Any benefits to high octane

Sam Spade wrote:

wwest wrote:

Just how does the computer adjust timing to prevent pre-ignition...??

It appears that we have at least one person here who understands the difference between "spark knock" and "pre-ignition".

I believe you wanted "pre-detonation".

Just checked to see that the portal bad word filters ****'d mine...

Back off the timing instead of re-tard the timing (hope the dash fools the computer)

The second one that was ****'d is a mystery, as that was a.d.v.a.n.c.e is dialed
in.

Comment that with the need to protect themselves from warranty costs due to both
the ever increasing power that can twist things into pretzels easily...and that
less and less folks actually know or wrench (hard knock schooling) themselves...that
they have to have more and more computers that are highly integrated into the
system.

From experience dealing with several auto-OEM design teams...that
they do NOT understand real time software control...nor do they
(generalization...the must be some...) understand real time
master/slave hierarchical control philosophy

Most think real time is to place the interrupt into the queue...real time for
this kind of application is to place that interrupt flag into level cache queue
Or microsecond/milliseconds to respond to whatever that flag was for

To the PM asking what is the coil rise time...it is the time the coil will recharge
after dumping to the spark plug

The FETs can fire in microseconds and my expectation of a performance coil is
to have it recharge in the order of 3 microseconds...but that is for a high
quality (mainly the lamination material) coil (transformer)...

And to the what is 'carbon build up' and 'glow'...it is in the CC
(combustion chamber) that has mineral/carbon build up.

Both increase the ratio a bit and to 'glow' hot enough to ignite the
charge without any spark. As the PSI increases, the higher the tendency
for that carbon/mineral deposit to glow hot enough to ignite

As for what is knock, it is where the charge ignites some other place
from the spark plug's electrical arc. So both ignitions will then have
a shock wave merging on each other to create a much larger PSI point

That is like a ~1,800*F flame front hitting another similar to then
cause HUGE PSI shock on all surfaces inside the CC...think of a sledge
hammer smacking the CC chamber surfaces

Betcha Turtle even has some of these busted parts sitting on his work
desk...most of us boy racers have them...the 'ex' tossed out mine... :M
But I see them all the time at the speed shop counters... :B



Both melt and break the CC surfaces....here are some pics of that










This is a good one showing the other ignition flame front hitting the
spark plug ignition fame front...and ICE's 'burn' during the power
stroke...it is *NOT* an explosion...of which the knock/pre-ignition
is...made worse when the two flame fronts smack into each other...

The computer will manage it for you...meaning the timing of the squirt, how many
squirts per combustion cycle, how much to squirt...most can NOT advance the timing,
just ****** timing (preset max advance and the amount of ****** is also dialed in).
Most will increase the amount of fuel to both cool the chamber and to avoid
knock/per-ignition/etc

If direct fire and no distributor...depends on how fast the coil raise is...it could
fire several times during the combustion cycle. Most are fired with FETs
and they are fast enough for multiple pulses during one combustion stroke...am
finding that they went El Cheapo and the coils too, so am
wondering if their metal lamination is good enough for microsecond rise times

The octane is NOT measured...just the results from combustion characteristics
for the next cycle

Much more and finally...go into limp mode if severe enough

Even direct fuel injection into the CC has the potential, albeit much less than
fueled in the manifold.

Research is currently going on with GDICI (no spark plug) and the every XX cycle
to dump fuel in to clean out carbon build up that glows...

wwest wrote:

Just how does the computer adjust timing to prevent pre-ignition...??

It appears that we have at least one person here who understands the difference between "spark knock" and "pre-ignition".

BenK wrote:

Bottom line: use whatever you wish that is available from name brand
gas stations and the computer will manage it for you...of course within
it's allowed limits set by the software

Just a comment since I'm not sure exactly what you are saying:

There is no sensor or computer in the vehicle that measures octane in the fuel directly. What it measures is what happens when the fuel burns: the oxygen sensors in the exhaust and the knock sensor mostly.

So.....if the knock sensor reports "all quiet on the home front", putting in fuel with a higher octane rating accomplishes EXACTLY NOTHING.

Now.....the exact composition of the fuel might make a difference if the other sensors see something different, in the exhaust gas for instance, but that is NOT because of the octane.

drsteve wrote:
No. Computer controlled engines adjust their spark timing to eliminate preignition under heavy load.

Just how does the computer adjust timing to prevent pre-ignition...??

Advance it... NO.

R e t a r d it... NO.

Enrich the mixture... Possible.

What with the computer controlled EVERYTHING...fill with whatever you wish and
the computer will re-adjust the setting on HOW2 manage the ICE...

Fill with lower octane and the computer will re-adjust to save the ICE

Fill with aviation 'gas' and the computer will re-adjust to increase performance...up
to the software set limits

Fill with pure toluene (what most refineries add as part of their octane
booster) and then you might have a problem with the computer's ability
to manage. Especially in cold weather running...

This topic is about technology/science/laws-of-physics and if truly wish
to understand...look up octane and how it affects ICEs (internal combustion engines)

Add: "compression ratio"..."pre-ignition"..."knock"..."ignition advance"

Oh...add looking up: "carbon build up"..."glow point(s) inside the CC"

Bottom line: use whatever you wish that is available from name brand
gas stations and the computer will manage it for you...of course within
it's allowed limits set by the software

My manual says absolutely do not use E85 fuel. It also says don't use less than 87 octane, even in the mountain states that offer regular in 85 octane.

It recommends use 87 octane when not towing or hauling.

It also suggest performance may be improved if premium is used when towing and/or hauling.

I have a 2014 F150 Eco-boost 3.5L engine.

Use what your manufacturer recommends. If it makes you feel better, use higher octane. But the only things you are affecting are your feelings and your wallet.

cbshoestring wrote:
WIFE: How come you put that cheap gas in my car, then use the expensive stuff in your truck and motorcycle?

ME: The BOOKS says use 87 in your car...my truck calls for 89, the H.D. gets the highest the pump has to offer.

WIFE: You're high maintenance :B


OP: Just use what the MFG recommends. No need for "better" fuel, if it isn't going to provide additional benefits. My 89 octange was 17 cents more per gallon than the 87 (at pump TODAY).....why pay it if you don't have to.

The gas the manuf recommended 10-15 years ago is different than today's gas!