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when considering batteries. what effects to volts have, and amps have. is it relavant to torque or horsepower. how do volts and mah effect my car?

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Good question, Booya2180. Voltage and current are the 2 components to electrical power(watts). In fact, the equation for one watt is W = V * I, where one watt is made up of multiplying one volt by one amp. Horsepower is a kind of a wierd one....because there's 2 kinds of horsepower, electrical and physical. Electrical horsepower is defined as 760 watts, where physically it is defined as the amount of work done at a rate of 550 foot-pounds per second. One mechanical horsepower is equal to 745.705 watts. That's the wierd part......why aren't they equal in watts? Beats me.

Anyway...all this is relevant to torque and horsepower, because the components of electrical power can be converted to watts and watts to horsepower, so in effect the more current and voltage you run, the more horsepower your xmod has. The more horsepower it has, the greater the capacity for torque and speed, which in turn converts to acceleration and top end. It's all about converting electrical power to physical power, in the most efficient manor. This calls for high current output cells(lithium polymers), low resistance switching(stacked FETs, externals), and an efficient motor, gearing, and drive train set-up for your race conditions(turns, straight-aways, etc.). I'd go into motors, but that'd be overkill......besides there's endless resources on that subject here already. Just do a search or a google on "DC MOTOR THEORY". But generally, you want a motor that will draw heavy amounts of current and efficiently convert current to electromotive force.
Voltage simply increases top end, while mAh will give you longer run-times and better instantaneous current supply for better acceleration. So if you can pack the highest voltage and mAh power supply possible in the tiny excess volume of the xmod body, you have more power to play with and you'll go faster and quicker. This is why lithium polymers rock, because they will maintain their nominal voltage while delivering up to 10C(roughly 10 times the mAh rating of the cell)worth of current, which will convert to a very decent top end AND acceleration if the setup is right.

To my fellow xmod'ers:

I had a terrible accident at my house last Thursday(10/26). Something caused an outlet to fail, behind my workbench, and my house caught fire, taking my workbench, tools, equipment, xmods, computers, etc. with it.

Needless to say, it will be a while before I will be into electronics, let alone xmods. I will try to keep up with your questions as best I can. You guys will be ok though. There's plenty of people here that are on the same page with questions and answers. I will post pictures of the damage later.

Take care and don't play with fire. Check your electrical situation and make sure all your smoke and fire detectors are functioning.

If you have an evo, I don't recommend externals at all. If your soldering is good, you should get by with a 2x2 stack of some "good" FET's. As an extra, you can epoxy a small heat sink on your stack. The reason I say 'no externals' is because the added power rating of the external is not going to compliment the extra weight, compared to a simple stack.

As far as YOUR situation goes.....whoever told you that running a 2s2p li-po pack with stock FET's was seriously jacked. You don't run lithium polymer cells to keep your current draw within safe limits for stock components. In other words....would you run pure alcohol in your ford tempo with the stock 4 banger in it? NO. WHY? Because you're using the alcohol for more power than your stock engine was even dreamed of putting out or handling.

So, to be more specific....when you added your lipos to your xmod, you made it where when you stall the motor(take-offs, or getting stuck), the lipos will provide more current, not just the marginal amount that the stock Ni-Mh would have provided, causing your FET's to heat up more than the Ni-Mh would have.

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so you recommend goin straight with stacked FETS, no V2 or Nelly, right?

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With the evo's, yes. The evo encorporated "charge pumps" for the FET's, so the driving capability will support stacks a lot better than gen 1's did. If you have a gen 1, I would recommend using a well built external with drive architecture capable of driving its own FET's. I believe ph2t was hip to this and has FET drivers on his board. I know little to nothing about the V2 though.

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do you know how or if it is possible to use resistors inline with the servo for evo to eliminate the jitter associated with lithiums?

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Yes. I won't be able to experiment and test to see which value is ideal, but theoretically it will work. With resistance in series with the servo motor, the current to the servo motor will be limited. With the current limited, the motor will not respond with as much torque, preventing the motor from jumping the steering mechanism past its predetermined position, overcompensating, and having to jump back(jittering).

The downside to this is that with limiting the current to your servo motor, you are reducing the force at which it will turn. Whether that is something to worry about.....your guess is as good as mine, as I'm unable to test this. I have nothing electronic, except my laptop computer......after the fire.