540 vs 550 motors

[Blackangelofdeath]

Im way confused on 540 vs 550 size motors and the power output of each and hope you can help! My questions are based on me and a friend wanting to build a 1/10 straight line top speed car.

Here are some specs we found on a couple 540 and 550 size novak ballistic motors:

Novak 540 4.5 turn kv=9000 watt=530

Novak 550 4.5 turn kv=5000 watt=890

If you do a RPM calculation of each motor the 540=66,600rpm and the 550=37,000rpm.

The low turn 550 motors are usually used in power hungry, heavy 4x4 buggies/trucks but the kv and rpm are lower than the same turn 540 motor. What am I missing here? Why do these 550s make more power or do they? In my quest for speed I would think I would want the higher rpm of the 540 motor? There's gotta be something I'm missing here. Here's another way of looking at it. Looking at the same novak chart a 8.5 turn 540 motor has the same 5000kv and 37,000rpm as the 4.5turn 550 motor. What gives??? Why is the 550 considered to be more powerful and what would make more sense for my application.

I would like a technical explanation not just "get the 550!!!" please!

Thanks!

[Sixtysixdeuce]

A 550 is a physically larger motor. Same 36mm diameter, but while 540s are typically 50mm in length, a 550 can be anywhere from 55mm to 90mm long.

Why do these 550s make more power or do they?

Again, they're physically larger. Bigger coils, longer rotors, more massive magnets. They make more power because they draw/use more power. Those max watt outputs you're seeing reflect not only a higher amp draw for the 550, but likely higher voltage packs as well.

Looking at the same novak chart a 8.5 turn 540 motor has the same 5000kv and 37,000rpm as the 4.5turn 550 motor. What gives???

Larger motors of the same turn rating will have lower KV. A 12T 370 series 1/18 scale motor is about 8,000 KV. A 12 turn 540 motor is about 3,300 KV. A 12 turn 42mm 1/8 motor is about 1,500 KV.

In my quest for speed I would think I would want the higher rpm of the 540 motor?

Nope. You want a motor/ESC/battery combo that will put down enough power. Speed will be accomplished through gearing.

what would make more sense for my application.

Probably a 700 series 42mm 1/8 scale motor in the 1,600-2,000 KV range running on 6S and geared to the moon. Might even need a 55mm 1/5 & 1/4 scale motor, depending on your gaols.

Speed is a game changer; Normally a 1/10 nitro is powered with a 2.0-3.4cc. Trying to hit triple digit speeds, I found that even the power of a 4.6cc Novarossi 7 port turbo engine and a 5.2cc high output LRP engine were insufficient for the 5.2 lb truck.

[dldiaz]

I believe what is missing is the torque output of the different motors.

Power equals RPM times torque (Power = RPM x Torque).

So, even though the 550 motor is turning slower, it produces much more torque at that RPM.
Therefore, its "power" output is much higher.

- I have no idea what's better for top speed runs.

[THEYTOOKMYTHUMB]

If you look at the top speed run cars around they use a ridiculously long track. Airport runways in most cases. The real question you want to ask yourself is "Where will I be making my speed runs?". If the answer is a 3000 foot runway then RPM is all you need. The car will catch up regardless of torque. If the answer is a nice stretch of blacktop where I get 500 feet of open space then you need a whole bunch of torque to go with that RPM, otherwise you'll never get up to speed. Down force is a whole other issue. If it's really fast the car will want to take off like a plane.

[bully]

Also the extra torque allows you to gear to the moon,540 would depending on how long you want to run for in minutes theoretically will not like a small final drive an will get to a number where there is no potential for more speed due to heat.. If you plan on running packs an not just up an down cpl times you may want 550 an higher voltage but then you run into packaging problems of big motor bigger an more packs in a small car. Depends on how serious you want to go, if you just want to amaze yourself an the locals go 540 low turn if you want to go more than 60mph probably 550