Drum brakes, disc brakes, or hydraulic disc brakes

What do you have for front brake? That is the most important one. Hydraulic 200mm disc brake.

Rear brake.. anything goes.. whatever is cheapest and easiest to setup. I run a 70mm drum and it's enough for a rear brake. I ran completely without a rear brake for 1k miles... only lowsided once on dirt at 15mph from front wheel braking.

Disk brakes are the best. However, you can install strong, weather proof drum brake wheels on any bike as they require no caliper mount. Drum brakes look better to me on a vintage style motorbike.
-Both drum and disk brakes on the rear make it tougher to mount the sprocket for the engine chain. (That is why I only used a drum brake on the front).
-Easier to do fix road side tire punctures with disk or rim brakes.

I concur about the front brake being the most important!!

Hydraulic disc brakes are the best.

No disrespect intended, but I highly doubt that you'll be making anywhere near the power of the real 'Pro' bikes... There's a lot more to making these engines powerful than just bolting on a few parts.
My personal race bike uses a hydraulic 200mm front disc brake & a rear coaster brake (it stops great & it's one of the fastest bikes on the track).
Honestly, a rear coaster works plenty well for these bikes as long as you have a good front brake.

If you're h*ll bent on having a rear disc?, look for a quality brand for both front & rear.

t6R said:

I have a cheap disc brake that came off a mountain bike, but i don't know what it is or how big the rotor is. I'm anticipating the finished build to be somewhere near as powerful as some of those "pro" bikes. I'm not sure what else to call them, no disrespect intended. I'm planning on adding a shift kit to this bike so i can put a rear disc on it too. If i were to do so, what would you guys reccomend for decent stopping power?

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The pros got there by learning to use the front brake effectively.... Using only rear it doesn't have to lock the rear, but if you're using the front to the max then locking the rear should come easy.

Alice in chains - confusion

Hydraulic disc brakes are definitely the most effective and depending on how fast you plan on making the bike, you should be able to use a 160mm rotor up front. If you plan on racing it or going faster than 40mph on a regular basis, the 180mm may be a better choice, the 203mm rotors are huge and will Stop just about anything repeatedly over and over without any fading issues. I'm running a hydraulic setup up front with a 160mm rotor and it'll flip the bike if I pull too hard on the lever, the bigger rotors will have even more stopping power as well as run cooler and the pads tend to last longer since it takes less friction on the larger rotors to get the same stopping power. Smaller rotors have the advantage that they are compact, out of the way, and less vulnerable to damage if your bike goes down, they are also really good for rear brakes with a 180 or 203 up front. You can get a 140mm for the rear if running a 160 up front but this size isnt as common as the larger ones.
My setup is the 160mm disc up front and V brakes on the back side, the V brakes will do just fine for the rears since they don't need to do a lot, but when I had the V brakes up front I was changing pads every few days.