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That Guy
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One great example of failing to keep things consistent is taking a car that showed 20 to 21 miles to empty and comparing it to a car with 7.5 gallons of fuel added. That's going to be around an extra 50 lbs, and you somehow logged a consistently higher trap speed (implying that there's more power) with that additional weight and a lower octane. That, in and of itself, should be enough for anyone to realize that there are errors unaccounted for.

You're right though, there's no ROI in using premium at the track short of keeping detonation at bay.
 

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But you only tested one aspect of higher octane and thats WOT

You can see and feel gains for take off , throttle response , tip in passing etc that wouldnt show doing WOT Testing

It didnt shock me that 87-91 on the track made no 1/4 mile gains , it takes about 7-10 HP gains to the wheels to really show any 1/4 gains and thats not what higher octane in the MK3 adds

Tom
 

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Cost > Benefit

Easy, someone forks over the cash to do some legitimate dyno work. That's really the only way.
... with over six years worth of time here we, as an entire community, have yet to spend the one hour worth of dyno time to actually see the answer.
... Over 2k posts debating it though, lol.
True, because the debating is free, easy, and entertaining, vs the cost and effort to dyno to prove or disprove the theories. Heck, even the drag strip runs are more effort than most are willing to put out.
 

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But you only tested one aspect of higher octane and thats WOT

You can see and feel gains for take off , throttle response , tip in passing etc that wouldnt show doing WOT Testing

It didnt shock me that 87-91 on the track made no 1/4 mile gains , it takes about 7-10 HP gains to the wheels to really show any 1/4 gains and thats not what higher octane in the MK3 adds

Tom
Tom,
I believe that you may be as qualified as anyone to help detail for us how the factory tune deals with changes in octane, and how that manifests itself in vehicle behavior.

What does the factory tune do with high octane fuel that results in better throttle response, tip in, gains in take off?

Can you tell us how the factory tune adapts to higher octane, how it knows there is high octane fuel in the car, how high of octane can it adapt to?

I'm hoping to understand how all of this theoretical benefit actually works with the factory tune.

THANKS!
 

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That Guy
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Tom,
I believe that you may be as qualified as anyone to help detail for us how the factory tune deals with changes in octane, and how that manifests itself in vehicle behavior.

What does the factory tune do with high octane fuel that results in better throttle response, tip in, gains in take off?

Can you tell us how the factory tune adapts to higher octane, how it knows there is high octane fuel in the car, how high of octane can it adapt to?

I'm hoping to understand how all of this theoretical benefit actually works with the factory tune.

THANKS!
This has been covered in this thread multiple times and even referenced in the current discussion. Timing is adjusted through the use of an Octane Adjustment Ratio multiplier that is derived from knock count (or the lack thereof) reported by the knock sensors. Tom can explain it too. I'm sure I've posted pictures of the strategy and its use in here before, though my pics were from the ST. Same tuning framework in the naturally aspirated version, but probably with different multipliers.

Sent from my SM-G930V using Tapatalk
 

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OK
I guess I'm done in this thread.
My test told me what I wanted to know, and it isn't worth the pain for me to pursue my other questions out of curiosity. I don't want to read thru 6.5 years containing 209 pages of mostly worthless posts to find a couple that may have some pertinent info. Then I'd still have to post questions that remain unanswered which would likely draw more unhelpful responses.

My attention now goes forward to seeing how Tom's tune improves performance at the track, and DCT behavior.
 

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Tom,
I believe that you may be as qualified as anyone to help detail for us how the factory tune deals with changes in octane, and how that manifests itself in vehicle behavior.

What does the factory tune do with high octane fuel that results in better throttle response, tip in, gains in take off?

Can you tell us how the factory tune adapts to higher octane, how it knows there is high octane fuel in the car, how high of octane can it adapt to?

I'm hoping to understand how all of this theoretical benefit actually works with the factory tune.

THANKS!
The MK3 NA Focus really has no way to tell what fuel your running ( E Fuels yes ) you could have 85 , 91 , 92 , 93 and the engine /ecu has no way of knowing

With higher octane fuel your less prone to spk knock which can pull timing and in most cases less timing means slower throttle response , less performance , lower MPG

Just because you run 93 doesnt mean you wont have spk knock it just means you have less then you would have with say 87

Thats kind of quick and dirty answer but its how it works

Tom
 

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The MK3 NA Focus really has no way to tell what fuel your running ( E Fuels yes ) you could have 85 , 91 , 92 , 93 and the engine /ecu has no way of knowing

With higher octane fuel your less prone to spk knock which can pull timing and in most cases less timing means slower throttle response , less performance , lower MPG

Just because you run 93 doesnt mean you wont have spk knock it just means you have less then you would have with say 87

Thats kind of quick and dirty answer but its how it works

Tom
Tom,
Thank you for your quick response!
I can tell that what I'd like to know is just digging into territory that has probably been discussed in the past and I can honestly walk away right now without losing any sleep over my questions.
WAY MORE trouble than it is worth.

As I mentioned, I am only thinking now about getting your tune installed and tweaked so that I know my car is optimally configured.
 

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Just to add, it seems that my car is much more accurate on the fuel economy running on premium. On 87 it would report at least 1 mpg higher than actual and at its worst 3.5 mpg higher. Over the past few fill ups the car has reported fuel economy within 0.2 mpg (0.1 if you round since the car reports only to a tenth of a mpg).
 

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Just to add, it seems that my car is much more accurate on the fuel economy running on premium. On 87 it would report at least 1 mpg higher than actual and at its worst 3.5 mpg higher. Over the past few fill ups the car has reported fuel economy within 0.2 mpg (0.1 if you round since the car reports only to a tenth of a mpg).
I'm not saying you are incorrect, but I'm not sure why the octane rating of the fuel would impact how much of it the car thinks it is using.

How controlled were your conditions while making this test?
What was your actual mpg with 87oct, and with ??oct gasoline?
 

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It’s not a scientific test. As a college kid also working I don’t have time to set up scientific tests. However I do live in an extremely hilly area. In North County San Diego we have extremely well developed marine terraces which means it’s not uncommon to drive within 3 miles and have an elevation change of 800 feet.

This leads me to believe that when I drove on 87 octane the car was constantly pulling timing and seemed to not be able to keep up when reporting the fuel economy because of the constant change.

Now because I’m a college kid who works and has a job as well as a long term girlfriend my driving schedule is pretty consistent. I pretty much only take the freeway (constant 75+ mph) on tuesdays and thursdays to drive to one of the campuses. When I was using 87 octane my actual fuel economy was about 26.5 mpg while the car would normally report 28.5-29 mpg.

Using 91 octane (this is the highest octane rating I can easily buy in california without buying $20 per gallon race fuel) my car reports 28.8 mpg while actually getting an average 28.67 mpg.

So again, I don’t think this would apply to everybody changing from 87 to 91. However because the speed limit for a regular road here in North County San Diego is 55 mph and the elevation changes so much, my hypothesis is that the pull in timing that happens more often when using 87 causes the computer in the car that determines fuel economy to become inaccurate.
 

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I hear you on the relative consistency of your typical driving. The steep hills would definitely load the engine more heavily.
I can see how higher octane to reduce the pulling of timing might get you better fuel mileage. However, what I am struggling to figure is why the car cannot keep up with how much volume of fuel it is consuming...
 

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Torretto!
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True, because the debating is free, easy, and entertaining, vs the cost and effort to dyno to prove or disprove the theories. Heck, even the drag strip runs are more effort than most are willing to put out.
Dragracing is not exactly that easy depending on the track, our local 1/4 mile track requires running purely water no coolant in case of leaks/spills, passing strict inspection, and then very long waits for the street legals...might be lucky if you get three runs in, usually only two
 

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I hear you on the relative consistency of your typical driving. The steep hills would definitely load the engine more heavily.
I can see how higher octane to reduce the pulling of timing might get you better fuel mileage. However, what I am struggling to figure is why the car cannot keep up with how much volume of fuel it is consuming...
Without knowing exactly how it determines how much fuel is being consumed I can only guess. Based on the only experience I have, I would guess that it doesn’t actually measure how much is being used but rather has an algorithm that takes into account what gear the car is in, the pedal pressure, and the rpms and it must just be easier to figure all of that out when timing is more consistent.

Edit: Or it could be completely coincidental, being caused by some other variable that I haven’t taken into account.
 

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Without knowing exactly how it determines how much fuel is being consumed I can only guess. Based on the only experience I have, I would guess that it doesn’t actually measure how much is being used but rather has an algorithm that takes into account what gear the car is in, the pedal pressure, and the rpms and it must just be easier to figure all of that out when timing is more consistent.

Edit: Or it could be completely coincidental, being caused by some other variable that I haven’t taken into account.
Hmmm... I was assuming it figured based on fuel injector control and fuel pressure. Either way, I'm not sure why fuel octane would change it's ability to calculate fuel usage.
 

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Dragracing is not exactly that easy depending on the track, our local 1/4 mile track requires running purely water no coolant in case of leaks/spills, passing strict inspection, and then very long waits for the street legals...might be lucky if you get three runs in, usually only two

I'd like to see the pure water rule since that is pretty inconvenient and never seen that at a NHRA certified track. I run at Bandimere in Denver and passing their strict rules is pretty easy for a street legal car and test and tune nights I could easily get in 5-8 runs with cool down breaks. A lot of tracks nationally are easy to get on and race.
 

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I'd like to see the pure water rule since that is pretty inconvenient and never seen that at a NHRA certified track. I run at Bandimere in Denver and passing their strict rules is pretty easy for a street legal car and test and tune nights I could easily get in 5-8 runs with cool down breaks. A lot of tracks nationally are easy to get on and race.
Antifreeze on the track sucks!!! [thumbd]
I recall Rockingham in NC saying water wetter only, but that was many years ago. The other tracks I've been to didn't mention it.

At my local 1/4 mile track, you can get quite a few runs in if you show up when the gates open. As the TNT goes along, more and more cars show up and the staging lanes get longer.
 

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All our track looks for is a catch can or reservoir which generally most street driven cars have them.
The track I primarily go to doesn't do any inspection for TNT.
No helmets required for my buddy's car that runs [email protected]
It is actually kind of nice not to have a bunch of hassle to run your car.
 
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