I'm no haten either, just trying to point out that unless you have actually tried something for yourself, and can prove from first hand experience that it works or doesn't, you shouldn't be coming on here making definitive statements about whether or not something will work or not, and shooting down peoples theories as ignorant. Truth is, you just don't know and are really only guessing or repeating what you've read elsewhere or heard on the internet. We all know how reliable that can be. I'm not haten, i'm testifying. I read all over that a 3" single from the cat out with no restrictions would be a great setup for a stock or mild modified 5.2. So I went with shroty headers, highflow cat, highflow muffler. All was great. Each component I added seemed to boost the top end, but bottom end always stayed the same. Then I changed the pipes from the cat out from 2.5" to 3". I lost low end, period. Top end, it screams, but I definetly lost low end. Can feel it under daily driving conditions, and could feel it when I towed. I didn't notice it at first, but over time as I tried to do things with the truck that I could do before with no problems, I could tell it was just not there anymore. This is not something I heard on the forums, or read on the internet. It is what happened on my truck, which is a 5.2 with a few mods. I could give a flying crap what Magnaflow says on their website. They're not talking about my truck, they're just trying to sell exhaust systems.

pcfixerpro, I suggest you also do a search for threads on this topic by steve05ram360 (or maybe he will chime in). He tested this same theory and can speak from first hand knowledge as well. His truck was even a 5.9, and he felt the 2.25" duals performed better then the 2.5" duals.

Bottom line is, exhaust systems are tricky. There are so many variables. You have at least five major components (headers, y-pipe, cat, muffler, and pipes) that your dealing with, not counting your engine's mods and performance and your PCM's abilities. Each has to work with the other to achieve the perfect balance of low end -vs- top end, scavaging -vs- backpressure -vs- flow speed, etc. Not many people on here ever try more then one combination. Then, when they have hundreds of dollars into it, you think they are going to quickly say that something didn't work right, and scrap it for a few hundred dollars more in exhaust components? I doubt it. They're going to come on here and say it works great, and everyone should do the same they did. I see it all the time. I do admire 20DodgeNeon00 for coming right out and saying his long tubes made his low end suffer. I hope he gets it fixed, but that was actually what I expected to happen, and have read it on other forums from guys who tried it first hand and had the same result. I didn't say anything because I hadn't tried them for myself. I was glad to see he posted real results. I think he'll be fine once he gets some other mods and a better PCM tune, but on a mostly stock truck, I wasn't suprised. I've been around here for awhile, and prior to Pacesetter coming out with those, people on these forums acted like longtubes, if they existed, would be the best setup ever, period. Had they ever tested them? No, they didn't even exist yet. So I guess my point is, use caution when taking the advice of someone who hasn't tried it for themselves (this goes for most mods, not just exhaust mods). Best thing you can do is try it for yourself, and then decide for yourself.

I'll gladly post results from when I get my 3" back down to 2.5", but I doubt that will be anytime soon. Too many other mods ahead of that right now. But it is definetly going to happen. 3" is too big for a 5.2. Have I said that already?

 

so whats the best size too use for a 5.9 duels 2.25 or 2.5 or 3 inch

 

lastrights, basically, from what I can gather from this thread, do whatever you think is best.

I have the 5.9, and I think I'm going to go ahead with dual 2.25 inchers. I'm only going to do a cat-back system right now (maybe a high-flow cat) with a performance muffler. But the only other mods I have planned at this point are a Fastman 50mm or 52mm TB and a K&N CAI. (You guys, on other threads, have convinced me that the Fastman TB is a good idea.) So if you have major mods planned, maybe you could use larger pipes. Or go true dual. Whatever you feel is best for you and your truck.

I will post once my exhaust is done with how I think it feels. Should only be another week or so before I have the funds and the time.

I know on my 1995 Dakota with the 5.2, I put a cat back system with dual 2.25" pipes on it. I noticed a very mild performance gain, not a great deal. Then I installed an open element K&N... and wow. The two in combination gave me a very noticable power gain over stock.

 

It is always best to test things for yourself.

Got a vice grip?
Got a set of sockets up to 3 inch or so?

Find yourself a safe spot to do acceleration runs
{ or go to a good rear wheel dyno with a trainned operator }
and make runs with your present exhaust
then make runs with different sized sockets
clamped in place inside your tailpipe exit with the vice grip.

You can improve your test by using your cell phone to video
the speedometer as you make the runs
and then use this highway dyno to get even more accurate hp
than all but the very best run rear wheel dynos
and save the expense too.

http://www.bgsoflex.com/dyno.html

If you want to find out what minimum backpressure does
go just after the exhaust manifold or header
and cut out half the pipe at the bottom for about 4 inches
to make the exhaust almost zero backpressure.
It won't cost that much for an exhaust shop to weld the two sections
you cut out back in place for you
...or you can use a DynoMax stainless steel clamp yourself.

What will you find?
{these tests have been done many times}

You will find that the guys on the internet who claim that backpressure improves torque
are 'wild a$$ guessers' who are repeating myths they read without doing any tests of their own,
in fact you will find these guys almost never do a proper test of any kind.

see next two posts for proof

 

as info to your question about backpressure always being a horsepower robber -
here is a quote from page 139 of the Austrailan book "21st Century
Performance"

begin quote

"Few tests have been done that clearly show the effect of changing back
pressure. Most muffler and exhaust comparison tests change more than one
parameter simultaneously, making the identification of exhaust back pressure
as a culprit difficult. However, Wollongong (Austraila) mechanic Kevin Davis
has done extensive testing of varying back-pressure on a number of performance
engines. These range from turbocharged Subaru Liberty (Legacy) RS flat fours
to full-house traditional pushrod V8s. In not one case has he found any
improvement in any engine performance parameter with increased exhaust back
pressure.

The tests came about because Kevin has developed a patented variable-flow
exhaust that uses a butterfly within the exhaust pipe. He initially expected
to use the system to cause some back pressure at low loads 'to help torque.'
However, he soon changed his mind when any increase in back pressure proved to
decrease torque on a properly tuned engine. What increasing the back pressure
does do is dramatically quieten the exhaust.

One of the engine dyno tests carried out by Kevin was on a modified 351 4V
Cleveland V8. Following the extractors he fitted a huge exhaust that gave a
measured zero back pressure. Torque peaked at 573Nm (423 ft-lbs) at 4700 rpm,
with power a rousing 329 kW (441 hp) at 6300 rpm. He then dialed-in 1.5 psi
(10.4 kpa) back pressure. As you'll see later, very few exhausts are capable
of delivering such a low back pressure on a road car. Even with this small
amount of back pressure, peak torque dropped by 4 per cent and peak power by 5
per cent. He then cahnged the exhaust to give 2.5 psi back pressure. Torque
and power decreased again, both dropping by 7 per cent over having zero back
pressure.

Figure 6.1 {which is a graph with three lines showing HP against rpm} shows
the power curves gained in the tests. These results were achieved on a large
engine with a large overlap cam - one of the type some people suggest is
'supposed' to like back pressure.

If, in fact, power does increase with increased exhaust back pressure, it is
most likely the air/fuel ratio and/or ignition timing that are no longer
optimal for the altered state of engine tune."

end quote

 

David Vizard
the man NASCAR recruited to run
the UNC-Charlotte Motorsports engine building trainning program
has written the best article about understanding exhausts:

Exhaust Science Demystified

http://www.superchevy.com/technical/...exh/index.html

People who think that tailpipe size influences torque
are just confused
and don't understand the difference between
primary header pipe diameter
and tailpipe diameter that is far behind the header primary pipe.

Director of Superchips Jim McFarland has tried to explain it simply:

http://www.n2performance.com/perform...tems/index.htm

in this lecture is the quote that many get confused over,
where he talks about too much overlap in race engines' valve timing
and how a little exhaust pressure might affect it by not drawing out unburnt fresh charge
but the thing to do is make the overlap right
not increase the exhaust backpressure.

Don't be a WAG'er
Don't repeat myths you haven't tested and proved to yourself.

 

Silver, that's fine if you want your opinion to be heard or to testify against somebody else, but again, there are better more appropriate ways to voice your opinion. You clearly came into the thread being derrogatory to me, and it's totally uncalled for. I also don't see how I'm not personally qualified to voice my opinion, seeing I originally had a catback system put into my truck. As I said before, I put a 3" in/out magnaflow cat in, and then a 3"in/2.5" dual out muffler on the truck. That's even more than what he is proposing to do with this y-pipe unit. I lost NO low end with my set-up, in fact I gained some. I am confident that if he runs that 2.5" y-pipe from his cat, he will loose NO TORQUE, but gain some. Again, a 5.2L is NOT A SMALL ENGINE, it's just smaller than the 5.9L, I'm pretty damn sure his truck can handle a little section of the truck being 2.5" fake dual. It's easy to get wrapped into making a catback a big deal, but really it is not. Again, people, do not just jump to your assumptions, or the assumptions you want to believe what you think about people. Clearly I've had a ton of experience with exhaust (my truck, and my brothers truck...he's had 3 different exhaust systems). If anybody ever has an issue with what somebody says, don't take the immature route and start dissing on somebody personally or call them out, there are more "Adult Like" ways to address it. Me, as an 18 year old, shouldn't be having to lay this out, but looks like I have to bring back how we should all each other, regardless of our differances at times.

 

I think it is ignorant saying you are wasting your time with 2.25". For true duals with no Y pipe 2.25 is about perfect for a 318, though If you went with a Y 2.5 would be better. If you had a 360 I wouldnt go bigger than 2.5 (do as I say not as I do, my setup has a littlehigher aspirations.) High flow cats help, muffler is really your preferance. My favorite for true duals is magnaflows muffler thats dual in dual out with the X pipe inside. It sounds good, and saves you money by having the crossover inside the muffler rather than having to buy a crossover and fit it someplace else. (thats actually something im contemplating going with)

 

Heres the problem. You don't have a gauge on power with the smaller pipes. You got rid of the stock muffler wich freeded up alot of flow so you might gain more by having the other pipes. You are right though 2.25 to 2.5 isn't a huge difference. There is a differnce between the 318 and the 360 maybe not HP wise but there is size wise. The 360 just barely touches the area where you would use a 3" pipe. The cut off is 350. So the 318 lies very solidly in the area of a 2.5" exhaust.

 

Well, I think your taking it way too personally, and i'm not trying to start anything with you. I apologize if I offended you, not my intention.

HankL, as always, that is some good reading. I always wonder were you dig this stuff up from.