Hi James,
I don't know much about Edebrock manifolds nor Carter carbs but do have
experience and training with Clayton chassis dynos and front engine / rear
wheel drive cars.
A factory quoted 210 HP at the flywheel will not produce 100 HP at the rear
wheels. I tested a lot of 300 + HP cars that couldn't reach 100 HP at the
rear wheels. But, that is all relative to all rear wheel drive cars. Power
to weight ratio determines acceleration. As power increases, traction
becomes a factor. As speed increases, aerodynamics and road drag become a
factor. Unless you are going to put the car in competition, all you have to
do is follow the basics and you will produce more HP than you can use in a
one ton V-8 powered car.
The small exhaust ports of the Buick / Olds / Rover 215 can be used to an
advantage at the RPM most street cars are going to use. Consider the
sequence of events. Cylinder pressure is still quite high as the exhaust
valve opens. So you get a (blow down) effect which sends the exhaust into
the headers at a high velocity. After that, the piston will start to push
the gases out. (This resistance to the piston does try to slow the crank but
you will gain back shortly.) A still somewhat pressurized charge of gases is
now moving very fast in the headers. This charge has mass and can not be
easily stopped even though the piston is decelerating and comes to a halt at
TDC with the exhaust valve still open. This forms a low pressure area.
(vacuum) in the combustion chamber. But, another event has occurred. The
intake has opened also. A slightly high pressure charge of air/fuel rushes
in (some of it from a dead standstill).
even when the exhaust valve closes the exhaust charge does not stop. So, a
low pressure area (vacuum) is formed in the exhaust port and header. This
low pressure area assists the next exhaust charge coming out.
Similar events are occurring on the intake side. A piston going down on an
intake stroke forms a low pressure area (vacuum) in the cylinder. With the
intake valve open, the atmospheric pressure 14. whatever it is that day,
pushes the air into the chamber, picking up fuel on the way. Here is where
it gets tricky.
Small carb, small port & small valve = high velocity, high kinetic energy,
but restrictive
Large carb, large port & large valve = low velocity, low kinetic energy and
not restrictive
With long single ports the problem is easy to correct. Use relatively small
carb, small port and extremely large valve with plenty of space just around
the valve. Air pushed in through a small carb and port form a high kinetic
energy so when the intake valve closes the air/fuel charge does not stop, it
continues in and pressurizes just under the head of the valve waiting for
the next open valve event. This is more difficult to achieve in a manifold
that shares other cylinders. However, the effects are still there. I have
not even mentioned shock waves which do enter into it. They are mainly
useful at high RPM so unless you plan to race the car. It is not worth the
trouble thinking much about them.
An engine with small exhaust ports and not much room to enlarge should try
long thin header pipes transitioning to larger pipes, a good amount of
overlap in the cam design, a medium sized carb with the largest intake valve
that can be put in and the area just under the valve should be enlarged even
at the expense of laminar flow.
Keep in mind that if there are 360 + million people in the US, this is the
opinion of just one of them.
Howard
http://hmfinc.home.mindspring.com
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