are not "designed for
premium gasoline." In fact, most turbocharged engines aren't designed
for _any_ gasoline, they are designed for diesel. OTOH, a
non-normally-aspirated gasoline engine (turbo'ed or
"blown"/supercharged) does generally require higher octane _under the
same conditions_ than the same engine normally aspirated; however,
"higher octane" does not translate into "premium" required. IAC, most
"production" cars with gasoline turbo'ed engines have lower compression
ratios than the non-turbo'ed versions, and moreover, no engine designer
worth a damn would set out to design an engine for such a car with the
goal of the highest possible octane requirement. If the absolute
minimum octane _required_ under the best possible (octane-wise)
conditions (i.e., a new engine in a cold, low humidity climate at high
altitude) for a particular vehicle was "premium," it would be an all but
useless vehicle to the general US public.

BTW, it's not a V8. I never said it was.

Fair enough.



Also BTW, premium gasoline is also strongly recommended for my
motorcycle, but that's because it has a pretty high compression ratio
(9.7:1).

FWIW, the compression ratio isn't the only reason, but a bike engine
ain't a car engine. Here's a hint - what's redline on your bike vs.
your car? Here's another - look at the "power band" on both.

TC,
R- Hide quoted text -

- Show quoted text -

'Unless the design is poor, turbocharged engines are not "designed
for
premium gasoline."
Modern engines (normally aspirated, supercharged or turbo-charged )
are designed not to knock and will run on the available ranges of
octane. They have detonation sensors ( little microphones ) that
listen for the ping and then retard the spark to the point that pre-
ignition doesn't occur.
When cars had real distributors and all you could get was low octane
gas you had to retard the spark by turning the distributor to retard
the spark.
The first cars to have ping detectors were I believe GMs in the 60s
May have been the Olds F-85. An aluminum block, turbo charged engine
with a 9.5: 1 compression ration needed something or you had to gas
them up at the airport.