87 Octane - Page 4 - Camaro5 Chevy Camaro Forum / Camaro ZL1, SS and V6 Forums

SnowyCamaro · 06-19-2016, 05:26 PM

This is really drawn out. Engine has knock sensors and will retard timing as needed based on knock heard by them.

If you fill up with 87 it will knock, sensor hears that and pulls timing to protect itself. It can't detect octane. It just pushes timing as far forward as it can with the given conditions.

Now although you don't hear it knock it likely did a couple of times before it pulled timing. Every knock is added stress on the pistons. Now I don't know what the metallurgy of the pistons are and how resistant they are to fatigue or metal creep. But over time it could be bad. Kinda like death by a thousand cuts right? The more you smack that piston the wrong way, the more chances of it cracking.

Give her a gas card maybe? And explain to her why it's needed cause it could cost you later. On top of that as much as the 87 is cheaper it's hurting fuel efficiency as well. I bet it's almost the same cost per mile driven with the premium fuel.

flipstyledsm22 · 06-20-2016, 08:49 AM

So how does this knock work? Are the top of the pistons smacking the valves? I thought when a piston was at top dead center, it is still supposed to have clearance?

Hocky · 06-20-2016, 09:46 AM

Quote:

Originally Posted by flipstyledsm22

So how does this knock work? Are the top of the pistons smacking the valves? I thought when a piston was at top dead center, it is still supposed to have clearance?

Knock is when the mixture uncontrollably ignites before the spark plugs fire, well before top dead center. It hammers down on the piston while it is still climbing up the cylinder wall and creates a massive pressure spikes when it does. It breaks stuff - pistons, bearings, rods. It is bad news.

ZO6 Bryan · 06-20-2016, 11:14 AM

Think of it like this. A controlled burn is like pushing the piston down smoothly vs detonation is like hitting the piston with a hammer.

Stephen12ZL1 · 06-20-2016, 11:40 AM

preignition/detonation occurs when the mixture burns too quickly due to many factors especially inadequate octane and too much ignition advance. That's why higher octane helps because it slows the combustion flame. So many people think higher octane fuel burns faster thereby making more horsepower...wrong answer!

SnowyCamaro · 06-20-2016, 08:11 PM

Octane is resistance to pre detonation. Meaning it resists being ignited by pressure. You can ignite fuel by spark or by pressure (diesel motors use pressure). One of the largest factors that affects efficiency and power is compression ratio the higher the ratio the higher the potential power and efficiency available. This is why higher horsepower cars have high compression ratio and by consequence more power. You'll notice the really efficient cars now have high octane required for this reason.

Now fuel actually has a flame front and a pressure front. The pressure front comes after the flame. You want to maximize the pressure front for the power stroke so your car will actually ignite the fuel before top dead center and then the pressure front will push the piston down as the reaction expands. This is what pushing / pulling timing does. If you ignite the fuel too early that pressure front can start expanding in the wrong direction ie before tdc creating knock. You can also cause the fuel to ignite by pressure which causes ignition at the wrong point in the cycle and also creates knock.

There is a good thread explain this in more detail. Let me find it.

SnowyCamaro · 06-20-2016, 08:18 PM

Read post number 5

http://www.camaro5.com/forums/showthread.php?t=453440

Now imagine you are spinning a bicycle wheel by hand. It's easy to keep the wheel spinning the same direction if you hit the wheel with your hand at a tangential point. If you try to hit it the opposite direction it hurts your hand. That's because you changed the direction of force being applied. Same goes for you pistons they are already in motion in one direction you induce knock by trying to push them the wrong way.

Even better example, you are driving on the freeway and get rear ended by someone going 50mph you are both doing about that speed so it didn't hurt that much he just pushed you forward a little faster. Now you are going the opposite way on the freeway and that guy hits you head on.... going to hurt a lot more....Same concept. Now that guy maybe didn't hit you that hard, you can still drive so you keep going then another car comes (another knock) and smacks you again. How long can you last with repeated blows? Well that's the question here right? And that's why GM doesn't give a definitive answer cause they can't the pistons aren't designed for knock but they are designed to handle some but how long will it take to create a stress point in the piston and eventually a crack... well that's all related to how good their casting was of that piston when it was manufactured. And any metal engineer will tell you that on a microscopic level no casting is ever identical to the last.

Capt'n ZL1 · 06-20-2016, 10:03 PM

I would hide the keys

flipstyledsm22 · 06-21-2016, 07:49 AM

Quote:

Originally Posted by SnowyCamaro

Read post number 5

http://www.camaro5.com/forums/showthread.php?t=453440

Now imagine you are spinning a bicycle wheel by hand. It's easy to keep the wheel spinning the same direction if you hit the wheel with your hand at a tangential point. If you try to hit it the opposite direction it hurts your hand. That's because you changed the direction of force being applied. Same goes for you pistons they are already in motion in one direction you induce knock by trying to push them the wrong way.

Even better example, you are driving on the freeway and get rear ended by someone going 50mph you are both doing about that speed so it didn't hurt that much he just pushed you forward a little faster. Now you are going the opposite way on the freeway and that guy hits you head on.... going to hurt a lot more....Same concept. Now that guy maybe didn't hit you that hard, you can still drive so you keep going then another car comes (another knock) and smacks you again. How long can you last with repeated blows? Well that's the question here right? And that's why GM doesn't give a definitive answer cause they can't the pistons aren't designed for knock but they are designed to handle some but how long will it take to create a stress point in the piston and eventually a crack... well that's all related to how good their casting was of that piston when it was manufactured. And any metal engineer will tell you that on a microscopic level no casting is ever identical to the last.

Great read! So much information!

m1key1111 · 06-21-2016, 12:24 PM

Tell her it's like using cheap toilet paper, while it works and gets the job done spending a couple extra bucks to get the good stuff goes a long way :-)

flipstyledsm22 · 06-21-2016, 05:41 PM

I already told her if the motor goes because of cheap gas, the money is coming out of her jeep fund.

Sven59 · 06-21-2016, 06:50 PM

I think you will be fine, I think you can trust the engineers, they built a beast.

06-19-2016, 05:26 PM	#43
SnowyCamaro Drives: 2013 Camaro ZL1, 2006 Chevy Equinox Join Date: Apr 2013 Location: Ontario, Canada Posts: 833	This is really drawn out. Engine has knock sensors and will retard timing as needed based on knock heard by them. If you fill up with 87 it will knock, sensor hears that and pulls timing to protect itself. It can't detect octane. It just pushes timing as far forward as it can with the given conditions. Now although you don't hear it knock it likely did a couple of times before it pulled timing. Every knock is added stress on the pistons. Now I don't know what the metallurgy of the pistons are and how resistant they are to fatigue or metal creep. But over time it could be bad. Kinda like death by a thousand cuts right? The more you smack that piston the wrong way, the more chances of it cracking. Give her a gas card maybe? And explain to her why it's needed cause it could cost you later. On top of that as much as the 87 is cheaper it's hurting fuel efficiency as well. I bet it's almost the same cost per mile driven with the premium fuel. __________________

06-20-2016, 08:49 AM	#44
flipstyledsm22 Let's go fishing! Drives: a car with 8 cylinders Join Date: Apr 2016 Location: Seabrook, Texas Posts: 1,129 View My Garage	So how does this knock work? Are the top of the pistons smacking the valves? I thought when a piston was at top dead center, it is still supposed to have clearance? __________________ "When choosing between two evils, I always like to try the one I’ve never tried before." Mae West 1892-1980

06-20-2016, 11:14 AM	#46
ZO6 Bryan Drives: 02 Z06, 95 Trans Am, 2012 ZL1 Join Date: Mar 2012 Location: Southeast Posts: 1,838 View My Garage	Think of it like this. A controlled burn is like pushing the piston down smoothly vs detonation is like hitting the piston with a hammer. __________________ Bryan 2018 ZL1 M6

06-20-2016, 11:40 AM	#47
Stephen12ZL1 Drives: '21 ZLE A10 Join Date: May 2012 Location: Mechanicsville, VA Posts: 6,824	preignition/detonation occurs when the mixture burns too quickly due to many factors especially inadequate octane and too much ignition advance. That's why higher octane helps because it slows the combustion flame. So many people think higher octane fuel burns faster thereby making more horsepower...wrong answer! __________________ '21 ZLE A10 Wild Cherry PDR 2:00.78 VIR Full 10.68@131.69 1.68 60' '17 ZL1 A10 Mosaic Black PDR/Nav 2:03.08 VIR Full 11.003@129.2 1.75 (sold) '15 Z/28 #325 Black a/c & stereo. 2:10.1 VIR Full (sold) '12 ZL1 A6 Black 10.52@131 1.55 60' 2:13 VIR Full (sold)

06-20-2016, 08:11 PM	#48
SnowyCamaro Drives: 2013 Camaro ZL1, 2006 Chevy Equinox Join Date: Apr 2013 Location: Ontario, Canada Posts: 833	Octane is resistance to pre detonation. Meaning it resists being ignited by pressure. You can ignite fuel by spark or by pressure (diesel motors use pressure). One of the largest factors that affects efficiency and power is compression ratio the higher the ratio the higher the potential power and efficiency available. This is why higher horsepower cars have high compression ratio and by consequence more power. You'll notice the really efficient cars now have high octane required for this reason. Now fuel actually has a flame front and a pressure front. The pressure front comes after the flame. You want to maximize the pressure front for the power stroke so your car will actually ignite the fuel before top dead center and then the pressure front will push the piston down as the reaction expands. This is what pushing / pulling timing does. If you ignite the fuel too early that pressure front can start expanding in the wrong direction ie before tdc creating knock. You can also cause the fuel to ignite by pressure which causes ignition at the wrong point in the cycle and also creates knock. There is a good thread explain this in more detail. Let me find it. __________________

06-20-2016, 08:18 PM	#49
SnowyCamaro Drives: 2013 Camaro ZL1, 2006 Chevy Equinox Join Date: Apr 2013 Location: Ontario, Canada Posts: 833	Read post number 5 http://www.camaro5.com/forums/showthread.php?t=453440 Now imagine you are spinning a bicycle wheel by hand. It's easy to keep the wheel spinning the same direction if you hit the wheel with your hand at a tangential point. If you try to hit it the opposite direction it hurts your hand. That's because you changed the direction of force being applied. Same goes for you pistons they are already in motion in one direction you induce knock by trying to push them the wrong way. Even better example, you are driving on the freeway and get rear ended by someone going 50mph you are both doing about that speed so it didn't hurt that much he just pushed you forward a little faster. Now you are going the opposite way on the freeway and that guy hits you head on.... going to hurt a lot more....Same concept. Now that guy maybe didn't hit you that hard, you can still drive so you keep going then another car comes (another knock) and smacks you again. How long can you last with repeated blows? Well that's the question here right? And that's why GM doesn't give a definitive answer cause they can't the pistons aren't designed for knock but they are designed to handle some but how long will it take to create a stress point in the piston and eventually a crack... well that's all related to how good their casting was of that piston when it was manufactured. And any metal engineer will tell you that on a microscopic level no casting is ever identical to the last. __________________ Last edited by SnowyCamaro; 06-20-2016 at 08:28 PM.

06-20-2016, 10:03 PM	#50
Capt'n ZL1 Drives: 2015 Camaro ZL1 SW # 945 Join Date: Feb 2015 Location: Omaha Posts: 73 View My Garage	I would hide the keys

06-21-2016, 12:24 PM	#52
m1key1111 Drives: 2012 ZL1 Join Date: Nov 2015 Location: Atlanta GA Posts: 88	Tell her it's like using cheap toilet paper, while it works and gets the job done spending a couple extra bucks to get the good stuff goes a long way :-)

06-21-2016, 05:41 PM	#53
flipstyledsm22 Let's go fishing! Drives: a car with 8 cylinders Join Date: Apr 2016 Location: Seabrook, Texas Posts: 1,129 View My Garage	I already told her if the motor goes because of cheap gas, the money is coming out of her jeep fund. __________________ "When choosing between two evils, I always like to try the one I’ve never tried before." Mae West 1892-1980

06-21-2016, 06:50 PM	#54
Sven59 HAMMER PILOT Drives: 13 ZL1#182, 85 CJ7, 16 Silverado Join Date: Nov 2011 Location: Tucson AZ Posts: 4,387	I think you will be fine, I think you can trust the engineers, they built a beast. __________________ "DO YOU WANT ME TO PUT THE HAMMER DOWN?"