What fuel do you use?

[A70TTR]

I feel that’s most turbo cars. My 1.8 Golf feels so slow in hot weather. Honestly seems it’s missing a good 30-50hp.

probably pulling timing at the very least if its noticeable

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[IS2000]

The best fuel without ethanol that I can get is 95RON (91 US octane). However we do have E20 and E85 widely available. Hopefully the car can run those higher octane fuels when modded.

 

[kona61]

The best fuel without ethanol that I can get is 95RON (91 US octane). However we do have E20 and E85 widely available. Hopefully the car can run those higher octane fuels when modded.

The Supra can handle full E85 with a tune.

 

[Haros]

94 octane is everywhere here in BC thankfully. Expensive though.

 

[diablo2112]

Regular (non-premium) Gas in the Supra

I've done a bit of testing the last few weeks to see how well the Supra tolerates regular fuel. My last 2 full tanks, I used 87 octane. Results and discussion are below.

TL;DR: it works fine, but I'm running at high altitude. YMMV.

As you're aware, the need for premium arises from high-compression engines which need to resist preignition, especially with delayed ignition timing. High-octane fuels accomplish this. All modern engines monitor for engine knock, and can advance the timing to reduce/eliminate knock. None-the-less, it's better to not have to engage this feature if possible. At a minimum, you lose performance. At worst, you can damage pistons, valves, and rods.

For the 2 tanks I just ran, I used Bimmerlink's Dashboard mode to monitor for engine knock. Not once during these 2 tanks did the engine ECU report knock. Now, there's a huge caveat here. I live at high altitude, over 5000'. This can and does have the effect of lowering compression which also lowers the risk of knock. The engine was run at high-boost for periods during this time frame, with no issues. For example, see below. Nearly 30psi boost pressure, and no reported knock.

I've owned many other cars the last 40 years, including about a dozen BMWs. All the BMWs called for premium. Given this, I've run regular gas (87 octane) in these cars, for many years at a time. The longest such period was 120,000 miles I put on a 2007 335i (with the N54). I've also had no issues running regular with a 2014 335i (N55), 2015 640i(N55), and 2017 440i(B58). I also did similar tests using Bimmerlink to monitor for knock. The 2007 BMW spent a few years at sea-level, also without issues. My own experience using regular fuel in the BMW FI-I6 has been trouble free.

Please note, this experience isn't universally true. The BMW N54/N55/B58 engines seem to accept regular fuel very well in my experience. Other cars I've run *have* experienced knock and required premium fuel. Examples here include a 2005 C6 Corvette, a 1996 Jeep Cherokee 4.0 (on which I installed a super-charger for use as a tow vehicle), and nearly all the 12-cylinder exotics I've owned over the years.

Conclusion: I'm comfortable using regular fuel in my Supra without worry. The only reason for higher-octane fuel is to avoid knock, and my circumstances (operating at higher altitude) lessen this concern. Now, I wouldn't do a track day on regular. That's more stressful and my testing didn't capture that use condition. For everyday driving with the occasionall spurt, regular works fine for me. YMMV.

edit: And I neglected a key variable in my original post. I did these tests in the winter. High-temperatures can exacerbate engine knock. I intend to repeat my monitoring tests this summer. It may be that in my case, regular case works fine in the winter, while higher grade (89 octane) is needed in the summer. We're fortunate that modern engine ECUs and apps allow easy monitoring of all these parameters, including knock detection.

 

[Ultimateone]

Honest question is why in the world would you choose to do this?

 

[diablo2112]

Premium is about $0.80/gallon more expensive here; that's about $10/tank. My OCD kicks in when paying for something I don't need. And, premium is actually slightly lower in energy content than regular; you'll get ever-so-slightly-better mileage with regular.

It's also more of a habit. One of the few auto advantages of living at high altitude.

 

[Rocksandblues]

The engine computers are so adept to change timing fuel octanes and combustion i believe you are correct that the Supra will have no ill effects from bottom gas

you are leaving performance on the table.

And if you are ok with a little less pep to save $10 that is all you.
I spill more whiskey than that in any given weekend.

 

[Snorlax27]

You drive close to a $60k brand new sports car and want save a few dollars? lol ?‍?‍?‍?‍?‍

I whole heartedly agree with you. Sacrificing performance to save a couple of dollars isn’t worth the trade off IMHO; however, it is ultimately OPs decision, so be it.

Although I will say, it’s quite strange buying a sports car just to cheap out on gas, even if modern day ECUs are capable of adjusting to lower grade fuels. It’s kind of a given that putting higher octane fuel on a car rated for 87 is a waste, but using lower octane fuel on a car designed for premium or better is kind of mind boggling

 

[diablo2112]

I'm not sacrificing performance. I've done a measured evaluation and shown for my circumstances, that there's no difference between 87 octane and the "premium" available in my state.

I don't see why this is such a risible finding. There's very good economic and environmental reasons to favor regular over premium. It not only costs less, it provides better mileage and has less of an environmental impact to produce.

BTW, you're probably not aware, but "premium" fuel here is rated at either 89 or 90 octane. 93 premium isn't even an option here.

 

[Xxyion]

I do wonder how much the higher altitude comes into play here. Its already well known that at higher altitude where the air is thinner, turbo engines already have a hard time performing, so him losing more performance by jumping to 87 wouldnt feel much different.

However my only concern is the fact that higher octane while it does really just prevent knock, it also helps with fuel economy and emissions. However the thing that i'm concerned about is a sudden change in air preassure and density while you are driving on 87. Lets say you are driving your car and all of a sudden you come down to sea level for whatever reason. The 87 at that point is doing some bad stuff to your engine. As you said, the lower compression due to altitude could be what allows you to run regular but on the off chance something changes all of a sudden, you wont have that cieling that higher octane gas will have in case the environment does change on you.

Personally i'm with a lot of other people here, i'm not skimping out on gas on a car that costs me over 50k. Its just one of those things that adds extra risk where there shouldnt be. And premium is only .30 cents over regular so its 3$ im willing to spend.

 

[Xxyion]

So here is a bit of interesting information i found. In the Owners Manual for the 2021 Supra. It doesnt specifically say what octane is required or recommended. it even states that we can use E25 or lower in order to fill up the car and drive. The only things that it is a hard no on, are fuels that contain metals and fuels with high sulfur content.

This tells me that Toyota engineers have effectivly built in a low end flexfuel system. Now obviously i'm not saying to run E85 or anything. But it seems like as long as the fuel itself is good, you can use whatever octane you want. This throws more weight towards the OPs original statement.

 

[diablo2112]

However my only concern is the fact that higher octane while it does really just prevent knock, it also helps with fuel economy and emissions.

That's a common misconception. Premium fuel is neither more fuel efficient nor does it lead to reduced emissions. It's just slightly the opposite, actually. Science behind this follows.

The heat of combusion of 2,2,4-trimethylpentane is less than that of n-heptane, as is its density. For this reason (see wiki entry on Octane rating): "The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced." (Note: You buy gas on a volume basis; the lower density and lower energy content of premium is a double-whammy with respect to fuel efficiency.)

The reason for this is basic chemistry. The H/C ratio of n-heptane is 2.286; it's 2.25 for iso-octane. The higher the H/C ratio in a fuel, the more energetic it is (because there's more energy in C-H bonds than C-C bonds) and the less CO2 it makes per unit energy. it also explains the higher density for n-heptane, there's a bit more hydrogen bonding via Van der Waals forces, bringing these molecules a bit closer together.

The premium fuel you buy isn't necessarily a mixture of just these 2 hydrocarbons, but the ingredients which give a higher octane rating still follow these general trends. In sum, this is why premium fuel is actually slightly less fuel efficient and has a bit more carbon footprint.

 

[Snorlax27]

So here is a bit of interesting information i found. In the Owners Manual for the 2021 Supra. It doesnt specifically say what octane is required or recommended. it even states that we can use E25 or lower in order to fill up the car and drive. The only things that it is a hard no on, are fuels that contain metals and fuels with high sulfur content.

This tells me that Toyota engineers have effectivly built in a low end flexfuel system. Now obviously i'm not saying to run E85 or anything. But it seems like as long as the fuel itself is good, you can use whatever octane you want. This throws more weight towards the OPs original statement.

If we are discussing running 87 octane on vehicles closer to sea level, there will be a difference in performance. There’s a reason why tuners will only tune for 93 (or in my circumstance crappy California 91) or higher.

As OP posted earlier, the higher octane helps with knock resistance, another reason why people prefer running premium gas or E85. I will admit that OPs elevation plays a role in his circumstances, so I will concede to that debate. If there is no benefit in going with a higher octane fuel under his circumstances (I.E. noticeable power difference or minimal fluctuations in knock resistance), then go for it.

 

[Xxyion]

That's a common misconception. Premium fuel is neither more fuel efficient nor does it lead to reduced emissions. It's just slightly the opposite, actually. Science behind this follows.

The heat of combusion of 2,2,4-trimethylpentane is less than that of n-heptane, as is its density. For this reason (see wiki entry on Octane rating): "The other rarely-discussed reality with high-octane fuels associated with "high performance" is that as octane increases, the specific gravity and energy content of the fuel per unit of weight are reduced." (Note: You buy gas on a volume basis; the lower density and lower energy content of premium is a double-whammy with respect to fuel efficiency.)

The reason for this is basic chemistry. The H/C ratio of n-heptane is 2.286; it's 2.25 for iso-octane. The higher the H/C ratio in a fuel, the more energetic it is (because there's more energy in C-H bonds than C-C bonds) and the less CO2 it makes per unit energy. it also explains the higher density for n-heptane, there's a bit more hydrogen bonding via Van der Waals forces, bringing these molecules a bit closer together.

The premium fuel you buy isn't necessarily a mixture of just these 2 hydrocarbons, but the ingredients which give a higher octane rating still follow these general trends. In sum, this is why premium fuel is actually slightly less fuel efficient and has a bit more carbon footprint.

This is all true except this is only the case if both types of fuel are being detonated at the same time. Due to your ECU pulling timing when it detects lower octane fuel, it can sometimes take more fuel to achieve combustion and there fore you are using more gas to go the same distance. Now to be fair i'm not a tuner or a mechanic, this is just what i've learned from reading shit on the internet soo take it how you will.

That being said i had a MX-5 Miata which could take either 87 or 91. I did some tests. Same route driven everyday for two weeks on either type of fuel. I averaged 32mpg on Regular and averaged 34mpg on 91. Didnt drive the car on weekends as that was saved for the BRZ i had at the time.

Now was that a perfectly scientific way of checking? no, but traffic conditions basically were the same, there was no holiday during those 4 weeks of testing and my working hours were consistent so i always left work at the same time. My theory is that due to the increased horsepower of the car, i was getting up to speed faster. And less time on the throttle equals less fuel used to get up to speed.

Now as far as emission, i just read that on a Road and Track article so take it with a grain o f salt.

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