Is this a workable combo
 

It is evident to me that my Mamba 7700 motor will not push a 5-8 lb car without killing the batteries, so after some research I have put the following together. Please let me know if this combo will properly propel my Super RS4 to the 45-55 mph range.

Castle Mamba Max ESC
Medusa v2 36x50 3300kv Motor
A123 4S1P 4600 mAh
Gear ratio - 2.16
Spur - 44t
Pinion - 15t

What vehicle is that...not sure. Also, what tires are you plan on running?

I think its a 1/7th onroad?

I tried to plug it into the speed calc., but w/out all the paramiters...it is a no go...

A Super RS4 is basically a 1/9 scale on road touring car. I'm running 2.2 hpi wheels.

As far as the set up goes...due to it's size, 4s may not reach your desired speed. If you step up to 5s you should not have a problem.
Also, I would consider the 60 series Medusa instead of the 50 series. I have a 50 series in my small, light crt.5

Besides the Medusa, what are other motor suggestions? I am running the MM for right now.

You could try a Neu 1512 series...they aren't cheap, but, they are the best electric motors available...period. I run a 1512 1YF ( 1900kv ) in my mbx-5 shown here...http://i271.photobucket.com/albums/j...e/DSC01625.jpg

It runs cool and it is extremely efficient....on 4s it v/fast. On 5s it is silly fast. If you jump up to 5s, you will want a different esc than a mm esc.

Also, if you plan to run 4s w/the mm esc you will need an external bec