The piano is a full range instrument, mianeng it has low bass notes at the bottom going to high treble notes are the top. The guitar is a midrange instrument, mianeng that it lacks the low bass notes. Therefore, if you want to find the E chords that sound the same, you have to find the lowest E chord possible on the guitar and match it to the piano. Then you have to find the highest E chord on the guitar and match that to the piano. Now you know the lowest and the highest. You can find every E chord in between. The low E string on the guitar corresponds to the E below middle C on the piano. Knowing that, you can map out the E chords on the guitar. The only other reason the chords wouldn't sound the same is if the intonation on your guitar isn't correct. So, first you tune your guitar . If your piano is in tune, then use that as a guitar to tuning your guitar. Secondly, you need to make sure the harmonics on your guitar are also in tune and this is referred to as the intonation. If the harmonics are not in tune, then you have to adjust the saddles on the bridge. If you don't know how to do this, then take your guitar to a guitar tech who will set it up and show you what to do. If you have an accoustic guitar and the bridge is not adustable, then you will have a hard time getting your guitar to the correct intonation, so again, see a guitar tech.