regular vs. premium gasoline?

[GalvanizedYankee]

I don't have it in front of me, but I bet the BTUs per gallon is the same 87-93 octane.

Octane is resistance to detonate or self ignite in the presence of pressure and heat in the chamber.
I'm not being a smart ass, reread my other post slowly. There are 130HP, 1.0L engines that run low octane fuel.


NOTE: Diesel fuel has 30% more BTUs per gal than gasoline and runs 19 to 1 compression. That's where it's mpg comes from.

 

[Eli]

I can't find energy specs for the specific grades, but...

A gallon of gasoline contains 109,000 to 125,000BTU, with the average being about 114,000BTU.

Diesel contains between 128,000 and 130,000BTU. That is one of the reasons that diesel powered cars get better gas milage, ontop of the diesel engine just being more efficient.

E85(85% Ethanol, 15% gasoline, a proposed alternative) contains ~81,000BTU/gal.

Pure ethanol contains appx. 75,000BTU/gallon.. MTBE contains appx. 93,000BTU/gal. That is one of the reasons why it is preferred over ethanol, but it is also toxic(compared to ethanol).

So, you can see that by adding oxygenates, it "dilutes" the overall energy content of the gasoline, while raising the octane.

 

[JBT]

MY GF's 95 Civic gets spark knock unless she puts in 93.

 

[Eli]

Originally posted by: galvanizedyankee
I don't have it in front of me, but I bet the BTUs per gallon is the same 87-93 octane.

Octane is resistance to detonate or self ignite in the presence of pressure and heat in the chamber.
I'm not being a smart ass, reread my other post slowly. There are 130HP, 1.0L engines that run low octane fuel.


NOTE: Diesel fuel has 30% more BTUs per gal than gasoline and runs 19 to 1 compression. That's where it's mpg comes from.

You're basically right. According to Chevron, the difference in potential heat is less than 1% between the grades. Oxygenating gasoline with a 10% Ethanol or 15% MTBE lowers its energy content by 3%, from 114,900BTU/gal to 111,400BTU/gal. But they can make up for the energy difference by reformulating the gasoline- obviously the formulations for the different grades must be different, or they would have to add different percentages of the oxygenates to get the correct octane rating.

So yeah, the energy issue is pretty much moot. The bottom line is that it is a waste of money.

 

[Howard]

Originally posted by: galvanizedyankee
I don't have it in front of me, but I bet the BTUs per gallon is the same 87-93 octane.

Octane is resistance to detonate or self ignite in the presence of pressure and heat in the chamber.
I'm not being a smart ass, reread my other post slowly. There are 130HP, 1.0L engines that run low octane fuel.


NOTE: Diesel fuel has 30% more BTUs per gal than gasoline and runs 19 to 1 compression. That's where it's mpg comes from.

Many run a compression ratio higher than that.

 

[Wheatmaster]

so can anyone some up this stuff in english? I don't understand much of it

 

[Crappopotamus]

ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

 

[NutBucket]

Originally posted by: JBT
MY GF's 95 Civic gets spark knock unless she puts in 93.

The somethings wrong with her car cause that ain't right.

 

[Eli]

Originally posted by: Wheatmaster
so can anyone some up this stuff in english? I don't understand much of it

Cliff notes:

RTFM.

 

[fyleow]

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

 

[Eli]

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

A higher compression ratio more than makes up for the energy difference. The higher the compression ratio, the more efficient the engine is, and the more force is exerted on the top of the piston.

 

[Wheatmaster]

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

 

[fyleow]

Originally posted by: Wheatmaster

Originally posted by: fyleow

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Read the thread, high performance engines need high octane fuel or they will knock.

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

It's all about the compression ratios. If your car manual says to use regular unleaded then just use that and don't worry about it.

 

[Eli]

Originally posted by: Wheatmaster

so most sedans like honda accord and ford taurus don't need premium fuel? why the heck do people buy it then?

Because they are uneducated.

It's actually genius, to call the higher grades of gasoline "plus" and "premium". It invokes some sense of quality, when in reality it has nothing to do with it.

Infact, it's entirely possible that Regular from one station could be better(higher quality), than Premium from another.. in theory, at least. Thankfully, we have gasoline quality checks here in Oregon.

We didn't until a few years ago, and some shady stations were known for mixing things like water in with their gasoline to stretch it out. :|

 

[JBT]

Originally posted by: NutBucket

Originally posted by: JBT
MY GF's 95 Civic gets spark knock unless she puts in 93.

The somethings wrong with her car cause that ain't right.

oh I know that the car plain sucks unless you go over 80mph on hills your going down to 65. There are a lot of hills here in Vermont so yeah it sucks and I hate driving the stupid car.

The manual says it takes 87 but 93 gets rid of the knock so she uses that.

 

[fyleow]

Originally posted by: JBT

Originally posted by: NutBucket

Originally posted by: JBT
MY GF's 95 Civic gets spark knock unless she puts in 93.

The somethings wrong with her car cause that ain't right.

oh I know that the car plain sucks unless you go over 80mph on hills your going down to 65. There are a lot of hills here in Vermont so yeah it sucks and I hate driving the stupid car.

The manual says it takes 87 but 93 gets rid of the knock so she uses that.

I'm no car expert but I think when you can actually tell the engine is knocking there are already serious problems with it?

 

[bigredguy]

POLL!

 

[GalvanizedYankee]

Originally posted by: Wheatmaster
so can anyone some up this stuff in english? I don't understand much of it

This should be a good read, I scanned it and it reads well. Roger recommended this site...
Text.. Read me slowly.


Not all high performance engines require 91 octane. This is a fact. We are talking non-owner modified..Mmmmkay.

 

[Pacfanweb]

Looking over the thread here, I've seen some good info and some bad.

Good: No advantage to using higher octane unless your car needs it. Just pissing away money otherwise.

Bad: Gonna have to disagree with my buddy ZV here, using higher octane most certainly DOES leave carbon deposits in your engine if it isn't designed for it.
I've seen too many engines that were designed for regular disassembled where folks used premium anyway, and the carbon deposits are amazing. Regular leaves enough carbon as it is.

Higher octane is harder to ignite, and burns slower. Don't believe me? Get a cup of regular, then get a cup of high octane, find some really high octane racing gas if you can.
Pour them on the ground a couple of feet apart and ignite: The regular will burn out much faster.

So basically: if your engine is designed to get a complete burn with 87 octane, it will NOT get a complete burn with 93.
Period, end of story.

 

[Pacfanweb]

Originally posted by: Crappopotamus
ive been filling the max with regular gas for its whole life. i heard that you should fill it with premium, or it will knock, and permanently damage the engine and or trigger the knock sensor, which will make the engine automatically scale down. oh well. :|

and if higher octane fuel is less powerful, why do people fill up with premium before hitting the racetrack?

Only helps them if their car can utilize the higher octane, otherwise, it's just making them feel better.

Cars that are designed to run on premium, but say you can run regular simply pull the timing back automatically when detonation is detected.
If no detonation is present, it will jack the timing back up for max power. Simple as that.

 

[Pacfanweb]

Originally posted by: JBT

Originally posted by: NutBucket

Originally posted by: JBT
MY GF's 95 Civic gets spark knock unless she puts in 93.

The somethings wrong with her car cause that ain't right.

oh I know that the car plain sucks unless you go over 80mph on hills your going down to 65. There are a lot of hills here in Vermont so yeah it sucks and I hate driving the stupid car.

The manual says it takes 87 but 93 gets rid of the knock so she uses that.

What does the manual recommend? If is says use 87, then the combustion chambers or pistons are likely carboned up, which can cause spark knock two ways:
1. Carbon can effectively raise your compression ratio by simply taking up space.
2. Carbon can get a hot, glowing spot that can act like a spark plug and ignite the fuel/air mixture prematurely.

Either is very common in older, higher mileage cars. A good carbon clean would probably help.

 

[Pacfanweb]

Originally posted by: Wheatmaster
so can anyone some up this stuff in english? I don't understand much of it

Use regular unless your car's manual specifies otherwise, or you just like giving money away. If the latter is the case, I'll send you my paypal address so you can hook me up.

 

[Eli]

Originally posted by: Pacfanweb
Looking over the thread here, I've seen some good info and some bad.

Good: No advantage to using higher octane unless your car needs it. Just pissing away money otherwise.

Bad: Gonna have to disagree with my buddy ZV here, using higher octane most certainly DOES leave carbon deposits in your engine if it isn't designed for it.
I've seen too many engines that were designed for regular disassembled where folks used premium anyway, and the carbon deposits are amazing. Regular leaves enough carbon as it is.

Higher octane is harder to ignite, and burns slower. Don't believe me? Get a cup of regular, then get a cup of high octane, find some really high octane racing gas if you can.
Pour them on the ground a couple of feet apart and ignite: The regular will burn out much faster.

So basically: if your engine is designed to get a complete burn with 87 octane, it will NOT get a complete burn with 93.
Period, end of story.

I would like to add to ZV's point..

Like anything else, it is going to depend on the operating conditions. Like you and I said, carbon deposits can be bad enough in an engine that is running on the proper spec gasoline. Complete burn just doesen't happen at low RPMs. So unless you regularly go WOT, it's probably a good thing to avoid. Carbon deposits can cause problems later in engine life.. As they build up, the compression ratio rises. It can also produce hotspots that can lead to preignition.

Heh.. In some Kart racing circles, it is common practice to run the engine extremely rich for a while, to build up carbon and raise the effective compression ratio, without violating the racing sanctions. Kinda a ghetto way to get a bit more power.

 

[Pacfanweb]

Originally posted by: Eli

Originally posted by: Pacfanweb
Heh.. In some Kart racing circles, it is common practice to run the engine extremely rich for a while, to build up carbon and raise the effective compression ratio, without violating the racing sanctions. Kinda a ghetto way to get a bit more power.

Interesting. I have no doubt that it works, too.
Guess if the rules limit you, you gotta find an edge somehow. Seems like after they started running WOT the carbon would go away, though, but maybe it doesn't.

 

[GalvanizedYankee]

A layer of carbon can provide some insulation, a heat barrier of sorts. There would be less heat loss into the head and piston so there would be a slight net gain in HP.

Racers are known to treat the cooling passages of aluminum heads with chemicals so the alloy doesn't suck off too much heat. Put too thick of a coating on and it will move into pre-ignition. The famous Smokey was one of the first to do this. If your interested in it Eli, I will PM you the books ISBN#.