Hydraulic lifters; all else being equal, will a longer valve stem yield more lift?
Hydraulic lifters; all else being equal, will a longer valve stem yield more lift?
I don't see how. The lifter will adjust so that stem plus lifter length will stay constant. That's kinda the point. If "stem plus lifter" increases, the valve won't seat.
Nope. Valve lift is fixed by two things; lobe lift and rocker ratio. Changing the valve stem height only changes the angle at which the rocker tip meets the valve stem (which can have negative effects depending on the geometry).
This holds true regardless of the lifter type; hydraulic, solid, roller, flat.
There is a possibility with shaft rockers where changing pushrod length or valve length will affect valve lift because it changes the effective rocker ratio.
We're talking a few thousandths, though, nothing terribly significant.
Shimming valves and cam towers used to be done in the 240Z world a lot because it altered the rocker geometry and would net more valve lift for the same camshaft. Or maybe it was shimming lash adjusters and cam towers. I forget, it's been a while.
Knurled wrote: There is a possibility with shaft rockers where changing pushrod length or valve length will affect valve lift because it changes the effective rocker ratio. We're talking a few thousandths, though, nothing terribly significant. Shimming valves and cam towers used to be done in the 240Z world a lot because it altered the rocker geometry and would net more valve lift for the same camshaft. Or maybe it was shimming lash adjusters and cam towers. I forget, it's been a while.
That's what I was thnking of. There ARE a few engines where just a few thousandths increase in lift means the difference between fully unshrouded valve flow (mo powah and efficency) and leaving significant torque on the table. The Ford CVH series engines are one of those that the rocker ratio changes with valve length. When the EScort GT was introduced, Ford increased the intake valve stem length a bit and it increased the max lift from .429 to .437. Not much, but they found an instant 10 to 12 hp with the old 1.9 GT engine.
Anyhoo, the exhaust valves in the head I just got from CHI had the stem tips refinished. When I compared it to a set of NIB Melling exhaust valves, the NIB valves are .030 longer. Multiplied by the 1.65:1 rocker ratio that means an increase in exhaust lift of .0495. I could actually improve exhaust flow enough to matter a little in this engine (2.0l SPI verision) because the bowl area is marginal, even with proper port/bowl work. So, would GRM use the longer valves in this case?
That's not the way it works. Adding length doesn't translate to an equal amount of extra lift. It's more like, total lift is affected by one or two percent. So .500 lift might be .510".
The 240Z guys were raising cam towers .100 or even .200 and they weren't seeing .150 or .300 extra lift.
Don't think "added lift", think "slightly altered rocker ratio".
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