91 vs. 93 | Are you giving up power?

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By Staff Writer
Aug 8, 2022 | Sunoco, Fuel Tips, Octane | Posted in Features | From the Dec. 2018 issue | Never miss an article

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The Rule: A lot of enthusiasts autocross in the SCCA Street and Street Touring classes, where the rules require a “fuel which is ‘Federally approved for use on public highways,’ and which does not exceed an octane rating of 93 AKI (Anti-Knock Index = [R+M]/2) with an allowed variance up to +0.9. Fuel may not exceed 15% ethanol (E15).”

The Availability: Those in the western half of the country usually only have access to 91-octane fuel, while 93 octane is fairly common in the eastern half. All things being equal, an engine can be tuned to make more power on 93-octane fuel than 91.

The Issue: At the Tire Rack SCCA Solo Nationals, drivers come in from both coasts–some carrying 93-octane fuel and some 91. Lincoln, Nebraska, the site of the event, lies in 91-octane country–although find93.com, a site dedicated to locating 93-octane fuel, shows a pair of outlets in Lincoln.

The Realty: The Street Touring ranks allow reprogrammed ECUs, and some newer production cars can automatically retune themselves based on what they’re fed. In both cases, the higher-octane fuel would be a plus. The Ford Focus ST owner’s manual lays out the advantage in black and white: 252 horsepower on 93 octane and 243 horsepower on 87 octane. “If this is a linear difference, that would put 91 octane making 249 horsepower,” says Zachary Santner, technical specialist at Sunoco Race Fuel. “How about a 3-horsepower difference for East Coast versus West Coast fuels?”

The Possible Edge: Ethanol may not increase miles per gallon or help a fuel’s shelf life, but it can yield more power, making it a possible way to gain an edge using those same SCCA rules. “The science says that the E15 is worth it because the fuel contains more oxygen,” Santner continues. He can’t say how much extra performance will be seen at the wheels, but tuning to a fuel containing 15 percent alcohol would, at least in theory, deliver more power than one containing 10 percent, the usual standard these days.

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David Elfering
David Elfering GRM+ Memberand New Reader
11/16/21 8:37 a.m.

Every time I see a site discussion about E85 or even E15 fuel and read through the details, it talks me out of farting with it. It would be interesting to know if there real benefits other than hopeful butt dyno ones. 

frenchyd
frenchyd GRM+ Memberand UltimaDork
11/16/21 9:08 a.m.

In reply to David Elfering :

Then there is the matter of enforcement. 
  How often do you see engines torn down at any event?   How often do you see fuel sampled? Do they even have the ability to determine what's in the fuel?   It's not just alcohol that can give an edge. 
    Maybe because Vintage racing is gentlemen ( and a few ladies) racing each other. There is no prize money or really any advantage to cheating. In fact In 40 plus years I've never seen anybody tear down an engine or sample fuel.  
     I've built small block Chevy engines up to 430 cu in. With parts straight off NASCAR  and WoO shelves.  I've also successfully raced  ( and won) with a Target master engine straight out of the crate.  
  It's a rare entrant who doesn't have at least something of dubious legality. The only question is will that person get caught and lose that $15 plastic cup. 
As far as advantage of E85?  You don't read Hot Rod  or watch U tube do you?  Or even read the articles in GRM ? 
      

z31maniac
z31maniac MegaDork
11/16/21 10:51 a.m.
David Elfering said:

Every time I see a site discussion about E85 or even E15 fuel and read through the details, it talks me out of farting with it. It would be interesting to know if there real benefits other than hopeful butt dyno ones. 

It's super simple. Most cars for E85, you literally just put in the GM fuel sensor, the rear O2 plug monitors for E content and tune. 

For a BRZ, you can call COunterspace Garage and get a full tune and kit for around $1300 IIRC.

I just used the OFT since I used it on my previous NC. It's a little more involved, but still not difficult for the quick 15-20whp pickup with no other mods. 

Colin Wood
Colin Wood Associate Editor
11/16/21 1:31 p.m.

In reply to David Elfering :

If you are looking for some actual hard data using E85, we were able to squeeze abut 20 extra wheel horsepower in our C5 Corvette project car–which you can read more about here: E85 Ethanol Fuel: How to Corn Your Way to More Horsepower

For additional information, here are some articles discussing E85 with our good friends at Sunoco:

jharry3
jharry3 GRM+ Memberand Dork
2/16/22 10:15 a.m.

 

When/where is this available?  

Ultra 94 Premium Gas - Nothing Less Will Do | Sunoco

kb58
kb58 SuperDork
8/9/22 12:52 p.m.
z31maniac said:
David Elfering said:

Every time I see a site discussion about E85 or even E15 fuel and read through the details, it talks me out of farting with it. It would be interesting to know if there real benefits other than hopeful butt dyno ones. 

It's super simple. Most cars for E85, you literally just put in the GM fuel sensor, the rear O2 plug monitors for E content and tune. 

For a BRZ, you can call COunterspace Garage and get a full tune and kit for around $1300 IIRC.

I just used the OFT since I used it on my previous NC. It's a little more involved, but still not difficult for the quick 15-20whp pickup with no other mods. 

Sometimes for fun, I'll tease people I see putting E85 into their Subaru, BRZ, or whatever, knowing they have no OEM support for it. I start off with "I didn't know that those could take E85", and see what they say.

Back on-topic, it's depends upon how the ECU responds to the higher octane or ethanol. While the engine can generate more power, whether it does or not completely depends up - reasons. My understanding is that modern direct injection engines use the knock sensor way more than previously, basically dialing in timing until it knocks, then backing off a bit. As for which cars do so and which don't, I don't know.

preach (dudeist priest)
preach (dudeist priest) GRM+ Memberand Dork
8/9/22 1:18 p.m.

My Cayman has been out west a few times. The difference between 91 and 93 is palpable. It breathes a sigh of relief when I hit Memphis and get a tank of 93.

It is the same if I am driving it in August heat vs November cool.

My Golf pops more, happily, on 93 vice 91.

The Cayman is like a well worn leather glove for me. If we were on that old newlywed game show we'd crush all the answers.

1988RedT2
1988RedT2 MegaDork
8/9/22 2:50 p.m.

The energy density of ethanol is approximately 2/3 that of an equal amount of gasoline.

https://energyeducation.ca/encyclopedia/Energy_density

The reasons for using ethanol derived from corn are misguided and purely political.

https://www.theatlantic.com/ideas/archive/2022/03/gas-prices-ethanol-subsidies-putin/627053/

And ethanol's use as a motor fuel endangers populations that already have difficulty with malnutrition.

https://www.canarymedia.com/articles/food-and-farms/biofuels-are-accelerating-the-food-crisis-and-the-climate-crisis-too

 

03Panther
03Panther UberDork
8/9/22 3:35 p.m.

In reply to 1988RedT2 :

You ought to know not to try to confuse anyone with facts!

"They" said ethanol is than horrible world killing distilled dinosaur will make everything better. 

Opti
Opti Dork
8/9/22 3:56 p.m.
1988RedT2 said:

The energy density of ethanol is approximately 2/3 that of an equal amount of gasoline.

https://energyeducation.ca/encyclopedia/Energy_density

The reasons for using ethanol derived from corn are misguided and purely political.

https://www.theatlantic.com/ideas/archive/2022/03/gas-prices-ethanol-subsidies-putin/627053/

And ethanol's use as a motor fuel endangers populations that already have difficulty with malnutrition.

https://www.canarymedia.com/articles/food-and-farms/biofuels-are-accelerating-the-food-crisis-and-the-climate-crisis-too

 

Energy density is lower, but you use more E85 and the octane rating is much higher, and when tuned for it e85 almost always makes more power.

My stock ND ran on e85. The difference  between an aftermarket 93 tune to an e85 tune was a larger jump in power than the difference between the stock tune and a 93 tune.

6gen camaro guys are picking up 20-30 whp only going e85.

E85 may be terrible politically and environmentally, I won't argue that with you, but if it's available at your local pump it's the best dang gas for fun.  It's like race gas you can actually find and cheap enough to run it all the time.

kb58
kb58 SuperDork
8/9/22 3:57 p.m.
1988RedT2 said:

The energy density of ethanol is approximately 2/3 that of an equal amount of gasoline.

Yup. Here in SoCal, E85 is roughly 3/4 the price of gasoline, so it "seems" cheaper. Put it a car, especially turbo'd, and more is burned, eliminating the price advantage. I get it, it's effectively higher octane, but most people don't bother to do the math and just fixate on the cheaper price per gallon as meaning something.

chaparral
chaparral Dork
8/9/22 4:03 p.m.

If you've got a turbo, it matters a lot. My 350-hp GTI can run hard all day without detonation on 93 (which has long since been more than 93 AKI) but on 91 it gets to choose between wheezing out and suddenly cutting power when the knock sensor picks up that it's going to blow up.

David S. Wallens
David S. Wallens Editorial Director
8/9/22 4:04 p.m.
jharry3 said:

 

When/where is this available?  

Ultra 94 Premium Gas - Nothing Less Will Do | Sunoco

Looks like Sunoco 94 is currently available here:

03Panther
03Panther UberDork
8/9/22 5:41 p.m.

In reply to Opti :

Absolutely correct! For a fun car, its fantastic. Used right, the potential for power can be great... and the burning of it in and of itself is cleaner. 
But E-10, or I think 20 is required some places? Not good. 
Power, at a loss of mpg and cost is great for some things laugh

03Panther
03Panther UberDork
8/9/22 5:46 p.m.

In reply to chaparral :

Till your post, I forgot we were supposed to be talking about 91/93. blush

My DDs all do as well on swill, as anything. Better mpg on better fuel, but not enough to offset extra cost, sadly. 
The Beemer (K bike) does only get non ethanol, despite the cost, but does not care what octane of it. 

chaparral
chaparral Dork
8/9/22 6:14 p.m.

Note that when we went from E10 to E15 the refiners didn't have time to adjust the high-test blend mix, so this summer's "93" is really "94-95" (and 101 RON)

 

 

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) GRM+ Memberand UltraDork
8/9/22 6:19 p.m.

Yes I am giving up power in my Civic Si.  I don't really care though since I'm driving for fuel economy.  FWIW, I've seen no difference in fuel economy with low, mid or premium in spite of the internet telling otherwise.  I will use premium if I ever autocross the car or take it to an HPDE. 

kevlarcorolla
kevlarcorolla Dork
8/9/22 7:09 p.m.

I built a cottage for a sunoco executive,he told me ultra 94 is a great money maker for them....costs them just 3 cents per litre more then regular to make it.

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
8/9/22 7:18 p.m.

In reply to kevlarcorolla :

Don't care when trying to make a 12:1 big block Chevy live on pump gas.

 

And it smells really good, too!

 

Incidentally, there was a mild push a few years back to eliminate lower octane fuels.  It would be cheaper to just make everything 93 and most cars would benefit enough for the national oil consumption to be noticeably affected.

alfadriver
alfadriver GRM+ Memberand MegaDork
8/9/22 7:20 p.m.

In reply to 1988RedT2 :

I wish we could use other sources for ethanol, but corn gets the tax break. Sugar down south, sugar beets up here. Don't take off sugar, ferment it all. 

wspohn
wspohn SuperDork
8/10/22 11:48 a.m.

Higher octane gets you zip unless your ECM has a hunt forward timing set up, otherwise the timing stays where it was and you are wasting money.

With a modern ECM that advances until it 'hears' the start of ping, you will get more power.

I run a custom set up on my Solstice - it runs c. 25 psi of boost and the tune is calibrated for our 94 octane fuel up here. When I go to the US I take it easy as I have to run 91 and although the ECM should cut back timing to suit I don't like bouncing of that limit by flooring it entering freeways etc.

My other sports car runs a stock 11.5 compression and they didn't change that for the US, so I guess the kick back does work....

z31maniac
z31maniac MegaDork
8/10/22 11:54 a.m.
alfadriver said:

In reply to 1988RedT2 :

I wish we could use other sources for ethanol, but corn gets the tax break. Sugar down south, sugar beets up here. Don't take off sugar, ferment it all. 

I thought the feds ended ethanol subsidies a few years ago? 

Pete. (l33t FS)
Pete. (l33t FS) GRM+ Memberand MegaDork
8/10/22 3:52 p.m.

In reply to wspohn :

The OEMs never hunt forward.  With some combustion chambers you can advance the timing until the engine stalls and never detonate.  This way lies poor performance, poor economy, and high NOx.

 

What there usually is, is a perfect timing curve, and the knock sensor pulls timing, sometimes adaptively long term (I know Subarus do this) and other times they just switch to a low octane set of maps until the next refueling (I know GM does this).

 

I am curious what the timing is like on the Ford 3.5/3.7 sixes.  I didn't know until fairly recently that they had 12:1 compression.   How many people lug those around in 5000lb trucks on the cheapest gas at the Getgo.

03Panther
03Panther UberDork
8/10/22 10:32 p.m.

In reply to Pete. (l33t FS) :

Our 11 4x eco boost (what a great but missed named engine) ran exactly the same on swill, as whatever better gas product available at the pump I ever put in it. No mpg difference, no noticeable power difference.

Including towing, sometimes max load.
Ran as good on swill as anything, and swill is easier on the pocket  

Disclaimer. I don't know if it was"rated" for E85. Would not have run it, in any event, as E85 should not be used in any DD. Despite it being a political "next greatest thing!" Fun stuff, heck yea!!!

never owned a ford V6 na, to compare. 

wspohn
wspohn SuperDork
8/11/22 1:20 p.m.
Pete. (l33t FS) said:

In reply to wspohn :

The OEMs never hunt forward.  With some combustion chambers you can advance the timing until the engine stalls and never detonate.  This way lies poor performance, poor economy, and high NOx.

Pete, you are right - they have a preset point they start at and retard when necessary from that. If the preset point is poorly chosen or they are using a lower grade of fuel , that means a lot of knock retard going on.

I used to use a manual timing control in one of my race cars which did allow me to advance until knock was detected and then manually back off a bit.

 

 

 

alfadriver
alfadriver GRM+ Memberand MegaDork
8/11/22 4:56 p.m.
z31maniac said:
alfadriver said:

In reply to 1988RedT2 :

I wish we could use other sources for ethanol, but corn gets the tax break. Sugar down south, sugar beets up here. Don't take off sugar, ferment it all. 

I thought the feds ended ethanol subsidies a few years ago? 

Maybe they did, but corn ethanol is still cheap, which doesn't make sense. 

alfadriver
alfadriver GRM+ Memberand MegaDork
8/11/22 5:02 p.m.
Pete. (l33t FS) said:

In reply to wspohn :

The OEMs never hunt forward.  With some combustion chambers you can advance the timing until the engine stalls and never detonate.  This way lies poor performance, poor economy, and high NOx.

 

What there usually is, is a perfect timing curve, and the knock sensor pulls timing, sometimes adaptively long term (I know Subarus do this) and other times they just switch to a low octane set of maps until the next refueling (I know GM does this).

 

I am curious what the timing is like on the Ford 3.5/3.7 sixes.  I didn't know until fairly recently that they had 12:1 compression.   How many people lug those around in 5000lb trucks on the cheapest gas at the Getgo.

The 12:1 part is pretty new for the NA versions- would have come with DI being added. 
 

Not many engines are super tuned to premium, some because customers are cheap and just put regular in, but more because it takes a lot of hoops to demonstrate the benefit for both requirements and the sticker. 
 

For me, if EPA and CARB would get on their regulation wagon, and require premium fuel at a nominal cost ( not the high profit margin it gets ) it would be an easy reduction in CO2 going foreword. And it would shift some of the burden to the oil companies. 

frenchyd
frenchyd GRM+ Memberand MegaDork
8/11/22 6:42 p.m.
alfadriver said:
z31maniac said:
alfadriver said:

In reply to 1988RedT2 :

I wish we could use other sources for ethanol, but corn gets the tax break. Sugar down south, sugar beets up here. Don't take off sugar, ferment it all. 

I thought the feds ended ethanol subsidies a few years ago? 

Maybe they did, but corn ethanol is still cheap, which doesn't make sense. 

If you're anti ethanol replacing it with methanol will happen.   It an easy and cheap  way to achieve the required octane  to use most of a barrel of oil.  

alfadriver
alfadriver GRM+ Memberand MegaDork
8/11/22 7:05 p.m.

In reply to frenchyd :

If you bother to read my posts, you would know I'm pro ethanol. Just want more sources than corn, since it requires a lot of energy just to get to the fermentation stage. 

GCrites80s
GCrites80s Dork
8/11/22 9:00 p.m.
alfadriver said:
z31maniac said:
alfadriver said:

In reply to 1988RedT2 :

I wish we could use other sources for ethanol, but corn gets the tax break. Sugar down south, sugar beets up here. Don't take off sugar, ferment it all. 

I thought the feds ended ethanol subsidies a few years ago? 

Maybe they did, but corn ethanol is still cheap, which doesn't make sense. 

I think they're still working through the backlog of corn that started piling up in the mid 2010s when the market figured out that E85 wasn't the magic bullet.

frenchyd
frenchyd GRM+ Memberand MegaDork
8/11/22 9:27 p.m.
alfadriver said:

In reply to frenchyd :

If you bother to read my posts, you would know I'm pro ethanol. Just want more sources than corn, since it requires a lot of energy just to get to the fermentation stage. 

Well sugar isn't going to be it.  Americans  pay twice the global price for it.  It has to do with the anti Cuban position.  Plus the investors in Florida sugar plantations. 
    You would need to untangle the politics tangle between Minnesota & North Dakota sugar beet farmers, plus Florida Sugar cane growers.  Cuban Expats and the political party they are all in.  

frenchyd
frenchyd GRM+ Memberand MegaDork
8/11/22 10:20 p.m.

In reply to GCrites80s :

Very little corn has gone into E85. Most has gone into E10&15.  
 Actually mostE85  has gone into wacko wanna be racers and those who can't afford $14 a gallon for racing fuel. Like me. 

03Panther
03Panther UberDork
8/12/22 12:02 a.m.
frenchyd said:

Very little corn has gone into E85. Most has gone into E10&15.  
 Actually mostE85  has gone into wacko wanna be racers and those who can't afford $14 a gallon for racing fuel. Like me. 

Just so you think before you type, you do realize those two sentences have absolutely NOTHING to do with each other, and very little to do with the discussion. 

03Panther
03Panther UberDork
8/12/22 12:04 a.m.
frenchyd said:
alfadriver said:

In reply to frenchyd :

If you bother to read my posts, you would know I'm pro ethanol. Just want more sources than corn, since it requires a lot of energy just to get to the fermentation stage. 

Well sugar isn't going to be it.  Americans  pay twice the global price for it.  It has to do with the anti Cuban position.  Plus the investors in Florida sugar plantations. 
    You would need to untangle the politics tangle between Minnesota & North Dakota sugar beet farmers, plus Florida Sugar cane growers.  Cuban Expats and the political party they are all in.  

Please. Just stop it. I was enjoying the intelligent  discussion. Preach your political nonsense elsewhere. Please.  

frenchyd
frenchyd GRM+ Memberand MegaDork
8/13/22 11:38 a.m.

In reply to 03Panther :

It's simply explaining why  Sugar won't be the source of ethanol.  I happen to agree with Alfadriver regarding the suitability to other sources for ethanol.  And why corn is the source. 

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