Some info that might help. . . .
If these engines were efficient, a cam having a duration of 228°, at a lifter rise of 0.050", should easily produce well over 700 HP, 'IF' the cylinder heads flow (as they should with a 2.165" Intake valve) ~368 CFM.
In fact efficient NA Engines having that cylinder head flow, as well as the correct camshaft can make ~900 fwHP on an Engine Dyno.
The camshaft above should make good HP to ~6,700 rpm.
While it is not easy to get a cylinder head to flow 100 CFM / Sq" of valve area, which is about what 368 CFM is, as a 2.165" valve has ~3.68 Sq." of flow area.
I am not going to get into valve lift requirements here, as that is very dependent on not only intake manifold pressure, but also on the 'Density Ratio', as fitted against the cylinder head flow and velocity profile, as well as the camshafts duration.
However let's assume the head will flow 368 CFM.
In this case we use the entire valve area, not just a fraction of that area, such as the 90% rule.
=> (2.165^2 * 0.7854)= 3.68 Sq."
So while that might sound easy, but believe me. . . .
Even well ported, low port entry cylinder heads have
difficulty achieving a flow value of 100 CFM per Sq." of 'Valve Area', the velocity across the valve seat, or MCA must be sufficient / but must not go into velocity choke, and the head must also have a well developed port.
Now let's solve for the
velocity across the valve . . .
=> ((368 * 2.4) / 3.68)= 240 fps. <= This is a good velocity value for ported heads for this engine platform.
***The velocity across the valve seat will be much higher. That number will be dependent on if the porter, ported the valve throat???? The valve throat on stock heads serves as the Minimum Circular Area or (MCA) and is ~2.61 Sq." If we use the 90% rule, it should be ported to 2.98 Sq.". A good value for these engines is 2.87 Sq." I can assure everyone that 'Not All Porters' perform the above operation(s).
-Velocity through the MCA - Here we will see just a small increase in the MCA can make big differences-
1) With an area of 2.61 Sq." with a head flowing 368 cfm will have a velocity of 338 fps and will be velocity choked.
2) With an area of 2.87 Sq." with a head flowing 368 cfm will have a velocity of 308 fps. This 'Might(?) work / Depends.
3) With an area of 2.98 Sq." with a head flowing 368 cfm will have a velocity of 247 fps. This will work well with our engine platform!
How can one tell if the cylinder head has been ported?
Many Trick Flow Cylinder heads sold to members of this forum were the 255 CC LS3 Head.
When returned after so called porting, the ports still measured 255 CC's?????
So one desires at least three things when purchasing heads.
1) The flow profile @ 28" of Water Drop / The industry standard.
2) The velocity profile
3) The runner size given in CC's
So, port your heads. Look over both the
cfm and velocity profiles and then carefully chose your camshaft. .
Cheers
