by twinturrbo406 » Fri Aug 21, 2009 12:59 am
Well, from my experience, the 2 main things that will more or less determine that ratio for you will be obviously, the limitation of the head it's self, cause when you start getting an intake port close to 300cfm before .600 lift, it's really tough to beat in that lift range with the exhaust port..... so, what we've seen here in Fl, being sea level, it's nothing to push it to 75%-78% or slightly more.... depending on where the intake port is at..... we have a lot of crap filler in our fuel down here, so we try to help the exhaust cycle out with as much of the "blow-down" event as possable.... there again, the off the seat performance is very crucial.....
Most, or at least some people don't realize it, but even with a blower, only half the motor is Forced Induction.... that poor exhaust needs some help over there, lol...... and for the 2nd main thing, that would be the type of power band you are looking for, as far as what exh/int% you should target, the higher the peaks, the more, to a certain degree, the exh/int% need be..... i've built a few 406sbc's with almost 79%exh/int ratio's and they all run high tens, high compression changes everything, these are pump gas engines and pull really strong to 7,200-7,300rpm.... solid rollers of course.... ???