Cam ramp design

[Tony Z]

I have 2 cams at home, one is an 86B and the other a 121/125. What I noticed when comparing the two is that the 121/125 has much steeper ramps and the base circle is cut a lot lower.

If you run the thought process thru your head....
A high ratio rocker adds 27% more lift than a stock one. Which means that the lifter has to move less and so does the pushrod. Less intertial weight to overcome by the springs to push them back (plus you also have 27% more spring pressure pushing them back) which means yuo can rev the engine a fiar bit higher, given the same lift. Remember, you have less distance to move the components, as well as less inertia to overcome because their speed is less, but then you have the double effect, as your pushrod and follower is now "seeing" a higher spring pressure. So in theory, you could run a slightly lower spring pressure for the same revs assuming the same lift and opening profile.

The cam profile can be slightly milder on a ratio cam, but the rocker will enhance the speed of lift, thereby keeping a fast lift profile. This can work one of 2 ways, either the cam can keep the radical ramp and the valve will open even faster, or the ramp can be made "softer" for long life and the valve will still follow the non ratio "opening profile".

Dont forget that your cam lobe is also trying to push the follower down (or up depending on cylinder), not only outwards. So by having less lift on the cam, friction is slightly reduced. If your cam profile is slightly softer, you will prob find a few extra hp if the valves open on the same profile.
Too steep a cam profile does cause wear, as I found out in my old 1600...

[1500SBR]

Tony Z,

Thanks for the reply, I hear you. But in practical terms I understand I shouldn't go through all the trouble of replacing my W140 with 1,25 rocker and Engle 6602 springs with a FK 87 with 1.4 rockers, because I would have to stick with the 6602s anyways right??

I mean in theory there is benefit to a certain extent, but my question now is: how much? would it actually make a difference in my engine. Would it live longer? Would it make some more power? Or it is just something to keep in mind when building the next one?

It's good to exchange ideas with someone like you, I understand you speak from experience. Here in Brazil the culture is not to build engines for long life, which I understand but I tore my engine with 2000miles on it and did not like some of the things I saw.

Best regards,
Marcelo

[Tony Z]

I honestly think an FK87 would make your engine live slightly longer, but I am guessing here, I have never tried anything like a W140 w 1.25s

You would prob surprise yourself, get a set of Titanium retainers and the new aluminum pushrods and you should be able to run stock duals.
Once again, I am guessing here, but I honestly think that if your cam and rocker combo can do what it is, I think that switching to a 1.4 ratio setup will not require changing your springs - depending on the final lift you achieve.