I always read piti: joy is mental happiness and sukha is physical. But lately i have been reading pīti is physical, sukha is emotional. At first i thought this didn't matter but now for Jhana training I'm reading move from the piti physical sensation to sukha emotional sensation, which completely throw me off. Any help?
Can't separate like that. Mental-emotional-somatical is a continuum, not discrete. Or, more precisely, they are layers of the same, like different frequencies that can be isolated within the same signal function - not separate.
Sukha is that mental/emotional state/feeling when everything is just right. Everything is just the way it should be. It feels peaceful, subtle and sweeeeeeet. It also has somatic component. The breath becomes fluid, the body feels light, the movements are spontaneous. It's like that feeling when you just woke up after wonderful sleep and you feel refreshed and blissful, gentle and peaceful.
Piti is a much more coarse condition. It is like that feeling when you listen to a very inspiring lecture or a song and suddenly realize - and feel - profound significance and gratitude, and then you may get goosebumps or the tears may start rolling. Somatically at that moment, you may feel being aflame or tingling or orgasm-like waves going through your body. Unlike sukha, piti is kinda taxing, one can get tired of it.
So yeah, piti is coarser of the two and sukha is subtler - in this sense you could say, piti has a stronger somatic component and sukha is more focused on the mental/emotional end of the spectrum.
Sukha as well as piti are both mental factors. The bodily unpleasant or pleasant sensations are domanassa and somanassa.
If you want to dive deeper into mental states and their accompanying factors you might want to read the Abhidhamma. A free pdf version can be downloaded here.
My answer below is not definitive but mere consideration.
The 1st four jhanas are called "rupa" jhana however I have never read a compelling explanation for this. However, it is known via experience that rupa jhana arises from the calming of the physical processes (breath & physical body) that are stressed by mental formations (sankhara). Thus, as the physical body is purified of mental stress, the nerves of the physical body start to bliss out. Once the breathing completely calms and the physical body is purified of stress, all the mind can be conscious of is the bliss (which is jhana). It appears the bliss of jhana has its basis in the nervous system of the physical body and possibly is physical in its basis. MN 111 refers to two types of feelings in rupa jhana, bolded below. The 2nd feeling is part of "nama" (refer to SN 12.2) and is definitely mental in it basis (because it remains in the arupa jhana) but the piti and sukha of rupa jhana could be feelings arising from/towards the rupa sense base (kāyāyatanaṃ).
There was the case where Sariputta — quite secluded from sensuality, secluded from unskillful qualities — entered & remained in the first jhana: rapture & pleasure born of seclusion, accompanied by directed thought & evaluation. Whatever qualities there are in the first jhana — directed thought, evaluation, rapture, pleasure, singleness of mind, contact, feeling, perception, intention, consciousness, desire, decision, persistence, mindfulness, equanimity, & attention — he ferreted them out one after another. Known to him they arose, known to him they remained, known to him they subsided. He discerned, 'So this is how these qualities, not having been, come into play. Having been, they vanish.' He remained unattracted & unrepelled with regard to those qualities, independent, detached, released, dissociated, with an awareness rid of barriers. He discerned that 'There is a further escape,' and pursuing it there really was for him.
Furthermore, with the complete transcending of perceptions of [physical] form, with the disappearance of perceptions of resistance, and not heeding perceptions of diversity, [perceiving,] 'Infinite space,' Sariputta entered & remained in the dimension of the infinitude of space. Whatever qualities there are in the dimension of the infinitude of space — the perception of the dimension of the infinitude of space, singleness of mind, contact, feeling, perception, intention, consciousness, desire, decision, persistence, mindfulness, equanimity & attention — he ferreted them out one after another. Known to him they arose, known to him they remained, known to him they subsided. He discerned, 'So this is how these qualities, not having been, come into play. Having been, they vanish.' He remained unattracted & unrepelled with regard to those qualities, independent, detached, released, dissociated, with an awareness rid of barriers. He discerned that 'There is a further escape,' and pursuing it there really was for him.