Okay guys I have been rc'ing for years, but have yet to understand how to tell if a specific esc is compatible with a specific motor. I know that more kv + more speed less torque and less turns equal more speed/less torque.
Can someone please explain to me how to tell if a brushless esc is compatible with a motor, what specs to look for, how many amps, etc, etc.
I need to fianally understand this so please help me out!!!! THANKS!

kV is pretty much a useless rating because every manufacturer rates it differently.

Pretty much any brushless motor will work with any brushless ESC. However, you also need to look at your uses. Are you going to be running on road or off road? 2s lipos or 3-4s lipos?

2s lipos and 1/10 on road cars, you're looking at 540 size can motors. Off road 1/10 and 1/8 scale cars are looking at 550 size can motors.

Off road motors are going to need more amperage than on road motors, in general. That's why you'll see many off road ESCs with 150a+ vs some on road 1/10 scale ESCs only needing 45a.

For sensored motors it is easy, just look at how many turns the motor is rated at, and how many the esc is rated for. Just don't exceed this. For others though, it can be harder. I. Think it comes down to common sense. The problem is, it is hard to go off of amp rating as well. The mmp is only rated for 65 amps con, yet people use those in 1/8 scale cars.

There is not a set in stone way though.

Ok so basically the more amps the esc has the bigger/heavier vehicle you can put it in?
Is this a good combo for a artattack snowmobile? I will also probably be using it for some light bashing in my hyper 7.
http://hobbyking.com/hobbyking/store...000KV_80A.html

I would not use that in a Hyper 7, that is a 1:8 buggy... I would suggest as a package looking at the 150a ESC and some 1:8 friendly motor less than 2000KV and running it on 4S.

In the end you will spend less if you get something that will last, and your Hyper 7 is a little too much buggy for that.

Is it a good system for the snowmobile though?

That is a 540 motor, way to small for eighth scale. What size motor does the snowmobile use? I would go with hobbywing electronics, not hobbyking, as hobbyking is just a cheap clone. Of most hobbywing products.

Well I think it uses a 1/10 scale system, its a 1/4 scale sled but its pretty small.
Its very lightweight, not much to it. Its 21 inches long I think

Might be best to consult the documentation of the snowmobile, at the very least I would think it would lend a starting point based on what it came with in the first place.... From there you can go up in power within some reason without issues.

It comes as a nitro and they don't specify what kind of motor system to use. I know its supposed to use a .21 engine though and the gearing for the nitro engine setup is one tooth less on the pinion than I will be running with the electric
I would greatly appreciate it if someone could recommend a 1/10 scale brushless system in the range of like $75 or less
Its gotta be in the range of like 1900 - 3000 kv, cause I want torque

A .21 nitro is most common in 1:8 scale, or some 1:10 Monster Trucks. More than likely a 540 setup will not be enough to run this. I would suggest on the small side to look at 4-pole 550 motor or better yet a 1:8 brusless system. Keeping it in your ideal price range will be real challenge.

It just sounds like you will need something with a lot of grunt to run this snowmobile.

Alright, thanks