Great post :thumbsup:The higher the octane, the harder it is for the fuel to ignite. The only time you will see a cylinder temp. drop is when you run a richer mixture or have a better than stock cooling system. In general terms...the more fuel you put in it, the cooler it runs, NOT the more OCTANE. The stoich level of race fuel is also a little different though. NA (naturally aspirated) stoich levels of say 110 octane is around 13.7 (depending on brand) instead of the industry typical 14.7 for 93 pump. So it can be confused with running cooler because the race fuel inherently burns at a richer (cooler) level than pump gas with no computer changes. FI (forced induction) cars have to run richer to keep detonation at bay at higher pressures. Pressure creates heat, heat adds to "hot spots" which if left unchecked, can turn red hot. That will cause pre-ignition (much more destructive than detonation).
N20 is a cool air charge, but does increase cylinder pressure. It chemically introduces more O2 molecules where as blowers and turbos do it mechanically. Again, more pressure = more heat...but ALL N20 applications require additional FUEL to burn right. If not you're just introducing additional oxygen without additional fuel which will lean your mixture. The leaner the A/F...the hotter the chambers are. Also why running colder spark plugs helps ward off detonation.
Well he said it will lower the temp but not because the combustion process itself is lower in temp but because the nature of the higher octane fuel creates a rich condition if the tune is not recalibrated.87 or 110 the temps will remain the same in the combustion chamber. But wouldn't 100 octane have more burnable material in it opposed to 93 causing it to be cooler? I'm assuming the answer to this is no.
Stoich is the point at which all of the energy in the fuel has been combusted, but the ratio at which this happens is different depending on octane.I though stoich was like idle/cruise afr, and that can be maniplated in the tune?
It has to do with the plug's ability to dissipate heat, not the spark itself. Hotter plugs stay cleaner but have more of a tendency to cause predetonation.So what's colder about a spark plug?
Because if the plug is too cold it won't stay clean and will foul out.So why wouldn't everyone run the coldest plug possible?
The higher the octane, the harder it is for the fuel to ignite. The only time you will see a cylinder temp. drop is when you run a richer mixture or have a better than stock cooling system. In general terms...the more fuel you put in it, the cooler it runs, NOT the more OCTANE. The stoich level of race fuel is also a little different though. NA (naturally aspirated) stoich levels of say 110 octane is around 13.7 (depending on brand) instead of the industry typical 14.7 for 93 pump. So it can be confused with running cooler because the race fuel inherently burns at a richer (cooler) level than pump gas with no computer changes. FI (forced induction) cars have to run richer to keep detonation at bay at higher pressures. Pressure creates heat, heat adds to "hot spots" which if left unchecked, can turn red hot. That will cause pre-ignition (much more destructive than detonation).
N20 is a cool air charge, but does increase cylinder pressure. It chemically introduces more O2 molecules where as blowers and turbos do it mechanically. Again, more pressure = more heat...but ALL N20 applications require additional FUEL to burn right. If not you're just introducing additional oxygen without additional fuel which will lean your mixture. The leaner the A/F...the hotter the chambers are. Also why running colder spark plugs helps ward off detonation.
good post only part i tought was not right was that pre-ignition. it is not worse than detonation pre ignition is still a burn when detonation is an explosion that smacks the top of the pistion which you do not want at all, all higher octane is is that it can handle more timing when you talk about or wanting cooler burns in example nitrometh burns cooler and slower but you need double the fuel supply to make the same power if not more
Hmmm interesting, thanks for the info!
I just noticed that my afr at idle is at like 16 or so with the ac on but when i turn it off the afr drop back down to 15, any ideas?
Thanks!!
Ok so this is what I am understanding:
87 or 110 the temps will remain the same in the combustion chamber. But wouldn't 100 octane have more burnable material in it opposed to 93 causing it to be cooler? I'm assuming the answer to this is no.
11.5:1 is going to burn cooler than 12.0:1 AFR
I though stoich was like idle/cruise afr, and that can be maniplated in the tune? Bot by octance rating, so what you are saying is that 100 octane may have a different afr than 93, bc my wideband doesn't show a difference whether I runn 100 or pump.
So is a degree of timing in refrence to an angle?
Any idea about my afr?
You're close...
Pre-ignition is a burn NOT caused by the spark plug. Pre-ignition happens when a piston or chambers area becomes hot enough (red hot) to ignite the mixture in the chamber which can happen when the piston is on the up-stroke. So naturally, ignited fuel mixture colliding with a piston on the upstoke = broken rods/crank/pistons.
Under normal conditions, the combusting air and fuel mixture inside the combustion chamber ignites in a controlled manner. The mixture is ignited by the spark, normally in the center of the cylinder, and a flame front moves from the spark towards the outside of the cylinder in a contolled burn. Detonation occurs when air and fuel that is ahead of the flame front ignites before the flame front arrives because it becomes overheated. Under these conditions, the combustion becomes uncontrolled and sporadic and often produces a pinging noise, or a "knock" noise when the conditions become worse. Detonation is a timing related issue (spark based event) usually happening at or near TDC when the piston is close or already on it's way down the bore...so it's more forgiving because it's not two forces colliding like with pre-ignition, instead it's a spark at the wrong time. A motor that is pinging can still run, but is just way down on power due to non-optimal spark event.
Burning cooler is kind of a way to describe nitromethane. Again you're close, but burning is still burning. But to "burn cooler" is kind of an oxymoron.
The high temperature of vaporization of nitromethane means that it will absorb substantial engine heat as it vaporizes, providing an invaluable cooling mechanism. The laminar flame speed and combustion temperature are higher than gasoline at 0.5 m/s and 2400 °C respectively. Power output can be increased by using very rich air fuel mixtures which also increases the cooling affect. This is also something that helps prevent pre-ignition, something that is usually a problem when using nitromethane. Due to the relatively slow burn rate of nitromethane, very rich fuel mixtures are often not fully ignited and some remaining nitromethane can escape from the exhaust pipe and ignite on contact with atmospheric oxygen, burning with a characteristic yellow flame. Additionally, after sufficient fuel has been combusted to consume all available oxygen, nitromethane can combust in the absence of atmospheric oxygen, producing hydrogen, which can often be seen burning from the exhaust pipes at night as a bright white flame.
You already answered the afr question.
So I know people run anywhere from 15-25+* of timing but what would be the result of running too little timing?
Thanks again!![/QUOc
car would perform like crap sluggish etc and you just leave alot power on the table
yes the preignition is not caused by the spark plug but by hotspots in the cylinder such as carbon which is still a burn rather than an explosive blast on top of the piston which you know causes alot of problems, now detonation is caused by overheating in the cylinder usually caused by a lean condition we can go in circles about which is worse and which will cause more enigne damage but what is seen doing more damage is detonation, now the oxymoron of it burning *cooler* which it actually does and reason why it takes 2x for the fuel supply thats why they are able to run very high on timing. either way we both are on same track just explained differently :beer: