Yes and no, depends on the goal, as well as the pocket book.
Mixing a different valve spring, say a spring by PAC with a slightly stiffer rate can help extend the rpm of the engine. AKA, no valve float at *** rpm.
In keeping with all one brand, your guaranteed (or should be) a certain expected level of performance and parts that work together correctly.
Going with another manufacturer of, let’s use rocker arms. With a verity of different companies offering “There version” of a rocker arm, you would think there all identical in the critical areas. But this is not the case. In articles by AndyF, there are different lengths and widths and weights. This is where things can go bad or get real good. Few people put in the time and (big) money into investigating which part works right with there equipment and why others dont. Even at a pair of rockers from each company can be expensive. As well as time consuming.
This is where people end up with failing engines or valve trains etc....
It is a failure to recognize a ill fitting, aligning or operating malfunction. And it is super easy to miss. Sometimes you can see it so fast like a lifter. However mixing different brand lifters shouldn’t be an issue. But different rockers should be looked at closer.
Using different intake manifolds or exhaust manifolds/headers can yield different torque and HP curves. Going with an all Edelbrock system is a good idea. However, sometimes a different intake from Weiand can curve the way an engine works, accelerates or just simply drives.
Of course, there is also the spirt of experimentation and curiosity to help satisfy the mad scientist inside us.
