Cams have both advantages and disadvantages.
By changing the Valve timing the engine characteristics also change. Usually the result is noticed at mid to top revs.
They also Usually have greater lift.
Why? Because opening the valve more can increase the flow of gasses.
Valve timing is set by the Cam design and you can't normally play with it.
But Valve opening can be increased!
If you picture a Tap like your garden hose is attached to, assuming it is the old style with a handle that you turn to increase or decrease flow.
The flow is varied by moving the washer away from the seat by turning the handle.
Now unlike a Tap, the Valves in engines are mostly called Poppet valves, and are tapered unlike your Tap.
This means when they come away from the Seat the opening gets larger the further they open.
So you may wonder wtf I am on about but keep reading.
With a small amount of work when building a Head this opening can be maximised by a couple of actions.
Firstly when seating the valve you can ensure the seat is closer to the stem than the head of the valve.
This effectively makes a greater opening Because from the very beginning of valve movement more of the valve is out of the hole (seat).
Also by de shrouding the valves the effective hole size is increased.
The Valve uncovers the port when it moves away from the seat.
The seat picture above shows what it looks like before de shrouding.
The following picture shows the material around the seat removed, I effectively will create a larger opening for the same valve lift.
There is less obstruction to the gasses flowing!
By changing the Valve timing the engine characteristics also change. Usually the result is noticed at mid to top revs.
They also Usually have greater lift.
Why? Because opening the valve more can increase the flow of gasses.
Valve timing is set by the Cam design and you can't normally play with it.
But Valve opening can be increased!
If you picture a Tap like your garden hose is attached to, assuming it is the old style with a handle that you turn to increase or decrease flow.
The flow is varied by moving the washer away from the seat by turning the handle.
Now unlike a Tap, the Valves in engines are mostly called Poppet valves, and are tapered unlike your Tap.
This means when they come away from the Seat the opening gets larger the further they open.
So you may wonder wtf I am on about but keep reading.
With a small amount of work when building a Head this opening can be maximised by a couple of actions.
Firstly when seating the valve you can ensure the seat is closer to the stem than the head of the valve.
This effectively makes a greater opening Because from the very beginning of valve movement more of the valve is out of the hole (seat).
Also by de shrouding the valves the effective hole size is increased.
The Valve uncovers the port when it moves away from the seat.
The seat picture above shows what it looks like before de shrouding.
The following picture shows the material around the seat removed, I effectively will create a larger opening for the same valve lift.
There is less obstruction to the gasses flowing!
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