There is a good difference among both, first of all, the TB 500 is costlier than TB 350, new TB is Rs. 1.82 ex showrom Delhi, while the 350cc is 1.43 lacs (ex showroom Delhi) , now in terms of engine, the TB 500 has bore of 500 cc while the 350 has 350 cc and hence 500cc is is more powerful. Another major difference is that Thunderbird 500 comes with FI technology while TB 350 has a carburetor, other than that , you can see difference in stickers, rest is same in both.