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Regular vs. Premium Fuel

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RollLeft

RollLeft 5040

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You engineer, chemist and mechanic types help me out.  So i know that premium fuel is chemically superior to regular gas but I have questions.  How significant is the variance to the average vehicle (eg. Tahoe)?  Also, on average, is it worth paying the premium financially?  I calculate for me the difference is about $500+ a year.   Not a whole vacation but that's a domestic flight somewhere.  Under what circumstances is paying for premium a must and also not worth it?  

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RPM

RPM 26317

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If your engine is designed for premium, it's best to use premium. It has a slower, more complete burn than regular. Your engine's adjustable timing can make up for some (not all) of the difference. But replacing the timing chain and adjustable tensioners pretty much negates any savings you may have from buying cheap gas. You don't want to buy premium? Buy a car that wasn't designed for it.

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elfenix

elfenix 34223

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a factory tahoe does not require premium (check inside the fuel filler door and also the manual), so you're wasting your money. 

 

https://engineering.mit.edu/engage/ask-an-engineer/whats-the-difference-between-premium-grade-and-regular-gasoline/

 

basically the difference is that higher octane resists detonation (aka pinging) better than regular, but an engine needs to  be designed to run at higher temperatures and pressures to take advantage of that property. 

Edited by elfenix
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Chewbacca

Chewbacca 7767

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55 minutes ago, RPM said:

If your engine is designed for premium, it's best to use premium. It has a slower, more complete burn than regular. Your engine's adjustable timing can make up for some (not all) of the difference. But replacing the timing chain and adjustable tensioners pretty much negates any savings you may have from buying cheap gas. You don't want to buy premium? Buy a car that wasn't designed for it.

This is accurate.  I think it was Car & Driver that did a test a few years ago to figure this out.  On cars that require premium, you can use regular but you lose performance and fuel economy because the car will protect itself.  The verdict was that you don't save any money (and you lose power) by using regular when your car calls for premium.

 

Similarly, I don't believe there is any benefit to putting premium in a car that calls for regular.

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shakahorn

shakahorn 1645

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Years ago I drove an Infiniti G35 and tried regular for a few weeks even though the label on the gas cap said 'premium only.'  The car knocked and pinged liked my buddies old Dodge (think 'Al Bundy Dodge') in high school.  Went back to premium and it was fine.  So I don't think you can use regular if the car 'requires' premium.  You might be able to get away with mid-grade, but at that point, why bother?

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52-80

52-80 19147

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premium fuel isnt richer, purer, more energy dense,  "more complete" than regular fuel.

it just has a higher octane rating.  for motors that require higher detonation resistance.  if you dont need it you dont need it. 

 

if you think you need it, squirt in some octane booster and see if it makes a lick of difference.

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crash_davis

crash_davis 23101

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buy octane for your car.  no benefit to buying premium if your car calls for regular.  and buy cheapest gas irrespective of brand.  all base gas is the same and the extra additives of name brand gas probably doesn't add anything.  

 

regular vs premium.

https://cars.usnews.com/cars-trucks/best-cars-blog/2016/08/premium-vs-regular-gasoline

 

no name vs brand name gas 

https://abcnews.go.com/GMA/Business/story?id=2978563&page=1

https://www.edmunds.com/car-maintenance/is-cheap-gas-bad-for-your-car.html

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Guest Lobo

Guest Lobo

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What's the compression ratio of your engine?  That'll tell you what to pump.

Related question---how do rental car companies make sure you are using the right gas?  Like SilverCar, all turbo Audi's but we're all just putting 87 octane in there.  How do they correct for that?  I've gotten some free upgrades in the past and ended up in some premium SUV or sedan and I know for a fact it requires 89 or 93.  But it's a fucking rental, so I just put in 87.  That can't be good to have those different octanes mixing around in there, is it?  

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elfenix

elfenix 34223

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20 minutes ago, Lobo said:

What's the compression ratio of your engine?  That'll tell you what to pump.

Related question---how do rental car companies make sure you are using the right gas?  Like SilverCar, all turbo Audi's but we're all just putting 87 octane in there.  How do they correct for that?  I've gotten some free upgrades in the past and ended up in some premium SUV or sedan and I know for a fact it requires 89 or 93.  But it's a fucking rental, so I just put in 87.  That can't be good to have those different octanes mixing around in there, is it?  

probably doesn't do anything but lose some time at the drag strip and maybe make emissions worse.  at first as the ECU re-learns what timing it can use it'll get worse mileage.  but then the ECU figures things out.  mileage may still be worse but it might be within the error bars.  *shrug*

https://jalopnik.com/why-putting-regular-gas-into-a-car-that-needs-premium-w-1796463139

Edited by elfenix
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Gil Bang

Gil Bang 25920

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3 hours ago, Lobo said:

What's the compression ratio of your engine?  That'll tell you what to pump.

Related question---how do rental car companies make sure you are using the right gas?  Like SilverCar, all turbo Audi's but we're all just putting 87 octane in there.  How do they correct for that?  I've gotten some free upgrades in the past and ended up in some premium SUV or sedan and I know for a fact it requires 89 or 93.  But it's a fucking rental, so I just put in 87.  That can't be good to have those different octanes mixing around in there, is it?  

Had a Mercedes loaner the other  day.  That question occurred to me as I was filling it up with premium. 

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52-80

52-80 19147

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On 10/18/2018 at 11:27 PM, Lobo said:

What's the compression ratio of your engine?  That'll tell you what to pump.

Related question---how do rental car companies make sure you are using the right gas?  Like SilverCar, all turbo Audi's but we're all just putting 87 octane in there.  How do they correct for that?  I've gotten some free upgrades in the past and ended up in some premium SUV or sedan and I know for a fact it requires 89 or 93.  But it's a fucking rental, so I just put in 87.  That can't be good to have those different octanes mixing around in there, is it?  

the car computer will detect knock and pull back the ignition timing.  no damage.

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52-80

52-80 19147

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1 hour ago, Elvis said:

So what is the mid grade for?  Cars require either regular or premium.  I've never heard of a car that said mid-grade on the filler door.

No car says standard grade or top grade or regular or premium. It's an actual number in RON or AKI units.

 

The top grade in California might be mid grade available in Texas and vice versa. 

Edited by 52-80
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elfenix

elfenix 34223

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8 hours ago, Viper said:

my car calls for 91 octane, so I mix premium (93) with plus (89).

trivial fact: the storage tanks only have premium and regular in them, the pump mixes the grades together in the necessary ratio to make mid grade

5 hours ago, Not that Bob said:

How often are the storage tanks tested to see if there actually are differing grades within? I can see a guy trying to cut corners by filling all his tanks with the cheapest grade, especially if he has just been tested and knows the  monitors won't be back for a year or so. 

i'd assume the state does random spot checks along with the volume test, but i have no idea. 

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Rimbo

Rimbo 25911

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"Octane" measures fuel's resistance to premature explosion.

High-performance engines that run at high temperature and pressure require higher octane fuel to make sure that the fuel doesn't detonate before it's supposed to and damage your engine, by pushing the piston down in the middle of an up-stroke.

If your car doesn't require premium, putting extra octane in your car is 100% a waste of money. If your car does require premium, putting a lower octane in it will damage your engine.

Some engines nowadays can use both, and will adjust their running to use what you put in. Again, see your manual to know.

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RPM

RPM 26317

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18 hours ago, Not that Bob said:

How often are the storage tanks tested to see if there actually are differing grades within? I can see a guy trying to cut corners by filling all his tanks with the cheapest grade, especially if he has just been tested and knows the  monitors won't be back for a year or so. 

There are only 2 grades, regular and premium. Mid grade is a blend at the pump. Every pump is supposed to be tested every 4 years or spot tested in response to a complaint. But there are only 72 inspectors for the entire state.

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Okie State

Okie State 3815

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The oil guys can correct me but CSB a Chevron guy told me years ago that it doesn’t cost them any more to make premium vs regular.
This is incorrect. Octane (Alkylate, Reformate, etc.) is valuable and if you don't have the units to make it, you have to pay the price to those who do.
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WithoutAClue

WithoutAClue 15341

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On 10/18/2018 at 4:27 PM, Lobo said:

What's the compression ratio of your engine?  That'll tell you what to pump.

not any more. The Mazda Skyactiv engine has a 13:1 compression ratio and uses regular (89) gas.

The next gen HCCI engine is supposed to be 16:1.  😮

ECU's have gotten really smart...

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Bill Brasky

Bill Brasky 1443

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18 hours ago, elfenix said:

trivial fact: the storage tanks only have premium and regular in them, the pump mixes the grades together in the necessary ratio to make mid grade

i'd assume the state does random spot checks along with the volume test, but i have no idea. 

most of them do blend regular and premium at the pump to create midgrade, but there are some older gas stations that still have dedicated underground tanks for midgrade fuel.   for those sites the midgrade is just blended together at the fuel terminal 

also gas stations have to submit reports to the state showing their inventory reconciliation to show that there isn't a leak.   if the inventory is out of tolerance then the gas station has to have someone come out and do further testing on the tanks to show their isn't a leak.   the state also sends out inspectors to each site to make sure the pumps are working properly (1 gallon sold = 1 gallon actually pumped), they also check to see if there is too much water in the tank, and they check the octane of the product being sold to customers to make sure that is within legal tolerance.  

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Stoogey

Stoogey 219

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On 10/18/2018 at 4:27 PM, Lobo said:

Related question---how do rental car companies make sure you are using the right gas?  Like SilverCar, all turbo Audi's but we're all just putting 87 octane in there.  How do they correct for that?  I've gotten some free upgrades in the past and ended up in some premium SUV or sedan and I know for a fact it requires 89 or 93.  But it's a fucking rental, so I just put in 87.  That can't be good to have those different octanes mixing around in there, is it?  

 

On 10/18/2018 at 7:49 PM, Gil Bang said:

Had a Mercedes loaner the other  day.  That question occurred to me as I was filling it up with premium. 

Governors. You can use the wrong grade of gasoline if the engine is limited. 

My premium fuel car is allegedly capable of 196mph but by electronic governor limited to 156mph. Other guys on the car forum with recoded chips report top speeds of 178 on the American version and slightly higher on the world version. 

Why would anyone want to do  that? Go ahead. Take your minivan to the track. No one's stopping you.

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Whitman

Whitman 694

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On 10/18/2018 at 8:49 PM, Gil Bang said:

Had a Mercedes loaner the other  day.  That question occurred to me as I was filling it up with premium. 

My SLK requires premium, but I just have the dealer fill it up when I go every week to check the tire air pressure, or top off the windshield washer fluid.

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52-80

52-80 19147

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1 hour ago, Stoogey said:

 

Governors. You can use the wrong grade of gasoline if the engine is limited. 

My premium fuel car is allegedly capable of 196mph but by electronic governor limited to 156mph. Other guys on the car forum with recoded chips report top speeds of 178 on the American version and slightly higher on the world version. 

Why would anyone want to do  that? Go ahead. Take your minivan to the track. No one's stopping you.

2 different things.  a governor is always a reference to speed governor.  it simply cuts the fuel above a certain speed . 155mph corresponds to 250kph which is a nice round number.  its also coincident to the V/W tire speed rating.  (most winter tires max out at V and W).  its also a very convenient way to upsell customers for a 2000$ speed-delimited option which cost them nothing in software.

 

if a car computer detects knocking, it'll retard the timing.  this will reduce maximum horse power.  which will of course decrease top speed.  but this fact is not correlated to the common 155mph governor.

 

***

 

so 99% of factory cars, its engineered to work with commonly available fuel.  for highly tuned motors (esp turbo motors where lots of tuning is done via software - fuel/air management and timing) , power output is driven very much by fuel.  these really get a boost from AKI 99, 103, etc fuel

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Stoogey

Stoogey 219

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1 hour ago, 52-80 said:

2 different things.  a governor is always a reference to speed governor.  it simply cuts the fuel above a certain speed . 155mph corresponds to 250kph which is a nice round number.  its also coincident to the V/W tire speed rating.  (most winter tires max out at V and W).  its also a very convenient way to upsell customers for a 2000$ speed-delimited option which cost them nothing in software.

 

if a car computer detects knocking, it'll retard the timing.  this will reduce maximum horse power.  which will of course decrease top speed.  but this fact is not correlated to the common 155mph governor.

 

***

 

so 99% of factory cars, its engineered to work with commonly available fuel.  for highly tuned motors (esp turbo motors where lots of tuning is done via software - fuel/air management and timing) , power output is driven very much by fuel.  these really get a boost from AKI 99, 103, etc fuel

156 mph. No turbo although I am considering recoding and a supercharger. 

Racing fuel not readily available. I have to drive quite a distance to buy non-ethanol 93 octane. My winter / utility truck gets better mileage.

A modern governor also effects shifting patterns. Which is why the world version - although identical mechanically to the American - is preferred. No big deal but I'd have to send for a reprogramming kit which plugs into the dashboard port. 

I am using my car as an example. 

Winter tires? I replaced the run-flats on my car. The suspension is rigid as hell. Streets are rough enough; I could feel every tar seam and pebble in the road. It's strange. The faster I go, the smoother the ride. Once I'm past 130 with the top down everything is pretty much just a sensation anyways. 

Went with Y rated tires in a summer compound. In my climate, she spends late September through early June in a heated warehouse. The tires aren't even supposed to be stored under 35° F much less driven.

I used to go to the airport for high octane leaded gasoline for my Firebirds. When I took them in for vehicle emissions, there were rollers built into the floor of the examining station and a flexible tube was put on the exhaust pipe. The examiner would sit in the car and put it through its paces. 

Nowadays those testing stations are closed. I go to one of those quick change oils places to be tested. 

If I still owned the Firebird (1967), how would it be tested? 
 

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