MID-LIFT

Jon:

Mid-Lift? Now that's odd. When you're building an engine with new and different heads, different rocker arms, or different valve stem lenghts, etc, what you do is put lightweight springs under the retainers of one intake and one exhaust valve then use adjustable push rods to adjust the rockers (by turning the engine over and adjusting the push rods), so the roller tips of the rockers transition across the valve stem an equal amount on either side of the valve centerline from closed to fully open position. You also check for cleance problems between the retainer and the rocker arm, and the push rod and the head or guide plate throughout it's travel . When you've adjusted your intake and exhaust pushrods to achieve that condition, you order some non-adjustable pushrods of the same or similar length. Doing it that way there is no Over-arching or Under- arching, and any roller tip rocker arms are essentially "Mid-Lift" rocker arms.

-- BottleBob

Let me add that this procedure is for stud mounted rocker arms like Big and Small block Chevies use. Shaft mounted rockers don't have as much adjustment leeway, without milling or shimming the rocker shaft mounts.

Not sure I understand why you wrote above is a good substitute for rocker arms that have been designed improperly. Here are some links discussing Mid-Lift further:

Jon Banquer San Diego, CA

Jon:

I was just giving you an alternate perspective on rocker arm Over & Under arching. And how do you KNOW that rockers other than Mid-Lift rockers are necessarily designed improperly? If the article was inaccurate about Over and Under arching, then that calls into question some of their other assertions.

These seem to be just forum members speculating on the pros and cons of rocker arm geometry. A lot of those posts remind me of the 10 blind men describing an elephant. Each one has a piece of the truth.

This seems to offer some insight.

Better than this forum or comp.cad.solidworks where no one cares about the ugly truth.

It's the basics that never seem to get fixed / the attention they need.

Jon Banquer San Diego, CA

Jon:

Is "Mid-Lift" a better method for measuring installed rocker geometry? Probably. Do "Mid-Lift" rockers make more power? I haven't seen any data to support OR refute such a claim.

You sure jumped off on a tangent there. Do you fancy yourself the "Jim Miller" of CAD/CAM?

If you read the thread he suggested Joe Sherman to do a test. Do you think Joe Sherman will do the test he was asked to do? I don't.

LOL.

Jon Banquer San Diego, CA

Jon:

Is someone going to financially back this test, or would Joe Sherman have to eat it himself? If the latter, there would not be much incentive for him to do it. There seems to be a power play & finger pointing situation going between parties with invested interests on with this issue. There are a lot of variables to take into consideration, early valve acceleration, late acceleration, and how it affects the "area under the curve", valve bounce due to high closing accelerations, advancing/retarding the cam to take advantage of the various rocker designs and ratio changes during operation, with charge/port velocity capabilities thrown into the mix as well, to say nothing of valve train harmonics & stability. Remember, in a V8 running at 8,000 RPM a valve is opening and closing some 66 times per SECOND. A lot is happening in a short period of time, so small changes can have drastic effects. Then you possibly have racers that may not wish to give out ALL their HP building secretes for fear of losing their competitive EDGE.

At least you TOTALLY haven't lost your sense of humor.

Agree, there wouldn't. He's after higher horsepower gains. I think it's all he cares about.

Isn't this almost always the case?

Joe's edge is years and years of trial and error at the expense of a more in depth understanding. Typical race engine builder. Mid-Lift might make his engines last longer and that's something I don't think Joe really cares about.

I expect much less from people now and I'm frequently rewarded with what I expect.

Jon Banquer San Diego, CA

So, with all of that said, do the same rules apply to a "shoe" type rocker?

If so, then what would have to be changed, the rocker, or the location of the shaft, relative to the valve tip?

"D"

Why wouldn't you ask the source this question rather than settle for anything else?

Jon Banquer San Deigo, CA

Why wouldn't you answer the question, seems to be a fair one.

"D"

I don't have an opinion on rocker geometry (yet). Might be quite awhile before I form one.

Jon Banquer San Diego, CA

When you do have one, I would like to discuss it with you.

"D"