Premium gas vs. regular: what's really better

[NeuroBeaker]

3 hours ago, WWWPerfA_ZN0W said:

Only the truck based 3.5EB has the dual injection systems currently in production.  May migrate to the smaller engines as well, don't know.  Hardly a new setup for overseas manufacturers.

 

I was based in the UK for 20 years and hadn't heard of Top Tier designations for fuels before, so it was the fuel type being a thing for over a decade that I am catching up on. I hadn't realized there was any difference between fuel options of the same octane rating.

 

In the UK, I used to exclusively buy Shell V-Power because I had a highly strung modified turbocharged engine that needed the higher octane rating. Here I went for the naturally aspirated V6 because I thought long-term maintenance would be easier.

 

All the best,

Andrew.

[akirby]

4 hours ago, WWWPerfA_ZN0W said:

Only the truck based 3.5EB has the dual injection systems currently in production.  May migrate to the smaller engines as well, don't know.  Hardly a new setup for overseas manufacturers.

 

Also the 2.7LEB in the F150.

[TheWizard]

6 hours ago, NeuroBeaker said:

 

I was based in the UK for 20 years and hadn't heard of Top Tier designations for fuels before, so it was the fuel type being a thing for over a decade that I am catching up on. I hadn't realized there was any difference between fuel options of the same octane rating.

 

In the UK, I used to exclusively buy Shell V-Power because I had a highly strung modified turbocharged engine that needed the higher octane rating. Here I went for the naturally aspirated V6 because I thought long-term maintenance would be easier.

 

All the best,

Andrew.

 

Octane and fuel quality are indeed two separate things.  There are also a couple of other specifications of gasoline which affect performance and are independent of octane rating.  Octane is just a measure of the fuel's resistance to pre-ignition (known as "knocking" or "pinging" because of the sound created when fuel doesn't ignite smoothly when the spark is applied).  Octane by itself has absolutely nothing to do with performance or fuel efficiency and higher octane is not "better gas".  However, some modern computerized engines have the ability to advance their ignition timing in response to detecting higher octane and this change in timing can improve both performance and efficiency.  If a particular engine doesn't have that timing change ability then using higher octane fuel is simply a waste of money.

 

Ethanol blending has a significant impact on both performance and mileage.  Ethanol has about 33% less energy by volume than gasoline so any ethanol blend will cause lower performance and mileage compared to pure gasoline.  Ethanol also raises octane and RVP so its exact impact can be difficult to determine.

 

RVP (Reid Vapor Pressure) is a measure of the volatility of fuel... its tendency to evaporate.  It is measured in PSI with higher numbers being more prone to evaporation.  In general, winter gas has an RVP of 9.0 while summer gas is usually RVP 7.8.  Winter gas is blended with butane which is plentiful and inexpensive but has a high RVP.  Summer gas can't take the volatility of butane so it contains much less and is therefore more expensive.  But butane also has less energy content by volume so winter gas, although cheaper, produces less performance and mileage.

 

Basic gasoline is the same regardless of which refinery produces it.  It's the additive package which makes the difference.  In fact, in many areas the base gasoline for all local stations (regardless of brand) comes from a single refinery or terminal.  The additives for each brand (BP, Exxon, Shell, etc.) are added to the tanker truck when it picks up a load at the terminal as appropriate for the brand of station it is delivering to.  All gasoline in North America must have a certain minimum standard additive package but the big brand names and Top Tier fuel providers add significantly more (and different) additives to improve their fuel and differentiate themselves from the competition.

 

[NeuroBeaker]

Wow, thanks Wizard, great write-up!

 

All the best,

Andrew.

[billfl]

17 hours ago, TheWizard said:

 

Octane and fuel quality are indeed two separate things.  There are also a couple of other specifications of gasoline which affect performance and are independent of octane rating.  Octane is just a measure of the fuel's resistance to pre-ignition (known as "knocking" or "pinging" because of the sound created when fuel doesn't ignite smoothly when the spark is applied).  Octane by itself has absolutely nothing to do with performance or fuel efficiency and higher octane is not "better gas".  However, some modern computerized engines have the ability to advance their ignition timing in response to detecting higher octane and this change in timing can improve both performance and efficiency.  If a particular engine doesn't have that timing change ability then using higher octane fuel is simply a waste of money.

 

Ethanol blending has a significant impact on both performance and mileage.  Ethanol has about 33% less energy by volume than gasoline so any ethanol blend will cause lower performance and mileage compared to pure gasoline.  Ethanol also raises octane and RVP so its exact impact can be difficult to determine.

 

RVP (Reid Vapor Pressure) is a measure of the volatility of fuel... its tendency to evaporate.  It is measured in PSI with higher numbers being more prone to evaporation.  In general, winter gas has an RVP of 9.0 while summer gas is usually RVP 7.8.  Winter gas is blended with butane which is plentiful and inexpensive but has a high RVP.  Summer gas can't take the volatility of butane so it contains much less and is therefore more expensive.  But butane also has less energy content by volume so winter gas, although cheaper, produces less performance and mileage.

 

Basic gasoline is the same regardless of which refinery produces it.  It's the additive package which makes the difference.  In fact, in many areas the base gasoline for all local stations (regardless of brand) comes from a single refinery or terminal.  The additives for each brand (BP, Exxon, Shell, etc.) are added to the tanker truck when it picks up a load at the terminal as appropriate for the brand of station it is delivering to.  All gasoline in North America must have a certain minimum standard additive package but the big brand names and Top Tier fuel providers add significantly more (and different) additives to improve their fuel and differentiate themselves from the competition.

 

 

For those compouters which do not adapt to octane changes, one could always install a customized tune which advances ignition timing but then you must keep using the octane level fuel for which the tune was created. Another notable item is that engines with significantly retarded timing (think 87 octane and going up hills or full of passengers) tend to run hotter. Heat is the enemy. It comes down to individual choices much like how often does one, if ever, flush their coolant, flush their brake lines, change their oil, use synthetic oil vs dino oil

etc.

 

My personal choice, if an engine is capable of producing more power and being more responsive with premium, then premium it is for me.

 

I've torn down enough engines and replaced enough components to see the results of being penny wise, but pound foolish.

[akirby]

Ford actually recommends Premium when towing or carrying a heavy load for that exact reason.

 

The myth that premium contains more detergents was actually true back in the 60s - 70s (maybe into the 80s) where companies like Amoco only put detergents in their "hi-test" or Premium products.

[NeuroBeaker]

1 hour ago, billfl said:

 

For those computers which do not adapt to octane changes, one could always install a customized tune which advances ignition timing but then you must keep using the octane level fuel for which the tune was created. Another notable item is that engines with significantly retarded timing (think 87 octane and going up hills or full of passengers) tend to run hotter. Heat is the enemy. It comes down to individual choices much like how often does one, if ever, flush their coolant, flush their brake lines, change their oil, use synthetic oil vs dino oil

etc.

 

My personal choice, if an engine is capable of producing more power and being more responsive with premium, then premium it is for me.

 

I've torn down enough engines and replaced enough components to see the results of being penny wise, but pound foolish.

 

This was the issue with my SmartCar in the UK. I has a turbocharged 700cc Brabus Roadster engine in a ForTwo with a custom advanced timing tune, requiring ≥99 RON, so I used Shell V-Power (99 RON, preferred because of the loyalty program) or BP Ultimate (102 RON). Not a lot of power in absolute numbers, but it was such a light car that it went like the proverbial bat out of hell.

 

Speaking of other personal choices, my CPO warranty just expired, so my Edge is at an independent today getting fully synthetic oil change, gearbox oil change, PTU lubricant change, rear differential lubricant change, brake fluid change, all tires balanced, and a 4-wheel alignment. We're using all Motorcraft fluids. ?

 

All the best,

Andrew.

 

 

[TheWizard]

2 hours ago, billfl said:

 

For those compouters which do not adapt to octane changes, one could always install a customized tune which advances ignition timing but then you must keep using the octane level fuel for which the tune was created. Another notable item is that engines with significantly retarded timing (think 87 octane and going up hills or full of passengers) tend to run hotter. Heat is the enemy. It comes down to individual choices much like how often does one, if ever, flush their coolant, flush their brake lines, change their oil, use synthetic oil vs dino oil

etc.

 

My personal choice, if an engine is capable of producing more power and being more responsive with premium, then premium it is for me.

 

I've torn down enough engines and replaced enough components to see the results of being penny wise, but pound foolish.

 

Occasional knocking under load is not damaging to an engine but persistent knocking can become a real problem.  As akirby indicated, using higher octane in those situations is definitely a good idea.

 

On the other hand, using higher octane because the engine can adapt to it and produce more power is not necessarily a good thing.  You have to remember that it's not horsepower which makes a car feel fast - it's torque that does that.  Horsepower gains from timing advance occur high in the RPM range.  The difference can be a couple of tenths in the quarter mile but it's something that most non-competition drivers will never even notice.  Add to that the cost differential between 87 and 91 octane fuels which is 65 - 70 cents per gallon around here now, and you have a very bad return on investment for the majority of drivers.  Even if you drive competitively or need more octane for occasional towing, it would be better for your wallet to run regular most of the time and switch to premium only when needed.

 

1 hour ago, akirby said:

Ford actually recommends Premium when towing or carrying a heavy load for that exact reason.

 

The myth that premium contains more detergents was actually true back in the 60s - 70s (maybe into the 80s) where companies like Amoco only put detergents in their "hi-test" or Premium products.

 

Also, up until the early 90s, Amoco (and BP after they bought Amoco) produced a higher octane gas called Amoco Ultimate which was refined an additional step to produce a gas which was clear rather than the slightly yellow color of normal gas.  That was the exception to "all base gas is the same" but it hasn't been produced for over 20 years.

 

[akirby]

10 minutes ago, TheWizard said:

 

Also, up until the early 90s, Amoco (and BP after they bought Amoco) produced a higher octane gas called Amoco Ultimate which was refined an additional step to produce a gas which was clear rather than the slightly yellow color of normal gas.  That was the exception to "all base gas is the same" but it hasn't been produced for over 20 years.

 

 

That's the one I was thinking of.  Back in the 60s I think they called it "white gas".

[WWWPerfA_ZN0W]

Premium does contain more detergents, possibly even a different pack, than regular.  Shell Nitro is a prime example.  Only available in premium grade.

 

Now Exxon/Mobil, not sure.  All grades are labeled to have Synergy.

[billfl]

5 hours ago, TheWizard said:

 

Occasional knocking under load is not damaging to an engine but persistent knocking can become a real problem.  As akirby indicated, using higher octane in those situations is definitely a good idea.

 

On the other hand, using higher octane because the engine can adapt to it and produce more power is not necessarily a good thing.  You have to remember that it's not horsepower which makes a car feel fast - it's torque that does that.  Horsepower gains from timing advance occur high in the RPM range.  The difference can be a couple of tenths in the quarter mile but it's something that most non-competition drivers will never even notice.  Add to that the cost differential between 87 and 91 octane fuels which is 65 - 70 cents per gallon around here now, and you have a very bad return on investment for the majority of drivers.  Even if you drive competitively or need more octane for occasional towing, it would be better for your wallet to run regular most of the time and switch to premium only when needed.

 

 

Also, up until the early 90s, Amoco (and BP after they bought Amoco) produced a higher octane gas called Amoco Ultimate which was refined an additional step to produce a gas which was clear rather than the slightly yellow color of normal gas.  That was the exception to "all base gas is the same" but it hasn't been produced for over 20 years.

 

Torque is a wonderful thing especially on my V-Twin motorcycle with 2 big jugs, but it doesn't rev very high. As for systems that adapt to higher octane, advancing the timing will result in increased cylinder pressure which in turn generates more torque. IDK how Ford does it with their computer and whether or not they also increase boost when higher octane is introduced and more boost also increases torque (does anyone here know?). Without knowing about boost, timing, when advanced for higher octane fuel, will increase torque thanks to increased pressure.

 

I love these types of discussions as we all benefit from each other.

 

Off topic and I guess I'd best read my owners manual but does Ford state not to use synthetic motor oils? Reducing friction (synthetics) is wonderful for an engine be it longevity as well as performance. I can't imagine a mfr stating that we can't use it. But then again, these are the same folks who go direct injection and don't add an oil separator to the engine.

[TheWizard]

Yes, increasing the ignition advance will increase torque along with horsepower because the two measures are related.  Torque is horsepower * 5252 / RPM.  Conversely, horsepower is torque / RPM * 5252.  The important point for this discussion is that engine speed (RPM) is a critical factor.

 

Increasing ignition advance isn't a magical gateway to power.  The fact is that all engines run with their ignition timing somewhat less advanced than is possible for the safety of the engine.  If the spark is generated too early in the compression stroke, it will tend to push back on the rising piston before it reaches top dead center (TDC).  That causes an abnormal rise in cylinder pressure which causes knock that can be so violent that it blows a hole in the piston (extreme case).  But the flame front burning the air fuel mixture takes time to burn the entire charge so you have to advance the spark to some amount before TDC so that the burning and expanding fuel mixture applies the most downward force starting at TDC.  Engines with adaptive timing use their knock sensors to advance the timing to a point just short of causing knock.

 

Higher octane fuel has two properties which help - it burns more slowly and it burns cooler.  That's what makes it more resistant to knock.  With lower octane fuel the timing must be more conservative because it burns faster so advance is set to complete the fuel burn slightly past TDC.  With higher octane fuel burning more slowly, the advance can be more aggressive and aim for completing the burn as close to TDC as possible, maximizing the performance.

 

Here's where we get back to torque and horsepower.  Ignition timing is dependent on engine speed.  The fuel charge burns at the same rate regardless of engine speed so it is necessary to advance the spark even more as the engine speed increases so that the fuel charge can burn completely in the shorter time before the piston reaches TDC.  But torque and horsepower are related to engine speed and they are always equal at 5252 RPM (the constant in the formula).  Above that engine speed, horsepower will continue to increase while torque will always decrease. 

 

The gain of advancing timing to take advantage of increased octane and its slower, more controlled burn is most noticeable at higher RPM when the time available to burn the fuel mixture is shortest.  But at those engine speeds, torque is already falling off.  So yes, the torque will be somewhat higher than it would be with less advance but it's still less than it was at lower RPM so it might be more accurate to say it isn't dropping off as quickly rather than it's increased.  And again, few daily drivers will push their vehicle into those RPM ranges so the effect is measurable but not very noticeable to the "butt" dyno.

 

[jamie1073]

Coming from a Focus ST I can tell you that yes the EB engines run just fine on 87 octane that they also retard timing more on 87 octane fuel.  When running 93, which is where Ford's HP ratings come from, it does get more HP..  According to the Supplement that comes with the car it has 252HP on 93 and 243HP on 87, with the same torque figures because it advances timing and Ford has torque targets programmed in to the ECU which supposedly are managed by boost control.  You could also see this when running tunes where the boost was limited to regulate torque targets, or so they say.  The Edge ST Supplement also states that the engine power of 335Hp and 380ft/lbs is achieved on 93 octane fuel.  I have not found yet what the engine is rated at on 87.  Either way it is winter so I am running 87 for now and it is not a hot rod so I will probably only run 93 to see if there is a boost difference or feel.  That manual also says the 2.7 has a boost limit of 19psi with 21psi overboost.  I find that highly unlikely and have only seen it hit 15-16 on the gauge before the waste gates open and drop it to 10-12psi.  Now that could be because it is cold outside and it is hitting it torque target or because of the 87 octane gas.  The book also suggests only one twin scroll turbo.  Anyway the ECU will adjust timing for 87, 91 and 93 octane gas and Premium is not required. 

[omar302]

9 hours ago, jamie1073 said:

That manual also says the 2.7 has a boost limit of 19psi with 21psi overboost.  I find that highly unlikely and have only seen it hit 15-16 on the gauge before the waste gates open and drop it to 10-12psi.  Now that could be because it is cold outside and it is hitting it torque target or because of the 87 octane gas.  The book also suggests only one twin scroll turbo.  Anyway the ECU will adjust timing for 87, 91 and 93 octane gas and Premium is not required. 

 

I haven't seen the manual myself, but I remember reading here a member stating that boost was limited during break-in, for 1000 miles or so.

 

Edit: Found the post I was referring to. it was based on his observation.

Edited January 7, 2019 by omar302

[jamie1073]

On 1/6/2019 at 11:43 PM, omar302 said:

 

I haven't seen the manual myself, but I remember reading here a member stating that boost was limited during break-in, for 1000 miles or so.

 

Edit: Found the post I was referring to. it was based on his observation.

 

Thanks.  That is interesting.  I will see what happens.  It is very nice so far, I am coming from a Focus ST so letting it shift for me is nice when just tooling around. It is not slow by any means so if it gets a little quicker after breakin that would be a bonus.  Not like I am really hammering on it now but I did slip a few times and get moving to test her out.  ?

[Xtra]

 With higher octane fuel my car runs better and it allows the engine to make more HP. I have time slips that prove it. Ford even says that the 2.7EB is listed at 315HP,  but with the caveat the gas must be 93octane.

Edited January 14, 2019 by Xtra

[WWWPerfA_ZN0W]

Answers to the question of which fuel is better is dependent on engine condition as well as tuning (stock or aftermarket).  Fuel by itself is not magic.

[TheWizard]

On 1/13/2019 at 3:57 PM, Xtra said:

 With higher octane fuel my car runs better and it allows the engine to make more HP. I have time slips that prove it. Ford even says that the 2.7EB is listed at 315HP,  but with the caveat the gas must be 93octane.

 

That's correct - there is enough of a change for it to show up as a couple of tenths in the quarter and that makes it worthwhile if you are doing that.  I can't find specs for the EcoBoost but in a Mustang first generation Coyote engine the peak horsepower was 412 with 93 octane and 402 with 87 octane in the 11-12 models, and 420 with 93 octane and 412 with 87 octane in the 13-14 models.  In both cases that peak is at 6500 RPM - an engine speed most daily drivers will not use (I haven't gone over about 5000 in mine).  That 8-10 extra horsepower is about 2%... significant and worth the extra cost for time slips but not so much for daily driving.

 

Edited January 15, 2019 by TheWizard
typo

[jamie1073]

5 hours ago, TheWizard said:

 

That's correct - there is enough of a change for it to show up as a couple of tenths in the quarter and that makes it worthwhile if you are doing that.  I can't find specs for the EcoBoost but in a Mustang first generation Coyote engine the peak horsepower was 412 with 93 octane and 402 with 87 octane in the 11-12 models, and 420 with 93 octane and 412 with 87 octane in the 13-14 models.  In both cases that peak is at 6500 RPM - an engine speed most daily drivers will not use (I've haven't gone over about 5000 in mine).  That 8-10 extra horsepower is about 2%... significant and worth the extra cost for time slips but not so much for daily driving.

 

Once she is fully broken in I will hit redline almost daily.  I like to drive hard especially after coming from a slightly tuned Focus ST.  Probably why I get crap gas mileage.  ?