Cheap alternative to premium?

[DriveHard]

There's a lot of inefficiency in going downhill. Especially since most people end up using their brakes.

I think for most cars if you dropped down 800 vertical feet with 100% efficiency and no losses, it would be going well over 100 MPH. You have to hit the brakes somewhere or convert the energy to heat/noise.

There are a lot of inefficiencies in both directions going up and down. It is a simple potential energy statement though...you get the same amount back as you require to go up. Any reduction in fuel economy is a direct statement of the inefficiencies of the system.

I have often wondered if a good hyper-miler could actually get better economy in a hilly area as a throttle controlled engine is more efficient at higher throttle settings. Higher throttle setting going up the hill, then closed throttle and zero fuel usage going down the hill. In theory it could be more efficient than a steady throttle with no hill? Obviously speed limits and other traffic throw the ideal out the window.

 

[y_p_w]

There are a lot of inefficiencies in both directions going up and down. It is a simple potential energy statement though...you get the same amount back as you require to go up. Any reduction in fuel economy is a direct statement of the inefficiencies of the system.

I have often wondered if a good hyper-miler could actually get better economy in a hilly area as a throttle controlled engine is more efficient at higher throttle settings. Higher throttle setting going up the hill, then closed throttle and zero fuel usage going down the hill. In theory it could be more efficient than a steady throttle with no hill? Obviously speed limits and other traffic throw the ideal out the window.

Depends on how it’s done. I usually go up this one steep road in 2nd gear. But it’s really that steep that I go down it in 2nd. But friction is everywhere, whether it’s the engine, the tires, or wind resistance. Going uphill requires adding energy regardless, and that’s typically done at a fairly low, steady speed. But if you want to recover all of that energy, it’s going to require not hitting the brakes and reaching speeds where the losses from aerodynamic drag go up exponentially.

I remember talking to a friend who liked fast cars, but we got into a similar discussion on energy recovery. He thought it didn’t really result in worse fuel economy. His rationale was that in gear with engine braking, it should be partially recovered by recharging the battery, which would otherwise require energy from the engine. Seemed like that explanation was missing a few details.

 

[jtay2024]

I'm surprised at the responses most of you are giving...

Modern engines constantly push timing to increase efficiency and torque output for a given engine RPM. Transmissions are programmed to hold on to a gear as long as possible before downshifting again to increase fuel efficiency.

Just because an engine is DESIGNED to run on RUG doesn't mean it can't see slightly more efficient operating conditions, or increased power from using premium. It just means that it can attain its performance targets for power and economy using RUG.

Using premium can certainly allow the engine ECU to push timing a bit more in lower engine speeds with larger throttle openings before knocking occurs (where the knock sensor would pull timing using RUG). This might allow the car to continue up the hill at a given speed with a certain throttle setting without downshifting using premium. Using RUG at the similar condition may have caused slight knock, which will cause the engine ECU to pull timing, causing the throttle position to increase to maintain the same torque output, causing you to now hit the mark where the transmission thinks it needs to downshift.

I too have noticed similar experiences when pulling trailers. The engine will hold a gear longer when using premium on slight grades. You do have to be very in tune with your vehicle to notice this.

While I don't advocate this...use a OBDII monitor and watch the knock retard during a tank of RUG, and a tank of premium, and report back.

I too have noticed this. I am very in tune with my car. It's a 250hp 2L direct injection engine. The manual states to use 95 octane fuel (In the UK 95 is equal to roughly 91 maybe? I'm not sure the conversion rate).

Anyway, I put a tank of 99 in, and straight away could tell a difference. It was definitely not "Power" increase (the upper limit is entirely set by the ECU really in modern cars). What it did achieve was a tendency to allow for much higher loads at a lower RPM. For example, I travel the exact same route to work every day of the year near enough. I get used to what hills run at what RPM and what gear.

A hill the car would previously drop to say 6th and 2000rpm, would now be possible in 7th at say 1600rpm with the higher octane.

Cars are very clever now, and will do whatever they can to make the most of their fuel. If it detects it can get away with a little more ignition timing rather than dropping a gear, it will definitely do so.


Another thing to take into account is that LSPI (Low Speed PreIgnition) is one of the issues with Direct Injection petrol engines. This will definitely cause an automatic to drop a gear (or a manual to pull timing) when at low RPM. Increasing octane helps to mitigate this issue and reduce the likelyhood of it.

 

[spk2000]

I have a possible solution to your situation that I have been using for years now. My 96 grand marquis is very similar in going up a hill I will get a rattle or octane knock using regular fuel. I have done tune ups over the years and nothing has changed this. The car flat out loves premium fuel. Drives so much stronger and climbs hills without the rattle and doesn't shift. Can definitely feel more power to the wheels but I have never dynoed it. So yes it is my butt dyno that is not calibrated just feels stronger. Will burn tires longer than regular fuel too. I found mixing E85 which is normally over 100 octane with regular I can get a premium fuel feel. It will usually lower fuel economy a little depending how much you add. Generally regular gets around 20.5 mpg and blended fuel will sometimes get as low as 18.5 but normally around 19.5 mpg. I started out adding 1 gallon and found it runs great up to 50/50 any more and the engine gets a very strange feeling that is hard to explain but it doesn't feel right and begins to lose power. Tried the same with my Montero and engine lights came on and it hated it. Might try it but definitely start low. I have normally done it to save money but E85 is the same price as regular here now so it is more for performance reasons now. I don't always do it but when I do I notice the difference. Hope this helps.

 

[kschachn]

I too have noticed this. I am very in tune with my car. It's a 250hp 2L direct injection engine. The manual states to use 95 octane fuel (In the UK 95 is equal to roughly 91 maybe? I'm not sure the conversion rate).

Anyway, I put a tank of 99 in, and straight away could tell a difference. It was definitely not "Power" increase (the upper limit is entirely set by the ECU really in modern cars). What it did achieve was a tendency to allow for much higher loads at a lower RPM. For example, I travel the exact same route to work every day of the year near enough. I get used to what hills run at what RPM and what gear.

A hill the car would previously drop to say 6th and 2000rpm, would now be possible in 7th at say 1600rpm with the higher octane.

Cars are very clever now, and will do whatever they can to make the most of their fuel. If it detects it can get away with a little more ignition timing rather than dropping a gear, it will definitely do so.


Another thing to take into account is that LSPI (Low Speed PreIgnition) is one of the issues with Direct Injection petrol engines. This will definitely cause an automatic to drop a gear (or a manual to pull timing) when at low RPM. Increasing octane helps to mitigate this issue and reduce the likelyhood of it.

Octane rating is not connected to LSPI. Regular old pre-ignition and LSPI are different problems and a different root cause.

 

[kschachn]

I have a possible solution to your situation that I have been using for years now. My 96 grand marquis is very similar in going up a hill I will get a rattle or octane knock using regular fuel. I have done tune ups over the years and nothing has changed this. The car flat out loves premium fuel. Drives so much stronger and climbs hills without the rattle and doesn't shift. Can definitely feel more power to the wheels but I have never dynoed it. So yes it is my butt dyno that is not calibrated just feels stronger. Will burn tires longer than regular fuel too. I found mixing E85 which is normally over 100 octane with regular I can get a premium fuel feel. It will usually lower fuel economy a little depending how much you add. Generally regular gets around 20.5 mpg and blended fuel will sometimes get as low as 18.5 but normally around 19.5 mpg. I started out adding 1 gallon and found it runs great up to 50/50 any more and the engine gets a very strange feeling that is hard to explain but it doesn't feel right and begins to lose power. Tried the same with my Montero and engine lights came on and it hated it. Might try it but definitely start low. I have normally done it to save money but E85 is the same price as regular here now so it is more for performance reasons now. I don't always do it but when I do I notice the difference. Hope this helps.

Considering the energy density of gasoline even at the same gas station will vary up to 4% that makes your observation very difficult to correlate with any specific variable.

 

[jtay2024]

Octane rating is not connected to LSPI. Regular old pre-ignition and LSPI are different problems and different root cause.

Fair enough, my bad! Either way, what I have noticed is very similar to DriveHards situation.

 

[spk2000]

Considering the energy density of gasoline even at the same gas station will vary up to 4% that makes your observation very difficult to correlate with any specific variable.

Agreed no arguing that. Just my own observations nothing scientific or proven and doesn't work for every car like my Montero but my grand marquis loves it. It's a 96 so definitely not flex fuel or e85 compatible either. When I was driving nearly 300 miles a day for several months I need a cheap alternative and this was it. Now it's for performance and cheaper than premium.

 

[benjy]

some vehicles note regular is ok but premium is recommended. todays ECU's can adjust timing etc allowing lower octane fuels to be used BUT power is REDUCED via less timing advance ETC. its not the higher octane per say BUT the changed settings that makes more power + turbo'd engines can vary the most. i had an APR switch chip in my 01 Jetta 1.8T, 150 hp stock about 196 hp + 240 TQ on 91 oct more with 93 octane, + this is port injected! todays DI that controls knock makes even more power, as the EA888 golf sportwagen makes 301 chipped torque + 245 hp, again the higher octane 93 this time is necessary, BUT agresive tuning makes the power. factory tunes are conservative for warranty reasons as well as emissions BUT most APR tunes are emission compliant!!

 

[MJS]

I'm surprised at the responses most of you are giving...

Modern engines constantly push timing to increase efficiency and torque output for a given engine RPM. Transmissions are programmed to hold on to a gear as long as possible before downshifting again to increase fuel efficiency.

Just because an engine is DESIGNED to run on RUG doesn't mean it can't see slightly more efficient operating conditions, or increased power from using premium. It just means that it can attain its performance targets for power and economy using RUG.

Using premium can certainly allow the engine ECU to push timing a bit more in lower engine speeds with larger throttle openings before knocking occurs (where the knock sensor would pull timing using RUG). This might allow the car to continue up the hill at a given speed with a certain throttle setting without downshifting using premium. Using RUG at the similar condition may have caused slight knock, which will cause the engine ECU to pull timing, causing the throttle position to increase to maintain the same torque output, causing you to now hit the mark where the transmission thinks it needs to downshift.

I too have noticed similar experiences when pulling trailers. The engine will hold a gear longer when using premium on slight grades. You do have to be very in tune with your vehicle to notice this.

While I don't advocate this...use a OBDII monitor and watch the knock retard during a tank of RUG, and a tank of premium, and report back.

^^^^This is the answer!^^^^

If your vehicle has a knock sensor (piezoelectric microphone) and it detects spark knock, the ECU will jerk timing back and then the vehicle will lose power and act sluggish.

If you want to do a simple experiment, monitor engine timing at idle and then take a metal tool a rap lightly on the metal part of a cylinder head and watch what happens!

 

[earlyre]

It really depends on the car. May two decades ago it was "premium recommended" with some cars, while others said "premium only" even though the owner's manual might say that regular was OK with reduced performance.

Still - a lot of cars these days recommend even 93 AKI. I have no idea where to find anything similar other than specialty gas stations that blend in unleaded race gas.

um...AKI(Anti Knock Index) is the octane rating we use here in the states... some times abbreviated as "(R+M)/2"
so that recommendation is just for 93 octane Premium, which is what all the Premium sold near me is... our gas is all E10. that 10% ethanol bumps the Octane rating a couple points.
so our 87 E10, is 85 E0 with 10% Ethanol. Similarly our 93 E10, is 91 E0 with 10%Ethanol.
there's the one chain in the area, Caseys, that also sells "Unleaded 88" which is just 85 E0, with 15% Ethanol. (E15)

 

[Hermann]

Shop around if you think you need premium. On Gas Buddy today 93 octane has a spread of 79 cents a gallon in about 10 sq. miles.

Early this year it was a $1 spread.

At the Sam's Club here, their premium 91 E10 is usually only 10-20¢ higher than their 87 E10

 

[Zee09]

At the Sam's Club here, their premium 91 E10 is usually only 10-20¢ higher than their 87 E10

Lucky dawg...

 

[bullwinkle]

Back in the day, Speedway 89 (plus) actually did as well or better than a lot of premium fuel from other stations, in my family's cars with somewhat higher compression ratios, aftermarket cams, etc. It would be worth trying, since it should be cheaper than TT premium.

 

[wpod]

Premium is slower burning and less volatile than regular. Try regular and if your engine does not ping or detonate, you don't need premium. Premium will not make your engine run better either. Some believe it does and I think it's all in their head.

More timing advance.

 

[ChrisD46]

*What about using premium 93 octane gas during the hot , humid months of Summer ? Any advantage over regular 87 octane when it's hot and humid out side ?

 

[y_p_w]

um...AKI(Anti Knock Index) is the octane rating we use here in the states... some times abbreviated as "(R+M)/2"
so that recommendation is just for 93 octane Premium, which is what all the Premium sold near me is... our gas is all E10. that 10% ethanol bumps the Octane rating a couple points.
so our 87 E10, is 85 E0 with 10% Ethanol. Similarly our 93 E10, is 91 E0 with 10%Ethanol.
there's the one chain in the area, Caseys, that also sells "Unleaded 88" which is just 85 E0, with 15% Ethanol. (E15)

Not in California though. Anything more than 91 AKI is blending in street-legal racing unleaded.

 

[silversport]

there is no advantage to using an octane other than what your owner's manual/car/engineers require...IF your car can advance timing enough with the higher octane you MIGHT have some performance improvement...too many maybes for me...also I don't believe using a lower octane than required (not recommended, required) by the owner's manual/car/engineers is beneficial to your vehicle...

of course YMMV...

Bill

 

[Rmay635703]

Test 88 octane e15

It should be cheaper than rug but on my car that required premium it seemed to give better fuel economy and performance than I expected (at least during summer)

 

[javacontour]

I know, I stopped doing it,beyond some peoples comprehension.
I wonder if the flat landers that move or visit here wonder why all the pumps show 2 points less?

Nope, some of us get it.
But then many times we are driving rentals, so we just put the cheapest fuel in the vehicle and shrug
I did drive my own car to Denver once and topped off with some 87 when leaving as I knew I was going to a lower elevation.

For the pedantic, I believe it's elevation on land and altitude in the sky.