Fuel choice..
August 7th, 2011, 02:16 PM
#1
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Fuel choice..
Didn't want to hijack another thread... I have seen the below statement more than once, so now I believe that it is time to get to the reasoning part. I have deleted the original posters name, since he isn't the only one to have made this statement.
I have seen this statement more than once, and I would like to hear the explanation as to why the engine will run worse on a premium fuel than on regular fuel. I will agree that it might not run better, but worse... I can't comprehend why.
I wouldn't put premium in it unless that's what's called for in the owner's manual. An engine not designed to run on premium won't run better with it and will likely run worse.
August 7th, 2011, 02:33 PM
#2
Connoisseur d'Junque
Join Date: Sep 2010
Location: The Hudson Valley
Posts: 21,183
Yeah. I remember when this comment was posted, and I decided to keep quiet so as not to sound like a jerk and distract the thread.
It's obvious BS.
The only significant difference (petroleum chemists, feel free to contradict me here...) between Premium and Regular is the octane rating, which is arrived at by measuring actual engine knock in a specially designed test engine. The difference in octane is achieved through the use of different amounts of certain additives. In the old days, it depended pretty much on tetraethyl lead, which is no longer used, so now it depends on other chemicals.
In practice, Premium gasoline is less likely to ignite under conditions of high pressure and temperature than Regular gasoline is, so it can be used in higher compression engines without causing preignition.
Aside from this one quality, there is no meaningful difference between the tow types of gas. If an engine has high cylinder pressures, Premium will convey an advantage over Regular. If it does not, then there is no advantage to Premium, and no perceptible difference between the behavior of Regular and of Premium.
You can use Premium gas in any gasoline engine (or, rather, any gasoline engine that doesn't require race gas), but you can't use Regular in engines that require Premium.
If you choose to use Premium in a low compression engine, you will be wasting your money, but there will be no other difference.
- Eric
It's obvious BS.
The only significant difference (petroleum chemists, feel free to contradict me here...) between Premium and Regular is the octane rating, which is arrived at by measuring actual engine knock in a specially designed test engine. The difference in octane is achieved through the use of different amounts of certain additives. In the old days, it depended pretty much on tetraethyl lead, which is no longer used, so now it depends on other chemicals.
In practice, Premium gasoline is less likely to ignite under conditions of high pressure and temperature than Regular gasoline is, so it can be used in higher compression engines without causing preignition.
Aside from this one quality, there is no meaningful difference between the tow types of gas. If an engine has high cylinder pressures, Premium will convey an advantage over Regular. If it does not, then there is no advantage to Premium, and no perceptible difference between the behavior of Regular and of Premium.
You can use Premium gas in any gasoline engine (or, rather, any gasoline engine that doesn't require race gas), but you can't use Regular in engines that require Premium.
If you choose to use Premium in a low compression engine, you will be wasting your money, but there will be no other difference.
- Eric
August 7th, 2011, 02:40 PM
#3
Just an Olds Guy
Join Date: Jul 2008
Location: Edmonton, AB. And "I am Can 'eh' jun - eh"
Posts: 24,525
Junkman,
I believe it has something to do with the detonation on the octane. The higher octane fuels combust differently than lower ones and if (an older) car isn't tuned right to the fuel you can get pre ignition and / or overheating + a crappy performance. New cars will burn almost anything nowadays because engines have anti knock sensors that feed info to the on board computers to control timing /firing.
I recently ran 2 tanks of premium through my 72 350 on a mechanics recommendation. I didn't notice any difference in the engine running smoother or more efficiently. Up here premium is anywhere from 91 to 94 octane. Price between regular and premium is approx 10 cents/litre (or around 40 cents a US gallon). All I did was spend more money to drive around. Maybe if I played with the timing to bump it up to 16 or 18 BTDC instead of leaving it at 12 there might be some difference. But in todays high priced gas markets, I'll keep putting in regular because I can't see any benefit from premium. And it meets the requirement set out in the 1972 owner manual.
Also, FWIW the standards for octane ratings have changed since the 72 model year. What we used to run as 91 octane back in the day is the same as 87 octane (not flex fuel) today. Don't know that this helps you any, but it's what I've run into.
I believe it has something to do with the detonation on the octane. The higher octane fuels combust differently than lower ones and if (an older) car isn't tuned right to the fuel you can get pre ignition and / or overheating + a crappy performance. New cars will burn almost anything nowadays because engines have anti knock sensors that feed info to the on board computers to control timing /firing.
I recently ran 2 tanks of premium through my 72 350 on a mechanics recommendation. I didn't notice any difference in the engine running smoother or more efficiently. Up here premium is anywhere from 91 to 94 octane. Price between regular and premium is approx 10 cents/litre (or around 40 cents a US gallon). All I did was spend more money to drive around. Maybe if I played with the timing to bump it up to 16 or 18 BTDC instead of leaving it at 12 there might be some difference. But in todays high priced gas markets, I'll keep putting in regular because I can't see any benefit from premium. And it meets the requirement set out in the 1972 owner manual.
Also, FWIW the standards for octane ratings have changed since the 72 model year. What we used to run as 91 octane back in the day is the same as 87 octane (not flex fuel) today. Don't know that this helps you any, but it's what I've run into.
August 7th, 2011, 04:01 PM
#4
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Location: Colts Neck, NJ
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OK, let me stick my neck out. I agree with Eric except in one situation. If you advance your car's timing significantly in order to boost power - which I am pretty sure it will - then you might need premium to avoid knock.
August 7th, 2011, 04:25 PM
#5
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Location: Poteau, Ok
Posts: 41,053
You can run regular in a most vehicles that requires premium. Todays computer systems will compensate for it! Understandably, you won't get the engine to perform the way it would with premium. I don't recommend it in permance motors, But cars like Lincoln LS's, T'birds, for example all required premium and alot of owners chose to run them on regular, with no apparent issues!
I run my 330HC/4V on the midgrade 91 with no pinging in 100+ OAT and 12deg advance with no pinging! I would do what works best for your situation.
As far as cars running worse on premium, the only reason I can see that happening is if they picked up a tank of contaminated gas. In alot of stations if premium ethanol sits for awhile due to lack of demand, it attracts moisture! If it sits in your tank in the garage for awhile it will do the same thing!
Thats my 2 cents worth.
I run my 330HC/4V on the midgrade 91 with no pinging in 100+ OAT and 12deg advance with no pinging! I would do what works best for your situation.
As far as cars running worse on premium, the only reason I can see that happening is if they picked up a tank of contaminated gas. In alot of stations if premium ethanol sits for awhile due to lack of demand, it attracts moisture! If it sits in your tank in the garage for awhile it will do the same thing!
Thats my 2 cents worth.
August 7th, 2011, 04:26 PM
#6
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Location: The Hudson Valley
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There's a point in any engine beyond which you begin to lose power by advancing any further, regardless of octane, and that point is not negotiable.
Up until that point, though, yes, you may derive gains from increased octane and advanced timing.
- Eric
August 7th, 2011, 04:28 PM
#7
One part at a time
Join Date: Jun 2010
Location: Missouri
Posts: 167
I run nothing but 93 octane Shell in my '67. I also put Lucas fuel treatment in with each fillup. I have no idea what kind of mileage I get but the car starts right up and runs and idles with no hiccups. When I shut it off it's quiet as a church mouse.
August 8th, 2011, 04:34 PM
#8
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Location: Colts Neck, NJ
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That's true, but really, all you're doing is maximizing the design capabilities of your motor in that case - getting the most performance out of it that you can by adjusting it to do what you want, and ignoring the engineers' specifications, which took into account things that you don't care about, such as production of oxides of nitrogen.
There's a point in any engine beyond which you begin to lose power by advancing any further, regardless of octane, and that point is not negotiable.
Up until that point, though, yes, you may derive gains from increased octane and advanced timing.
- Eric
There's a point in any engine beyond which you begin to lose power by advancing any further, regardless of octane, and that point is not negotiable.
Up until that point, though, yes, you may derive gains from increased octane and advanced timing.
- Eric
Is there any formula for determining your HP gain? My 1978 Trans Am with a 400ci engine was a bit of a dog with the factory rated 270HP. I did run it for periods with the timing up a few degrees and it was only then that I could leave a reasonable (not great) amount of rubber with the posi.
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