Regular gas for the US spec STI

[CompUser]

(e-mail address removed)>,
(e-mail address removed) says...

I thought that was pre-ignition.

It is.

Steve

 

[Chris Phillipo]

I thought that was pre-ignition.

No, pre-iginition is caused by the metal surfaces in the ignition
chamber being so hot they ignite the fuel/air mix without a spark. They
both screw your engine in about the same way by burning fuel before it
is intended to ignite.

 

[Dan Duncan]

They called back and said it had been filled with
regular. They filled it with premium and give it
to a saleslady to drive around. We came back a couple
days later, test-drove it and bought it.

You might want to get that story in writing in case you
have a warranty issue down the road.

-DanD

 

[Ken Gilbert]

[devil's advocate]

....he COULD fit an aquamist (or similar) water injection setup and
then fill with 87 octane all day...

[/devil's advocate]

ken

 

[Florian Feuser /FFF/]

[devil's advocate]

....he COULD fit an aquamist (or similar) water injection setup and
then fill with 87 octane all day...

[/devil's advocate]

ken

ah, why don't people top off with evian after a tankful of 87?
OK, H2O and gas don't mix, but it's not really that simple.

florian

 

[Mark Santa Ana]

Hi Mark, All!



Not quite, but same results. Detonation is where the air/fuel charge
basically explodes instead of burning with a nice even flame-front
pattern. It's caused by too lean of a mixture, or poor fuel (lo octane
or other). Pre-ignition is where you have a hot spot in the combustion
chamber that ignites the mix prematurely, causing excessive pressure
in the combustion chamber. That is caused by too hot of a spark-plug,
glowing hot carbon deposits on piston crown or combustion chamber,
etc. They _are_ closely related, however, Detonation frequently leads
to pre-ignition. It's a vicious cycle that can destroy an engine in a
few cycles.

ByeBye! S.


Steve Jernigan KG0MB
Laboratory Manager
Microelectronics Research
University of Colorado
(719) 262-3101

Thanks for clearing that up, I have a hard time distinguishing between
the two. Is there a more general way to distinguish between them?
I think I've read that running with too much ignition retard can also
cause pre-ignition by heating the exhaust valves too much. The exhaust
valves are hit with the flame front and cannot dissipate the excess heat
in time for the compression cycle.

 

[Dan]

or he could just run with the gas that you're supposed to run on any
turbocharged car and not worry about it.

[devil's advocate]

....he COULD fit an aquamist (or similar) water injection setup and
then fill with 87 octane all day...

[/devil's advocate]

ken

ah, why don't people top off with evian after a tankful of 87?
OK, H2O and gas don't mix, but it's not really that simple.

florian

 

[CompUser]

Thanks for clearing that up, I have a hard time distinguishing between
the two. Is there a more general way to distinguish between them?
I think I've read that running with too much ignition retard can also
cause pre-ignition by heating the exhaust valves too much. The exhaust
valves are hit with the flame front and cannot dissipate the excess heat
in time for the compression cycle.

Pinging or detonation refers to simultaneous, or
closely following, ignition from a residual heat
source in the chamber AFTER the ignition spark.
The shock wave generated by the collision of the
burning wave fronts creates the "ping" and does
the damage. Some degree of detonation can be
tolerated without damage, tho it can damage
pistons etc.

Preignition refers to ignition prior to the
ignition spark, while the piston is still being
driven down the cylinder in the compression
cycle. Earlier preignition is more destructive
than later, closer-to-the-ignition spark,
preignition, as the piston is being mechanically
forced down the cylinder for a longer portion of
the compression stroke, while the burning fuel-
air charge is trying to expand. It is considered
*much* more destructive than pinging, with the
occurrence of even a single incidence of
detonation being enough to destroy the engine.

Steve

 

[y_p_w]

Pinging or detonation refers to simultaneous, or
closely following, ignition from a residual heat
source in the chamber AFTER the ignition spark.
The shock wave generated by the collision of the
burning wave fronts creates the "ping" and does
the damage. Some degree of detonation can be
tolerated without damage, tho it can damage
pistons etc.

I'll also add part of the reason is because the
explosion from the ignition spark increases the
pressure in the entire chamber - even in parts
where the flame hasn't reached.

Preignition refers to ignition prior to the
ignition spark, while the piston is still being
driven down the cylinder in the compression
cycle. Earlier preignition is more destructive
than later, closer-to-the-ignition spark,
preignition, as the piston is being mechanically
forced down the cylinder for a longer portion of
the compression stroke, while the burning fuel-
air charge is trying to expand. It is considered
*much* more destructive than pinging, with the
occurrence of even a single incidence of
detonation being enough to destroy the engine.

From what I understand, it takes some serious
neglect for there to be preignition. There would
have to be some awfully heavy carbon deposits
before it would reach that point.

You guys should have read a thread in the Toyota
group a few years back. I mixed up preignition
and detonation, and there was an ensuing argument
over whether or not "predetonation" was a correct
term. One guy was telling me no way, and it
devolved into a discussion about English syntax.
My point was that some mechanics and even a
well known tuner used the slightly bastardized
word "predetonation".