4 x 2 is no where near sufficient~!
IMO that is~! I've kept my share of bloods and I breed Borneos...I keep ALL my adults in 6 x 2 enclosures. Bloods can get up to 8 or 9 feet in captivity...not very likely, but it has happened. Bloods/Borneos love hot and humid enclosures as well. If you get a blood, make sure it is a neo/baby and you won't have any problems with it's temper. The scary thing about Bloods is that they are abnormally strong compaired to their body size/length. Though Bloods have a very girthy body size and are very heavy, they are super fast. Easily the best snake I have worked with though~!

Hope this helps a bit.