firstly I assume your doing mig? (metal inert gas)
The way I would do this (welder by trade but i work on big pipe
When I work on any kind of pipe we have to do butt-welds... because the inside wall has to be smooth we cant stick one pipe in the other and do a single fillet weld<so easy... but cant do them:(
With an exoust your running one pipe in the other.. (fillet weld)-
^^have you welded up the muffler to the inlet?--if so brake it off and put the hole thing on the bench, Unless of you have a hydrolic hoist, and unless you welded it all up instead of just tachs*
But for your tips, your saying that the pipe doesnt fit inside of them?.. for a butt-weld like this you have to clamp the pipes so they dont move. When you have them so you cant see daylight between the two peice of metal.. do some tachs ever 2cm around the pipe (why it shouldnt be tucked up under the car) then put it back under the car hook it into you inlet (or if you just using a small pipe your outlet) and see if everything lines up

^^^^^^^^^^only to confuse you more :?

i went to the store today couldn't find 2.75 to 2.5 adaptors...anywhere...so i think im goin to try to butt weld it the 90 degree pipe...i think ill weld that first then weld the inlet on...


are you sa ying that you can put one pipe into another and weld?

IM still confused about what ur doing.
usually on muffler pipes they do slide into one another. Then you can clamp or/and do a single fillet weld.