87 Or 91? Which Fuel Is Best And Why Ethanol-Free

GJ-Molestor

Banned
:
2011 BMW 528i, 2015 Mazda 6, 1995 Nissan Maxima Manual
91 octane is more preferable for a turbo engine. It cleans your injectors better over the long run and reduces the chance of a fuel pump/injector issue down the road. considering how terrible North American fuel is, I would be looking for ethanol-free fuel. 10% ethanol blend is not as good for your engine in the long run and the car will run poorer. the increased MPG from using ethanol-free 91 octane fuel is so good, it almost completely repays the price difference yet you are gaining a cool 40hp.

Some of you guys are experiencing ping/knock, especially at low RPM from using s*** quality fuel. You will see noticeably improved fuel economy by switching to ethanol free gas, especially if it is 91. the car will run better, smoother and accelerate more effortlessly resulting in less fuel used. It is far more efficient then any ethanol blend fuel.

Choosing between 87 or 91

- while not as good as 91, 87 is more effective in higher altitudes
- if you frequently carry a full load of cargo/passengers or tow, use 91
- if you drive in hot weather or climb lots of inclines especially while carrying things, use 91
-91 will help the ping or knock some of you hahe been mentioning, but not necessary. Ethanol-free 87 is also fine.

Try to stick to one type of gas as much as you can.

Regardless whether it is 87 or 91, do a search and look for ethanol-free fuel in your area.
 
91 octane is more preferable for a turbo engine. It cleans your injectors better over the long run and reduces the chance of a fuel pump/injector issue down the road. considering how terrible North American fuel is, I would be looking for ethanol-free fuel. 10% ethanol blend is not as good for your engine in the long run and the car will run poorer. the increased MPG from using ethanol-free 91 octane fuel is so good, it almost completely repays the price difference yet you are gaining a cool 40hp.

Some of you guys are experiencing ping/knock, especially at low RPM from using s*** quality fuel. You will see noticeably improved fuel economy by switching to ethanol free gas, especially if it is 91. the car will run better, smoother and accelerate more effortlessly resulting in less fuel used. It is far more efficient then any ethanol blend fuel.

Choosing between 87 or 91

- while not as good as 91, 87 is more effective in higher altitudes
- if you frequently carry a full load of cargo/passengers or tow, use 91
- if you drive in hot weather or climb lots of inclines especially while carrying things, use 91
-91 will help the ping or knock some of you hahe been mentioning, but not necessary. Ethanol-free 87 is also fine.

Try to stick to one type of gas as much as you can.

Regardless whether it is 87 or 91, do a search and look for ethanol-free fuel in your area.



None of the current set of consumer fuels on the market today will do much to fight against the inevitable carbon build up that comes with DI engine designs. The "ethanol" panacea has never really been a panacea for those who pushed it and I agree, it does or will cause problems eventually for the interior components of almost any modern day automotive combustion engine.

The formulation I've been able to rely upon for eons has been: Redline Oil in the engine + 91 Octane from the pump + 0.5qts MMO in the tank (per 18 gallons). This typically equals clean valves, piston heads, cylinder walls, clean valve lifters, light wear on shaft lobes, linear valve faces, retained power/compression/throttle response and fuel economy long range.

For my CX-9, I've just made the switch Amsoil and now include their PI fuel additive per 20 gallons of fuel. I'll be doing that once per month on average depending on how much I drive. Two (2) days (48hrs) prior to each oil change, I'll be running 0.25qts - 0.5qts MMO (Marvel Mystery Oil) to the crank as a flush.

So far, engine seems to love the Amsoil 530/MMO/91oct formulation. Cold starts are slightly quicker/smoother, engine warm up is slightly shorter, idles nice and smooth, throttle response great, pulling up the RPM curve "feels linear" (impossible but good feeling though), no 'noticeable' ping/knock/miss on bottom or top of RPM curve and very important - no noticeable power fade on high ambient outside temperature days.

Can't wait for someone to fabricate a good 'Cold Air Intake' for this new Kodo design 4 barrel CX-9 4.
 
None of the current set of consumer fuels on the market today will do much to fight against the inevitable carbon build up that comes with DI engine designs. The "ethanol" panacea has never really been a panacea for those who pushed it and I agree, it does or will cause problems eventually for the interior components of almost any modern day automotive combustion engine.

The formulation I've been able to rely upon for eons has been: Redline Oil in the engine + 91 Octane from the pump + 0.5qts MMO in the tank (per 18 gallons). This typically equals clean valves, piston heads, cylinder walls, clean valve lifters, light wear on shaft lobes, linear valve faces, retained power/compression/throttle response and fuel economy long range.

For my CX-9, I've just made the switch Amsoil and now include their PI fuel additive per 20 gallons of fuel. I'll be doing that once per month on average depending on how much I drive. Two (2) days (48hrs) prior to each oil change, I'll be running 0.25qts - 0.5qts MMO (Marvel Mystery Oil) to the crank as a flush.

So far, engine seems to love the Amsoil 530/MMO/91oct formulation. Cold starts are slightly quicker/smoother, engine warm up is slightly shorter, idles nice and smooth, throttle response great, pulling up the RPM curve "feels linear" (impossible but good feeling though), no 'noticeable' ping/knock/miss on bottom or top of RPM curve and very important - no noticeable power fade on high ambient outside temperature days.

Can't wait for someone to fabricate a good 'Cold Air Intake' for this new Kodo design 4 barrel CX-9 4.

Nice, Redline and amsoil are both great oils. I’ve been using liquimoly 5w30 in my mazda 6 because the additives specifically formulated for DI motors are really helpful. I also strongly recommend motul, this is a top notch racing oil and provides lots of protection. I would also recommend using shell rotella 5w40 in your engine occasionally, at higher mileage to help clean things out. I remember I used this stuff once in my 75k mile BMW and the oil filter came out much cleaner looking then with the castrol I was using previously.

Mazda has designed a special EGR system which virtually eliminates any sort of carbon buildup across their whole lineup of engines, so don’t worry about any buildup. It will not happen.

There is absolutely no need to run an oil flush every oil change, I think this is excessive. The additives can wear out the metal in your engines when used excessively.

Agreed, ethanol really is the enemy of an internal combustion engine. A good quality ethanol-free 91 octane fuel is the best bet for your motor and fuel lines.

I wouldn’t bother with a cold air intake. It lowers the amount of low end torque your car makes for slightly more power in the high end, which I think makes absolutely no sense because the 2.5L turbo is specifically designed to delivery punchy daily driving torque up to 4500RPM. I would never rev your engine past that unless you have an ECU tune because not only are you not getting the most power from your engine by redlining, but turbo engines run really rich at high RPM to protect the engine from the heat and stress of the turbo. When you’re trying to go fast, try shifting no higher then 5000RPM. You will feel a big boost of torque as the transmission shifts into the next gear.

You live in California, and you seem to like driving fast so do not be hesitant at all to switch to a 5w40 oil. It will provide more engine protection given your hotter climate. If you do your oil changes yourself, optimally you want to change the oil filter every 3000 Miles. This will keep your engine oil nice and clean, so provided you are using a high quality oils like whatever we mentioned, you can safely change your oil at an extended interval and not need to worry about your oil providing insufficient protection.

Remember - it is very important to always have clean oil in a DI engine.
 
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Nice, Redline and amsoil are both great oils. Ive been using liquimoly 5w30 in my mazda 6 because the additives specifically formulated for DI motors are really helpful. I also strongly recommend motul, this is a top notch racing oil and provides lots of protection. I would also recommend using shell rotella 5w40 in your engine occasionally, at higher mileage to help clean things out. I remember I used this stuff once in my 75k mile BMW and the oil filter came out much cleaner looking then with the castrol I was using previously.

Mazda has designed a special EGR system which virtually eliminates any sort of carbon buildup across their whole lineup of engines, so dont worry about any buildup. It will not happen.

There is absolutely no need to run an oil flush every oil change, I think this is excessive. The additives can wear out the metal in your engines when used excessively.

Agreed, ethanol really is the enemy of an internal combustion engine. A good quality ethanol-free 91 octane fuel is the best bet for your motor and fuel lines.

I wouldnt bother with a cold air intake. It lowers the amount of low end torque your car makes for slightly more power in the high end, which I think makes absolutely no sense because the 2.5L turbo is specifically designed to delivery punchy daily driving torque up to 4500RPM. I would never rev your engine past that unless you have an ECU tune because not only are you not getting the most power from your engine by redlining, but turbo engines run really rich at high RPM to protect the engine from the heat and stress of the turbo. When youre trying to go fast, try shifting no higher then 5000RPM. You will feel a big boost of torque as the transmission shifts into the next gear.

You live in California, and you seem to like driving fast so do not be hesitant at all to switch to a 5w40 oil. It will provide more engine protection given your hotter climate. If you do your oil changes yourself, optimally you want to change the oil filter every 3000 Miles. This will keep your engine oil nice and clean, so provided you are using a high quality oils like whatever we mentioned, you can safely change your oil at an extended interval and not need to worry about your oil providing insufficient protection.

Remember - it is very important to always have clean oil in a DI engine.


Very interesting point you make about 5w40 given the climate and conditions around here. I might give that a try - though I would not want viscosity issues during some cold morning starts. We don't have a ton of those around here, by the way. However, I have noticed one thing about this CX-9 that I don't like. The engine is a heatsoak for sure. It really does run warm and probably hotter for those of us with warmer OATs on average. I'm going to pull over a few times after sitting in routine freeway traffic on a hot day and shoot the engine block and turbo with an infrared gun and see what comes up. I'm almost afraid to know.

Mutol and Liquimoly, I knew about prior but decided on Amsoil and their longevity in the synthetic oil business instead - though for racing applications Mutol in particular has a great reputation and following. Being in aviation as well, I went with Amsoil because I know some aircraft engines run it. Plus, I like their limited warranty which says a lot about the confidence they have in their product. If I'm not mistaken, Rotella was a synthetic blend until T6. In my research before making the switch from Redline to Amsoil, I came across a bunch of Saab owners who like using Rotella - but those always seemed to be in older Saab engines.

Regarding carbon build-up as a result of direct injection design. As you know, this could be either in the engine or in the exhaust. Most manufacturers can lay claim to solving the problem at the back end. However, this was a problem for years on the front end with many manufacturers though most of them have put forth design effort to mitigate as much as possible by now. The new iSkyActive-G engine used in the CX-9 is just that - new. Not all of it, but enough of it to matter. As such, I don't think there has been enough time to know what the net effect will be up front (valves) or out back (electronically controlled manifold that now sits between the turbo and cylinder head). In my pre-purchase research, I've come across Mazda Engineer, Dave Coleman, and his many iterations of explanations involving the new dash-G design elements.

On cold air pros and cons, a lot of that depends how Mazda encoded the fuel mapping which determines how the engine "learns" to do remapping based on air flows. Won't know until I try. I installed a Vortex cold air system in a 2000 MN6 C5 (which of course ran the LS1 V8) before I had it Lingenfeltered. That experience is what caused me to want the twin-turbo Lingenfelter package installed. I am (of course) not expecting such results with my CX-9. But, I would not mind having a little extra punch off the start. If the ECU maps right, that might happen.

Or, as you say, it could actually lose a slight amount of lower end power. That actually happened to some people who installed Cold Air Intake Systems on their C5 during the 2000 period - I distinctly remember that happening. However, many of us thought it was due to faulty installation or a damaged MAF sensor during installation. The C5s ECM too care of the rest and handled the remapping on its own. Mine in particular loved cold weather conditions throughout the entire RPM range. Of course, I also had a lemon. So, right up to about 4,300 RPM, the power curves on my LS1 began to drop like a rock (this was both before and after the Vortex - so that did not cause the problem). GM could/would never solve the problem and I decided at that point - what the heck, I'll ship it to Lingenfelter and let them rebuild it in "their own image." And, rebuild it they did indeed. This was not too long before John, passed away.

I think the only performance mods I want on my Signature is Cold Air (fingers crossed on it working), anti-sway bars front and rear (if both are necessary). I saw someone on this forum contemplating the installation of a Strut Bar on top, but conversation and debate ensued about the efficacy given the unibody design of the CX-9 not allowing much body roll in the first place. Probably bumping up slight to 265/50/20 summer performance tire as well, if I can find a good set of 8.5" rim-to-rim replacements. I've got my eyes on some Yokos, Kumhos and Michelins that might work. But, in all honesty, I do like the way these Falkens behave themselves.

Nice post.
 
Very interesting point you make about 5w40 given the climate and conditions around here. I might give that a try - though I would not want viscosity issues during some cold morning starts. We don't have a ton of those around here, by the way. However, I have noticed one thing about this CX-9 that I don't like. The engine is a heatsoak for sure. It really does run warm and probably hotter for those of us with warmer OATs on average. I'm going to pull over a few times after sitting in routine freeway traffic on a hot day and shoot the engine block and turbo with an infrared gun and see what comes up. I'm almost afraid to know.

Mutol and Liquimoly, I knew about prior but decided on Amsoil and their longevity in the synthetic oil business instead - though for racing applications Mutol in particular has a great reputation and following. Being in aviation as well, I went with Amsoil because I know some aircraft engines run it. Plus, I like their limited warranty which says a lot about the confidence they have in their product. If I'm not mistaken, Rotella was a synthetic blend until T6. In my research before making the switch from Redline to Amsoil, I came across a bunch of Saab owners who like using Rotella - but those always seemed to be in older Saab engines.

Regarding carbon build-up as a result of direct injection design. As you know, this could be either in the engine or in the exhaust. Most manufacturers can lay claim to solving the problem at the back end. However, this was a problem for years on the front end with many manufacturers though most of them have put forth design effort to mitigate as much as possible by now. The new iSkyActive-G engine used in the CX-9 is just that - new. Not all of it, but enough of it to matter. As such, I don't think there has been enough time to know what the net effect will be up front (valves) or out back (electronically controlled manifold that now sits between the turbo and cylinder head). In my pre-purchase research, I've come across Mazda Engineer, Dave Coleman, and his many iterations of explanations involving the new dash-G design elements.

On cold air pros and cons, a lot of that depends how Mazda encoded the fuel mapping which determines how the engine "learns" to do remapping based on air flows. Won't know until I try. I installed a Vortex cold air system in a 2000 MN6 C5 (which of course ran the LS1 V8) before I had it Lingenfeltered. That experience is what caused me to want the twin-turbo Lingenfelter package installed. I am (of course) not expecting such results with my CX-9. But, I would not mind having a little extra punch off the start. If the ECU maps right, that might happen.

Or, as you say, it could actually lose a slight amount of lower end power. That actually happened to some people who installed Cold Air Intake Systems on their C5 during the 2000 period - I distinctly remember that happening. However, many of us thought it was due to faulty installation or a damaged MAF sensor during installation. The C5s ECM too care of the rest and handled the remapping on its own. Mine in particular loved cold weather conditions throughout the entire RPM range. Of course, I also had a lemon. So, right up to about 4,300 RPM, the power curves on my LS1 began to drop like a rock (this was both before and after the Vortex - so that did not cause the problem). GM could/would never solve the problem and I decided at that point - what the heck, I'll ship it to Lingenfelter and let them rebuild it in "their own image." And, rebuild it they did indeed. This was not too long before John, passed away.

I think the only performance mods I want on my Signature is Cold Air (fingers crossed on it working), anti-sway bars front and rear (if both are necessary). I saw someone on this forum contemplating the installation of a Strut Bar on top, but conversation and debate ensued about the efficacy given the unibody design of the CX-9 not allowing much body roll in the first place. Probably bumping up slight to 265/50/20 summer performance tire as well, if I can find a good set of 8.5" rim-to-rim replacements. I've got my eyes on some Yokos, Kumhos and Michelins that might work. But, in all honesty, I do like the way these Falkens behave themselves.

Nice post.


Well I wont suggest you switch to another oil because theres nothing wrong with what you are currently using, but Id recommend you try out liqui moly, especially motul and maybe even redline one more time just to see how t compares to AMSoil. All great oils but I think Redline and Motul are the two best ones. 5w40 would be an important consideration given your climate for sure. As long as you stick to a 5w oil weight, your cold starts will always be nice and smooth unless you see -20c weather in California which I am strongly doubting. Hell, even 10w30 or 10w40 is a totally reasonable choice given your climate, but Id stick to 5w40 because its easy on your engine during cold starts yet provides good protection at full operating temp.

This is what made me particularly fond about the shell Rotella oil I tried in my BMW by the way. The cold starts were astoundingly smooth for such a heavy duty oil. I remember with the Castrol I used, the cylinder head was very rattly and noisy. This shell oil quieted down the motor on cold starts and helped the motor come up to temp quickly, yet maintained consistently lower temperatures at full operating temp and the engine ran very, very smooth with this stuff. Loved the oil, very cheap for how good it is, but I am hesitant to use it repeatedly because of all the Diesel engine detergents it has. It wears out the metals in your engine.

I believe that the 2.5L turbo engine in your CX-9 is based off the NA 2.5L found in the Mazda 6, and Mazda took precautionary steps to ensure no carbon buildup in that engine. Highly doubt they would make any backwards steps developing your newer engine, so I can confidently say that you dont need to worry about any sort of carbon buildup with your motor. I will say however, that an occasional full throttle pull will help clean out your injectors and possibly exhaust system too. If I switch cars with my Dad and he was using the Mazda for a long period of time (he never revs the engine hard) when I get the car back and do a full throttle pull with it, the exhaust smells like complete ass until its cleared out by the third redline, so this is something to keep in mind for a conservative driver.

Mazda has a super well designed intake from the factory. Not sure if your CX-9 is the same, but my 6 draws cool air from in between the hood and touching the air box after a drive, its completely cool to the touch. If yours is just a little warm but not hot, then heatsoak is not an issue in your car. If you are worried about excessive heat in the engine bay, a vented hood will do wonders. A vent toward the front of the hood, right behind the radiator will help increase radiator flow, extract hot air from within the engine bay resulting in lower oil temps and Im sure this would improve intake temperatures too.

Anyways, your stock intake is well designed so I wouldnt recommend replacing it with some metal piping unless its drawing cool air from outside the engine bay or is a closed air box design. If its not one of those two, dont waste your money.

If you want good bang for your buck and a sweet exhaust note, look into a downpipe or maybe have a custom one fabricated for your car, and dont forget the ECU tune. Much more effective power increase and you will not sacrifice any low-end torque.

The sway bars are an excellent idea, highly recommended you get both front/rear. They will improve steering precision and remove body roll without sacrificing ride comfort. If you like to corner aggressively, I would pop your alignment strut pins on the front axle or get camber plates for more negative camber. This will improve front axle grip and result in a more neutral, tail happy behaviour around corners.

I have some high performance Yokohamas on my mazda 6 that came from the factory, and I find these tires to be extremely well tuned to mazdas chassis. They are noisy on the highway, but they ride comfortably and treadwear is good. The grip, particularly in the rain ridiculously good and steering precision is spot on - cant recommend them enough.

Very interesting point you made regarding the fuel mapping adapting to a modification in airflow. Ive actually had personal experience with this modding the exhaust system on my BMW, but I am indeed very curious to see how well Mazdas ECU would adapt to an exhaust/intake mod. I am considering to delete my secondary cat and try it out on the Mazda as well.
 
The only thing I agree with here is that poor quality gasoline gives poor results. Good quality gasoline of 87 or higher works fine including E10. As Mazda says, higher octane gives more power IF you run at high rpms. Almost everything else is just shade-tree mechanic myth or just plain wrong.
 
Octane has nothing to do with how clean your injectors stay or how much power you make, and Ethanol is good for corn farmers and emissions, but not your car. It probably won't damage anything unless your car's old enough to have a carburetor but it's definitely not a good thing for your engine.

There is absolutely no reason to use higher-octane fuel unless your car explicitly requires it. The higher the octane, the more compression/heat required to combust the fuel. Yes, the more SLOWLY it burns. In high-performance engines (turbo-charged, high compression cylinders, etc), a higher octane fuel is needed so the fuel doesn't combust prematurely (knocking).
If you put this fuel in a "normal" engine, it may even have detrimental effects, since the engine will have a harder time combusting the higher octane fuel.
 
The only thing I agree with here is that poor quality gasoline gives poor results. Good quality gasoline of 87 or higher works fine including E10. As Mazda says, higher octane gives more power IF you run at high rpms. Almost everything else is just shade-tree mechanic myth or just plain wrong.

Octane has nothing to do with how clean your injectors stay or how much power you make, and Ethanol is good for corn farmers and emissions, but not your car. It probably won't damage anything unless your car's old enough to have a carburetor but it's definitely not a good thing for your engine.

There is absolutely no reason to use higher-octane fuel unless your car explicitly requires it. The higher the octane, the more compression/heat required to combust the fuel. Yes, the more SLOWLY it burns. In high-performance engines (turbo-charged, high compression cylinders, etc), a higher octane fuel is needed so the fuel doesn't combust prematurely (knocking).
If you put this fuel in a "normal" engine, it may even have detrimental effects, since the engine will have a harder time combusting the higher octane fuel.

I agree that different octanes have little effect on how clean everything stays. Just buy from a reputable station that seems to have a lot of traffic so they’re more likely to have fresh fuel in their tanks.

I don’t have a CX9, but I do have a Ford Explorer Sport with the 3.5 Ecoboost. The recommended octane is 87, but the engine sees a benefit up to 93 octane(power figures were run with 93 octane). Do I see a 40hp drop with 87? Not from seat of the pants feeling. I’m sure there’s some drop, but it doesn’t feel like that much.

I have run different octanes fuels(for extended periods to allow the engine to adjust) and saw zero difference in fuel mileage between high and low octane with ethanol. Also, running non-oxy 91 octane did not compensate for the (at least) 30% higher cost over 93 octane with ethanol. I maybe saw 10% higher mileage.

In the end, I’ve been running 87 octane for over a year and have been perfectly content with the performance. I’m sure the guy in the new VW GTI that tried to outrun me up the freeway on-ramp would agree(i.e. it didn’t end well for him).
 
I agree that different octanes have little effect on how clean everything stays. Just buy from a reputable station that seems to have a lot of traffic so they’re more likely to have fresh fuel in their tanks.

I don’t have a CX9, but I do have a Ford Explorer Sport with the 3.5 Ecoboost. The recommended octane is 87, but the engine sees a benefit up to 93 octane(power figures were run with 93 octane). Do I see a 40hp drop with 87? Not from seat of the pants feeling. I’m sure there’s some drop, but it doesn’t feel like that much.

I have run different octanes fuels(for extended periods to allow the engine to adjust) and saw zero difference in fuel mileage between high and low octane with ethanol. Also, running non-oxy 91 octane did not compensate for the (at least) 30% higher cost over 93 octane with ethanol. I maybe saw 10% higher mileage.

In the end, I’ve been running 87 octane for over a year and have been perfectly content with the performance. I’m sure the guy in the new VW GTI that tried to outrun me up the freeway on-ramp would agree(i.e. it didn’t end well for him).

if the recommended octane is 87 and the ECU does not adapt to 91, don't even waste your money.

I am talking about the CX-9 here which is compatible with 91, not an ecoboost ford here.

while I agree that the octane fuel doesnt make as much of a different for your fuel system compared to switching to ethanol-free fuel, I will admit that 91 octane fuel does pose efficiency and power benefits + it should clean your fuel system better.

you did not notice and difference in power or fuel efficiency using 91 octane fuel because your Ford is not designed for this type of fuel.
 
if the recommended octane is 87 and the ECU does not adapt to 91, don't even waste your money.

I am talking about the CX-9 here which is compatible with 91, not an ecoboost ford here.

while I agree that the octane fuel doesnt make as much of a different for your fuel system compared to switching to ethanol-free fuel, I will admit that 91 octane fuel does pose efficiency and power benefits + it should clean your fuel system better.

you did not notice and difference in power or fuel efficiency using 91 octane fuel because your Ford is not designed for this type of fuel.

I know that the 3.5 Ecoboost engine does adjust for different octane ratings. The recommend fuel is 87, however, in the brochure, it does specifically state that the power figures were obtained by using 93 octane. The manual also states that the engine will benefit with running higher octane. The ECU is designed to "play" with the parameters to obtain the best performance with the given conditions, including the fuel octane. So, if I was looking for peak performance all the time, I'd run 93, but I have no issues with running 87. I really wish someone would run one of these engines with 87 and 93 on the same vehicle and dyno to see the differences. I haven't had any luck finding such a test.

As for the ethanol vs. e-free fuel, at cruising speeds(i.e. highway driving), e-free fuel should provide better mileage regardless if the ECU compensates for the different octane. Ethanol has less energy than the same amount of straight gasoline, so the same amount of e-free will have more energy than an ethanol blend. That in turn will provide more power with the same amount of fuel/air. Since it provides more power, you can give it less throttle input, therefore less air and fuel to maintain the same speed(all other things being equal).

In addition, ethanol blended fuels have a lower air/fuel ratio for stoichiometric burning. E10 is about 14.0:1 and straight gas is 14.7:1. Since most ECU only look at lambda values, it targets 1 lambda for cruising. 1 lambda = all fuel and oxygen is consumed. 1 lambda is 14:1 for E10 and 14.7:1 for straight gas. So, in order to burn all the fuel and oxygen, the E10 system will have to supply more fuel(by volume) than the straight gas. At normal cruising speeds and inputs, the computer is always trying to hit stoichiometry.

As I mentioned, I saw maybe 10% increase with the e-free fuel, which doesn't sound like much, but it's actually a decent increase. The problem is that e-free fuel is typically 30% higher cost than the stuff with ethanol, so the mileage bump doesn't compensate for the cost increase. If there was only a 10% difference between the 2 fuels, I'd run the e-free.
 
I know that the 3.5 Ecoboost engine does adjust for different octane ratings. The recommend fuel is 87, however, in the brochure, it does specifically state that the power figures were obtained by using 93 octane. The manual also states that the engine will benefit with running higher octane. The ECU is designed to "play" with the parameters to obtain the best performance with the given conditions, including the fuel octane. So, if I was looking for peak performance all the time, I'd run 93, but I have no issues with running 87. I really wish someone would run one of these engines with 87 and 93 on the same vehicle and dyno to see the differences. I haven't had any luck finding such a test.

As for the ethanol vs. e-free fuel, at cruising speeds(i.e. highway driving), e-free fuel should provide better mileage regardless if the ECU compensates for the different octane. Ethanol has less energy than the same amount of straight gasoline, so the same amount of e-free will have more energy than an ethanol blend. That in turn will provide more power with the same amount of fuel/air. Since it provides more power, you can give it less throttle input, therefore less air and fuel to maintain the same speed(all other things being equal).

In addition, ethanol blended fuels have a lower air/fuel ratio for stoichiometric burning. E10 is about 14.0:1 and straight gas is 14.7:1. Since most ECU only look at lambda values, it targets 1 lambda for cruising. 1 lambda = all fuel and oxygen is consumed. 1 lambda is 14:1 for E10 and 14.7:1 for straight gas. So, in order to burn all the fuel and oxygen, the E10 system will have to supply more fuel(by volume) than the straight gas. At normal cruising speeds and inputs, the computer is always trying to hit stoichiometry.

As I mentioned, I saw maybe 10% increase with the e-free fuel, which doesn't sound like much, but it's actually a decent increase. The problem is that e-free fuel is typically 30% higher cost than the stuff with ethanol, so the mileage bump doesn't compensate for the cost increase. If there was only a 10% difference between the 2 fuels, I'd run the e-free.

Ethanol blend fuel will ALWAYS result in poorer fuel economy then an ethanol-free one.
 
You’re so annoying and you know absolutely nothing about these cars. Can you do us all a favour and look it up please?

Annoying?! Lmao,you looked into a mirror lately? Funniest thing I've heard all day...

Can you gain 40hp with 87 to 91,sure you can,with a tune,but good luck just pulling up to the pump and dumping in 91 octane on a stocker.

I gained almost 50awhp adding methanol injection to 93 octane,but that's with a handful of mod goodies and myself and a friend with a dyno tuning it,but keep talking like a know-it-all and I know nothing. I own a 4cyl FI car that puts down almost 250awhp per liter...I want to be nice to you,but you're the laughing stock of this website,and too damn hard headed and wet behind the ears to take anything into account.

Copy and paste on my friend...
 
23hp difference in 87 vs 91 octane in a CX-9 (per Mazda).

Tell us again how 23=40?!? We all know in your thinking it does,but for the rest of the real World,you're wrong!
Imagine that...

Side note: I was getting almost 15awhp in my Evo as a stocker just because I can get 93 octane at the pump,and the boys in Cali couldn't. They didn't like it too well...
 
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23hp difference in 87 vs 91 octane in a CX-9 (per Mazda).

Tell us again how 23=40?!? We all know in your thinking it does,but for the rest of the real World,you're wrong!
Imagine that...

Side note: I was getting almost 15awhp in my Evo as a stocker just because I can get 93 octane at the pump,and the boys in Cali couldn't. They didn't like it too well...

my mistake, last time I read up on the CX-9 I swear I recalled reading 210HP on 87 fuel. Guess I was wrong about that.
 
I know that the 3.5 Ecoboost engine does adjust for different octane ratings. The recommend fuel is 87, however, in the brochure, it does specifically state that the power figures were obtained by using 93 octane. The manual also states that the engine will benefit with running higher octane. The ECU is designed to "play" with the parameters to obtain the best performance with the given conditions, including the fuel octane. So, if I was looking for peak performance all the time, I'd run 93, but I have no issues with running 87. I really wish someone would run one of these engines with 87 and 93 on the same vehicle and dyno to see the differences. I haven't had any luck finding such a test.

As for the ethanol vs. e-free fuel, at cruising speeds(i.e. highway driving), e-free fuel should provide better mileage regardless if the ECU compensates for the different octane. Ethanol has less energy than the same amount of straight gasoline, so the same amount of e-free will have more energy than an ethanol blend. That in turn will provide more power with the same amount of fuel/air. Since it provides more power, you can give it less throttle input, therefore less air and fuel to maintain the same speed(all other things being equal).

In addition, ethanol blended fuels have a lower air/fuel ratio for stoichiometric burning. E10 is about 14.0:1 and straight gas is 14.7:1. Since most ECU only look at lambda values, it targets 1 lambda for cruising. 1 lambda = all fuel and oxygen is consumed. 1 lambda is 14:1 for E10 and 14.7:1 for straight gas. So, in order to burn all the fuel and oxygen, the E10 system will have to supply more fuel(by volume) than the straight gas. At normal cruising speeds and inputs, the computer is always trying to hit stoichiometry.

As I mentioned, I saw maybe 10% increase with the e-free fuel, which doesn't sound like much, but it's actually a decent increase. The problem is that e-free fuel is typically 30% higher cost than the stuff with ethanol, so the mileage bump doesn't compensate for the cost increase. If there was only a 10% difference between the 2 fuels, I'd run the e-free.

bottom line, 87 octane fuel will suffice in low RPM situations. casual driving particularly highway or limited stopping. no hard acceleration or hauling people/cargo in mild weather.

but in hot weather with a car full of people, possibly towing something, A/C cranked, going up hills and needing to rev the car hard in particular is when 91 octane would be much more preferable. considering the fact that I have observed noticeably improved fuel economy switching to ethanol-free 91 fuel, the extra costs of the better fuel are completely offset due to the gains in efficiency let alone the extra 23HP you gain.

keep in mind that we are getting owners experiencing ping/knocking with 87 fuel. that is NOT a good sign for the long-run of the motor, and even though the vehicle can run on 87, I recommend against it if the engine pings unless you use 91.
 
Mazda actually rates the 250 hp when using 93 octane. Does anyone know what its outputting on 91?

Maybe a couple horsepower less, nothing significant.

An ethanol-free 91 is more efficient and will produce more power then your average 93 octane fuel while being cheaper.
 
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