Re: alfa-digest V8 #813

[christian147@domain.elided]

C M Smith wrote:
>A recent post appearing to rely upon what the "best engine minds" do
about 
>combustion chamber shape draws one (at least) unwarranted conclusion. 
>Assuming the writer intended to refer to racing engine designers, and of

>F1 engines at that, then it is correct that the pent roof is the ideal 
>shape, as Keith Duckworth so cleverly demonstrated all those years ago 
>with the Cosworth DFV. It is incorrect to deduce that this is because
the 
>shape is ideal, far from it.

Now now, you are putting words in to my mouth.  I said if well designed
it was the fastest burning.  I can't afford F1 level engineers, but I
have employed a very competent consultant.  The subject came up in terms
of  minimizing work done by the engine BTDC and maximizing work done
ATDC, fasting burning chambers can do this.  This is a view also held by
the tuners i have spoken to at trade shows and SuperFlow conference.  I
think you will agree that not all pent roof chambers are created equal,
and subtleties in design can optimize it for intended use.  That said I
don't believe it to be a magic bullet, just another part of the system. 
Still it has proven it's self useful over a wide range of conditions,
from high mileage low emission econo boxes to high boost high rev grand
prix sidecar racers. 

>The cylinder filling resulting from intake effects 
>is as much about resonance as it is about inlet tract to valve port
angle 
>or valve area or lift. Bigger valves breathe better, all other things 
>being equal. More precisely, bigger total valve opening area breathes 
>better AOTBE.

I wish more tuners though like that, it would be easier to make a living,
less real competition.  If you ignore velocity you are doomed to V.E.'s
of less then 105% if you are lucky.  Use velocity for all you can and
130% is possible  (160% in theory).  Every dimension from the initial
flair of the intake cone to the tip of the collector outlet is important
if it is touched by the working gas. Every dimension is dependent on how
the engine will be used.  Get it wrong, and you are driving a pig. 
Computers modeling helps greatly here.  Know of an affordable CFD package
that will run on a small cluster?

>The 164 
>engine also uses hemi heads in the two valve version even with a healthy

>oversquare engine.

You may recall I don't consider them "true" or "pure" hemis as they only
use about 30 degrees of latitude on a larger sphere, as a "true" hemi
uses 90 degrees of latitude on a sphere close to the same diameter as the
bore.  I use Fords term "semi-hemi", and it creates a much more open
chamber that addresses most of the problems of the true hemi.

Yes true hemis do have a place.  High pressure forced induction, nitro
methane as a mono fuel.  Lots of room to pack that bomb in to.

Chris Hall
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