compression engines can effect it as well as turbo size, and other additional modifications that would release more/longer duration of exhaust gasses. Larger turbos tend to lose less rpm on a shift but take longer to spool, smaller turbos being the opposite for obvious reasons.
1992 Nissan Skyline GT-R Gunmetal Grey - Long Live the Z and Godzirra! - "Love cars. Love people. Love life." - Mr. K.