BIG JOHN

I have a 2003 2500HD and installed a Magnaflow muffler, duel 3" in and single 4" out, I coned the 4" outlet down to match the factory 3.5" tail pipe.

OK now the problem.. lost some low end and has a major resonance in the cab at low speeds especially loaded(1500-1900 rpm) other wise the midrange and top end (5700 rpm shifts) is great and the actual exhaust note is perfect for me.

I talked to Magnaflow and Flowmaster (exhaust engineers not sales clowns) and they BOTH gave me the same recomendation- cone down the lead pipe's from 3" to 2.5" to increase exhaust velocity thru the muffler (lowers the resonance) and the backpressure from the smaller pipe will really help the low end torque.

NOW I'm an old drag racer and I know a 1.5" header pipe on a small block is good for over 350HP VS "I want 1.75" headers on my small block because its cool even if it kills the low end" routine... SOOOO I'm thinking duel 3" pipes coming out of my "small block" is over kill and the 2.5" will be a major improvement in tourqe without sacrificing any hp.

Any inputs on this??-thanks BJ

slaterbj

I would think that dual 3" in and 4" out would be too big in the first place. It would work great at higher RPM's but your low end torque would die! I had the same problem and I have the same engine. I am running 2 - 3" in and 1 - 3" out. I can't say that it helped my torque but I know it didn't hurt it either measuring with my technologically advance butt dyno.

Just my 2 cents.

Deckhand

iTrader: (1)

When I first installed my true dual setup, the low-end was definatley worse. Eventually, I installed longtube headers, and a X-pipe as well. Now it feels good again.
But, I am running dual 2.5" exahust, and I could see how a dual 3"/4" would really lose the low-end torque. Good luck.

BigTex

iTrader: (16)

Being an old drag racer, how about a cam swap? Get a minor reverse split cam like a 212/208 Comp XE high lift. The smaller exhaust duration should keep cylinder pressure up longer (more torque). With the open exhaust you don't have the need for the stock cam's large standard split pattern. At this point, you are able to expel all the gasses quicker and don't need that much exhaust duration. With a custom cam, you'd gain low end torque and gain that upper end punch.

You might think about putting an X pipe a few feet before the muffler. I know the exhaust merges back inside the muffler, but the exhaust notes merging together in the X, then splitting up will change the tone. Worst case, put a bullet muffler after the X pipe on each side before the Magna to help cut down resonance.