The ratio of exhaust area to intake area actually can be as low as 1.5:1 when the intake area is good, intelligently restricted intake. Block out parts of the intake where that air won't cool anything. It'll actually cause you promlems at the exhaust unless that's much larger in area than needed.

BTW, the exhaust also needs to be looked at for more than it's area. If it's in a low pressure area (outside airflow sucks the inside air out) it can be smaller. If it's in a high pressure area (outside air wants in) it will have to be larger. How do you know whether an area is high or low pressure? Look at your airplane from the very front. One simpleminded way..... The fuselage you can see from the very front is high pressure. If you can see into the exhaust from the very back, it'll be low pressure. Also, an area behind a projection (like behind cowl flaps which are opened) will see negative pressure.... uh, will be a low pressure area.

Control line speed airplanes used to burn their engines up quite often. They needed cooling BIGTIME. And they were cooled very well with tiny openings directly ahead of the cylinder and with about 1.25X the opening directly behind. And their cowl was built up inside to force all the airflow directly around the cylinder. There was almost no clearance. And if the flyer didn't set his needle too lean, the engine would HONK and stay cool enough doing it. Heck, some of those speed guys thought that ratio was too generous.