Re: Increased Compression?

[Mark Johnson <mjohnlit@xxxxxxxxxx>]

> Don't know where Mark Johnson took math, but think
> about it...
>
>
> Example:
>
> 500cc total volume (swept volume + chamber)
> 50cc combustion chamber
>
> CR = 10:1
>
> Now take away 5cc chamber volume:
>
> 495cc total volume (500cc - 5cc)
> 45cc combustion chamber (50cc - 5cc)
>
> CR = 11:1
>
> Looks like the CR is higher to me!!!
>
> ;-)
>
> Steve
> (I are an Engineer!)  ;-)
>
>> > -----Original Message-----
>> > From: owner-bmw@domain.elided [mailto:owner-bmw@domain.elided]On Behalf Of
>> > Mark Johnson
>> > Sent: Monday, February 18, 2002 10:04 AM
>> > To: bmw-digest@domain.elided
>> > Subject: Increased Compression?
>> >
>> >
>> > I don9t know where JK took physics, but think about it...
>> >
>> > Yeah, if there is carbon (or a dome, or a melted top of a spark plug
>> >  did
>> > that once
>> >  or whatever on a piston it decreases the chamber volume.
>> > However, the chamber volume is increased on the intake
>> > stroke, as well as
>> > the compression stroke.  Assuming the intake pressure is at
>> > one atmosphere,
>> > the compression ratio would be the same with or without the
>> > reduced volume.
>> >
>> > Also, as DASUTO said, it increases detonation.  Sorta becomes
>> > a 3glow plug2
>> > on top of the piston.  When the fuel-air mixture starts to
>> > burn before the
>> > intake valve is completely closed, you tend to lose the
>> > advantage of all
>> > that 3increased compression.2
>> >
>> > Unless I9m missing something...
>> >
>> > Mark Johnson
>> >
>
You9re right, Steve.

The ratio is increased but the volume is less.  Displacement, i.e. bore x
stroke is unchanged.

Functionally, you are running a smaller engine with a higher compression
RATIO.

My point on the detonation remains the same.  If the valve is open when
detonation of the fuel/air mixture begins, the increase is well for nought.

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