Thanks for all the advice.

I will look into either 4S2P or 3S2P config. and run my buggy with the body.

skip 3s - too low a voltage.. 4s min

Yeah, I was suggesting 3s LIPO instead of 4s1p A123 because the voltages aren't that far off, because he was concerned about size. I too would opt for 4s ideally.

How about 5S1P on a 2350kv motor?
For 1000W motor, it would require about 60A (1000W/16.5V, assuming 3.3V under load). would this config work?

Probably be closer to 2.9-2.8 under load with a motor that high a Kv. And probably with 200 amp peaks.

Jeff

I run 5s2p on my Savage Flux now and get 150A spikes.

Batteries after a 20 minute run at worst come off luke warm

i run 4s2p with great sucess and power.

i know what motor you are talking about and they do best on 4s. i've seen the rotors burn up on 5s and especially 6s. that motor with a turnigy 5000mah 20-30c pack should do just fine.

Thanks for the info.

If 4S2P A123 does not fit, I will use higher quality 4S Lipo.

A little off topic:

If I were to place the motor to the front (opposite to the steering servo), that means I would have to raise the center diff 3-4mm from the chassis in order for the diff gear to clear the bottom, would this setup have any bad effects? or it is better to cut a diff gear slot on the bottom of the chassis?

Do I also have to raise the front and rear ends of the buggy as well to preserve the proper length/angle of the drivetrains?

Better to cut a diff gear slot.

A single A123 cell is able to provide between 200-300W peak (100-130A @ 2-2.3V) depending on cell temperature, cable lenghts, solder joints ... Feigao XLs might require as much as 2000W in when pushing a monster truck. A 4 cell a123 setup would not be able to provide that much power. With 800-1000W peak at your disposition (4s1p A123) a 1:8 buggy is already fun to drive but can't compete with good nitro setups. Feeding your 7xl properly would require atleast 8 cell as 4s2p A123. Power will come from Amps which is what a 7Xl needs to generate power. Your ESC also should be able to provide up to 200A burst to feed the motor properly.

On the other site: My buggy required around 400W in to maintain a calculated top speed of 44mph. With 4s1p your buggy would require around 35A @ 11.4V = 400W. At this power level your runtime would be down to 3.5 minutes and your cells would be very hot at the end of your run. The fasted i managed to deplete my A123 cell setup was in 5 minutes (running a truggy with 9s1p A123) which translated to an average Amp draw of 25A. Having less peak power at your disposition will translate in slower acceleration. If you want to maintain an acceptable runtime of say 8 minutes your average amp draw should not exceed 15A. At 15A your average cell voltage will be at 3V. Multiplying this by 4 cells gives you 4s x 3V x 15A = 180W in. With a 4s2p setup you get 360W average maintaining the same runtime. With 360W average and 1600-2000W peak power and a gearing to reach 44mph you could easely compete with high end nitro setups. Ultimatively the biggest shortcoming of your setup will be the 7XL motor as it will heat up fast when it has to generate good power levels. With a 1p setup it will stay much cooler as the cells are not able to provide as much amps as a 2p setup.

I was able to fit up to 10 A123 cell in my older style buggy. Actual buggys have a shorter wheelbase providing less space behind the center diff to arange A123 cells as 2x 2s2p or 2x 4s1p. My newer buggy only had space for 9 A123 cells. You have to be creative and solder your A123 cells yourself to fit as much cells as possible.

And +1: cut a diff gear slot.