Engine building philosophy. rocker or cam

[Thephranc]

All else being equal, for the sake of argument, is it better to increase lift at the cam or at the lifter via ratio?

[MonzaRacer]

build the cam to the engine spec, ie design it right, THEN you use a different roller rocker too tune the engine. See basically you attempt to design an engine as best you can, but you cant cover every contingency, so you use different things to tune.

[TLWiltman]

I hate to say this, but it depends on:
-The cylinder head
-The valvetrain geometry inherent to the cylinder head

The current theory in many racing applications is to use milder lobes with a higher rocker ratio, but again, it really depends on the head.

[BEEBE]

Depending on the engine platform... Most like to keep the cam profile as less aggressive "as possible" and allow the rockers to increase lift.

This is especially helpful in a engine like a traditional pontiac ... where the lifter bore area of the block is not the strongest.

Beebe

[kimosabi]

Engine building is all about compromises and you make different compromise for different use.

For endurance engine for example, I'd stay low ratio rockers because the higher ratio the more guide wear, valvespeed etc.

If I wanna squeeze every little pony out of it and run 1/4mile at a time I wouldn't mind playing with rocker ratios.

[sam 74]

like others have said it depends on the engine and its intended use, if you're looking for a more streetable cam but want more lift then i'd use the rocker ratio, but if its a max effort race engine thats going to see alot of sustained high rpm id use a larger cam profile, and don't forget to check for proper geometry after new rocker arms, you probably need to change your pushrods also.

[Joe87MonteSS]

http://www.knowyourparts.com/technical-articles/performance-rocker-arm-history/

This is an interesting read. When I first read this thread, I thought of which would require less effort to do its job. This is the article I read about it. Seems the higher ratio requires less effort.

Just something else to think about.