[alfa] Re: Jim K's porting

[alfa@xxxxxxxxx]

Ron
That is kind of a blanket statement you have there, and may not actually apply
to reality.  

The generality works if you use the typical very long duration, high overlap
cams that Alfa is well known for, where you need the momentum to keep the air
flowing into the chamber.

But if one uses the cams that Jim K tells you to use in the book, his ports
probably work quite well- his are higher lift, with relatively shorter
duration.

It all works as a system- need to match the cams to the ports to work like you
want.  And good CFD software that will properly predict the flow in an
individual port is very hard to come by- the non steady condiditions are a PITA
to work with.   Especially all the back flow from the combustion gasses into
the intake when the valve first opens, during overlap.

And I know a guy who DID use the Jim K book, as a system, and that car was a
ROCKET.  Just have to be really careful when you do it, as there are some
coolant passageways nearby.

Eric Storhok
Ann Arbor, MI


Ron said:
> 
> I've never bothered to measure a Kartalamakis designed port, and I hate to
> be a naysayer, but I can tell you from inspection that regardless of the
> relative merits of his other advice, Kartalamakis' port geometry is NFG.
> 
>  In porting, what you really want is a "steamlined" flow pattern with the
> gasses travelling at the maximum possible velocity. If you have a bad
> geometry, you can't get the gasses going very fast before the flow gets
> excessively turbulent and the CFM falls off. The Kartamalakis geometry
> isn't particularly streamlined, it just slows the gasses down a lot. That
> may give you higher CFM, but not high energy, and it won't give you the
> best integral of power vs. RPM, nevermind throttle response, charge
> turbulence, and all of that,
> 
> Think of it this way, for you to have maximum "inertial ramming," first you
> have to have maximum inertia. Increasing the port radius increases the port
> area by the square of the radius, so the (mv**2)/2 term falls with the
> fourth power of the radius. Mindlessly "hogging out" a port without resort
> to flow bench CFM and velocity testing and / or a fairly accurate CFD model
> is foolishness.
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided