rocker arm geometry on eq vortec head

[BLstangin]

I did a little more work with this today and I got my hands on some crower aluminum body centerline rockers and redid the pushrod length using the midlift technique. I came up needing a 7.400 pushrod just like before and after checking the pattern it was still way towards exhaust and under .030 sweep but I was almost .030 short on lift after lots of shorting the pushrod .050 at a time I ended up with a .045 wide sweep closer to the center of the valve with the stock 7.200 length and was within .005 of what the lift is supposed to be on both the intake and exhaust. I think this is as good as it's gonna get and now the pushrods come though the center of the pushrod hole instead of the bottom of it. I'm pretty much convinced the whole problem is the stud location is to close to the valve as now my pattern looks more typical of what I expect to see with a .100 long valve.

[wyrmrider]

going .200 shorter on the pushrod
you are starting with the rocker angled way up
as you come to max lift on the cam the rocker is more tangent to the valve and of course you are going to get more lift
but
don't do it
lots of side strain on the valve
and the valve is not really doing what the cam grinder intended- lots of action later leads to valve float extra ratio over the nose where the cam is trying to let the springs control the valve- stop it and start closing it
you want more lift get a higher ratio
otherwise you will rpm better with the correct length pushrod
comments??

[Geoff2]

For whatever reason, the rocker you have tried are too big for those heads. That is, the distance from the centre of the fulcrum to the centre of the axle of the roller tip is too long, by about 0.050" judging by the pics. You mentioned Crower rockers. Excellent rockers. I would call Crower & tell them you need a rocker that is 0.050" shorter. Hopefully they will have the dimensions of their rockers recorded & one from another engine will fit.

[BLstangin]

Here is the pattern with the 7.400 pushrod and the crower centerline rocker which is backseat .050, this is the short rocker that crower makes. For some reason it comes up .030 short on lift though with this pattern?

[wyrmrider]

pattern looks good
do not sweat the .030 lift, no rocker ratio is perfect just advertised
are those patterns parallel with the line of valves or cocked? if cocked get some adjustable guide plates

[BLstangin]

They are parallel

[wyrmrider]

looks like you are good to go
must have been the camera angle on a couple of those earlier pics
Whew

[A_VAS]

For whatever reason, the rocker you have tried are too big for those heads. That is, the distance from the centre of the fulcrum to the centre of the axle of the roller tip is too long, by about 0.050" judging by the pics. You mentioned Crower rockers. Excellent rockers. I would call Crower & tell them you need a rocker that is 0.050" shorter. Hopefully they will have the dimensions of their rockers recorded & one from another engine will fit.

I thought this would be the case too...called and discussed with Terry at crower and got no help at all. Couldn't supply me the dimension of the rockers...after multiple messages I gave up

[gowest]

As a quick check of geometry, I've heard it mentioned that if the center of the roller tip is at the same spot at full lift as it is at zero lift then pushrod length is correct. I did an engine with mid lift on valve side and it sure looked like the quick check method held true.

[wyrmrider]

Great reminder, I'd forgotten that one
wonder where they would be with a .200 different pushrod length...