If I’m not mistaken, the only way to change the initial velocity of the particle along the SOP’s normal is to manually edit the normals, like for example doing a SOP to CHOP > Math > CHOP to SOP picture below.
It would be great if there was just a slider parameter on the Particle SOP that modified the initial velocity along the normals instead of having to use 3 additional OPs.
If there’s a better way to do this already, maybe I’m unaware.