Why is it...

MP states to get the duration @050, multiply the advertised duration by .850. It was just easier for us MoPar guys to say I’m running the .590 cam. Right there, if you were an engine guy or racer, that this was a big solid cam designed to take advantage of ported heads and high compression. Just stating the cam size should tell you most of what the engine should be built up like.
(Or at least if you were a serious fella.)

FWIW info for the new guys to camshafts:

Two different cam grinders can have the same advertised duration on there cams but wildly different numbers @050.
Also, via comparing any cam @050 should be done. When two cams are compared @050 and have the same numbers, there cruise and power bands are similar but not the same because there’s more to a cam than the advertised and 050 numbers.

Two cams could have the same advertised and duration @050 numbers but have different lifts at different points on the lobe. It is possible to find this. But that’s looking through hundreds of cams from all grinders. Good luck!
LMAO!

But! What you’ll find is cam A is a streetable cam and cam B is a street strip cam and then cam C is a drag cam. There numbers are very similar. You can see this in some Ford racing camshafts.

A Hyd cam is designed for longevity and quite operation in a general performance arena.
The solid cam more rpm and overall performance. S/S type of grind.
The solid roller more strip.
Let’s just say…. The numbers can be seen something like this;

Hyd. ———-- 280/230 - .480 - Gen performance/cruiser
Solid ———-- 280/238 - .500 - More serious hot rod
Solid roller —- 280/244 - .550 - race grind

This is why the industry went to the 050 for comparisons. It helps level the playing field.

What these numbers are telling you is how aggressive the ramp rate is on each cam. But you can also look at lift rates anywhere you like. Commonly done in .100 Increments.

What a lot of people don’t know is a aggressive solid flat tappet cam can have a quicker off the seat rise of the valve than a solid roller. I don’t know if it is possible with the Chevy lifter being so small, but getting into a larger Ford lifter helps. Even better is our .904 lifter size. This is only beat by a 1.00 lifter. At the moment, IIRC, and I’m not betting on that one right now, but I think it was GM’s Caddy or Oldsmobile.

(Someone correct me here if I’m right, wrong or other.)

The only way you can actually get to a roller cam performance (or just a hair shy off) is with a mushroom lifter.

The rollers main advantage is the ability to open the valves up quicker and higher as well as hang the valve open longer since the roller wheel is “rolling” around the lobe which can get very aggressive except on initial lift. To what exact degree or length of time in lift is another totally dependent cam lobe grind design.

To top this off, there are more numbers to look at that can change the way the cam acts and performs. It can be a heck of a time looking at all the numbers and getting a grip on what’s going on with them. Even though the numbers can look the same they can be very very different in performance.