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The "wherethefuckdoesthisbelonganyway" thread

Westy

Westy

the teste
Nov 22, 2002
55,944
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Sleazattle
kidwoo said:
?

Higher air density = greater tendency for detonation
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At a given power output the cylinder pressure will be the same but with lower temps. At max power it would largely be a wash but the components in the cylinder will still be cooler and detonation is usually started at a hot spot. So under normal driving conditions the risk will definitely be lower. If you are at full throttle for extended periods the risks would probably be marginally lower.
 
kidwoo

kidwoo

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Aug 25, 2003
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Westy said:
At a given power output the cylinder pressure will be the same but with lower temps. At max power it would largely be a wash but the components in the cylinder will still be cooler and detonation is usually started at a hot spot. So under normal driving conditions the risk will definitely be lower. If you are at full throttle for extended periods the risks would probably be marginally lower.
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I would think it would be less variation on the high comp type motors that would need the higher octane.....

moar air = moar fuel on injected motors sure but if your car needs 91, I would think it just needs 91. The spark temp stays the same but there's definitely more air being compressed = higher real time compression

brb......pv=nRT
 
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Westy

Westy

the teste
Nov 22, 2002
55,944
21,975
Sleazattle
kidwoo said:
I would think it would be less variation on the high comp type motors that would need the higher octane.....

moar air = moar fuel on injected motors sure but if your car needs 91, I would think it just needs 91. The spark temp stays the same but there's definitely more air being compressed = higher real time compression
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Think of it this way, if you need 10 HP to drive at a specific speed on a colder day the air will be denser, so you will require a smaller throttle opening to achieve the 10 HP, which will actually expand and further cool the air as it enters the cylinder which will ultimately run the same peak pressures but at much lower temperatures. Detonation is a function of density and temperature, so at a given power output the detonation risk is much lower.

At wide open throttle you will get more air into the cylinder but at a lower temp, peak pressure will be higher but temperatures will still be lower so possibly a wash, but hot spots in the cylinder such as the spark plugs will be cooled a lot more by the denser cooler intake charge so the hot spots will be a heck of lot cooler and less likely to initiate detonation.
 
kidwoo

kidwoo

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Aug 25, 2003
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Westy said:
Think of it this way, if you need 10 HP to drive at a specific speed on a colder day the air will be denser, so you will require a smaller throttle opening to achieve the 10 HP, which will actually expand and further cool the air as it enters the cylinder which will ultimately run the same peak pressures but at much lower temperatures. Detonation is a function of density and temperature, so at a given power output the detonation risk is much lower.

At wide open throttle you will get more air into the cylinder but at a lower temp, peak pressure will be higher but temperatures will still be lower so possibly a wash, but hot spots in the cylinder such as the spark plugs will be cooled a lot more by the denser cooler intake charge so the hot spots will be a heck of lot cooler and less likely to initiate detonation.
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did you just to tell this guy to drive his corvette slowly?

 
Jm_

Jm_

sled dog's bollocks
Jan 14, 2002
20,065
10,630
AK
Detonation and cars pulling timing to prevent it is definitely more of a concern with hot and high density altitude. Basically, the hotter and higher, the worse it is. Most modern cars, even those that use higher octane, will pull timing to prevent damage in those conditions, but then you'll be more limited on power and less efficient for that engine. My WRX would go into "limp mode" in Phoenix at times for this reason. Anything that is high compression, whether by compression ratio or forced induction, generally loves higher octane, but depending on environmental conditions, you may not need to go super high to prevent pulling timing and then there are the people that will do "race tunes" to take advantage of race fuel.

And then with airplanes, they tell us to "richen the mixture" to prevent or fix detonation, usually a result from running too lean. The additional fuel vaporizing only helps to cool. That's one of the reasons turbo-engines ram down the fuel during acceleration, if you've ever looked at the fuel/air ratio on a tuner while they are doing it, you see ridiculous numbers that NA engines do not come close to, because they are using fuel to help cool and prevent detonation.
 
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Westy

Westy

the teste
Nov 22, 2002
55,944
21,975
Sleazattle
Jm_ said:
Detonation and cars pulling timing to prevent it is definitely more of a concern with hot and high density altitude. Basically, the hotter and higher, the worse it is. Most modern cars, even those that use higher octane, will pull timing to prevent damage in those conditions, but then you'll be more limited on power and less efficient for that engine. My WRX would go into "limp mode" in Phoenix at times for this reason. Anything that is high compression, whether by compression ratio or forced induction, generally loves higher octane, but depending on environmental conditions, you may not need to go super high to prevent pulling timing and then there are the people that will do "race tunes" to take advantage of race fuel.

And then with airplanes, they tell us to "richen the mixture" to prevent or fix detonation, usually a result from running too lean. The additional fuel vaporizing only helps to cool. That's one of the reasons turbo-engines ram down the fuel during acceleration, if you've ever looked at the fuel/air ratio on a tuner while they are doing it, you see ridiculous numbers that NA engines do not come close to, because they are using fuel to help cool and prevent detonation.
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Modern CPUs can do a lot of shit to avoid detonation including changing cam timing to reduce the dynamic compression ratio.


Water/Methanol injection adds power by cooling the intake charge, but on its own it does little to nothing, what it allows you to do is run much higher compression or boost by reducing the risk of detonation by cooling the IATs.
 
MonkeyGut

MonkeyGut

Monkey
Dec 8, 2006
163
108
I should have mentioned it was gas for my moto. I use StarTron in the ethanol laced crap when it's the only gas available. My sweetie has never had a drink of ethanol, she's a sober bitch.
 
mandown

mandown

Poopdeck Repost
Jun 1, 2004
21,626
9,003
Transylvania 90210
Atomic Dog said:
Wife looked at me like I was out of my mind last year when we happened to walk past Hollywood High and I just stood there for a moment, gawking at that handrail.
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Just down the street from me. I don’t go by there often but over the last couple of decades I’ve certainly seen a few attempts at it.
 
6thElement

6thElement

Schrodinger's Immigrant
Jul 29, 2008
17,149
14,625
kidwoo said:
okay that post is still showing up blank for me. I was joking when I responded to it because there's nothing there.

@Westy is that a facebook image or something?
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Code: 
<img class="lg-object lg-image" src="https://scontent-sea1-1.xx.fbcdn.net/v/t31.18172-8/23735975_1977985209125011_2107249354430762071_o.jpg?_nc_cat=106&amp;ccb=1-7&amp;_nc_sid=7f8c78&amp;_nc_ohc=seBEYnI34XoAX-W14Fo&amp;_nc_ht=scontent-sea1-1.xx&amp;oh=00_AfC1sY5VgAF4wvmk47_FBWXD7SHhpRSychE9_-GW5yysvQ&amp;oe=65CBFF75" data-scale="1" style="transform: scale3d(1, 1, 1);">
 
kidwoo

kidwoo

Artisanal Tweet Curator
Aug 25, 2003
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Squirtin ketchup n' mustard on charred flesh
6thElement said:
Code: 
<img class="lg-object lg-image" src="https://scontent-sea1-1.xx.fbcdn.net/v/t31.18172-8/23735975_1977985209125011_2107249354430762071_o.jpg?_nc_cat=106&amp;ccb=1-7&amp;_nc_sid=7f8c78&amp;_nc_ohc=seBEYnI34XoAX-W14Fo&amp;_nc_ht=scontent-sea1-1.xx&amp;oh=00_AfC1sY5VgAF4wvmk47_FBWXD7SHhpRSychE9_-GW5yysvQ&amp;oe=65CBFF75" data-scale="1" style="transform: scale3d(1, 1, 1);">
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yeah that's facebook

ever since the war on terror I've made myself safeandsecure™
 
Toshi

Toshi

butthole powerwashing evangelist
Oct 23, 2001
39,638
8,684
that's why you should remember to wear your plastic ass plug when flying

/tmyk
 
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