just cut the muffler off and then run a glasspack depending on your preferences.Most of my EA81/ea82 vehicles haven't had mufflers.My 93 legacy had an 11" glasspack because the exhaust was a little too high pitched and sounded tinny.With that little glasspack it sounded like an STI.
No you will not damage your engine by running a different muffler or even non at all.The muffler is far downstream that the engine just sees a reduced diameter pipe(check the flow rate of pipe to an equal size muffler).
While we are on the subject an engine does not NEED backpressure. What it needs is a certain exhaust velocity.Too slow and bottom end suffers,while too fast the top end suffers.
small pipes have high velocity,
large pipes have low velocity.
the problem with high velocity is it leads to something known as backpressure, in other words resistance to flow.
The exhaust travels in pulses so there will be a positive pressure than a negative pressure.When velocity is about right when the exhaust valve opens exhaust will be drawn out and the fresh air charge will get drawn into and trapped in the combustion chamber to start the cycle again.When exhaust velocity is too fast the intake charge will be partially sucked out the exhaust.Too slow and the engine has to expend energy to push the exhaust out.Not to mention most of the combustion chamber will be full of exhaust which doesn't burn.
so too small of pipe will choke the top end,while too big of a pipe will kill low end power.
On just about any subaru 2-2 1/4 is about ideal.On turboed things a much bigger downpipe is allowed for a different reason.
Edited by Uberoo, 20 March 2013 - 03:56 AM.