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Old 05-05-2015, 01:16 PM   #24341
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Originally Posted by Joe Perez View Post
When you say that "midgrade is usually cheapest by $.10-.20," are you saying that it's cheaper than whatever the lowest grade is?




I have no idea what idea you're trying to convey here. Are you saying that you've observed an improvement in cruising fuel economy by using high-octane gasoline?


It occurs to me that now that I own a modern car, I could pretty easily plug in ye' olde scanner and do some WOT pulls on both 87 and 93 to see if there's any meaningful difference in ignition timing, VE, etc., between the two.

I'm glad im not the only one confused by that post.
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Old 05-05-2015, 01:21 PM   #24342
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When you say that "midgrade is usually cheapest by $.10-.20," are you saying that it's cheaper than whatever the lowest grade is?
Yup, I think it was Iowa my neighbor was talking about. I think maybe because it's more ethanol? Is that possible? That they just take 5-10% ethanol 87 octane and add more ethanol until it's 89 octane?

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Old 05-05-2015, 01:23 PM   #24343
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I put midgrade in my Tacoma. I always track mileage on my vehicles, and mid grade gives the best bang for the buck. Premium gave the best performance, but it's a truck, not a racecar. It's the way the computer retards timing for the lower grade fuels, from what I've read.
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Old 05-05-2015, 01:36 PM   #24344
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define performance.
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Old 05-05-2015, 01:49 PM   #24345
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Originally Posted by rleete View Post
I always track mileage on my vehicles, and mid grade gives the best bang for the buck.
(...)
It's the way the computer retards timing for the lower grade fuels, from what I've read.

This is what puzzles me, and why I'm curious to do some logging on my own car.

It's quite easy to understand that the ECU will back off the timing when knock is detected. But knock is generally a problem only at high-load conditions; I wouldn't have thought that most engines would be knock-limited at moderate cruise power, inasmuch as that I'd think that, at cruise load, peak torque would be reached before knock became a factor, even for the lowest-octane pump gas available.

The only way this would make sense (and this is where my knowledgebase on how modern OBD-II ECUs are configured starts to get thin) would be if the ECU were integrating this retard into a single long-term-timing-trim which is applied under all load conditions.

And that wouldn't make sense.


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Old 05-05-2015, 02:05 PM   #24346
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Surprised Joe is not mixing his own fuel to obtain optimal pricing AND optimal (R+M)/2 performance.

Now I will suggest a pump with a slider to replace the multi-button. Just slide the dial from 87 to 93 for any octane and price you want!

Everybody pumps:

Evangeline Lilly


Denise Richards


Hot Pole Vaulter Alison Stokke


Paris Hilton


Daisy Duke


even My wife


And this chick too


Not shown: about 5000 of the Kardashians in various cars.

edit: cokgobblers not allowing hotlinking makes me sad.
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Old 05-05-2015, 02:11 PM   #24347
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almost positive the ecu in my subby advances spark (within a range) until it detects knock or the authority has been reach.
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Old 05-05-2015, 02:32 PM   #24348
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Quote:
Originally Posted by y8s View Post
Now I will suggest a pump with a slider to replace the multi-button. Just slide the dial from 87 to 93 for any octane and price you want!
Years ago, Sunoco used to have those:









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Originally Posted by Braineack View Post
almost positive the ecu in my subby advances spark (within a range) until it detects knock or the authority has been reach.
Understood.


As all of us who have comprehensively dyno-tuned an ECU know, more advance does not always equal more power / economy, particularly at low to moderate load conditions. Ignoring knock, there is always a point at which further increases in ignition advance stop yielding increases in power, and in fact power begins to drop back off again.



http://link.springer.com/article/10..../fulltext.html


At high-load, it's uncommon to reach this point before knock becomes a limiting factor. But at the much lower load conditions experienced in cruise, I would expect most passenger car engines to be able to achieve optimum ignition advance without knock on 87 octane fuel, and that the ECU software would not attempt to advance ignition timing beyond the point at which, for any given load condition, peak BMEP is known to occur.

http://www.sid.ir/en/VEWSSID/J_pdf/856200801B07.pdf






This is the source of my bepuzzlement.

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Old 05-05-2015, 03:24 PM   #24349
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Quote:
Originally Posted by Joe Perez View Post
This is what puzzles me, and why I'm curious to do some logging on my own car.

It's quite easy to understand that the ECU will back off the timing when knock is detected. But knock is generally a problem only at high-load conditions; I wouldn't have thought that most engines would be knock-limited at moderate cruise power, inasmuch as that I'd think that, at cruise load, peak torque would be reached before knock became a factor, even for the lowest-octane pump gas available.

The only way this would make sense (and this is where my knowledgebase on how modern OBD-II ECUs are configured starts to get thin) would be if the ECU were integrating this retard into a single long-term-timing-trim which is applied under all load conditions.

And that wouldn't make sense.
Not sure of the actual programming aspects of it, but I read it on the Tacoma forums, and decided to try it myself.

First tank (from dealer) got about 24.5 MPG, but I was babying it pretty much the whole time. Second tank (87 octane), and my mileage plummeted, to like 16-17. So, I decided to try midgrade (89 octane), and mileage was about 22MPG. After that I tried the 87 again, with same result. Tried the high test (92 octane?), and that again delivered the highest mileage, but the cost difference was too much, being 11-12 cents more per gallon over mid, which is 10 cents over low.

All fill-ups are always at the same station, and if possible at the same pump. I tend to be picky about that for no logical reason. I always record miles (via trip odometer) and gallons purchased. Just a habit, but it will alert you if something is off.
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Old 05-05-2015, 03:28 PM   #24350
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define performance.
Purely by butt dyno when driving. I have no actual numbers, but the truck felt quicker. Also, the best mileage numbers.
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Old 05-05-2015, 03:49 PM   #24351
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I sometimes find the mid-grade cheaper than 87 at Huck's.
Does your Tacoma have the 3.4?
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Old 05-05-2015, 03:57 PM   #24352
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Originally Posted by rleete View Post
First tank (from dealer) got about 24.5 MPG, but I was babying it pretty much the whole time. Second tank (87 octane), and my mileage plummeted, to like 16-17. So, I decided to try midgrade (89 octane), and mileage was about 22MPG. After that I tried the 87 again, with same result. Tried the high test (92 octane?), and that again delivered the highest mileage, but the cost difference was too much, being 11-12 cents more per gallon over mid, which is 10 cents over low.
Now my curiosity is aroused.

I'm going to spend some time digging around in the stock ECU to see if I can locate some data in the OBD-II stream that shows me ignition trim.

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Old 05-05-2015, 04:26 PM   #24353
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I wonder, could a modern ECU use timing to find the lowest pulsewidth for a steady state load, like rolling down the highway? I guess that could stand a chance of giving economy gains with higher octane, while the performance is probably only really noticed at full load when the fuel really does make a difference..

There's a really straight and flat section of highway near my place with two roundabouts for on/off ramps so you can circle back over and over. Once I get some GPS logging I'm gonna go out and see if I can find the optimal number for different loads.

Around here I always see Casey's gas stations with cheaper premium than regular, but the pump actually says may contain up to 15% ethanol. Sometimes the regular could be 20 cents more expensive in the little tiny town I used to live in.



Not here, but still
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Old 05-05-2015, 05:07 PM   #24354
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Quote:
Originally Posted by rleete View Post
I put midgrade in my Tacoma. I always track mileage on my vehicles, and mid grade gives the best bang for the buck. Premium gave the best performance, but it's a truck, not a racecar. It's the way the computer retards timing for the lower grade fuels, from what I've read.

Ooooohhhhh is this the "octane sensor" argument?
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Old 05-05-2015, 05:56 PM   #24355
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Even I had trouble rereading my ramblings.

What I meant to communicate is that, on my 2012 Mazda3, I'll get about 2-3mpg hwy better with 93/94 octane than with 87 octane. That equates to about 20-30 miles extra distance on a 10 gallon tank of 93/94 versus the 87 octane. 20-30 miles is an extra day of commuting withough having to fill up.

I can't post my image from my phone. Google des moines gas prices. The BP is see on my phone is showing:

Regular: $2.66
Midgrade: $2.46
Premium: $2.86
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Old 05-05-2015, 06:36 PM   #24356
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Ooooohhhhh is this the "octane sensor" argument?
The numbers don't lie. I certainly wouldn't be putting that extra money in the tank if there wasn't a definite cost benefit. I got much worse mileage with the 87, so I have been sticking with the 89. 91 just isn't worth the cost, because the mileage doesn't go up proportionally.

Winter gas causes even worse mileage changes. I jumped up almost 3MPG when the warmer weather hit and they switched back. But part (most?) of that is the fact that I don't warm it up when the temp is above 25 or so.

Yes, monk, it is the 3.4, automatic. Whoops, no it's not. 4.0 liter.

Toyota GR engine - Wikipedia, the free encyclopedia
"The 1GR-FE is the 4.0 L version. Bore is 94 mm and stroke is 95 mm. Output is 236 HP (176 kW) at 5200 rpm with 266 lbft (361 Nm) of torque at 4000 rpm on 87 octane, and 239 HP (178 kW) at 5200 rpm with 278 lbft (377 Nm) at 3700 rpm on 91 octane"
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Old 05-05-2015, 06:47 PM   #24357
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almost 2 million views in this thread.

my WRX averages 23-24mpg right now.

in winter it was 21-22mpg. more to do with temp and ideal gas law and everyone on vacation.
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Old 05-05-2015, 06:49 PM   #24358
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Originally Posted by rleete View Post
The numbers don't lie. I certainly wouldn't be putting that extra money in the tank if there wasn't a definite cost benefit. I got much worse mileage with the 87, so I have been sticking with the 89. 91 just isn't worth the cost, because the mileage doesn't go up proportionally.

Winter gas causes even worse mileage changes. I jumped up almost 3MPG when the warmer weather hit and they switched back. But part (most?) of that is the fact that I don't warm it up when the temp is above 25 or so.

Yes, monk, it is the 3.4, automatic. Whoops, no it's not. 4.0 liter.

Toyota GR engine - Wikipedia, the free encyclopedia
"The 1GR-FE is the 4.0 L version. Bore is 94 mm and stroke is 95 mm. Output is 236 HP (176 kW) at 5200 rpm with 266 lbft (361 Nm) of torque at 4000 rpm on 87 octane, and 239 HP (178 kW) at 5200 rpm with 278 lbft (377 Nm) at 3700 rpm on 91 octane"
Just a funny thing. There was a local moron that was convinced his car knew what octane fuel it was running because of the "octane sensor."

He was making the same argument you are, but going about it all wrong.
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Old 05-06-2015, 09:44 AM   #24359
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I always love a car with 4 wheel turning.

click to play

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Old 05-06-2015, 10:10 AM   #24360
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Atlas V rocket? Probably for the May 20th launch if that's a recent vid.

In other aerospace news, the Spacex pad abort test just finished. I think MT.net will strip off the time formatting so its at 15m48s: https://www.youtube.com/watch?v=OpH6...tu.be&t=15m48s
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