1K.260

Factory exhaust is 2.75" on the Envoy with the 4200 Vortec. I'm looking at replacing the factory muffler which is on it's last legs with a Dynomax Super Turbo. I have decided on this based on reviews as it being a rather quiet muffler and is somewhat free-flowing.

I still plan on using a resonator to keep any drone down at hwy speeds but the issue I have is the longer 20" case is avail in 2.5" and 3" but not 2.75, except for the 14" case model.

I tried the Walker quiet flow but the muffler chokes down to 2" on the inside and it's noticeable at the top end.

My question is does the Super Turbo keep the same piping diameter as the inlet/outlet and if so, should I go with a 2.5 or 3"? I assume the 3" but wanted some clarification.

I also tested the backpressure and the walker was twice as much. I had .2-.3 PSI at 3K with the stock and .4-.5 PSI with the quiet flow.

Low97tahoE

go with 3". a short piece of 3" pipe will slip over the stock 2.75, weld that, then muffler slips right over that. If you are keeping the stock tailpipe, cut the turn off the end, as in cut it where it points down right before the turn behind the tire. that makes a HUGE difference in drone, cuts out alot of that. You wont have hardly any drone with 14" with stock manifolds and cats and such so the 20" will have no drone at all even without a resonator. i dont have any drone with my cam/heads/longtubes/ORY 4.8 with a 14" ultraflow.

EDIT: just read the envoy part so of course doesnt turn behind the tire. but still go 3"