There is about 2mm of cylinder head on the intake ports showing proud of the gasket. Almost the exact same thing on the intake manifold. If the gasket were the size of the ports, I expect they would line up perfectly. Is this a gasket matching scenario? (I know this is like putting racing stripes on a turtle but it bugs me) And, If I go ahead and gasket match the head and intake manifold, I plan to slather rags in grease to block the ports as the engine is out for re-sealing and thrustwashers, not a rebuild. Any better ideas? (Triumph Spifire)
I would match the head and not the intake, for a step-out in the direction of airflow. It helps prevent reverse flow in the port, which has to stop and change direction before it can move forwards again.
Really the solution is a smaller gasket, if you really want to be picky. The trap you can fall into with gasket matching is that you get a "bulb" in the port where the cross sectional area expands and contracts again, which makes the air slow down and speed up, which costs energy, which means less inertial flow in the port. Depending on how bad it is, this results in less flow than if you just left it alone, provided that the two ports line up with each other.
Pete is dead on. Gasket matching works on crap heads like old Ford E7 castings but I wouldn't do it on modern aluminum. Modern engines are really good at moving air and modern manufacturing produces great heads. It's the stuff after the head and before it that most affects performance due to packaging, emissions, noise and many other considerations.
You bulb both sides gasket matching and performance might even be worse.
I was wondering about the bulb that would be created. From the best I can tell, the ports line up and the ports ARE the same diameter. That means I'll have a crack about 1 1/2mm wide (gasket thickness) and 2mm deep at the ports where the intake bolts on. I think I'll skip it. Thanks for the information!
Just how do you go about making your own intake/exhaust manifold gasket?
