So I'm just browsing around the other night, dreaming about having some money and being able to do some upgrades haha, and I was reading through some head flow data for Clevelands and M's, and I saw that the intake side always flowed about 25% more than the exhaust (a very rough average, but MUCH more is the point). I also realized that the exhaust gas multiplies in volume many many times compared to it's volume at ambient air temp, and that really made me wonder.

I'm sure there's some reason, since it is pretty much universal that the exhaust valve is smaller than the intake, but why is that? Why are they not equal? Or even, why isn't the exhaust valve WAY bigger than the intake, since it has to deal with SOOO much more gas volume?

Just something I'm curious about, AleX

 

I always figured the intake is bigger because it works under vacuum (negative pressure), the piston has to "suck" the intake charge in while the exhaust works under pressure (positive pressure), the piston "pushes" the exhaust out.
As a rule of thumb, the exhaust is usually around 80% the flow of the intake.