[Diy_efi] Timing Advance Curve?

[Programmer]

Well, that's nice it's been recently covered. This has been dealt with here
several years ago also.

> Its possible to contrive fuels to be either fast or slow burn at
> either high or low octane, there is no causal relationship<

That's because 90% of the test data out there is performed on a single
cylinder slow RPM
test engine used for octane tests. Saying there's no "casual" relationship
while stating
it's possible to be either fast or slow at either high or low just confirmed
my answer.

> In fact a porsch tuner commented to me some time ago that the higher
> octane fuels seem to burn faster<<

Ooooh....I'm glad you mentioned that. The TAG-Porsche team sought
fuel blends that would burn fast enough at 13+K RPM which allowed less than
.75 millisecond burn time. To quote "...the aromatic yielded higher flame
speed
than isoparaffins, and provided enhanced performance despite its lower
motor octane number...the low motor octane of the fuel required spark
advance
below MBT to avoid detonation, but the high energy of the fuel more than
compensated for this power loss..." end quote.

Distillation curves have everything to do with flame speed.

We've tested high and low research octanes in short stroke engines and
have also found more streetable torque and HP out of a fast burning fuel.
Now
we've got the other way to a methanol injection with long stroke V8 to move
this heavy car faster. Funny thing was that "HotRod" magazine came out with
an
article several years after we'd already played with 13to1 CR ratios and 87
octane.

> Also there is no causal link between octane and energy levels, you
> can have high octane - such as methanol with abysmally low (50%)
> energy level of petrol and the opposite can also be arranged.

**BUZZER**

Methanol is about 97 MON octane. But it's stoich is also around 6.5 to 1.
The secret is oxygen content, but this also requires jetting to nail down
best burn. We need to burn the most amount of fuel with the most amount
of oxygen for max power. Methanol will yield more energy in a combustion
chamber than gasoline ever will.
Methanols is still around 18,000 BTU's per lb.
Some of the best high octane of VP racing fuels for example, their
C16 racing gasoline is 18,786 BTU's per lb. Hardly the 50% level
you claim.

Although "octane" is typified as a value for knock resistance, it
can be readily identified. Clearly--I mean clearly, some fuels burn faster
than others and are more suitable for high speed engines. Oxygenated fuels
burn faster than nons...but create artificially lean mixtures.

Different perceptions or faq's on the internet should be taken and tested
against
real data. Flame speed is not only dependent on the type of fuel, but the
air
fuel ratio and turbulence in the combustion chamber. Top fuel dragsters
shoot
flames from exhaust because of incomplete combustion in the chamber--it's
still burning
out the pipe--and believe me, methanol burns slow in comparison to gasoline.
Specific density, volatility--all have relavence to flame speed.

>
> In summary, at the pump there is no direct causal relationship
> between higher octane and burn rate, people seem to report different
> perceptions - there is a faq on this as posted initially by Brian

So you say...I guess I do have a different perception.

Lyndon.







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