Can they be manipulated? I know that differnt dyno's the numbers can be manipulated by the tuner and some dynos read higher or lower than others.

But in regards to measuring CFM's when doing a head can they be manipulted to read higher or lower than a different head?

Also if Example A head flows 12 CFM more than Example B, does that equate to a larger gain in Hp over example A or are we talking about 1-4 hp difference?

 

Well, there are factors when measuring CFM that can make a difference in flow. Like if you use a computer or manually figure out the flow meaning mistakes). You're attempting to make the flow numbers as realistic compared to real flow as possible. ie. Some ppl flow heads with the intake manifold connected. I used to flow them with putty aroung the ports to get rid of the sharp edge, and act as the manifold.

Ive used both the manual method and flow computer on a superflow 600 machine.

Flow does not necessarily = hp. If that were the case you'd open the ports as far as you could without running into a coolant passage.

On the intake side youre attempting to increase flow while maintaining good atomization and swirl. On the exhaust youre trying to remove restriction and try to repel reversion.

If the ports were super big you may risk having of exhaust gas entering back into the combustion chamber.
Look up velocity- very important

Youre freeing up hp yes, but youre also manipulating your power curve too.

 

So is there a standard way of checking CFM's and if you get all of the correct atmoization and swirl to the best of the head ability?

How does one know when the ports have been milled too far?

has any shop pushed the limits of a head to wear they see a negative or a drop in Hp after doing too much?

 

good thread, subscribed

 

Unless flow data between two heads is performed on the same brand and model of flowbench, set up identically and using the same pressure drop, a realistically accurate comparison would be difficult. There are far more variables to be considered with a flowbench than with a chassis dyno.


That depends on many other variables. Flow data just gives one an idea of the performance potential of the head. It says nothing for the efficiency of intake, cams, exhaust, turbine side, and many other variables. But generally speaking, a better flowing head means more power potential, but not necessarily more power.


With an EVO head, breaking into a water jacket is usually a good indicator.