Thanks for all the help!:)
A SOLUTION: after trying various combinations for awhile it turned out i had to actually increase the mass scale multiplier . makes sense i guess... a peice of paper flying into gordon at 1000 mph has a lot less force than a lump of iron,just didnt expect this. the phys engine still amazes me.
I used env_impact over physexplosion in the end, it seemed to have more force, not totally sure whether its a better choice yet, i imagine the force is just directional instead a spherical but... im not sure. Anyway, i still had to set the magnitude extremely high for gordon to get any lift, around 1,000,000. gordons sure is packed into that suit. suprised he can breath!
As for the trigger, iv had a look and im not sure how to template a brush and spawn it so... i guess its kinda lazy but i just used an extremely high strength coupled with the " on health chaged" output. ill come back to this:/
i tried using the "block bullets" texture but that seemed to also block explosions.
thanks again for the help n ideas
works a charm... well,almost.