It s best to lower the port when needed.
Raise the roofs of the intake and exhaust ports.
That s why some port the intake by removing material from the bottom of the skirt of the piston.
Again you don t need to do this on your first saw.
Intake timing is measured from the floor of the port.
It enters via the intake port as the piston rises into the crankcase and then is transferred to the combustion area via the transfer ports as the piston descends and the piston top uncovers the port opening to the cylinder.
With the way i ported this last exhaust port i lost 4 5 cfm when i tried raising the roof about 050.
I need additional exhaust ventilation in my roof with the planned installation of a whole house fan in the attic of my home located in sf bay area.
Geometry setup the parametric intake port model was created in caeses and a set of seven parameters were selected for the optimization.
Be it the intake or exhaust the worst part of the port for air to negotiate is the short side turn.
You mention exhaust vents shouldn t exceed intake vents in the roof for proper circulation.
Two stroke port duration port timing basics.
It enters via the intake port as the piston rises into the crankcase and then is transferred to the combustion area via the transfer ports as the piston descends and the piston top uncovers the port opening to the cylinder.
Do not raise the roof or the rings may drop below the top of the port and catch.
All we care about is velocity and pressure.
However with only two 1 ft x 2 ft gable roof vents i ll need an additional 7 sq ft of exhaust vents.
The port was a typical geometry for an si engine combined with a pent roof combustion chamber and four valves per cylinder.
Air gasoline enters the engine from the carburetor at a ratio close to 15 1.
Removing the thermactor boss did raise the high lift numbers about 1 2 cfm after porting but then leveling the lateral.
A competent port designer will raise the floor as shown in fig 10.
Nearly every single exhaust port today except for ford 302 5 0l and 351 heads are big enough.
After it is burned the exhaust gas exits via the exhaust port.
Developing a port profile before flow benches the only way a head porter could tell if his work improved airflow was if the car ran faster on the track or the engine made more.
I have cut another exhaust port and still according to my flow tests i certainly cannot recommend raising the roof.
