If you have a stock system, you need the 2 1/4" ones.

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D630122&N=700+400304+301736+4294788249+4294906122+4294906130+115&autoview=sku

Did you see this post with all the dyno and DB numbers? The summit fully welded beat the turbo in every test, but are raspy with a DP or U-bend delete, but are $20 more per muffler.

http://www.grandprix.net/ubb/ultimatebb.php?ubb=get_topic;f=1;t=010599

These are the fully welded mufflers I have on my GP

http://store.summitracing.com/partdetail.asp?autofilter=1&part=SUM%2D633221&N=700+4294922710+400304+4294891681+4294788248+4294904107+4294906130+4294783374+115&autoview=sku

My wife's monte has these, but they are 2.5"

http://store.summitracing.com/partdetail.asp?CP=1&part=MPE-11226&N=700%200&Ntt=MPE~11226%20or%20MPE~12226%20or%20MPE~11366&Ntk=&rsview=sku&Ns=P_SRE_DisplayPrice|0