After changing my muffler (rear can) from a round custom made approx 15" inch to a Scorpion oval approx. 10" x 15", my turbo boost patter went from 12 - 9 - 12 to 7 - 4 - 7.

I do not have a cat; just straight 5".

Can it be the muffler that effected my boost ?

 

yes if it is more restrictive, however, shoudl not effect boost in really high gears as much. try it in 5th up a hil, snd see what you get.

 

one morething, I doubt you woudl lose 5lbs boost from a muffler, sounds like you have a boost problem.

 

Actually, it can... I've had it happen before w/ the early non-straight through HKS Super Dragers.