You didn’t say what heads you are using so I’ll just make general statements here. If you read Mike’s tech pages you should have had this cleared up in your mind because it’s rather simple to understand but more complicated to achieve.
Any shaft system, ANY shaft system is the same. The relationship between the centerline of the shaft, the tip of the valve and the amount of lift must be engineered into the original location of the shaft. And the designed rocker arm geometry itself changes things. You can make a 1.5 ratio rocker several different lengths and each one will change the geometry if you start swapping them out. It’s as simple as that.
Any one of those parameters you change, or all of them means you OUGHT to correct your geometry. It’s that simple. So let’s say you buy some Trick Flow heads and TF established the geometry using brand X rockers and you use brand L rockers the probability is the geometry will be wrong. Valve stem height is critical. Let’s say with the above heads you want to make an upgrade and you decide you need to use .100 long rockers you have now affected the relationship between the tip of the valve and the centerline of the shaft.
It used to be the only way to correct this properly was to mill the rocker stands down and use blocks to get the geometry in shape. Mike’s‘ shims are by FAR a easier, simpler and cheaper than using blocks. And they work.
How many times have you seen engines where the rocker and the retainer hit with relatively small diameter springs? I see it all the time. And the number one response is put a beehive spring on it. Can you do that? Sure. Is it correct? Not even close. You didn’t fix the core issue, you just used a band aid where you really needed an amputation.
I can tell you for a certain fact if you change any one of the above parts of your valve train as in going away from whatever the OE design criteria was you’ll certainly need to correct your geometry. Start changing more than one of those criteria and you will have issues. You’ll be down on power. Your valve train will be unstable. You will lose RPM capability. And you’ll fail parts. The number one killer of rocker arms (outside of cheap junk) is bad geometry.
Invariably, the shafts will need to go up and away from the valves. It’s worth every penny to measure your particular set up and then see how much correction you need. I think you’d be surprised how much you’ll need.
I'm doing a 5-speed conversion, and this is the motor that was in the car that I'm playing with while I'm building the real motor. It's a stock '71 383 Magnum with headers that I'm changing cam and intake on, and since I need to do this right on the other motors I'm building, I may as well start on this motor. I had Comp rollers, so I tried those, and the pushrods were too long. I read Mike's B3 page, and I started this thread to clear up conflicting information I was reading. His page makes sense, but then again, there's AndyF who set up many different rocker combinations and didn't find any improvement in power. I still get the same max lift with the rollers being too low, or the stock rockers being too high using the perpendicular rocker at half lift method. My final decision is just saving the Comp rockers for the stroker motor, using the stock rockers on this one, and getting 8.50" pushrods, which are .075" shorter, to give me .055" lifter preload.
