General Cylinder Head Flow Numbers discussion

[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?

[SSDiv6]

Originally Posted by Glenn Briglio

So how much valve loft are we talking about?

On circle track restricted engines, with a combination of a specific valve guide height and lobe design, I have seen a valve launched as high as 0.160" during Spintron testing. Because of valve to piston clearance, it is a bit of trial and error.

[Stan Weiss]

Originally Posted by SSDiv6

On circle track restricted engines, with a combination of a specific valve guide height and lobe design, I have seen a valve launched as high as 0.160" during Spintron testing. Because of valve to piston clearance, it is a bit of trial and error.

Do you have an idea how much more area under the curve there maybe verses the dwell type setup we ran years ago?

Stan

[SSDiv6]

Originally Posted by Stan Weiss

Do you have an idea how much more area under the curve there maybe verses the dwell type setup we ran years ago?

Stan

Stan,

I will have to look at my notes and I will share the info.

[Glenn Briglio]

Originally Posted by SSDiv6

On circle track restricted engines, with a combination of a specific valve guide height and lobe design, I have seen a valve launched as high as 0.160" during Spintron testing. Because of valve to piston clearance, it is a bit of trial and error.

Got to be pretty destructive application and not for roller lifters.

[SSDiv6]

Originally Posted by Glenn Briglio

Got to be pretty destructive application and not for roller lifters.

Just on restricted travel and solid lifters. As long you have good quality lifters and checked the spring pressure often you are good. Prior to the allowance of aftermarket roller rockers, you needed to have a box of spare OEM rocker arms because the tendency of the pushrod to go thru the rocker arm cup.

[Stan Weiss]

Originally Posted by SSDiv6

Just on restricted travel and solid lifters. As long you have good quality lifters and checked the spring pressure often you are good. Prior to the allowance of aftermarket roller rockers, you needed to have a box of spare OEM rocker arms because the tendency of the pushrod to go thru the rocker arm cup.

Been there done that.


Stan

[Adger Smith]

-Head A stock completly untouched
-Head B has flow characteristics that make me feel like it will be okay (.5 under)
-Head C has flow characteristics the make it a record setter

IMHO
And Head C has correct port volume, but probably has a larger CSA at several key places in the port.