| HRD Racing Heads
7791 Aqua Circle, Unit 4
Dalton Gardens, ID 83815
Phone (208) 762-9600
Fax (208) 762-1597
We were recently featured
in Drag Illustrated!
Click here to read.
AIR FLOW FACTS
||In the past, and to a large extent
even today, head porting has been not much more than making large
shiny holes out of smaller ones, with the resulting head actually
performing no better than stock. The blame for this is laid on
the presumed fact that these "ported" heads need other
related equipment to make them work. This is NOT true. A properly
"flowed" head will perform better regardless of the
nature of the other components used. Of course, it is a fact
that the proper coordination of engine parts will produce the
||An engine, being no more than a
highly refined air pump, makes the amount of available air to
be compressed in the cylinders directly proportional to the amount
of energy (h.p.) it will produce. Very often too much emphasis
is placed on static compression ratio, and if the means to gain
this higher compression interferes with air flow, then nothing
has been gained. For example: a very high dome piston can cause
an actual loss in operating pressure, since during the valve
overlap it can disrupt smooth air flow, which in turn will limit
the total amount of air available to be compressed in the cylinder.
Maximum flow must be the prime consideration over any other factor
because our "air pump" must have its #1 commodity -
||There is a definite intake to exhaust
ratio in terms of air flow that must be attained in order to
produce maximum efficiency. This is one of the things the amateur
head porter often overlooks or isn't even aware of. When an intake
system is improved, the exhaust system must be brought into the
proper ratio or balance to achieve maximum horsepower.
||In most cases American engines
have sufficient port area and simply increasing the size of the
port is not the answer. The real secret is in modifying those
areas that will allow the air to more efficiently move around
obstacles in the air flow path. Such things as the turns or bends
in the port, the valve guide bosses, and most importantly the
valve, can affect air flow much more than the actual size or
smoothness of the port.
||It is the shape and not the shine
at critical areas that counts. Air flow and dyno tests have proved
without a doubt that a super smooth finish will not gain horsepower.
In fact, in some areas a certain amount of texture or roughness
os needed to insure fuel suspension in the air stream. Port shape
is the prime consideration in air flow improvement.
||Valve seat angles and valve shapes
are very critical. The straightest and best-contoured port will
not work well, unless the seat valve area and the valve itself
are specifically designed to work with that same port.
||The naked eye cannot tell how a
port system will flow, especially a strange one. Even the familiar,
most popular ones must have every single port flowed and retouched
to get consistency. Ports looking exactly the same can vary from
10% to 12% and even more.
||The cam shaft and cylinder heads
work very closely together, so closely in fact, that they are
a function of each other. After a head has been reworked to its
maximum flow efficiency, a proper cam can then be selected to
match the head and the intended use of engine.
Here at HRD, we have proved these facts to be valid and true,
and are interested in producing cylinder heads of high functional
quality. This is to say that we are trying to give our customers
heads that will produce horsepower. To do this, and still
keep the cost at a reasonable level, we concentrate on those
modifications that actually produce results and not on such things
as satin smooth finishes, super large ports and eye blinding
shininess. These things look good and require a lot of time to
achieve, but do not have anything to do with performance and
horsepower. Since time is money, we feel that it can be better
spent in areas other than the "spit and polish." As
an example, we flow test and balance every port in all out competition
something that some of the most respected head companies
In conclusion, and keeping the above facts and statement in
mind, you are not going to keep up with your competitors unless you use a
head service such as ours.