34slo

needing some advice on my r34gtt rb25det neo. firstly my 34 is majorly modified with 450hp running on ethanol. secondly I just finished doing my timing belt. waterpump. radiator . drive belts. the timing lines all line up i rotated the motor and the timing all lines up. I put it all back together and went to start it and it keeps crankin but wont start and just backfires and pops very loudly.what is the issue?? im hopeing its somethin simple like cas moved upon reinstalling it? please help. lol.