cyclerider57

For his engine... not needed. For 90% of proper built 50 based engines they aren't needed. If you notice a major difference then you should probably check your ring gaps and alignment cause you are building quite a bit of excess pressure. Yes, the least amount of pressure in the cases the better off you are; that's why I run my engines on negative crank pressure. At the least, I have a one way valve on the crank breather, which your 250f has in the crank compartment and some high rpm street bikes even come with built into the head breathers stock. If you want to test this the correct way you will go to a dyno. They aren't just for power numbers you know. You can test the seconds it takes to get from one rpm level to another. If you don't see a difference then you know the truth for that particular engine... Wait a second, I have done that on my dyno on a few of my mini engines (that I built to my standards). None showed an improvement in either power OR rpm pick up time from just the addition of a head breather. The small displacement horizontal engines just shouldn't build pressure to the head when built right. To each his own though. For my mini engines, no I don't run them. On the grand national dirt track engines I build... they all have negative pressure with head breathers.

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