Originally Posted by
dirtdobber
Cup,
Reading your post number 56, you are talking about two different things, although they are related. ArgoJim noted that "cold air intake" is a phrase commonly used with regard to combustion air - the air drawn into the carburetor. The reason "cold air" is important in the combustion process is because it is more dense than hot air, and the more air/fuel you can put into the cylinder the more power that results. The engine does run better and more efficiently. The combustion air also help cool the engine. So, in this sense, a "cold air intake" would simply be to route the intake to a point that it is drawing air from some place other than the hot engine compartment. To do this, a duct of the same diameter as your carb intake neck (2 inches or so) would be sufficient.
The other cold air intake you are talking about is that of forcing the engine cooling fan (flywheel) to draw fresh air into the engine compartment, rather than recirculating hot air. A simple way to determine the duct size needed is to measure the intake area of the flywheel housing. Let's say it is a 12 inch circle, which yields an area of 113 square inches. The true calculation is much more complex as it involves friction and other factors, but that's way over my head. Provide enough ducts to equal the same area, so in my example of a 12 inch circle you need 9 four inch ducts or 4 six inch ducts. You will also need to shroud the ducts to the engine or it will just recirculate hot air.