GR86 Premium MPG

[Sasquachulator]

Why would you buy a car that requires premium and then try to save a few bucks at the pump and use regular?

If you dont want to deal with the required upkeep to keep the thing running at optimal performance, dont buy a car that has a specific level of upkeep....

always put the minimum required octane in the car.....unless you have no choice...and even then try to drive the car gently.

I dont get why some people buy something expensive and try to cheap out somewhere else.

[Lelandjt]

Originally Posted by Sasquachulator

Why would you buy a car that requires premium and then try to save a few bucks at the pump and use regular?

If you dont want to deal with the required upkeep to keep the thing running at optimal performance, dont buy a car that has a specific level of upkeep....

always put the minimum required octane in the car.....unless you have no choice...and even then try to drive the car gently.

I dont get why some people buy something expensive and try to cheap out somewhere else.

At high altitude you don't put lower octane in a NA engine to save money. You do it to make more power. With modern engine managment it's hard to guess if this is still true. It may be able to advance timing enough to make better power with high octane.
I watched that Engineering Explained video back when it came out but he's in Idaho and his idea of "high elevation" is half the height of mine so I decided to use 85 in my new Ford T150.

[StormTrooper]

If you watched the video you would know he pulled charts out to 10k feet.
Might want to go back and watch it again with a full night's rest.

[Dzmitry]

Originally Posted by Lelandjt

At high altitude you don't put lower octane in a NA engine to save money. You do it to make more power.

? Let me go fill up a tank of 85 real quick.

[StormTrooper]

Originally Posted by Dzmitry

? Let me go fill up a tank of 85 real quick.

Maybe he meant e85 😆 🤣

[Lelandjt]

You guys don't understand the relationship between octane and explosive energy. Lower octane is more powerful. At 10,000ft it's hard to say if the computer can make enough use of 91's extra resistance to predetonation compared to 87 to make up for its lower energy. My Ford T150 seems to run best on 85 but I suspect the Twin will run best on 87. When I drove my T150 to the coast I switched from 85 to 87 at 5000ft near the CO/UT border

[Sasquachulator]

Originally Posted by Lelandjt

You guys don't understand the relationship between octane and explosive energy. Lower octane is more powerful. At 10,000ft it's hard to say if the computer can make enough use of 91's extra resistance to predetonation compared to 87 to make up for its lower energy. My Ford T150 seems to run best on 85 but I suspect the Twin will run best on 87. When I drove my T150 to the coast I switched from 85 to 87 at 5000ft near the CO/UT border

Regardless.....
The twins are officially rated for 91 minimum. The first gen user manual actually says to use 93 but 91 is fine if 93 is unavailable. So that's what its getting at the minimum....not 89, not 87, not 85....91.

[Lelandjt]

Originally Posted by Sasquachulator

Regardless.....
The twins are officially rated for 91 minimum. The first gen user manual actually says to use 93 but 91 is fine if 93 is unavailable. So that's what its getting at the minimum....not 89, not 87, not 85....91.

This whole altitude and octane thing is just flying over your head. But that's okay, following instructions is a safe fall back to thinking.

[StormTrooper]

Pretty sure you are the one not understanding things. There is more energy in Gas than Ethanol but drag cars don't run 87 they run 115 octane ethanal because you can run higher compression and more advanced timing.

You absolutely will not make more power with 87 than 91 or 93 on a car tuned for 93. no matter the altitude. Run a Data logger and see how much timing is being pulled running shit gas at 8-9-10k feet it'll still be less power than running the required fuel.

[Lelandjt]

Originally Posted by StormTrooper

Pretty sure you are the one not understanding things. There is more energy in Gas than Ethanol but drag cars don't run 87 they run 115 octane ethanal because you can run higher compression and more advanced timing.

You absolutely will not make more power with 87 than 91 or 93 on a car tuned for 93. no matter the altitude. Run a Data logger and see how much timing is being pulled running shit gas at 8-9-10k feet it'll still be less power than running the required fuel.

I think you have a weird bias against lower octane numbers ("shit gas") and an overconfidence in guessing exactly how much ignition advance can be used with 91 vs 87 octane gas at 9, 10k, as well as a complete disregard for the difference in burning speed (power) between these octane grades. Someone needs to make a youtube video to settle this using several different new NA cars. Where's the highest altitude dyno?

[Dzmitry]

Originally Posted by Lelandjt

You guys don't understand the relationship between octane and explosive energy. Lower octane is more powerful. At 10,000ft it's hard to say if the computer can make enough use of 91's extra resistance to predetonation compared to 87 to make up for its lower energy. My Ford T150 seems to run best on 85 but I suspect the Twin will run best on 87. When I drove my T150 to the coast I switched from 85 to 87 at 5000ft near the CO/UT border

I think you're simply stating it incorrectly, hence the confusion. Lower octane is not more powerful, it just has a faster burn rate. There is simply less oxygen in the air at higher altitude, therefore negating the need for the typical octane you may use - at which in any case, you will have reduced power. A car is built to a specified octane rating (91-93 in the case of twins) and is designed to perform optimally at that rating. I'd say it would be risky with a twin to test 87, even at high altitudes. At 91, even at sea level, twins tend to bog down and not drive at their best. Running on lower octane isn't BEST, it's just that most standard cars that run on 87 at high altitudes can get away with a couple octane points lost. In fact, they are probably designed to withstand that from factory and I wouldn't be surprised if some manuals for such cars mention the use of 85.

As you already understand, a higher octane rating is ONLY there for the sole purpose of avoiding detonation, particularly for high compression engines in sports cars, race cars, etc. Therefore, dropping octane rating isn't giving anyone any kind of power or improving the way an engine runs in any sort of way. If you believe so, it's only placebo. The simple fact is that twins ask for 91 minimum. We don't know the math behind how many octane points you can lower and still run SAFELY based on the altitude you're at. So why risk it. You can certainly perform the test yourself, and it's very possible it will work out, but you're certainly not promoting the engine to run at its peak potential. Just like when you're running 91 at sea level, you're not giving it the full potential that 93 would give. This is just because the twin was designed to run on a fuel that burns slightly slower but avoids detonation - as detonation is highly likely in this engine due to its design.

P.S.
justinco resides and races at high altitudes (not exactly sure how high). You can look him up on youtube and see how each tune and performance mod made power for him. Power gains were quite similar to those at sea level. So it seems ignition advance would provide far greater benefit than a lower octane fuel.

[Lelandjt]

Originally Posted by Dzmitry

Lower octane is not more powerful, it just has a faster burn rate.

I learned hose things are the same. A faster burn creates more push on the piston = more power. Putting a higher octane in an engine than it's designed for makes it less powerful because of the slower burn. Is this not true?

Whether ignition needs to be retarded with 87 at 10,000ft is the question, because that would likely reduce power greater than the faster burn increases it.

[Dzmitry]

Originally Posted by Lelandjt

I learned hose things are the same. A faster burn creates more push on the piston = more power. Putting a higher octane in an engine than it's designed for makes it less powerful because of the slower burn. Is this not true?

Whether ignition needs to be retarded with 87 at 10,000ft is the question, because that would likely reduce power greater than the faster burn increases it.

This is very true. By raising the octane above what the vehicle is rated for, you are likely to actually drop in power. How much, I don't know. I would bet it's very little. So your statement is true in the case of adding octane. I don't know that it works the other way around exactly, but quite possible for more common vehicles that use 87 octane. But in general, the vehicle has a spec octane and the engine is designed based on that. So an engine isn't learning that its fuel is now capable of burning a little faster and making adjustments to gain a little power. Instead, an engine is typically tuned to provide optimal power at specified octane rating prior to any detonation. When lowering octane, in the case of the twins, all it see's is that it's more prone to detonation and retards timing, etc.

But... in the situation you describe, where one is at high altitude, the engine is breathing less oxygen and trying to compensate by reducing the fuel flow. Pressure is reduced, effectively reducing the compression ratio and negating the need for high octane as detonation is less likely to occur. In other words, the safety margin is improved, which doesn't higher octane a necessity. But by reducing the octane rating, you are only accommodating to the fact that your engine no longer needs the high rating with a "reduced compression ratio". It will not produce more power through this.

Theoretically, it can with a tune. Just like you can take a twin and tune it up on 91, and still gain more power than the guy that's running 93 on his stock twin.

To get back on subject, dropping to 87 may certainly work for a twin at 10K elevation. But it wouldn't gain any power in doing so, but rather lose some, as the higher elevation effectively loses power. I do understand what you're getting at though. I could also be wrong about some of this stuff, so don't take me to be factual. I understand some about the subject from doing my own reading, but I don't know any deep math behind it.