Hangwire

I'm curious as to what goes into the decision making process when deciding which side of the head to put the dual valves on and which to keep single on 3v heads.

What are the benefits/downfalls of having 2 valves on intake as opposed to the dual valves on the exhaust side?

What variables are there that could have significant effect on the above question? Such as.....having LTs on a cylinder head with 2 valves on the exhaust side.

What are your opinions on the true benefit of having that extra valve on either side as opposed to a 2v setup?

67mustang302

Exhaust leaves under high pressure differentials, sometimes over 5 ATM pressure ratio, whereas intake is drawing air in at slightly less than 1 ATM pressure ratio on a n/a engine, and maybe only 2-3 ATM on a blown application(approx 29lbs boost would be a pressure ratio of about 3). With equal numbers of valves the intake valve(s) are larger, or in odd number multi valve setups, there are more intake valves. It's basically to account for the fact that it's easier to get exhaust out than fresh charge in, so the intake side is bigger. Same reason the intake port is bigger than the exhaust port.

Multi valve configurations when properly designed can allow for better flow, particularly at high rpm. But they're also more expensive and complex.

GreyStang

6v >4v > 3v > 2v

67mustang302

You don't really gain much, if anything past 4 valves actually. The compromises in chamber and port design as well as plug placement offset any flow benefits. Yamaha messed with a 5v setup years ago, and the chamber design was such that the engine needed around 50* total ignition timing to get good combustion, the plug was way far from the piston and the chamber design impeded combustion rates. And especially when you consider the huge cost in developing a 5 or 6 valve head, it's just not worth it.