Just put Mamba 6800 in rc18mt!!

when i had my rc18t i ran a 3 cell li-po, it was a polyquest 1800N

I'm using lipos in all 3 of my 1/18ths. No comment on the 2 cell setups since all of my packs are 3 cell. Your best bet is the Apogee or Thunder Power. Apogee seem to have a higher discharge rate which will deliver slightly more power and the Thunder Power cells seem to have longer run times. The Polyquest would be the best fit that joey is suggesting or you will have to mod the chassis slightly.
Both brands work great. The 3 cell packs are rated at 11.1 volts. They peak at an average of 12.5 volts.
If you think that the 6800 is fast now see what happens when you give it more juice.
Make sure that you program the esc's cutoff voltage properly or you will ruin your packs if they discharge below 3 volts per cell. Take a look at this;
http://www.castlecreations.com/products/airplane/brushless/castle-link.html
It is the easiest way to program your esc not to mention it will allow for custom throttle, braking and voltage cutoff.
If you do switch over to lipos make sure that you have the correct charger or you can burn your place down.

Thanks a bunch guys! Is there a charger that you would recomend? I know it would depend on the voltage, mAh, cells, ect.. of the battery but what would be a good overall charger, or brand of charger?

This one has given me good service.
http://www.dynamiterc.com/Products/Default.aspx?ProdID=DYN4053
The street price is less.

heres another good charger, this is the one i used to use but you will need a powersupply for it....

http://www.deeteeenterprises.com/NS.Apache.Charger.php

Thanks a bunch for the tips. We will see what option I go with. The local hobby store here has some lipos so I might go check them out tomorrow. I have also seen the deans there before so I will be sure to pick those up if I get new batteries. I have run alot of nitros lately and am just now getting back into electrics, so with all of the new technology....the tips and tricks are much Appreciated. Thanks!

First I use small pinions with my two mamba motors,this way they heat less and can operate within safe limits longer.

And I use an Apogee 3 cell LiPo pack.All the juice that is needed to propel the little rocket to blazing speeds.