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DSW
Dodge Dakota
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6/02/2005
04:57:06
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 Subject: How restrictive is a 4.7 OEM muffler
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I know the Flowmaster XXX whatever question has been beaten to death, but really, how restrictive is the stock muffler on a 4.7. Does replacing it with a Flowmaster, Magnaflow, Gibson, whatever, muffler increase performance by a significant amount or are we just talking about a couple of HP and ftlb of torque.
I have a 03 4.7 QC and the exhaust doesn't look that restrictive, smooth bends from the manifolds to the Y pipe, cat and muffler. The pipe after the muffler has pretty poor bends and could use a mandrel bent pipe though.
I am looking at replacing the muffler with a high flow performance muffler to boost torque/HP and hopefully improve gas mileage a bit. A sweet sounding exhaust would be nice but not worth sacrificing performance, gas mileage or not gaining anything except noise.
I guess I am really wondering if it's worth $100 to replace the muffler or $300 for a cat-back. This ain't no race truck so what ever gets bolted on need to pay for it's self either by saving gas or producing more power.
The perfect sounding exhaust (to me anyway) has a low rumble at idle, quiet cruising speed and almost F'n obnoxious (outside, not inside) at WOT
Thoughts, observations, do's and dont's ???
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krellco
Dodge Dakota
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6/02/2005
14:02:53
|  RE: How restrictive is a 4.7 OEM muffler
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All relevant-none specific-sound matter of personal taste. Try just replacing OEm muff w/ same lenght glass-pak(or steel pak) to start.
If too loud, add another g/p in front of it, & after 3rd cat. Want more-add splitter after last g/p & got to dual tail pipes. Or just order above from JC Whitney (Heartthrob Deep tone sys)
I did same-lost mech. fan & K&N aif filter & city
MPG jumped & noticible power increase also. More noise, but tamed by the 3 glass-paks.Goodluk
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Android287
GenIII
6/02/2005
16:43:15
| RE: How restrictive is a 4.7 OEM muffler
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A muffler swap or cat back is done for sounds. There really isn't much to gain in the HP department or MPG. You may see a slight increase in MPG. The flomaster 70's series is pretty mild in the cab and is quiet at cruise. Loud at Wot. Same with magnaflow, which is what i have. If you want a better sound stick with the factory pipes and buy a muffler that will fit. Any decent exhaust shop should be able to weld it in for cheap.
The worst bottleneck in the stock system is the press bent Y pipe. You could have a shop fab one up using larger 2.5" pipe. You should see some gains in HP and MPG with this.
If you plan on modding your truck with other mods like intakes, throttle bodies, cams, custom PCM flash and heads, then a higher flowing exhaust maybe necessary.
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DSW
Dodge Dakota
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6/02/2005
17:47:33
| RE: How restrictive is a 4.7 OEM muffler
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I have heard people complaining about the Y pipe before, but the one on my 03 4.7 looks like it should flow pretty good. It has the 2 manifold pipes dumping straight into a single flared pipe, looks like a 2>1 union from a set of tri-Y headers, something like this;
I am guessing that some of the earlier 4.7's might have had a realy bad design for the Y pipe. Can't remember what my ol'2000 looked like but I think it was a poor design, something like the drivers side pipe plumbed into the passanger side pipe at an angle which would not promote good exhaust flow. Do the restrictive Dak Y pipes look like the 2-1 union in the pic?
I am considering a Magnaflow with the stock pipes also. I was looking at a Flowmaster because everyone and thier brother swears by them, but don't see how deflecting the exhaust against baffles can help maintain good exhaust velocity.
Has anyone cut open a stock muffler to see how they are constructed, dampened like a Magnaflow or baffled like a Flowmaster?
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krellco
Dodge Dakota
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6/03/2005
09:29:56
| RE: How restrictive is a 4.7 OEM muffler
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yeah, Y pipe on 01 4.7 not greatest design ever seen HOWEVER ck FIRING order-the Y pipe does keep the exhaust PULSES evened out, which does help keep exhaust velocity up, which does help scavenge cyl, which might help HP & MPG IF the REST of exhaust sys is "straight THRU" hence my stubborn insistance on NON-BAFFLED glasspaks. ANY baffle, or deflection WILL send a reverse pulse back up the pipe & kill scavenge effect. Of
course the cats dont help much in this dept, so all are correct-chg muffs MARGINAL for HP/MPG increase-you MUST ad other improvements to MAX.
Dualouts/lost fan/k&n upped MPG about 1.5mpg City
Total cost about $300. No, not cost eff-do like sound & SOMEWHAT imprvd performance. Fact muff is STd multipl baffld & reversed flow- Good Luk
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Magnaflow
Dodge Dakota
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6/05/2005
01:08:59
| RE: How restrictive is a 4.7 OEM muffler
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http://www.dodgedakota.net/boards/per/10858.html
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Stick Shift
Dodge Dakota
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6/06/2005
02:16:46
|  RE: How restrictive is a 4.7 OEM muffler
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I had a post in May about a "Too Loud Muffler", but it seems to have disappeared! Beware, on the 4.7, anything "performance" is going to be LOUD. See Gibson's comparison of Ford, Chev and Dodge. Dodge beats 'em all. http://www.gibsonperformance.com/sounds.asp
They also claim a whopping 4 HP increase!
Magnaflow claims +13 Hp with a cat-back http://www.magnaflow.com/02product/dynos/15611.jpg
I'm happy with just my 24" Magnaflow, p/n 14250, $106 e-tail(it's a bolt-on in place of stock). Sounds like what you want. Anything shorter is going to be loud. Don't waste money on Cat-backs as the 2-1/2 stock exhaust is big enough per Flowmaster. http://www.flowmastermufflers.com/cgi-bin/flowmaster/muffsys.html
Any performance gains from a muffler are only going to be at high RPMS. It'll never pay for itself. I think the easiest power/mpg gain is a K&N Filter!
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Stick Shift
Dodge Dakota
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6/06/2005
02:36:45
| RE: How restrictive is a 4.7 OEM muffler
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Found my post. http://www.dodgedakota.net/boards/gen/21383.html
Copy and paste it into your browser. My previous post is what I did to solve the problem.
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DSW
Dodge Dakota
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6/06/2005
11:30:57
| RE: How restrictive is a 4.7 OEM muffler
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Thanks for the replies. After looking around I decided to go with a 24" Magnaflow like Stick Shift recommended.
I was also thinking of getting a 90 degree mandrel bent pipe and dumping before the rear tire instead of using the restrictive stock pipe over the axel. Has anyone tried this and does this make the exhaust considerably louder? My main reason for this is to keep water out of the exhaust while launching my boat. I guess I can try dumping before the axel while leaving the stock pipe under the truck, if I like it the stock pipe goes, if I hate it the stock pipe gets connected and the 90 goes.
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Stick Shift
Dodge Dakota
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6/09/2005
02:26:28
| RE: How restrictive is a 4.7 OEM muffler
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If you're worried about water getting up the exhaust over the rear axle, you better be worried about water in your differential breather tube as well.
Dumping the exhaust in front of the RR tire is going to be louder than out the back. Also it will be uncomfortable for the RR passenger as well, especially getting in with the engine running or leaving the window open when idling.
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TexasTodd
Dodge Dakota
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6/09/2005
15:05:27
| RE: How restrictive is a 4.7 OEM muffler
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My third cat on my 01, 4.7, was very restrictive with a screen going all the way accross the pipe.]
removed it and it's louder, low rumble, etc.
Just right
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black034x4
Dodge Dakota
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6/09/2005
15:07:27
| RE: How restrictive is a 4.7 OEM muffler
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any performance gain TexasTodd?
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DSW
Dodge Dakota
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6/10/2005
17:27:37
| RE: How restrictive is a 4.7 OEM muffler
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Stick Shift, No worries about water in the axel breather tube, the water level doesn't get that high. I'v just been throwing around the idea of dumping at the axel,,, good points on not dumping at the axel. I'll find out how loud it is when I put the muffler on as I am leaving the tail pipe off initially to see how it sounds.
Changed my mind, looks like I'll be getting a Dynomax Ultra Flo SS muffler #17289. Pretty much the same thing as the Magnaflo except it's more expensive (for what even reason) and a couple of inches shorter. It runs $140 from Jeg's, but there's a $75 rebate, $65 for a SS muffler isn't too bad ;-)
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shank
GenIII
6/10/2005
23:12:05
| RE: How restrictive is a 4.7 OEM muffler
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I saw a noticable difference when I switched from the Stock to the Flowmaster40 S/I & D/O, Especially when towing. I haul a very heavy boat, occasionally a camper, other vehicles and various farm equipment on a regular basis. Drawback: uncomfortably loud.
I Upgraded my tires to LT265/75/16Durango XTR's. Excellent traction off road + 10ply tread & 6 ply sidewall helps with thorny bushes. Drawback: uncomfortably loud highway noise.
The Flowmaster 40 has toned down after 6 months, now it only gets loud at WOT without any pops/belches or burps.
The Flowmaster is way too loud for when I'm in the woods scouting areas or hunting, I have to park 1/2 mile away and walk entirely too far. The muffler shop said they have a Dual chamber S/I & D/O muffler that is only slightly louder than stock and I won't lose HP. I didn't bother to ask the Make/Mod/Brand due to $$, Drawback: $110 + $65 install.
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TexasTodd
Dodge Dakota
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6/11/2005
13:44:07
| RE: How restrictive is a 4.7 OEM muffler
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black 4x4,
I didn't dyno just that change.
When I dynoed the pre superchips tuner,
I made 218RWHP.
That was w/o the 3rd cat, but also HO cams and intake, no belt clutch/fan, ported 68mmTB, home brew true CAI, etc.
Makes sense that it helped some, as that screen accross had to have SOME restriction.
But the but dyno thing doesn't work for me, too subjective, placebo effect, etc.
Change a muffler, change the sound.
Show me a dyno with that as the only change, on a 4.7, that has ANY gain. Have you seen one posted?
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