Properly designed Evo X's valve cover breathers can release excessive crankcase pressure under boost, while having a check ball to block unmetered air from entering. To my understanding, normally Evo X's crankcase is under slight vacuum:

Do these valve cover breathers have benefits? Do full bolt-on and tuned Evo X's experience excessive crankcase pressure problems?

Thanks for any inputs in advance!!!

 

Hey just some input on this. The evo x crankcase and pcv system is very sensitive to changes. We discovered this at CBRD when developing our turbo kits. A change such as an extra breather may cause the pcv system to work incorrectly. I don’t think it’s needed until the car is a full built high power deal where crankcase pressure is a bigger issue. Hope some of that info helps.

 

You helped hugely! So, is it the best to keep the OEM oil cap for bolt-on Evo's, MHI TF06-18K Evo's, and Garrett GTX3071R Evo's? These daily driver builds barely hit 400whp, thus the crankcase pressure should be okay without the breather, I guess?

 

Yep keep the oem oil cap or if you want an aftermarket cap that’s fine but no need for any type of extra breather on the cap. Excessive blow by or crank case pressure is really only seen with a super worn engine where the rings and cylinder bores are tired or when the engine is fully built with different ring end gaps that allow blow by until they expand to proper final size. Huge high power cars will naturally have more blow by and at that point could benefit from venting the crankcase. Less then 500wheel a stock breather system is fine. 👍🏻