Help me understand valve angles?

[Maelfyn]

From my favorite Toyota resource:
G = twin cam (wide angle, 45 degrees or more between the intake and exhaust valves)
F = "economical" twin cam (narrow angle, around 22 degrees)

I understand that G is a head tuned for performance and F is economically tuned. I'm assuming this affects the engine's breathing but I'm having some trouble visualizing what they are trying to say.

45 degrees or more between the intake and exhaust valves? I'm assuming they mean the angle the intake and exhaust valves make? Just wanted to be sure. Why exactly does this have such a huge impact on engine performance? I would assume simply better air flow.

Thanks in advance for clarification on this.

[Chui]

Usually, the valve angle is measured from the vertical. If the number you give for the G head is measured or referenced from the vertical then the angle between the two valves is 90 degrees. I don't know of any hard and fast rules. I used to believe that the wider the angle the better, but later engines used narrower valve angles. There is so much else to consider and if you oversimplify too much your claims will become erroneous at best.

[yakkosmurf]

What Chui posted is correct about how to measure them. So why is 45 deg better for performance? Look at the flow path. The curve the air has to go through is less on the 45 deg than on the 22 deg. This means you can flow faster through the head. It will give better performance in the high rpm range. The F heads give you more turbulence since your flow path has a bigger curve. This gives you better low end response since you get better swirl on your intake charge. That's why Toyota usually coupled their variable intake system with the G head engines. It allowed them to have more turbulence of the intake charge at low rpm with the G head engine. Prime examples are the 4A-GE and 3S-GTE engines for the MR2.

[Maelfyn]

Yeah that makes sense. Thanks.