Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Octane and Mileage

Originally posted by Viss1:

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Couple followups:

- The 320 mi. trip is from my place to my Mom's house, and I've made the trip probably 25 times in all types of weather. And yet the fuel mileage is always almost exactly the same. IMO I can eliminate weather from the equation.

About the only other non-PCM variable I can think of is that I somehow got an extra-full fill. This is unlikely, though, since I always use the same method when filling up.

- Other than timing, are there any other parameters that the PCM supposedly adjusts in response to octane?

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Originally posted by Port:

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1. 9.8:1 is the cuttoff for running 91 octane pump gas at sea level.

If you run high octane where you don't have the compression to get it to ignite, you are wasting fuel and potential energy in the wasted fuel every time the cylinder fires. Resulting in lost power and fuel mileage.

2. Wow, seems like the ocatane rating may have something to do with performance and fuel economy according to cylinder pressure. Whadda ya think guys?

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1. You have contradicted your first statement yourself at least twice.

Just to pick one manufacturer, Ford, has several engines at 9.8 to 10.3 to 1 that run on 87 octane fuel. I mean that's what is recommended to run. That's not including any of their vehicles tuned for premium that are capable or running lower octane fuel.

Several folks have run 11.25 to 1 hybrid 3L's on 87-89 octane fuel. Even some using ethanol blended fuel with all it's drawbacks.

Your ignorant statement that certain compression ratios automatically require higher octane fuels is missing the rest of the equation entirely. Compression ratio is just one part of the formula/puzzle.
Just the timing curve alone throws all of your statements into the garbage. It's as simple as this; "BUILD A NEW TIMING CURVE" That easily trumps compression ratio.
Your way of thinking is very 50's and 60's. That's a polite way of saying it's horribly out of date and mistaken.

Not only that but the engine in this post is 10 to 1 and most discussion revolves around engines with a range of 9 to 1 - 11.3 to 1 CR. Yes that includes supercharged and turbo charged engines so it encompasses cylinder pressures much higher the typical NA engines.

2. Octane is ONLY a fuel's resistance to preignition. It has little to do with the fuel's stored energy and performance or efficiency ability. Higher octane will "ALLOW" (not generate) use of higher cylinder pressures, leaner fuel mixtures, and/or greater ignition timing so the engine can make more horsepower. It's called tuning. A higher octane rating itself does not make more power or efficiency.
This same TUNING is why running more octane then needed can decrease the efficiency of the engine. The engine is not "TUNED" to run with fuel of a significantly higher flash point and slower burn rate.
Most cars now days that require premium are backwards adaptable to run lower octane fuel. (That's that technology you do not seem to know about based of your posts btw) However adaptive timing trim is caused by the engine experiencing pre-ignition or detonation and adjusting itself. (timing retard)

Originally posted by Port:

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Originally posted by Y2KSVT:

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Way to contradict yourself.

You sir, are wetauded

Mark

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I guess you missed the sarcasm. My bad, I should have realized it was a little over your head. He didn't actually give a lecture before the wheelie, besides how scared of the car he was, I was just commenting on how rediculous the movie is, and how you all seem to live by it. If you stop watching it, and actually go out and learn something, you might be a little better off. You get it now?

BTW, what was up with loosing the floor pan in the Eclipse when the manifold pressure got too high?

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Dude. It's a movie. Get a life.

To respond to your other foolish posts:

1.) No one was bench racing here. That is when someone claims they can beat you with such and such mods without proof of time slips or video or actual track head-to-head.

2.) You are plain wrong about the compression and the fuel requirements. Modern engines designed for natural aspiration are runing 9.8 on the low end and up to 10.5:1 on the high end. 20 years ago 8.8:1 was considered low and high was considered 9.5 or 10:1 Now days 11:1 is considered high and 9.7 is considered low. Times change. Cylinder head design improves, electronics improve, even fuel composition is altered.

3.) You came on a contour board, a car that runs 9.7:1 stock compression from 1995 and runs on 87 octane with no issues, and claimed we needed race gas at 9.8. Even to imply that we needed to "look at it" at 9.8 is just showing you are ignorant of new engine design. Hell its old news now, this engine is TEN YEARS OLD! THe SVT motors are 10:1 and 10.2:1 stock. They recommend 91 octane but it will run with 87 by pulling back timing as necessary.

4.) My car runs "massive boost" at 6-10psi because I have a 10:1 compression ratio motor. So far I have run 12psi on 93 octane and no problems. For this motor that is massive boost. That 6psi I pulled 300 Horsepower at the wheels in that weather. For 8.5psi I pulled 328 Horespower at the wheels. All on 91 and 93 octane respectively. THe dyno graphs are posted on my site.
Oh, and 1/4 mile times are also posted. As I stated, I OWN3D your ass on that one.

5.) I could post a dyno with A/F data showing 14:1 at the tailpipe on 92 octane and no issues. In fact, it was hosted long ago by someone and may still be up. I'm not going to waste my time because the boosted graphs on 91 octane are sufficient to prove the point.

6.) You sir deserve a for you foolish posts. You are a troll. I wouldn't waste my time on you alone, but this topic may come up again and next time I want to see people to tell you to search.
Get educated by reading instead of watching the fast and the furious for you lectures. Grasshopper.