Newby Question

Hi,

Can anyone guide me to the correct formula to calculate a throttle body size for a engine,

Thank you

Well, throttle body size on and efi system has to be related for two important things , to not restrict air flow to the engine

and to measure the load or the change of loads aplied to the engine by the user , the throttle body measures load for the amount that

open the blade . So to little the throttle body for an engine size and the airflow will see restrictions and too big a throttle body for an engine

size and it s not going to measure engine loads and load change accurately. Attached is an explanation and formula for throttle body size

coming from Corky Bell book Maximun Boost , with the explanation and the formula your going to have a better idea for the concept and

if you want to be more accurate with the formula you have to measure the throttle body shaft area and substract that amount to the total

throttle body section area, because the shaft is a restriction , the formula dont take into account the throttle shaft area because is for differents types of throttles .

But you could enter only the throttle body area too without the throttle body shaft area calculation and have a ballpark idea of the measures and

more important the concept. Usually while the throttle body could measure accuratelly the rate of load change of the engine it could be bigger

in terms of total area for determined engine size.

The CFM data for this formula is the airflow rate demand of the engine at peak HP RPM ,for example if is a 2000 cc engine convert to cubic inches

2000 / 16.39 = 122 cubic inches

(122 x 7000 rpm) / 3456 = 247 CFM