Worked on rocker arm geometry. Used Comp checking pushrod #7702, 6.8-7.8 inches long. For LA block, magnum heads, and flat tappet hyd cam, ended up with 7.65 pushrod length for Comp magnum roller tip rocker 1.6 ratio. I've decided for now to use the magnum rockers on the exhaust, and Crower 1.8 full roller rocker on the intake because...
I always knew the mopars had a 59 degree lifter angle, didn't mean much until today. So I'm checking cam lobe lift, valve lift, etc and seemed like I had the wrong cam, the valve lift was not there. I checked the cam lobes, its the right cam. Well, that 59 degree tappet angle means the lifters are moving sideways as they move "up". The result is a loss of lift to the tune of 5-6.25% in my case.
What this means is the .547 exhaust lift I thought I'd get with 1.6 rocker turned out to be .514 lift. (6.25 % loss) That's pathetic.
Part of the reasoning behind today's roller cams is "the most lift for the least duration". The measely 514 lift is not "the most" in my book.
ONe benefit of the magnum cylinder heads is all these rocker ratios are available for small block chevy. If I use a 1.8 rocker on the intake, then subtract the 5% loss of lift that I measured for that rocker, the end result is a 1.71 rocker ratio. Just a little less than used OEM on a 1965 Ford 352 truck engine.
One way to beat the opponent is to study what they are doing. Obviously the ramchargers and mopar weren't looking.
So in the end I'll have 0.563 intake lift using 1.8 rocker, and 0.514 exhaust lift using 1.6 rocker. I'd like a little more exhaust lift, but the budget $$ can do only so much. I'm going with the Crower's because they have a good reputation, and I don't want roller needle bearings floating around from a busted cheap rocker. From what I've read, current thinking is the sky is the limit on intake lift, where as the exhaust need duration to expell the fumes.
The old super stock drag racers back in the 70's knew about flow "Dwell time". Even if the port stops flowing at 0.50 lift, don't just put in a cam with that lift, because that lift is only seen for an instant. Instead, put in say a .525 lift or much more, so the port 'sees' that peak flow for a bunch of crank degrees rotation, not just for an instant.
So I did a quick check on another cam I have, happened to be a small block mopar Comp 268AH-10. The rated lift assumes your getting ALL of the rocker lift, no loss due to 59 angle. So in the end, the "extra lift" (0.464) of this particular Comp cam is used up by the reduced rocker ratio. The 1.5 ratio, minus 5% equals 1.425 ratio, so the lift at the valve is about 0.441 which is real close to old 340 auto cam specs.
So the lift stated on some (or all??) the cam cards is NOT the actual lift the valve will see for a mopar V8.
I mocked up a brass pushrod tube for the intake ports, pressed it flat against the port wall. Looks good, pushrod clears, and won't have that big choke in the flow. So I"m told, the port flow should NOT have rapid changes in velocity, which is exactly what the pushrod pinch does especially on the magnum heads intake ports.
First photo shows the 90 degree cylinder banks, second pic the brass pipe is the lifter angle ( not parallel to the cylinder), Theres an exhaust rocker full open, and pushrod clearance with valve closed (not much clearance, but its there). Pushrods move toward the rocker stud as the valve opens, so plenty of clearance when valve is open. I aligned the pushrod guide plate with the intake pushrod, but photo shows the exhaust pushrod is OFF so rocker does not align with valve, need to cut and weld the guide plates to correct this. Last pic is the brass tube flattened to intake port wall. I'll epoxy the tubes in place when they go in for real.
