Variable hydraulic lifters for 440 engine
When you "time/degree" a cam, this is the thing you are moving; the intake closing angle. Yes, of course, all the other points are simultaneously moving, but the Ica is the only one we are usually concerned about.
So that is when I put 2 and 2 together, why my intake vacuum was so low.
So, as this cam has .008" @ 68* After BDC lift, the valve will close even later, it is more than likely the intake valve is fully closed in the 75* area.
Yes, i agree that the when the cam was advance 14* the vacuum should have been higher as a lot less air is being pushed back in the intake.
But at that time still the valve would seat around 61* After BDC (compared with the assumption above) which is still late, and might not improve much on the vacuum as there is still heaps of air being blown back.
However, in my case, I didn't believe that it was the only reason. I eventually traced a portion of my problem to another source, fixed it, and then I had a monster-engine.
I think we have searched for all other sources already on this one, but anyway i want to ask where did you find the other problem?
I don't know if a different type manifold would help? Now have a dual plane intake but what if i used a single plane intake would that reduce the effect of the blow back?
Because as 1 piston is pushing air back in the intake, it will be spread more rapidly in the intake and another cylinder that is still filling might "absorb" this partially, reducing the effect and increase vacuum?
I already got a reply from Rhoads and they recommended using the V-Pro lifters and set them at .030" to provide max. leak down.
This should reduce the duration around 15* @.050" lift and increase manifold vacuum up to 3".
The only thing i am doubting about that is that it will increase the dynamic compression ratio again, and my cranking pressure will also go up.
