3.5" Flowmaster muffler

[Craig M]

I have an unused but older diesel 3.5" Flowmaster muffler. It is not a straight flow thru design like most seem to be using now. It enters in the middle and exits on one side. The newer 4" muflers are straight thru. Is there enough performance difference to justify buying a 4". This will be going on our 6.5 Yukon with 3" downpipe and 3.5"/4" exhaust.

[DA BIG ONE]

I've seen performance take a dump using Flowmasters w/turbochargers because of this I would not use em, even if billed for diesel use IMHO. STRAIGHT flow through design is far better on diesels and there are some newer designs that quiet them down too w/o power loss.

[Craig M]

I have seen a few of the 4" flow throughs. Most look like the old cherry bomb mufflers of the past. A "good" one could have enough muffling to quiet the roar a little. Flowmaster even shows a 4" flow through for the Duramax in their current catalogue.

[diesel65]

I am using the Flowmaster Big Block muffler #53550.

I found I was getting a headache with John Kennedy straight thru muffler. I had first installed it with the louvers the with the flow then I turned it around so the louvers was against the flow, didn't find much difference; then I fabricated a dummy cat convertor to act as a resonator.
I still was getting a resonance in the cab. At the time I searched the internet for mufflers I found that there wasn't much of a selection in 3.5 inch muffler, so I decided to try the Flowmaster.
There isn't much room under the 2 door Tahoe chassis but I was able to shoe horn it in, the muffler is big.

The Flowmaster made it much quieter, I don't know if I lost performance, I haven't installed a backpressure guage.
The truck seems pretty fast and tows my camper real well. I wouldn't mind going on a chassis dyno to see what the real numbers are.