Jerry
Jerry UltraDork
9/14/16 7:02 a.m.

I know Mid Ohio has multiple grades, some unleaded, some leaded.

I was curious what would happen if I put a gallon or two of unleaded in with my 93 octane? Bad things? Any things? Somehow I don't think a full tank is a good idea but maybe a little mixed in would help?

spitfirebill
spitfirebill UltimaDork
9/14/16 7:05 a.m.

I would say much of nothing is going to happen, unless your car has a high compression engine and needs higher octane.

Toyman01
Toyman01 GRM+ Memberand MegaDork
9/14/16 7:06 a.m.

Nothing bad. You probably won't even notice the difference unless you were having knock problems beforehand.

z31maniac
z31maniac MegaDork
9/14/16 7:11 a.m.

Unless you're experiencing knock, or plan on tuning for the higher octane, you will see no benefit other than a lighter wallet.

bentwrench
bentwrench Dork
9/14/16 7:19 a.m.

Do not listen to the marketing lies, we have been told the same lies about fuel from commercials for so long its now accepted as truth.

Octane needs of a motor are determined by mechanical design parameters (cylinder pressures).

More octane than your motor needs to run efficiently (without eating itself up) is not a plus and can actually reduce performance and increase emissions.

Do not fall into the marketing psychosis that tells you your car runs better on premium if it does not need it. Most Cars that were designed for premium fuel will suffer performance or economy losses if not fed premium fuel.

Why does Ethanol free fuel cost twice as much as gasohol? Ethanol costs more to make than gas, so a fuel that is cheaper to make and contains no ethanol should not cost more. This is marketing at its best! (well besides convincing folks their made for regular car will run better on premium)

Gas distributors are making up for the higher cost of ethanol by blending it with lower grade gasoline, and relying on the higher octane of the ethanol to meet the pump grade they are blending for. Here since I have brought up the cost of ethanol I should point out that ethanol is a federally subsidized product from the corn that is gown to make it all the way to the fuel distributor.

I have some tinfoil hat theories about yesterdays waste products now being todays gasoline, I won't go there without real facts though.

I do know that there is going to be some big fallout from the problems with direct injected cars choking on the caked on Gack from ingesting their own crankcase vapors. Some models are only going 40k miles before the head needs to come off to clean the valves and prevent misfires and performance loss.

alfadriver
alfadriver GRM+ Memberand MegaDork
9/14/16 7:52 a.m.

Here's what's going to happen....

As you as you turn the key to start, and hold it in the start position long enough- the engine will start running.

And it will keep running as long until you turn the key to off unless you stall the car for whatever reason.

It will continue to do this until you run out of gas. At which point, you can fill the car with more gas, or just let it sit.

alfadriver
alfadriver GRM+ Memberand MegaDork
9/14/16 7:53 a.m.
bentwrench wrote: More octane than your motor needs to run efficiently (without eating itself up) is not a plus and can actually reduce performance and increase emissions.

I was trying to keep this thread light, but that line isn't true. It won't reduce performance, nor will it increase emissions (nor reduce fuel economy, which wasn't said). Especially if it's a fuel that is approved for on road use.

trigun7469
trigun7469 Dork
9/14/16 7:58 a.m.

Jerry
Jerry UltraDork
9/14/16 8:01 a.m.
alfadriver wrote: Here's what's going to happen.... As you as you turn the key to start, and hold it in the start position long enough- the engine will start running. And it will keep running as long until you turn the key to off unless you stall the car for whatever reason. It will continue to do this until you run out of gas. At which point, you can fill the car with more gas, or just let it sit.

Fair enough. $ saved.

Ovid_and_Flem
Ovid_and_Flem Reader
9/14/16 8:04 a.m.

It smells.....RACY.

Other than that, your car will likely be faster by milliseconds due to the lighter weight of your wallet

johndej
johndej Reader
9/14/16 8:06 a.m.

Yup, made that mistake at VIR last year. Didn't change a thing other than make my bank account lighter.

They had "98-octane (260 GTX) unleaded which is Ethanol Free. For off-road and racing applications only", smacked that key instead of the 93 octane I was intending to hit. Stuff was like $8-9/gal. Luckily I caught it only a couple gal in as it was up to ~$20. Added a little 93 on top to get me through the last 2 HPDE sessions that day.

Stock 92 miata ran fine on it.

bentwrench
bentwrench Dork
9/14/16 8:15 a.m.
alfadriver wrote:
bentwrench wrote: More octane than your motor needs to run efficiently (without eating itself up) is not a plus and can actually reduce performance and increase emissions.
I was trying to keep this thread light, but that line isn't true. It won't reduce performance, nor will it increase emissions (nor reduce fuel economy, which wasn't said). Especially if it's a fuel that is approved for on road use.

I have proven this to myself on a dyno.

So yes it is true, higher octane fuel does not light as easy thus does not burn completely in a lean burn late spark low compression motor. This equates to lower HP and higher emissions. This is a well documented and proven fact.

alfadriver
alfadriver GRM+ Memberand MegaDork
9/14/16 8:26 a.m.
bentwrench wrote:
alfadriver wrote:
bentwrench wrote: More octane than your motor needs to run efficiently (without eating itself up) is not a plus and can actually reduce performance and increase emissions.
I was trying to keep this thread light, but that line isn't true. It won't reduce performance, nor will it increase emissions (nor reduce fuel economy, which wasn't said). Especially if it's a fuel that is approved for on road use.
I have proven this to myself on a dyno. So yes it is true, higher octane fuel does not light as easy thus does not burn completely in a lean burn late spark low compression motor. This equates to lower HP and higher emissions. This is a well documented and proven fact.

So have I, with many cars on many tests.

Just high octane isn't the reason you had issues, it was some other reason. I've tested so many times using 100 RON cert fuel vs. 91 RON fuel that for good fuel- there is no penalty for higher octane- only potential if the car is designed for higher octane.

The reason is probably that the maker of the fuel was cheap with the octane enhancers. And the cheaper ones tend to be alcohol derivatives.

As for the "light" myth- higher octane only prevents auto ignition- it does not care about an external source. And it burns just fine. BTDT. Many, many, many tests.

simontibbett
simontibbett Reader
9/14/16 8:36 a.m.

All these negatives but you all forget to mention the positive. It smells better.

simontibbett
simontibbett Reader
9/14/16 8:37 a.m.

$7.95 for 100 octane unleaded but it costs me $10.50 for 110 leaded? Seems like a big difference.

iceracer
iceracer PowerDork
9/14/16 9:48 a.m.

Lead is expensive

intrepid
intrepid New Reader
9/14/16 10:35 a.m.

It does smell better. I like to keep a little on hand to use as aftershave...

-chris r.

codrus
codrus GRM+ Memberand SuperDork
9/14/16 10:54 a.m.

The short answer is that if you put 2 gallons of 100 octane into a 12 gallon tank and fill the rest with 93, you'll have 12 gallons of (2 * 100 + 10 * 93) / 12 == 94.2 octane gas.

Will your car run any differently on 94 octane gas instead of 93? In most cases, probably not. There is a chance that if the car is turbocharged, it's particularly hot, and if the car is being run particularly hard (like, say, if you're at the track) that it might knock on 93. Modern cars are designed to detect knock and dial back the timing, so in this hypothetical situation you might prevent a temporary reduction in power output.

93 is one of the higher octane "premium" fuels commonly available, so outside of limited situations like that there's little benefit. If you lived in California and the best you could get was 91, that might be a different story.

As far as cost goes, there are a lot of things that go into the price of gas other than just the raw materials. Things like manufacturing plants, distribution infrastructure, and regulatory compliance costs have a large fixed component, and since race fuel is low volume that fixed cost is being divided over a much smaller number of gallons sold.

Jerry
Jerry UltraDork
9/14/16 11:49 a.m.

In reply to codrus:

Actually, a short answer would have been "no".

MadScientistMatt
MadScientistMatt PowerDork
9/14/16 11:50 a.m.

We didn't find any more power on kbchw's Miata by going from 93 to 100 octane:

GRM article where we dyno tested different octanes on a Miata

Knurled
Knurled MegaDork
9/14/16 12:17 p.m.

Only way to find out is to run your car on it A-B-A test-style.

In your Fiat? I'd run it just to see. I've found European cars respond well to higher octane fuel.

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