Where does sasuke's speed and strength come from?

[Sound]

His speed increased from getting Hagoromo's chakra. More chakra=Faster shunshin [KCM Naruto proved it]

And no a pair of new eyes don't give you speed Lol​

 

[Mr Akatsuki]

Simply hacks

 

[TimothyTheTomato]

Didn't Karin say sasukes chakra was colder then when get used the curse mark when he used ms, and tobirama said special chakra comes from the brain when the sharingan is activated,when sasuke used susanoo every cell in his body was effected and as it developed his chakra changed, stronger chakra = overall boost ex.modes such as sage mode (becomes stronger due to chakra being enhanced ) and kcm. It only makes sense that sasuke's strength and aSPEED increase, which it has.Also hashirama's dna could've also augmented him. ♤♜◆??????????????????

 

[Styles]

Sasuke's chakra hasn't increased since he absorbed Orochimaru, and plot is the answer your looking for.

Chakra does increase during time and training Kakashi's chakra increased. One time he could only use kamui once or twice and faint now he can use kamui nearly 5 times or more and still use other jutsu's. So Sasuke's chakra did in fact increase and get stronger with the implanting of Itachi's eyes. Also you have to remember when he absorbed Orochimaru Sasuke had to use a large part of his chakra to keep Orochimaru at bay from taking over his body.

 

[To Whatever]

He probably uses his chakra to beef his physical capabilities

Like how Sakura punches shit.

 

[AlphaScythian]

Their current sage's chakra is very powerful thus it enhances body.
Speed however can be enhanced by quantity and quality of chakra put into shunshin.