Why porting and does it work? When someone decides that they want to increase the performance of their
particular engine, many options are available to be able to do that. For example changing
cams, after market manifold, exhaust improvements, different carburation, ignition
systems, computer chips etc. etc. etc… But, (a secret coming up) The most horsepower
you are going to get out of your fully accessorised engine is what the cylinder head will allow it to FLOW. FLOW? What flow? AIR FLOW. The
amount of horsepower an engine will produce is
directly proportional to the amount of air drawn
into the engine. Simply FLOW = POWER. The aim of porting a
cylinder head is, to increase airflow or more precisely Volumetric Efficiency
(VE). VE in simple terms, is the % that the cylinder is filled with air and fuel mixture, just after the intake valve
has closed. A typical V8 engine in standard form would be achieving VE of
only 60% to 75%, where as modern multi valve engines, reach between 80% to 95% VE. A race engine would be operating in the 100% VE mark, although it is possible
to achieve up to 120%-130% VE normally aspirated, mainly in the very top racing
applications like Formula 1. By utilizing what is called Inertia supercharging, i.e. using
the kinetic energy of the moving air or ramming effect and valve timing to trap more air
in the cylinder. Porting Cylinder Heads Knowing that an engine needs more airflow
to make more power doesn’t necessarily mean
that you simply bolt on the latest racing cylinder
heads available or do an all out racing porting
job. Porting a Cylinder
Head for a particular engine and its application requires careful research and planning to
achieve a desired effect, many factors have to be taken into account, for example Horsepower aims, operating RPM, size of the
vehicle, diff ratio, CID of engine and many more. This information is taken by us at RACETECH HEADS to be able
to formulate the CFM (airflow) and Air Velocity needs of a particular engine. Yes, Air Velocity, another secret. Airflow in and out of a cylinder as to be kept in
certain air speed ranges to achieve maximum VE. Porting is not
restricted to the intake side alone, the exhaust has also very definite airflow goals to meet. In particular depending on
engine application, it has to reach between 65% to 85% of inlet CFM figures and
considerably higher air velocity speeds. But that’s not all.
For a balanced engine the intake manifold, has to be chosen carefully and in many
cases needs porting to adjust cross sectional
area and entrance area, all this related to the correct air velocity, to produce Horsepower at the desired RPM range. One of our most important tools is our SuperFlow flow bench. One of the best tools to use to
unlock Porting secrets. A flow bench is essentially a tool, which blows or
sucks air through a cylinder head, at a constant
pressure, which allows us to measure the amount of air that is allowed to flow, at various valve lifts. This measurement is expressed in Cubic Feet per Minute (CFM) at x”
inches of water pressure. Tests are most commonly conducted at 3”, 10”, and 25'
or 28” inches of water. We mainly use 10”of water. By using flow testing
and our Computer Programs, we can easily measure our progress and make sure that our
Customer ends up with cylinder heads that have
equal flowing ports and the expected flow
figures for their particular engine application. Having
true and factual knowledge of what an intake system flows.
Is not the only reason for measuring flow. KNOWLEDGE = POWER
Flow figures are used by us to; More realistically, pick Camshafts for our customers. We can make a more accurate power prediction of the finished engine. We can advise a better intake system. Find carburetor needs. Choose optimum compression ratio… and more. The money you spend on flow testing
will get you closer to what you are after, by knowing your limitations. As stated
earlier “The amount of horsepower an engine
will produce is directly proportional to the amount of air drawn into the engine. Simply FLOW = POWER”. By knowing this and using
a simple formula from the flowbench
manufacturer, you can estimate *Potential Horsepower
from CFM, flow figures of an intake system at maximum valve lift. Potential Horsepower
= .43 x (CFM AT 10” OF WATER) OR Potential Horsepower
= .256 x (CFM AT 28” OF WATER) OR Potential Horsepower
= .272 x (CFM AT 25” OF WATER) Then multiply by number of cylinders *These Horsepower figures are for a
well developed racing engine. Where everything, has been optimized. Cylinder heads The most common misconception, when it comes to porting is that the bigger and shinier the port,
the better it is, this is not necessarily the best way to judge how good a port job is, even bigger valves doesn't guarantee
a better performing cylinder head. Another important area were a cylinder head separates itself from your average port job, is in the valve seat, were considerable
low lift improvements can be made. The secret is in the way the seat is cut, namely a
three-angle cut, but not just any three angles. We
use a Sunnen VGS 20-seat and guide cutter, regarded by many as a leader in its field.
Known for its accuracy and ability to do performance seats, with a single cut. In
addition, is the machine of choice of many Nascar and Pro-stock racing teams. When
a cylinder head is going to be ported, we are more concerned with port shape
and not size, we are looking more along the
lines of a narrow smooth and fast flowing river, rather than a wide slow and muddy river. Port shape is not mentioned very often when people talk
about porting but take it from us this is where
a lot of money is spent when an engine is being developed by the car manufacturers. We
also have invested a lot of time, money and effort in port shape
research. Since most people are limited to existing cylinder
head castings, we have made sure we know their limits. Research and Development Cylinder Head porting is no longer a black art, there are
definite scientific do's and don'ts. Effective porting is a quest to
find the best port shape, which will give us the results that we are
looking for. Shaping the often involves the use of various grinding tools to remove material, but it can involve adding material by welding or the use of various epoxies and resins. Our research has meant that, we first have to have an idea, of what port shape
we are starting with, which has lead us, to basically cross- sectional cut literally
dozens of cylinder heads, to reveal to us where improvements can take place. (See below).
It is painful when it is done to expensive after market heads. Another useful and revealing procedure, is the use of special rubber
material, which when poured into the port and
then hardens, gives us a three-dimensional port shape, so that we can take accurate measurements to
achieve our aims.
|
|||||||||||||||||||||||||||||||||||||||
