The reason the ports on the Holbay head are smaller is to increase low end
torque. It is correct that smaller ports increase the velocity of the fuel
air mixture, as in Bournoulli's theorom "when a gas or fluid flows through a
restricted area as in a nozzle or venturi, its velocity increases and
pressure decreases". The velocity helps to create inertia in the incoming
flow, pulling more air into the cylinder. Once the engine winds up to higher
RPMs, the demand for air is greater than the port can flow without
mechanical force (blower, turbocharger). Then the engine chokes out and
loses its ability to produce gofast.
The Holbay head was put into a production car that was meant to be
driven around rather than at a race track. This factor must be taken into
consideration when considering it for a Hot performance upgrade". Lou
----- Original Message -----
From: "Tom Hill" <tom.hill@att.net>
To: <alpines@autox.team.net>
Sent: Friday, March 09, 2001 6:57 AM
Subject: RE: More Power from the 1725
> I had the same discussion with Smitty when I bought my Holbay setup. When
I
> talked to my engine builder about the port differences, he smiled and
said,
> "its right the opposite of what we always thought". His point was in many
> cases bigger ports are not always better. Flow is not just a funtion of
the
> capacity of the port. The shape of the port and the velocity of the flow
> are also very important factors. This guy has been in business forever
and
> has a great deal of drag and circle track engine experience.
>
> We will have flow numbers on both heads in a few weeks.
>
> Tom Hill
>
>
>
> -----Original Message-----
> From: owner-alpines@autox.team.net
> [mailto:owner-alpines@autox.team.net]On Behalf Of
> sosnaenergyconsulting@home.com
> Sent: Friday, March 09, 2001 8:44 AM
> To: Greg Locke
> Cc: Jarrid Gross; Tom Hill; Christopher Albers; alpines@autox.team.net
> Subject: Re: More Power from the 1725
>
>
> Y'know, Smitty has a Holbay head and we were puzzling over the smaller
> intake ports recently. He thought that going from a large carb opening
> to a small intake port would increase the velocity of the air/fuel mix.
> Wouldn't that contribute to better torque?
>
> I think that somebody else (apologies for not remembering who) wrote
> yesterday that the intent of the Holbay head was to make better low-end
> torque rather than high-end horsepower.
>
> Regards
>
> David Sosna
> 56 S4 GT V6
>
> Greg Locke wrote:
> >
> > I heard that holbay originally delivered the H120 powered rapier (or
> > hunter?) with decent sized ports and rootes said... "No way. this is too
> > fast, make it slower". The reduction in port size was holbays answer. I
> > thought they only reduced the size of the intake manifold runners, and
the
> > head ports were standard, but I may be wrong here. Would take a lot of
> work
> > to weld up the ports and re bore them.
> >
> > more information form vague sources.... The original engine did put out
> > 120hp, but the port mods reduced it to about 107.
> >
> > Kindof defeats the purpose of the webers in the first place, but it was
> more
> > of a sales gimmic anyway, as a result of the london-sydney win.
> >
> > Greg
> >
> > ----- Original Message -----
> > From: Jarrid Gross <JGross@econolite.com>
> > To: Tom Hill <tom.hill@att.net>; Christopher Albers
> > <Christopher.Albers@bubbs.biola.edu>
> > Cc: <alpines@autox.team.net>
> > Sent: Friday, 9 March 2001 09:02
> > Subject: RE: RE: More Power from the 1725
> >
> > > tom wrote,
> > >
> > > >I am referring to the port diameter at the intake manifold not the
> valve
> > > >size. I think the valves are the same on the standard and Holbay
> heads.
> > >
> > > >tom
> > >
> > > CNA wrote,
> > >
> > > >Huh? That doesn't seem right. How does the head breath with an
intake
> > > >only, what, 1.2"? I can't recall the stock size, I seem to recall
> > > >about 1.4" for the intake & 1.2" for the exaust.
> > >
> > >
> > >
> > > This is correct, the ports on the holbay are about 1.25.
> > >
> > > The valves are 1.30 and 1.52, the same and SV alpines.
> > >
> > >
> > > Jarrid Gross
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