First off, changing from 1.5 to 1.6 gains you about 7% in lift. So a cam that gives you .450 lift with the 1.5 will give you .480 with 1.6. Thats .030 at max lift only, the area under the curve is increased very little. It would take more calculus than I can do in my head tonight to figure it out exactly so think of it like this: You are increasing the size of the nipple, not the whole boob. Ever hear of anyone getting a nipple-job?
Setting up a valvetrain is not a boob job. If I wanted .600 lift cam @ 260 of duration, I would have bought one. What I wanted was something closer to a hydraulic roller profile without spending a $1000. This is not calculus but basic math. I used my cams profile as an example. Obviously I would much rather have the profile on the 1.6 side.
Cam lift---@Valve w/1.5 Rockers-----@Valve w/1.6 Rockers
.100----------- .150--------------- .160
.150----------- .225--------------- .240
.200----------- .300--------------- .320
.250----------- .375--------------- .400
.300----------- .450--------------- .480
.320----------- .480--------------- .512
The main drawback however is the increased loads on your valvetrain. The loads don't just increase by 7%. Sure, the cam and lifter faces now experience 107% of the force of the valvespring (and 107% of the mass of the valve). But thats static pressure, we are accelerating that valve back and forth so loads increase exponentially. More wear, more HP losses in the valvetrain.
Loads do increase exponentially in a dynamic enviroment but the 7% increase in load will not. The load only increases by a 7% relationship to the valve spring pressure at any given lift. Ford 351C engines run a 1.73 ratio rocker from the factory without any problems. A 351C engine that I had built 20 years ago ran just fine for 70K miles, again with Crane rollers. The same load increases would also be seen from a 7% higher lift cam or 7% stiffer springs.
Geometry is a function of the relationship between pushrod length, valve tip height, and pivot point. With shaft mounted rockers the pivot is pretty much fixed, so you either change the length of the pushrod or the valve by using a lash cap.
Changing the pushrod length does nothing to the tip/stem geometry on a rocker shaft engine. Pushrod length is changed only to establish the correct preload and adjuster screw position.
There are two geometries that are spoken of on a LA engine. One is on the pushrod side, and isn't all that great from the factory. Anything that can be done to straighten it out will add stiffness, strength and increase reliability as well as add power through the reduction of flex.
The other is the relationship between the rocker tip and valve stem as a function of the pivot point at the rocker shaft and the valve stem height. Rocker shaft spacers can be used to raise the pivot point and as you say, lash caps could be used, but a good valve job to start with would have alleviated the situation.
Fitting oversize valves is a time honored way to raise the valve heads relative to their seats, as you do recess the valve a little every time you do a valve job. If the seat is recessed much at all the seat shrouds the valve at low lift. You'll gain more from a good valve job than you will with fancy rockers,
And you'll gain reliability and power when you combine a good valve job with a well set up valve train. My heads flow quite well up to .520 lift and I will gain nothing leaving my lift @ .480. Why not get a bigger cam? Because of my specific application. This particular engine is in a 4WD truck that I need to keep as driveable and as efficeint as possible. In other words, I didn't want to increase my duration. It's all about the combination and application. Higher ratio rockers are not a cure-all and aren't a instant hp bolt on, but they have their place.
and maybe save enough cash to buy a set of implants (or tires).
I saved over $80 by buying the 1.6 Crane Golds vs. the 1.5 Crane Golds. IIRC I paid $225 for them and thats with hardened rocker shafts. That $26 more than a set of crappy Proforms. You also never mentioned how much a poor quality valvetrain will flex under load.
I know nothing about implants, nipple jobs or boob jobs but I do know valvetrains.
