Li-poly problems + modified mini-t engine in heli?

[bonesvw1]

i have a ikarus pic fixed pitch, pro picoboard with heading lock, alum. swash, hub,and ars, ikarus tuning engine running on e-tech 2 cell Li poly batt 7.4 volt. it seems to be underpowered a fair bit compared to my 8 cell 700 mah Nimh packs. dont get me wrong these li poly batts last forever-----just a little weak in power anyone else have this problem? do i have to go to a 3 cell pack? also has anyone tried a mini-t rebuildable modified engine in a mico heli like the ones from orion?
here is a couple o links to some of these style of engines

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXFWS4&P=0

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXGTE2&P=0

[ThorPrime]

Unfortunately, Each Lipo cell is 3.7 colts so you can either have slightly to little power or lots and lots of power at 3 cells. I've heard that a decent brushless system will work well under 7.4 volts.
I've also never heard of using a micro car motor in a heli. I don't see why it wouldn't work, you might fry them with 8 cells as they are meant for 5-6 .