here are some formulas, some very advanced, for finding anything from engine life to carb size to exhaust pipe length/diameter:
1)average piston speed, used to determine engine lifespan.
= (stroke x R.P.M)divided by 6= piston speed in feet per min.
*use R.P.M normally driven at.
3500 fpm= excellent reliability
4000 fpm=good
4500=fair
5000=poor, anything under 3500 is best.

2)engine redline to determine life of engine.
=average piston speed(desired*) x 6 divided by stroke
*use table of average piston speed above ie: for excellent reliability 3500 F.P.M , the result will be a redline that will yield excellent reliability if reliability is no concern find redline at 5,000 feet per min. example#2 if a 390 is never redlined above 5,550 r.P.M reliability will be excellent, if you run your 390 at 7,936 rpm, it will be a very poor life expectancy.(kind of a high tech way of saying DUHH, I guess!)

3)max carb or throttle body diameter(venturi size)
=square root ofRPM* x bore x bore x stroke)divided by 108000)=venturi size in inches, this figures only one cylinder, add 15% for each of the other cyls.ie: for 8 cyls, basically double it.
*use rpm you want your power band in. this is at sea level as well, so, decrease venturi size by 5% for every 1000 feet above sea level.

4) optimum intake tract runner lenght, determined by by the capitalization of the 2nd, 3rd or 4th accoustic wave(caused by exhaust pulses) for street use 2nd pulse, 3rd pulse for mild race, and 4th for full race applications.
formula is:
2nd pulse= (1100* x one half of intake duration x .960)divided by R.P.M**
3rd pulse=(""........"" x .705) divided by R.P.M**
4th pulse=(""........"" x .538) divided by R.P.M**
* 1100 refers to speed of sound in feet per second.
** use R.P.M in desired power band

5) exhaust pipe diameter based on exhaust gas velocity, ideal velocity is 280-300 feet per second.
=(piston speed at desired R.P.M power band divided by 60)bore squared divided by pipe diameter squared)=velocity.


I have got some even more technical ones, but I thought I would post these more significant ones, can use these to build for power, and use them for finding streetability/reliability of a motor, I learned these in school, Harley Davidson performance, but they can all be applied to automotive as well.
I was bored!!!, but hey, maybe someone will find them helpful.
I thought that the venturi size would help in the discussions of throttle body size selection, of course ya gotta know the diameter, not cfm, but nonetheless.
Justin

 

On the exhaust pipe diameter formula, where the expression face is, that is a times sign, guess my computer took that as a command for expresion, also where the smiley face is, that is a :
Justin