dunno if this is possible to do, but it seems like it would be. im looking for some type of equation or site that has a calculator for the exact amount of air an engine will need. the reason being is id like to see if the stock TPI setup on my car is sufficient or if it could be starving for air a little. it is only a 305 with stock heads, cam, intake manifold, runners, ported EGR wall in the plenum, stock throttle body, stock MAF and cut off air box bottoms. i want to get SLP runners and have my throttle body bored to a 50mm, i know a guy that does it. but if these things arent nessisary i dont want to do em. hopefuly i dont sound like an idiot here, any insight would be appreciated

 

I think that this is correct and might be what you are looking for:

CFM requirements of engine = (cu.in. * RPM)/(2*1728)

At 6,000RPM, my project 395cu.in. SBC would eat 685CFM.

I am going to look for this equation in my many books to confirm what I have.


OK, I found it!!
Take the cubic inches and convert it to cubic feet,,, thats the cu.in./1728 gives the engine displacement in cubic feet.

Then to calculate the required CFM of the engine:

required CFM = (cubic feet * eng RPM) / 2

 

so does that mean ull need like a 50mm throttle body, that flows around 700cfm i think?

 

Thanks for those calculations.

I got 465.27 cfm for my motor.

 

Nice car, your car looks just like mine.

 

so i guess that means the stock TPI setup is plentiful for my engine?

 

The TB is good,, at 48mm you dont need to spend money on that. Maybe the SLP runners would be a slight improvement. If you are running with an ET of 13.9sec, your 305 is really fast for being nearly stock!!!!

 

thanks, yeah it goes good, but mostly ive learned to drive it really well at the track so that made a huge difference in ETs. its all about the 60 foot. ill try the slp runners when i get the $$ hopefully i can get a bit more power out of it.

 

is this calculation the same for forced induction engines or is that a whole differnt ball game

 

I am sure that this equation is for normally aspirated engines only.

I am not sure how to figure in the boost for a turbo or SC,,, but if you had 8psi boost pressure, would you multiply the NA calculated CFM by (14.7+8)/14.7 ????? Dont know.

 

hmmm