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95octane vs 98octane dyno sheets

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image_2.jpeg

image_3.jpeg

98 octane fuel is the upper graph in pics.

95 is beneath.

Standard drzsm

Edited by jonboots28
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Don't understand how the lower octane fuel can give a nicer torque curve.

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Don't understand how the lower octane fuel can give a nicer torque curve.

 

Noble, I thought the same until I looked at the HP in red upper left. 1st one is the 98, the one below is the 95......next one is the 98 and then the one below is the 95 etc.

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It is not the max numbers it is the shape and slope, but I see what you mean.  It would be nice if the graphs had RPM rather than road speed.

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Two tests, run back to back will not ever match unless done by computer. You need to do 20 runs on a setup to get an accurate average.

 

A few points in octane will do next to nothing, certainly nothing to power, at most a hiccup on acceleration due to detonation if the octane was too low. If the lowest octane was good, then slightly higher octane will do nothing measurable.

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we're seeing the 98oct burning slower, or what?

Yes, the higher the octane of the fuel the slower it burns, which is why using a higher octane fuel than the engine needs to stop detonation will result in less power, as the fuel is still burning when the piston is moving down the bore.

 

The engine needs to be optimized (higher compression ratio & /or more ignition advance) to get the extra power

Running 98 in an engine that doesn't detonate with 95 won't yield any more power, unless other changes are made, and may even result in less power

 

The graphs appear to be in different gears as the torque and power curves don't cross at the same indicated road speed, which makes torque & power curve comparison impossible, unless there was tyre slippage on second run resulting in a lower indicated rolling speed

Agreed it would be much better if it were engine speed on the X-axis

Edited by GuyGraham
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Higher octane allows you to add more ignition advance, which will make a power gain over a lower octace fuel.

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