At 12:21 PM 6/25/98 -0400, you wrote:
>Actually, the major factor in having the "bang" happen closer to the
>"spark" isn't the exhaust valve opening. It's that the "bang" has to
>happen when the piston is just about at TDC (actually a tiny bit after).
> Much later than that and you lose power (you don't get the maximum "push"
>out of the "bang", making more of the "bang" result in waste heat), much
>before that and you get knocking and engine damage (the "bang" tries to
>turn things the other way). (The reason that you need to advance the
>ignition timing at higher RPMs is that the time lag between "spark" and
>"bang" is relatively constant, but the faster the engine turns, the more
>degrees of rotation happen in that time interval.)
>
I think the flame travel varies upon a number of factors, instead of being
constant. That is why engines ping when you step on the gas, even though
the rpm is the same. If this was constant, I think there wouldn't need to
be a vacuum advance unit.
Les
>It seems to me that if you can minimize that time lag, you stand a better
>chance of being able to make the "bang" happen consistently at the optimal
>moment. Can anybody confirm/correct this supposition?
>
>Chris Kotting
>ckotting@iwaynet.net
>
>On Thursday, June 25, 1998 12:50 PM, Editors, Molecular Vision
>[SMTP:jboatri@emory.edu] wrote:
>> True and I agree with you and Les: throwing in a hodgepodge of smoke and
>> mirrors may do a lot more harm than good. OTOH, like Chris Kotting, if I
>> can avoid gapping points by using a Hall cell, I'll use it if I can
>afford
>> it. Having sold a couple of parts lately, I could afford it. A higher
>> voltage coil allows one to increase spark plug gap, but as Chris points
>> out, the coil and other downstream components (be they Hall cells or
>> points) must operate at higher temps and so could fail, or rather, have a
>> lower mean time between failures. The issue of whether increased spark
>plug
>> gap does _anything_ beneficial or harmful appears to be the largest point
>> of discussion.
>>
>> >From a practical standpoint, if 0.025 plug gap ignites a real-world
>range
>> of mixtures that vary with winter/summer grade fuel or other fuel quality
>> issues, density altitude variations, and acceleration demands, then there
>> is little reason to go to a larger gap. But two questions remain: (1)
>does
>> a 0.025 gap always ignite real-world ranges of mixtures? and (2) can
>> further performance (whether economy or power) be realized with an
>> increased gap leading to a shorter lag time between spark and bang (to
>> quote Chris). Would this allow for more of the mixture to be burned
>before
>> the exhaust port is opened? Is a faster burn better inherently, or must
>> many other variables (mixture quality, cylinder and piston design,
>timing,
>> etc) be matched?
>>
>> Finally, let's face it, the 500 lb gorilla here is that those gold Sport
>> coils look really cool...:)
>>
>> At 9:00 AM -0500 6/25/98, Shawn J. Tobin wrote:
>>
>>
>> > I used to think that throwing a kluge of performance parts together
>would
>> > result in a really wicked ride. This kind of thinking was due to a
>vivid
>> > imagination and the naive assumption that advertising claims were
>> > guaranteed to be true because the government kept them to their word.
>> >
>> ...
>>
>>
>>
>> Jeffrey H. Boatright, PhD
>> Senior Editor, Molecular Vision
>> http://www.molvis.org/molvis
>> Mailto:jboatri@emory.edu
>> 404-778-4113
>>
>>
>
>
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