I have a 8hp snowthrower and it doesn't throw snow very well especially in thick snow do I need to replace something to make it work better

Is it a single stage or two stage? Single stage blowers are only good for light snow. Two stage blowers have the main blades that cop up and pick up the snow and then the second stage blade actually blows the snow. Unless your belts are slipping, there isn't much you can do. 8 hp is actually a smaller size blower. If you live in an area with lots of snow, you may consider a larger, high quality , two stage commercial style blower. Some companies over estimate what their blowers can do. I would go online and read some of the reviews on different blowers. Owners of blowers will tell the truth and give you real-world examples to compare. BEWARE that some of the biggest names out there have really gone downhill and/or offer low price,cheap units to stay competitive, so don't just go by name and price. Cheaper is not always the best route to take.
Good luck in your search
GTO DAN