Originally Posted by flyingputz
I need some affordable pushrod recommendations for this vortec headed 383. Spring pressures are 130# at the seat, around 340# open. I don't think I should chance the stockers, even though the geometry is real close. Summit has a special deal on TFS pushrods right now. Anyone have any opinions on these? Are chromoly 5/16" plenty strong, or will 3/8" rods fit through stock holes? Too late to enlarge holes, as intake is installed.I also have some concerns with the mid-lift theory. Jim says use the roller tip axis, not the valve tip. I notice some roller rockers (mine) have a rather large (1/2 ") roller tip, while others have a considerably smaller dia. tip. Should this factor in when measuring? A larger roller would automatically equate to a longer pushrod, correct? Wouldn't a larger roller also leave a wider footprint on the valve tip, ie, a larger contact patch much like a larger tire does? I've got a nice footprint (.050") just slightly exhaust side of center, but at mid lift, trunion axis to valve tip is 90* to stem, but I have to go almost full lift to get axis to axis at 90* to valve stem. I am losing some accuracy because I'm not using a solid lifter for measurement. Any thoughts?
No guide plates? The stock Vortec pushrod hole is ~7/16", so you should
be OK using a 3/8" p-rod, but this still needs to be checked because of variations in castings and manufacturing. If you can, get hold of a 3/8" p-rod and try it in each position- int. and exh, both sides. The problem is, w/o the engine running you can't see where the p-rod actually rides. And what you do not want is for the p-rod hole in the head AND the rocker arm's tip to both try to guide the p-rod (assuming self aligning rockers). But you still should be able to get a good idea of whether there looks to be a problem or not.
You can use a thick wall (0.120") 5/16" p-rod, but they wouldn't be the ones you're looking at now. And I have heard a 3/8" p-rod at 0.060" is more resistant to flex than a 5/16" p-rod at 0.120"...
You really need a solid lifter w/the same dimensions between foot and p-rod seat (or a hydraulic lifter filled w/grease, or tiny stacked washers) to do your measuring with. If the lifter's compressing, that skews what you're seeing.