I have a 4 lower and a 2.8 upper and it sounds just fine.

 

I guess it depends on which brand you buy.... TampaBlack and my self had to order a longer belt for the REM 2# lower. You can get the stock belt on but it's way too tight.... but I know there are people out there who didnt have to change it out

 

I have a 2.8 upper im getting ready to put on when i find someone with a puller i can borrow to put it on. This is on top of a 4 lower and ported s/c

 

I started hearing cavitation after adding my #1 upper to the #6 lower. I had my chip burned to add the extra RPMs....no more problems.

 

good info.... thanks guys