Does 93 octane gas burn hotter than lower octane gas? [Archive] - Classic Cougar Forums

: Does 93 octane gas burn hotter than lower octane gas?



jimk127
July 4th, 2009, 12:44 AM
Does 93 octane gas burn hotter than the lower 87 or 89 octane gas?

CAL-KAT
July 4th, 2009, 02:25 AM
Does 93 octane gas burn hotter than the lower 87 or 89 octane gas?

Actually from what I read octane is a burn retardant - it burns cooler. It slows the bang down for a more even cooler burn. That's how higher octane 'cures' pinging - by burning cooler and calmer.In simpler terms higher octane tames the bang. Lower octane however will have a more more violent explosion for lack of a better way to explain it and burn hotter. When you have 87 octane this means roughly 87% octane and 13% heptane. It's the heptane in the gas that burns hotter which is why having high percentage mix of it in a high compression engine is a bad idea. and that's our chemistry lesson for the day. Tommorow we'll all learn about alcohol content in the blood on the holiday weekends..BURRRRRRP :beer:

S-Code
July 4th, 2009, 02:57 AM
I've read it burns slower so more of it is used efficiently which causes better gas mileage.

mopardon
July 4th, 2009, 03:09 AM
It also alows for higher compression ratios

Don

TundraCat
July 4th, 2009, 09:10 AM
I could be wrong but the higher octane seems to take a higher degree of timing, @ 36 degrees of timing with 93 octane the motor runs cooler and no pinging or surging vs. 87 octane seems to run 5-10 degrees hotter and engine pinging when getting on it. So I run straight gas, Shell 93 octane in my 69 351w,9.5 compression, converted to a 4 barrel when I really shouldn't have to.

catscratch
July 4th, 2009, 09:19 AM
The idea behind higher octane is that it is more difficult to ignite. Lower octane may begin to ignite prematurely, just from the heat of the cylinder or by compression. Higher octane will more likely wait for the actual spark. This is why it is neccessary for advanced timing and higher compression.
Not sure about hotter or colder.

DeadBoss302
July 4th, 2009, 10:31 AM
From what I've read, higher octane is more difficult to get to ignite but burns faster and hotter once it starts to burn. Lower octane ignites quicker but burns slower and cooler.

JimmyXR7
July 4th, 2009, 10:48 AM
Actually from what I read octane is a burn retardant - it burns cooler. It slows the bang down for a more even cooler burn. That's how higher octane 'cures' pinging - by burning cooler and calmer.In simpler terms higher octane tames the bang. Lower octane however will have a more more violent explosion for lack of a better way to explain it and burn hotter. . .

Good explanation. Also, when the lower octane makes the pinging the sonic explosion waves can cause the rings to vibrate and even unseat the rings temporary. Then more of the burning gases can leak by into the crankcase and less power. The correct octane is important is use. Donot use regular if your engine is rated for higher octane.

Jim

1970fastcat
July 4th, 2009, 11:15 AM
it doesnt burn cooler than lower octane, it just take a higher temp to make it burn, it actually burns hotter. I beilieve it is that for every 5 octane points it takes another 100 to ignite the fuel

jimk127
July 5th, 2009, 10:17 PM
Would the 93 octane make the engine temp higher than lower octane fuel?
I run 93 octane with a CR of 9.5:1. The engine temp runs between 200 and 210. Is the high temp because of the 93 octane?

68xr7gt4spd
July 5th, 2009, 11:12 PM
higher octane gas will make your engine run cooler. temperature does not ignite it, spark does.

1970fastcat
July 5th, 2009, 11:43 PM
higher octane gas will make your engine run cooler. temperature does not ignite it, spark does.

Oh no? then why when i ran 93 octane with 12.5:1 compression did i get detonation issues? Yet when i ran 114 it ran great. It may run cooler with higher octane, but only because it is running more efficient. Lower octane gas is essentially diesel fuel in high compression engines and will cause it to run hotter, and burn things up, but because it burns slower, not because it burns hotter. An engine with 9.5 should have 93 octane in it, if it were a 7.5 engine you wouldnt notice a differance between 87 and 114 as long as you have strong enough spark

yeloxr7
July 6th, 2009, 12:50 AM
Here come all the misconceptions and misinformation on octane/mileage/performance. Again.

My 69 Cougar 351W with standard compression (9.5:1?) and an Edelbrock Performer cam,manifold and carb, runs fine with no pinging on 87-octane fuel. And it gets reasonable mileage.

68xr7gt4spd
July 6th, 2009, 01:19 AM
Oh no? then why when i ran 93 octane with 12.5:1 compression did i get detonation issues? Yet when i ran 114 it ran great. It may run cooler with higher octane, but only because it is running more efficient. Lower octane gas is essentially diesel fuel in high compression engines and will cause it to run hotter, and burn things up, but because it burns slower, not because it burns hotter. An engine with 9.5 should have 93 octane in it, if it were a 7.5 engine you wouldnt notice a differance between 87 and 114 as long as you have strong enough spark



agreed on all. 93 octane would not be considered high octane in an an engine with 12.5:1 comp. preignition would be a given and it causes increased heat.

Udo
July 6th, 2009, 02:57 AM
When you have 87 octane this means roughly 87% octane and 13% heptane. It's the heptane in the gas that burns hotter which is why having high percentage mix of it in a high compression engine is a bad idea. and that's our chemistry lesson for the day.

Not to cause any more waves here, but where does that leave 114 octane fuel? -14% heptane? Not sure if your description is very accurate. (Keep in mind, I really know nothing about octane ratings, but I do know a bit about math)

1970fastcat
July 6th, 2009, 07:40 AM
Here come all the misconceptions and misinformation on octane/mileage/performance. Again.

My 69 Cougar 351W with standard compression (9.5:1?) and an Edelbrock Performer cam,manifold and carb, runs fine with no pinging on 87-octane fuel. And it gets reasonable mileage.

you are right, 87 would be fine to run as long as it is set up and timed right, i am just used to running 93 in my bike that has 10:1. I'm not throwing anything out there about mileage or performance, octane does not increase it. The only effect that octane has on mileage or performance if if you have too little octane for the setup you are running. As long as the engine runs efficiently on 87 you will not notice a difference if you try 93.

simon
July 6th, 2009, 08:18 AM
I once wrote emails to Shell and and BP. In their reply, they explained there would be no significant difference in burning temperature, but they also admitted that combustion research in general would still be in its early stages of development, compared to other sciences.

On the other hand, Korean manufacturer Hyundai and Ford Cologne do not permit the use of premium fuel in some of their cars that have been designed to run on regular gas, stating this would void the warranty and damage the catalytic converters due to the higher burning temperature of high test.

I run a low-compression 1972 block, Edelbrock F4B, standard camshaft, cheapo headers, and a 650cfm holley. On regular gas, it does not ping and gets 18 mpg. On premium, it does not ping either and gets the same mileage

jimk127
July 6th, 2009, 10:28 AM
Guys... I'm not concerned about gas milage, and the engine seems to run good with no pinging. My concern is engine temperature. My engine temp is 200 -210. 9.5:1 CR. Assuming all other factors are perfect, could the 200-210 temp be a result of 93 octane fuel?

1970fastcat
July 6th, 2009, 03:19 PM
no, shouldnt effect it, you can try 87 and see but it shouldnt make a difference, making sure the timing is set good would help a little

CAL-KAT
July 6th, 2009, 09:49 PM
Not to cause any more waves here, but where does that leave 114 octane fuel? -14% heptane? Not sure if your description is very accurate. (Keep in mind, I really know nothing about octane ratings, but I do know a bit about math)

The description is accurate. Granted with the math but some fuels are more knock-resistant than than your standard iso-octane at the pump so the definition has been extended to allow for octane numbers higher than 100. The perfect example is your product lines of race fuel. Use a 87 octane with a 12.5:1 compression and make sure you put that on youtube - the last sound you hear is the whistling noise from your wallet.

Bad69cat
July 9th, 2009, 01:30 AM
Looks like the octane rating debate could go for days. Heat = inefficiency. 200+ means that somehow you are not losing it quickly enough. Fuel is least likely the cause. I'd check several things - first pressure test your cooling system. Check your timing. What plugs are you running? You could try adjusting timing a bit if cooling looks good....

mopardon
July 9th, 2009, 01:41 AM
If you are running to lean ,That will cause the engine to run hotter.Check for vacume leaks and carb jetting

LeftHook
July 9th, 2009, 02:55 AM
Not to cause any more waves here, but where does that leave 114 octane fuel? -14% heptane? Not sure if your description is very accurate. (Keep in mind, I really know nothing about octane ratings, but I do know a bit about math)

87 Octane does not mean that it contains 13% octane.

Octane ratings are based off of a common standard. 87 octane will behave exactly the same as a mixture that is 87% iso-octane and 13% n-heptane... but it probably has different hydrocarbons altogether. 100 Octane will behave the same as 100% iso-octane. So 114 octane is fuel that behaves say 14% higher than 100% iso, if that makes sense. It is just applying the same scale mathematically.

Octane rating has nothing to do with the temperature at which it burns.. what it refers to is an anti-detonation rating, or more accurately, a detonation resistance rating.

Under a given pressure at a given heat, fuel will combust without the presence of a spark. This is what is known as "pre-detonation", "knocking", "pinging", etc.

It takes energy to create a chemical reaction. A lower octane will take less energy to create that reaction.. ie, if you are running higher compression and the motor is hot, you will create the reaction at an unpredictable moment, like before the spark is introduced.

One of the big reasons modern engines produce so much more hp these days is because of advances in cooling technology. When the combustion chamber is cooler (heat is energy, so less heat = less energy) then you can introduce more compression without the detonation.




If you are running to lean ,That will cause the engine to run hotter.Check for vacume leaks and carb jetting

bingo.


If the engine is running hotter, there is more than likely a mechanical reason for it.







Long story short is, if you are using higher octane than is necessary, you are generally just burning more expensive gas, in your vintage cars. There are some cleaning agents present in the higher octane fuels, but their usefulness is debatable at best.


Newer cars with knock sensors and such that will retard the timing you will actually be costing yourself hp and efficiency/fuel economy. If your owner's manual specifies premium, best to run premium.

69AIRCAT
August 31st, 2009, 11:07 PM
OK, OK, I give up, what octane fuel should I run in my 69 Cougar with a 351 4v. I am using the called for spark plugs???? I normally put Shell 93 octane fuel in the car.

CATDOG-427 GTE
August 31st, 2009, 11:32 PM
Keep on keepin' on!

adam 138
August 31st, 2009, 11:51 PM
If you can afford it run it. Doesn't seem to b any negative arguments about running 93 octane except the price.

73Qvert
September 1st, 2009, 09:31 AM
Higher octane does not burn any hotter than lower octane. It is all in the ratio, if your engine is set up correctly then 14 oxygen molecules to one molecule of octane will cause complete combustuion. If it is 12:1 then you are burning rich, 16:1 will be lean. This is why putting in a higher rated octane gasoline than needed is a waste of fuel. It will just spit out the unburned hydrocarbons out the tail pipe.