oxidizr

iTrader: (4)

Increased flow will have diminishing returns without proper calibrations or the actual exhuast pressure needed to support a dual 3" exhaust. The two mufflers you have selected can support over 660 CFM / muffler ... well over what you you woudl need for normal operation.

In all honesty an 8.1L with bolt-ons doesn need more than a single 3.5" or dual 2.5" exhaust to see gains.

Normally i would say "Quik" is a moron and doesn't know what the hell hes talking about (but i think i already did that when he mouthed off earlier - https://www.performancetrucks.net/fo...highlight=quik) but this time his half witted answer is a reasonable solution ... a more restrictive muffler will in fact help the situation.

Whether the muffler is product of Flowmaster or a Dual 2.5" inlet / Dual 2.5" outlet 5x11x22 MagnaFlow these are more suited mufflers for the situation when calibrations are not available or not within your consideration.

The 8.1L motor and 6.0L HD motors have calibrations set and optomized for hauling and operating under load. Creating a exhaust system with as little restriction as you did changes the ability of the calibrations to function udner the correct load table. These type of modifications for a Zero Loss WOT "drag or strip" truck are not always most suited to those seeking utility from their vehicle.

If you need some help in selecting a possible resolution measure to your existing system another alternative woudl be to run dual 2.5" tail pipes from the mufflers to the exit locations at least behind the rear axle. One concern in doing this is in fact the possible introduction of harmonic resonance by increasign the tuned length of your exhaust system.

Please let me know if I can be of furhter assisatance.

Submariner

Last night I spent a good half hour on the phone with both Gibson and Magnaflow. Gibson told me since I haul such a large trailer I should go with a single side exhaust and Magnaflow concurred. In the end I ordered the Magnaflow catback stainless system which exits in the stock position. (Got it for $450 shipped) I settled with Magnaflow for 3 reasons one was the type of stainless steel they use is a higher quality, 2 they in house dyno test thier system to get the gains (Gibson would only give me an estimate) and three the guy at magnaflow seemed alot more informed about what he was talking about than the Gibson rep. I've called Gibson twice and have gotten 2 different stories from 2 different reps recommending 2 different systems for the same application. Magnaflow has been consistant all along. I'll be installing it hopefully next weekend and will update you with the results.

1ImperialSS

iTrader: (5)

glad to hear you and some body else have everything under control! maybe when you tell us about the results you can post an exhaust clip too so we can hear that sweet BB soound

bigredexpress99

iTrader: (15)

you'll definetely like the sound of that magnaflow system. Put it on my boss's 8.1 3/4 tonner, and he loves it! sounds nice, and picked up power. We pull a 250 Bobcat all day for landscaping, and its not any trouble! if only I could really talk him into a Duramax though...much better mileage. It's the only thing he complains about on the truck.

1ImperialSS

iTrader: (5)

man i hope you got a raise for doin that install for your boss!!! unless hes your father in law or something

hog

The 8.1 and 6.0 HD Vans come with dual 3" pipes which come together at the muffler. I have measured the dual 3" pipes myself with calipers.
The cats were dual 3" units as well, these gM exhausts are huge.

peace
PAuly

jmproductions

Then I'm assuming it's a single tailpipe out of the muffler?? I may have misunderstood, I thought you were saying that they had a 3" true duals system.

hog

Yes thats right, dual 3" headpipes (from manifolds to cats) dual 3" cats and dual 3" pipes into a dual 3" in single 3.5" tailpipe.

Sorry for the confusion. MAybe the restrictive stock muffler provides enough backpressure to aid in the stock 3" setup's low rpm torque?????

peace
Hog

1ImperialSS

iTrader: (5)

sounds like thats exactly what the issue is

hog

Just to clarify some things. About 15 miuntes ago, I measured the exhaust on a 2006 Chev 6.0L 2500 truck with a Vernier Caliper. The truck was on the alignment rack to get its frame straightened

here are the findings:
From the factory the 3/4 ton exhaust exits the exhaust manifold into about two inches of 2.5" pipe that expands into dual 3"tubing, this goes into dual 3" cats, the cats exit into dual 3' tubing into a dual 3" inlet muffler with a single 3.5" outlet into a single 3.5" tailpipe.

I really wish I had a digital camera handy, I cant beleiev how big this dual 3' mandrel bent factory exhaust looks. Its a big improvement over my stock Vortec 350's dual 1 7/8" headpipes(pipes that connect the manifolds to the cats). My stock headpipes were crimp bent from the factory. On both headpipes there was bends that crimped the diameter down to under 1 1/2"'s.
Now these newer trucks are running dual 3" headpipes with mandrel bends, the exhaust diameter is practically double, but the engine only has 14 more cubic inches of engine dispalcement. if I put dual 3" headpipes on my truck, low rpm torque would suffer as well.

I ran my longtube headers open once and los a TON of low rpm torque, the truck wouldnt launch hard at all, but would scream above 4500rpm.

I am now running dual 2.5" headpipes and cats and wouldnt suggest to go any bigger than that on a 350 unless forced induction came into play.

A 2" h-pipe, connecting both banks of exhaust, placed before the cats would certainly help the low rpm torque. But it has been stated that an H-pipe is allready in use.
I have read that placing an H-pipe as clos eto the headers as possible that is 1/3 the diameter of the rest of the exhaust will bolster low/mid rpm torque WITHOUT sacrificing ANY high rpm power. This type of H-pipe allows the exhaust pulses to scavenge the exhaust charge out of the combustion chamber more than when dual exhaust has no H-pipe at all.

Getting a proper PCM tune by 1 of the many PCM tuners will help, that Superchips unit isnt what you need in this case. I would go to Nelsons in this case, or possibly Westers, they both have a nice 496 8.1L tune.

peace
Hog