Thanks Serum.

Should i just use one of the Li-savers wired in where i have the ubec(controller wires) or would it be better to use one per pack somehow?The FMAs i was going to use have one per pack.
I guess in series the packs are acting like a single 8s pack so one would be OK?

Yes, one should be fine actually.

question, would a 8000mah 3s2p lipo pack that discharges 10C be ok with the 9xl? that would be 80 amps max and it says 40-48 amps continuous. would this be ok?

If it is a 10c continous it would be 80 amp continous. Which would be good.

but its 10c max. i think it would be ok but i dont really know. also, what would happen if it was exceeded? or would it just not deliever the power?

40amps cont. should be plenty for that motor. But 3s Lipo isn't enough voltage. You need 4s absolute minimum. I would consider 5s to be the minimum for usable purposes!

The lower C rate cells won't deliver the same voltage that the higher C rate ones will. Plain and simple, that is the main difference.

well i was gonna run 2 in series. also, what kind of run times should i expect?

-corey

EDIT: what happens then the motor draws more than the lipo batteries can deliever?

Others may be able to give you a better estimate on runtime than I could.

When a motor draws more from the battery is rated for, the voltage won't drop too low, unless it is for a long time. For RC car use, we will never see a Lipo drop low from a long burst, as long as the battery is being used properly. The worst thing that could happen would be that the LVC would kick in @ 3v/cell, which is why they are absolutely necessary.
Usually Lipos have a burst rating, and this is a burst rating for a period of time, usually 10secs.

with gp 3700 18 cells 25 -30 min on a 9xl so on 8000 mah I would say about and hour.

I would use a minimum of 4 cells as well. 5/6 is better. it is not about the mAh's only it's about the total available power.