Re: Gasoline grade BTUs per gallon?


"Pooh Bear" <rabbitsfriendsandrelations@xxxxxxxxxxx> wrote in message
news:4477601A.B1ECBE3@xxxxxxxxxxxxxx


"K. Jones" wrote:

Bill, would it be more accurate to say an engines can "*be built* with
slightly greater efficiency by utilizing a higher effective compression
ratio"?

That's a diesel ! They have much higher compression ratios than gasoline
engines
and are therefore more efficent.

I didn't didn't mean *that* much more compression. :) While a typical car
might have a static compression ratio of 8.5 or 9:1 compression, diesels
have in the order of 20:1 compression. I've owned and "wrenched" several
diesel vehicles. Love 'em. Large part of a diesel engines efficiency has
to do with no throttle plate, and lean idle/low throttle.

Saab's new bio-power gasoline engines that run on E85 are more efficient
on
ethanol by turbocharging at a higher boost pressure than on gas that
utilises
the higher octane of ethanol ( a bit similar to having a higher
compression
ratio too ).

AFAIK, on a typical, un-modified, car engine, as delivered by the
factory,
built to use say, 87 octane gasoline, you will see no "preformance
improvement" by using "premium" (say 91 octane).....more likely less
performance.

Less performance ? Why do you say that. It flies in the face of
experience.

Well, I used to think that too. The experience of many years of racing, and
the thousands of timeslip that proved me wrong. I kept a log for sometime,
of track temperature, air temperature, relative humidity (dry bulb),
barometric pressure, and wind speed for hundreds of passes over a couple of
seasons (helps less experienced drivers dial the car better). Looking at
ETs and top speed after each run, "experience" has shown me that you get
more 'bang for the buck" on the lowest octane fuel you can run without
having to retard anythng.

It's only on engines that have a higher effective compression
ratio, that performance gains will be found.

Higher compression ratio engines can make better use of it.

Well yes and no. If my engine runs fine on low octane fuel, I'll realize
zero gains from a higher octane fuel (won't "hurt" it, just slightly less
performance). If my engine requires higher octane fuel, I will see a major
loss of performance, and possibly damage to the engine from running it on
fuel with too low an octane. Much more so on an engine with "power adders"
(ie turbo or super charging, nitrous, etc)

If my engine is designed for "regular" gasoline, I'll get slightly more
miles/gallon, and a higher "max power" from regular gasoline, than I will
from premium.

Probably not. It depends hugely on the ECU programming. though.

It may be one of those "Your Mileage May Vary". "Stock" maps are usually
fairly conservative (ignition/fuel curves, etc), so there is even less of a
chance of getting any gains from using a higher than recommended octane.
Few cars that I drag raced had stock maps, or ran "regular" gas, but my
mustang did (and the vehicle I was thinking of in the example with the
timeslips). Harley recommends 91 octane. If it's not very hot outside, it
runs on 87 octane fine, and I get 7 km/tankful more on "regular" than on
"premium". If it's very warm out, it doesn't "like" 87, and I have move up
to 89 or 91. That's with a mild cam and the stock (conservative) ignition
map. If I remapped it so it wasn't quite so "conservative", then I'd most
likely have to run 91 all the time.....but it's fast enough for me as it is
(for now *smile*).

Graham

K. Jones


.

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