General Cylinder Head Flow Numbers discussion

[HawkBrosMav]

Hi All,

I'd like to keep this discussion as general as possible to encourage dialogue on the topic. If you're open to disclosing specifics that is totally up to you, but I feel like there are probably a few opinions on this topic and it could be a bit of an interesting discussion.

Basic question here is when you have your heads done or you do them yourself in legal stock eliminator form (whatever that means in this day and age to you individually) what is the most important improvement in flow characteristics you are looking for? 80-90% of us have less than .500 lift, so are you looking to see the numbers from .400-500 to jump? Are you looking at port velocity? are you looking at average from specific lift values? something else?

This isn't really a discussion on "HOW TO GET THERE" but more with your end results compared to where the heads started stock what makes you decide the heads are going to make you .800 .900 1.00 under capable verse the stock castings?

Brad

[SSDiv6]

Originally Posted by HawkBrosMav

Hi All,

I'd like to keep this discussion as general as possible to encourage dialogue on the topic. If you're open to disclosing specifics that is totally up to you, but I feel like there are probably a few opinions on this topic and it could be a bit of an interesting discussion.

Basic question here is when you have your heads done or you do them yourself in legal stock eliminator form (whatever that means in this day and age to you individually) what is the most important improvement in flow characteristics you are looking for? 80-90% of us have less than .500 lift, so are you looking to see the numbers from .400-500 to jump? Are you looking at port velocity? are you looking at average from specific lift values? something else?

This isn't really a discussion on "HOW TO GET THERE" but more with your end results compared to where the heads started stock what makes you decide the heads are going to make you .800 .900 1.00 under capable verse the stock castings?

Brad

Port velocity and optimize the valve opening and closing events.

[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

[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.

[Glenn Briglio]

Originally Posted by SSDiv6

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.

So how much valve loft are we talking about?