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Octane arguments

Duane Black

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So i thought about putting this into the tech section for s197 since i have a 2013 3.7L. I thought its more generic and may get more attention here.

Personally, i feel like too many people get 93 octane for track and never test this. Ive used 87 to 93. I have the tuner. On track, the on board timer, wherever, I've never seen an improvement in economy or performance going to 93.

I've even tuned the car for 93 and it never mattered. I cant say ive run tracks on both fuels in a way that matters and came to any conclusive result. The car seems to happily burn anything i give it.

I have put no ethanol in it just fir fun since pure gas should have more energy vs the resistance to detonation that octane offers.

On the street, ive run e15 and no notable difference in power or economy.

Ive read reports tested in various ways, the closest thing ive ever seen was an e30 test where the car did worse as it heated up on high octanes.

So my question after all that... has anyone seen any data in a track environment, specific to our cars or otherwise, indicates that higher octane is better? Not subjective feel, i mean data showing higher straightaway speeds, etc. Obviously I'd love specific to my 3.7 but i know thats a stretcj to ask.
 

Grant 302

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My argument is that there is no argument.

Higher octane ratings benefit engines that are actually TUNED for it.

Ditto for higher specific energy fuels.

Having OEM ‘flex’ type tunes skew the data and make many arguments and observations ‘faulty’.
 

TMSBOSS

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Comparing none alcohol fuels with alcohol fuels also skews things. Add it the fact that some cars and adapt to alcohol on the fly and others cannot and you have too many variables for a discussion. Then throw in the fact that pump gas mixed with alcohol has a sometimes large variance in alcohol content...........
Will your Butt Dyno notice the difference? Not likely. Running alcohol mix in an engine not tuned for it will lean the mix and likely kill the motor.
 

AdmirC

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Modern engine management systems are really good at detecting spark knock and will pull timing accordingly. The only way to check if anything is different between the fuels is if you have the ability to look at live data or datalog while on track and look at the spark retard or knock sensor activity. With that being said running 93 will just give you the greatest threshold for running as much timing as possible without knocking and in theory more horsepower.
 

TMSBOSS

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When ever possible Ill run a half tank of more of 100 octane at track events. I never fill up with anything less than 93 octane. Do I need this, maybe.
 

Tonymustang302

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I own a service company with 8 transit connects and an e-450 install box truck v10.

my dad started the company, he’s lived his whole life on 93 with every vehicle we’ve ever owned...i was a ford mastertech/diesel master, til jan 2009.......i took the company over last year at 35yrs old.....i argued with him that the vans only need 87....... we tried my theory on a new 19 transit connect.....only put 87......random weird issues, throttle body went out 15k......we had one of our techs runs 87 for 10k on his 2018.....nothing but problems....... (we only allow the techs to get BP gas too)

i still am against it, But we have absolutely no engine issues on any vehicles running 93.......superstition, who knows..........but i will only put 93 in every single car i own (except my 1000hp 17 twin turbo GT gets e85) (And except my ex wifes, she gets lead additive with 87)
 

VoodooBoss

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I think most of us that run higher octane on track think of it as cheap insurance from knocking. Modern electronics do adjust but driving on track is completely different than driving around town. I usually rotate between 91 and 100 every other fill up at the track. Is it necessary? Probably not but as a guy that blew his motor to itsy bitsy pieces on track I will continue to do so. And yes the one time I didn’t mix in higher octane gas was when my motor blew. I don’t think there was causation because of the lower octane but it was #8 cylinder in my Boss that blew.
 

Tonymustang302

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I think most of us that run higher octane on track think of it as cheap insurance from knocking. Modern electronics do adjust but driving on track is completely different than driving around town. I usually rotate between 91 and 100 every other fill up at the track. Is it necessary? Probably not but as a guy that blew his motor to itsy bitsy pieces on track I will continue to do so. And yes the one time I didn’t mix in higher octane gas was when my motor blew. I don’t think there was causation because of the lower octane but it was #8 cylinder in my Boss that blew.
its like a stephen king novel.......the dangerous 87/89.
 

docs302

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Adam at Revolution Auto said the 100 octane tune I have vs the 93 octane is worth about 10hp in his experience. The difference in fuel cost is not worth it and I may go back to a 93 octane tune or maybe 96 and use a half and half mixture.
 

flyhalf

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I'd like to clarify one thing.
This was a lesson from a tuner in italy :)
Without a tune,
The higher octane gas doesn't add addditional power.
It allows you to reach the max output that the car can do

In other words
Is the lower octane gas that reduce performance vs max output of the car
Not
The higher octane that increases performance OVERA THE OEM limit.
 

Eric62

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I have payed around with adding E85 to the 93 I always run with a 93 octane tune in the 5.0. Mixed to about E15, no issues, E20-25, no issues and E30-35, again no issues.

My Butt Dyno did feel a difference running E30. Fuel mileage decreased and the Long Term Fuel Trims got a bit on the high side as one might expect. Typically they run about +/-3% and they were running about +10-15% with E30. The car was compensating just fine for the added fuel flow needed with E30 and the spark knock incidences on the street reduced.

The whole point of this experiment was to determine if running 30-35% ethanol in the engine would run OK so that I could run this at the track to cool the engine a bit and provide the wonderful octane boost that ethanol can bring. The jury is still out on track performance. Will update once I can get to the track...in Florida.....in June. Can we say HOT? Yes, we can.
 

JAJ

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Interesting thread.

Back in 2012, I had a 2011 GT Brembo that I did a whole season of track days with. It was equipped with a TVS 2.3 blower, and because the cal file that came with the blower had a weird driveability problem, I got the SCT Pro Racer software and with enormous help from the professional calibrator who'd done the calibration for the supplier, I redid the calibration (many iterations). In the course of all this, I logged gigabytes of data off the ECU at a race track running laps. Real data off the engine in a dynamic situation gives you a whole different view of what's going on in the engine than you would get with a couple of dyno pulls.

Two things stand out regarding fuel and this thread. First, the Coyote ECU was brand new at the time and it did things that ECU's had never done before. One of those things was a little subsystem that constantly ramps the timing up to the point where the knock sensor says stop. It's constant. You can control how fast it goes and how far (beyond the main timing tables) but it's there to extract the most out of the fuel that it can get, so if there's a higher octane available, you'll get the benefit because this little subsystem will put in more spark advance. That's why Ford says you'll get optimum performance with 93 octane - the ECU will read it and give you more spark advance if the fuel can handle it.

The second thing that stands out is what I learned about the fuel itself. I live in an area where every Chevron station sells 94 octane E0 gasoline. Every one of them. However, in Washington State where I did most of my data logging, the highest octane is 92 with an unknown ethanol level. I did a test one time where I filled up with 94 E0 and drove to the track with 15 extra gallons of 94 in the trunk, then ran 94 for the morning sessions. I ran the same cal file that I'd used before with pure WA 92. Comparing the two sets of logs, from a timing advance standpoint, both fuels had about the same advance limit. You could see the ramping and backing off happening, but from a horsepower output and spark timing perspective, there was no practical difference. For the purposes of tuning, I used the acceleration rate on the long straight as a horsepower measurement (more realistic than a dyno pull) and there was no measurable difference between the two fuels.

Three takeaways - 1. good quality fuel matters; 2. your engine will get everything out of the fuel that's available; and 3. don't expect too much of a difference between different types of pump gas.
 

Bill Pemberton

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Simple comment from Engineer friends at Ford and FCA was that the HP and tunes for the Boss 302, GT 350, Viper ( and some other Dodge Machines ) were based on 93 Octane. All list 91 Octane as fine for the machines , but I know tracking a Viper I was told to relay to customers that the vehicle ran best with 93 Octane ( and in fact recommended). Same comments were made especially with the Boss and GT 350 ( obviously and other Blue Ovals too ) and I have always made sure I had that Octane in the car through pumps that carried it or mixing with race fuel.

Just simple comments made to us, and since in both cases we were told the factory tune was with 93 , logic says the HP was likely down with 91 octane.
 

TymeSlayer

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In Colorado the highest octane is 91 at your standard gas station. I do mix 100 octane from tyme to tyme. My question would be, approximately what ratio would it take to get to 93. I've been running about half and half for two years now but never thought what octane level you get when you mix the two.
 
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Grant 302

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In Colorado the highest octane is 91 at you standard gas station. I do mix 100 octane from tyme to tyme. My question would be, approximately what ratio would it take to get to 93. I've been running about half and half for two years now but never thought what octane level you get when you mix the two.
Just a little over 20% is needed. I use 25% as a minimum for track use and up to about half depending on the weather.
 

Coz

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Based on a 16 gallon tank:

91 x 12 = 1092
100 x 4 = 400

1092 + 400 = 1492 ÷ 16 = 93.25

You're probably safer with 5 gallons 100 and 11 gallons 91. That's probably easier since you can just use a full 5 gallon pail. That will give you 93.8.

91 x 11 = 1001 + 500 = 1501 ÷ 16 = 93.8125
 

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