General Cylinder Head Flow Numbers discussion

[HawkBrosMav]

Originally Posted by SSDiv6

Port velocity and optimize the valve opening and closing events.

Curious what you man by "optimize the valve open and closing events" when it comes to the valve job or flow characteristics of the cylinder head. Maybe I'm just completely naive, but wouldn't this been completely controlled by camshaft design after you already know the flows and velocities of the ports?

[Larry Hill]

On the V6 truck engine I went to core suppliers to get the best sets of heads for each approved casting number. How I judged the heads by valve protrusion into into the chamber. I bet I looked at 200 + pairs of heads. I think I had 4 or 5 sets of heads of each casting number to clean and test on my flowbench. Most of my winnings from Atlanta were used to buy the bench Jimmy Bridges did my first set heads for the truck. I think he picked the two best out of six.

[Ralph A Powell]

You want a port that continues to flow well past your max lift point and not go turbulent and is quite on the bench!

[HawkBrosMav]

Originally Posted by Ralph A Powell

You want a port that continues to flow well past your max lift point and not go turbulent and is quite on the bench!

Ralph not being in the room when the heads are being flowed and not owning my own stuff to do it... is there a way to know if the port is quiet by looking at CSA and port velocity? Do I just need to ask the head guy if they were quiet?

How far past max lift would you like to see it "flow well" .050?.0100? more? and by "flow well past" do you mean the CFM should still be increasing or just not backing up a lot? if it just holds the peak CFM from say .350-.500 at a fairly constant CFM but isn't gaining anything or dropping off at all is that okay?

Thanks
Brad

[SSDiv6]

Originally Posted by HawkBrosMav

Ralph not being in the room when the heads are being flowed and not owning my own stuff to do it... is there a way to know if the port is quiet by looking at CSA and port velocity? Do I just need to ask the head guy if they were quiet?

How far past max lift would you like to see it "flow well" .050?.0100? more? and by "flow well past" do you mean the CFM should still be increasing or just not backing up a lot? if it just holds the peak CFM from say .350-.500 at a fairly constant CFM but isn't gaining anything or dropping off at all is that okay?

Thanks
Brad

Brad,

It needs to be on the flow bench and the quietness is the sound of the air. Usually test 0.100" ~ 0.150" past your required maximum lift and don't worry about the behavior past that limit.

[Dissident]

Folks interested in flow bench testing:
These days I can't hear worth a dip, but I do know a fair amount about flow bench testing and there are multiple ways to discern the stability of airflow in the cylinder head or manifold without hearing....
The cylinder head should be tested with the manifold and carb/throttle body attached so the "real" flow test is indicative of what the system is doing. That kind of testing is a bit more difficult, but much more meaningful. From that flow data, potential power can be predicted as can the rpm at which peak power will occur. Measuring a load of intake manifolds is worth the effort. Unless one follows the outline that I posted previously. You might find some worthwhile tips in HPBooks, Engine Airflow

Regards,
HB2
Dissident

[Billy Nees]

You guys might want to take a look at the "odd" little rule change that's in the 2020 to 2021 rule changes. It just might have been put in there for a reason.

[GTOMayhem]

Originally Posted by Larry Hill

How I judged the heads by valve protrusion into into the chamber.

Was that to minimize chamber volume?


Rick Thomason
GTOMayhem

[Larry Hill]

I’m not a head guy but with the valves hight in the head, if you had to sink one to get the cc’s correct it usually didn’t hurt the flow real bad. In most of the old cast heads one or two runners are just turds and are difficult to get to respond. I have made a few test valves.

[SSDiv6]

Originally Posted by HawkBrosMav

Curious what you man by "optimize the valve open and closing events" when it comes to the valve job or flow characteristics of the cylinder head. Maybe I'm just completely naive, but wouldn't this been completely controlled by camshaft design after you already know the flows and velocities of the ports?

I should have explained better. Optimize the velocity, and like Ralph Powell said, go at least 0.100" ~ 0.150" past your maximum lift and you want a quiet port.

Seen too many heads with big flow numbers and low velocity that do not make power. Your valve job angles are also critical and different for each head manufacturer.

The reason why you want to have a good flow past your maximum lift is because you can make more power by doing a controlled loft of the valve past your maximum allowed lift. The cam lobe is designed to toss the lifter and increase valve lift to make more power while still checking legal during a static lift inspection.