More Compression = More Low End?

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2001kdx
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Post by 2001kdx »

Neither can I.. for the ride impression that is!

Jeb, what kind of hills are you pullin, cuz I have a 200 with stock carb, rev pipe and boyesens, 12/48. I don't ride huge hills, but it pulls my 220lb lard quite nicely. You have a 220 and you're whining about low end???
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Jeb
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Post by Jeb »

^ Oh, no, not low end - just more power overall . . . especially mid-to-high end
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canyncarvr
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Post by canyncarvr »

You've been all 'round the high-octane-don't-necessarily-work-what's-the-distillation-curve stuff...right?

The most common effect of high octane 'race fuel' in a bike is...Bye Bye Throttle Response....

It'll be fun trying it, though!

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Jeb
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Post by Jeb »

>|<>QBB<
canyncarvr wrote:You've been all 'round the high-octane-don't-necessarily-work-what's-the-distillation-curve stuff...right?

The most common effect of high octane 'race fuel' in a bike is...Bye Bye Throttle Response....

It'll be fun trying it, though!
I did see some mention of "distillation curve" in prior threads although only in brief mentionings. In my line of work, we use distillation curves to help us predict how much of one component(s) will separate from another component(s) at given pressure/temperature. I gather that there's an optimal octane range for a given compression ratio.
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canyncarvr
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Post by canyncarvr »

No.

That's the rub. The octane rating really doesn't have much to do with anything. The whole idea of 'more octane' taken to mean 'more power' is simply bogus.

'More' octane is needed or prescribed when an engine design needs it. Generally speaking, the lowest octane you can run and MEET the needs of the engine, the better. Well...'better' meaning 'more' isn't going to get you anything.

Distillation curves of a given octane will vary by the hydrocarbon 'soup' that the petrochemical engineer put together for the particular fuel in question.

Somewhat of an aside, but combustion pressures (a dynamic issue) are more useful in determining fuel requirements than is compression ratio (a static issue). A 13:1 ratio sounds pretty darn high..and if you had a cam with 30º of valve overlap, combustion pressures would be REAL high. Likely the cam of choice in an engine with that particular ratio would be in the 70-80º range, though. So...more squeeze...but less TO squeeze.

There are rules of thumb regarding volumes (%) of fuel vaporizing at particular points (%much gone by 180º 'fer instance) that suit particular applications and engine design. Exactly like: '..how much of one component(s) will separate from another component(s) at given pressure/temperature. No...I don't know how that all fits into your can of c-whatever-it-is.

But...it WILL be fun!

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Post by Jeb »

What I meant by optimal range is actually pretty close to what you implied earlier and then stated on your last post: too much octane has a potential negative effect (throttle response) on performance. More octane means a slower burn (burn rate is how they measure octane); more power, on the other hand, only comes through more energy produced during combustion. 'Course you already know this - why else would you be rubbed when folks claim that more octane is more power? :wink:

The idea, as I understand it, is to target an octane level that provides a slow-enough burn to prevent detonation yet not so slow that throttle response and low-RPM performance suffer.

I suspect that some blend of VP 110 and premium pump will get me where I need to be.

Whatever it takes to unleash the xtra power out of that "other" head . . .
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