[Diy_efi] The Hunt effect

[Geoff Harrison]

The only engines I have seen that approach a true hemispherical 
combustion chamber, are low compression 2 strokes. Many engines 
are described as being "hemi" to give some idea of the shape of 
the combustion chamber. It's an ideal shape. No plug masking 
being a plus. However, flat top pistons are not the strongest, 
so it's desirable to have a dome. Good by true hemi shape. Then 
we want to increase compression, so the dome gets raised, flats 
are milled so the valves can open. It's traditionally called a 
hemispherical combustion chamber. A bastardisation of the word, 
but that is commonplace these days. It's also commonplace to 
refer to the area around the valves and spark plug in a cylinder 
head to be known as the combustion chamber. Even by 
manufactures.
In Chrysler's situ, it may just be a marketing ploy as Adam 
suggested. Nothing new in that. In my humble opinion, the first 
requirement for a 4 stroke hemi, is a true crossflow head. Not 
one where the valve stems are parallel to each other as in the 
Ausie 6 cyl Valiant / Chrysler Hemi. But it was probably as 
close to a hemishephical shape as possible with that valve 
layout. Hemi - verb or noun?

BTW, what happened to the "Hunt Effect"

Geoff H

Adam Wade wrote on  October 27, 2005 3:15 PM

--- John Gross <jogross3 at hotmail.com> wrote:
> There is most definitely a combustion chamber in a
> cylinder,

Yes, there is.  I didn't say that, though.  I said
there's no combustion chamber *in* the head.  The
combustion chamber is composed of part of the head,
part of the cylinder, and the piston crown.

> where the last "face" of the 3D volume is an
> imaginary face coplanar with the deck of the
> head.

Then it's not a chamber.  By definition, it is an
imaginary distinction.  What's more, it has very
little in and of itself to do with turbulence, squish,
combustion, and even spark advance.  You can't figure
out what is going on with only half the important data
about the shape of the confines.

> While it is in and of itself not a physically
> closed volume,

And therefore, is not a chamber...

> it is ALWAYS called the "combustion chamber"

By whom?  I've never heard anyone who actually knew
what they were talking about who did not include the
shape of the piston crown in their discussion of the
combustion CHAMBER, and in fact it is meaningless to
discuss only a partial description of the space in
which combustion takes place.  See my above comments.

> because that makes a whole hell of a lot more sense
> than saying "that part of the engine's combustion
> chamber that is the undulating pocket in the deck of
> the head"....

Which is why it is referred to as the "roof" of the
combustion chamber, as you so astutely pointed out in
your previous post in this thread.

> Oops, sorry for not knowing what you've been working
> on for the last 20 years...

Ah, sarcasm, how delightful.  I can see you haven't
read any of the archives, either.  Or clicked the link
in my sig file, for that matter.  A shame, regardless.

In fact, my comment was a subtle hint that if you
could not even remember what was written in the post
to which you were replying, with it there in front of
your eyes, that perhaps that would lead people to
consider the possibility that your replies were
crafted with the same amount of attention on your
part.  I'm sorry it had to be spelled out for you...

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