Gas

[NewGuy]

Does it make a huge difference to your car running on the right gas?

I just got a batch of high octane last night from Mobil and its way better than the so called high octane 96 from my local caltex.

My motor used to pink a tiny amount when i went up my hill just as i got to the top and it was changing to 3rd, it now seems all good.

What dif does it make to your cars?

[Mike-e]

in my ute dont notice any difference at all. mind you its prob tuned for 7* octane

[fuel]

96 from caltex? no such thing dude - it's 91 or 95 these days. Gone are the days of 96. Generally the higher the octane the better, if your engine has advanced timing to take advantage of higher octane the engine will run better and more efficiently. Running 91 to save a few cents is false economy, you end up paying more in the long run.

[alfalfa]

- but only if your can can use the extra octane!

100 octane actually has less energy/L (or kg, cant remember which) than 91! So unless your engine has advanced timing or high comp, and needs the extra octane, you are wasting money. ie spraks gaylant has no need for 98, unless he puts mean camzz/flat tops in it.

Petrol companies say heaps of shit about cleaning additives etc in their "premium" fuels, no idea if they are worth anything other than marketing hype..

[CaMpylobacter]

FLATTY RUNS 95 in his vxg galant, ~98 model.

gets better mileage around town and open road on average than on 91. saves him at least $10 a week on his moderate to high commuter mileage etc

I roll on at least 96 in everything.

[Gaz]

In my exp with 2l sohc ohc poo poo engines 98 has been the go, the way I have it tuned its slightly pinks under load with 96.

[NewGuy]

Is a slight pink going to cause any damage?

pretty sure my timings retarded hard.

I didnt get the cam back in the right position but its almighty close.

The dizzy is pulled right one way.

i Think i might be chewing the gas aye.

[Gaz]

Any detonation you can hear is not good.

Ya timing will be advanced not retarded if pinking. Pinking is cause by too much advance in timing. Wham it back a tad ans see results.

[mikuni]

I didn't think it would make a diffence at all between 95 to 98 but I think it does heaps. At Taupo the first time and when I raced at meremere I was running Gull 95 (I think it's 95 rather than 96) because its cheap. In 4th under full throttle you can feel and hear it fluctuating and pulsing slightly in power delivery. I thought it was just the tuning but since I have been running it on BP ULTIMATE!!!!1!!ZOMG! and it has actually seemed to be alot smoother. Any power increase is negligible but it certainly sounds like its running better under load in the high gears where you can hear and feel exactly whats going on.

[NewGuy]

Any detonation you can hear is not good.

Ya timing will be advanced not retarded if pinking. Pinking is cause by too much advance in timing. Wham it back a tad ans see results.

Ive got it almost fully one way if i change it the other way it pinks hard.

It does not seem to pink on this fuel.

91 way defiantly the worst it pinked like crazy.

[nismo.capri]

Is a slight pink going to cause any damage?

Detonation/pinking is the fuel exploding insted of burning.

When fuel burns it expands at about 700 feet per second IIRC

When fuel detonates it expands at about 4000 feet er second and the noise you hear is the shock wave hammering in to the piston.

[NewGuy]

Is a slight pink going to cause any damage?

Detonation/pinking is the fuel exploding insted of burning.

When fuel burns it expands at about 700 feet per second IIRC

When fuel detonates it expands at about 4000 feet er second and the noise you hear is the shock wave hammering in to the piston.

MMMM thats how my old pistons got fucked.

Mine does not seem to do it on this fuel i think thats what i was trying to say, but yes you are right.

I like your explanation Boe

Water and timing on number one blew out my Piston rings like this.

Old piston.

[nismo.capri]

^ can't see the pics here at work I'll have a look tonight. Detonation often causes little craters on the pistons

[NewGuy]

Hmm ok i took the piston to like 3 different, mechanics and they all told me it was caused via pinking. The noise was so loud when this happen.

[nismo.capri]

Hmm ok i took the piston to like 3 different, mechanics and they all told me it was caused via pinking. The noise was so loud when this happen.

Has it blown out a chunk of ring land?

That's usually from rather extreme detonation like 17 psi of boost + hot day and too much sterio that drowned out the death rattle

[NewGuy]

Lol No man, well it could be but i was doing about 2000RPM crusing to go get my warrent haahaha

[Gaz]

the noise you hear is the shock wave hammering in to the piston.

Isnt the actual noise from the crank. The piston being forced down and then back up again and it slaps around the crank end. Is what ive been told anyways. Could be wrong.

[nismo.capri]

Looks like it might be the whole engine ringing

from : http://www.streetrodstuff.com/Articles/ ... Page_2.php

Detonation

Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.

Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike.

One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. Detonation is not necessarily destructive. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes.

Detonation causes three types of failure:

Mechanical damage (broken ring lands)

Abrasion (pitting of the piston crown)

Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)

The high impact nature of the spike can cause fractures; it can break the spark plug electrodes, the porcelain around the plug, cause a clean fracture of the ring land and can actually cause fracture of valves-intake or exhaust. The piston ring land, either top or second depending on the piston design, is susceptible to fracture type failures. If I were to look at a piston with a second broken ring land, my immediate suspicion would be detonation.

Another thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation; you might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.

[NewGuy]

Yup

Mechanical damage (broken ring lands)

[peteretep]

so the spark plug 'sparks' then as it comes to tdc the rest of the fuel blows up? shouldnt there be minimal unburnt fuel left after the spark?