Why after i changed distributor when i hit fifty it makes popping noise?

Where do you hear this popping noise ? Intake manifold ? or front of engine ? How does the vehicle run at higher rpm's ?

Reasons for popping noise:
Popping noise could occur due to the malfunction in the ignition system, leaky valves, weak cylinder compression, carbon accumulation in the combustion chamber or lean fuel.
1. Ignition system malfunction (Misfire).
Check:
- The ignition timing.
- Spark plug gaps.
- Use colder type spark plugs.
- Ignition module and ignition coil.
- Distributor cap and rotor.
- Spark plug high tension cords.
2. Cylinder compression:
- Check valves clearance.
- Perform cylinder compression test.
3. Fuel system (For lean state).
- Check fuel filter for clogged.
- Check fuel injectors.
- Check fuel pump pressure.
- Check fuel regulator.

Are you sure you have the cap down correctly and all 4 anchor points engaged? I have seen (and heard) GM caps that only had 3 of the 4 correctly locked down and the rotor was hitting the inside of the cap making a ticking noise. Take the cap off and inspect the inside, look to see if it shows marks from the rotor. If that is all ok than yes, it could be that your timing is off. You can also hear "ticking" if you have a crack in the sparkplug wire; the spark from it to metal does make a ticking noise; so inspect your wires also if they are over 5 years old.

check for play in the distributor sometimes the slop will make the pick up window under the cap will hit the distributor cap , the squeaking noise may be your belt or tensioner pulley bearing the knock can also come from a bad tensioner as well .

re-align your timing , or check spark plugs, or re-align your distributor cap

Ok can hardly make a noise that the dealer can be is what you have run a little and listen to the dealer to hit a spark, if you get the dealer must mark the position in which you pull it out and put the new one in the same position time to suit you and then you move a bit where you hear the engine works well. if you have a lamp of time you would be better .... Thanks

If it sounds like backfiring you may have some spark plug wires mixed up.Also you may want to check the compression in the engine cylinders.

check to see if two plug wires are plugged into the wrong areas. That will make the engine miss with a soft popping noise if you have that sort of miss

check your disc pad they maybe worn out already. then check the disc plate also.

Sounds like you need new front struts since it sounds like it is coming from under your or towards the center of the car it most likely is either the driverside front strut or strut housing. I would take it to a certified safety mechanic asap. It might just be worn struts but it could be alot worse then that. Better safe then sorry.