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josh
Dodge Dakota
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4/30/2007
19:34:49
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 Subject: should i add an x-pipe?
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whats up guys, i have an 04 dakota extended cab with the 4.7 and the 45rfe auto tranny. i have stock 3.55 and a k &n intake, gibson headers and true dual exhaust with flowmaster mufflers. i cut the y- pipe apart and had the duals ran that way with 2 1/4 in. pipe. sounds great, but the milage went down on the highway and in town due to not having the scavanging effect. should i have a y-pipe added in or an x-pipe to help with this and improve power at the same time???
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01Motorsport
Dodge Dakota
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4/30/2007
22:21:47
| RE: should i add an x-pipe?
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josh, does your true duals have catalytic converters, or none? With intake, headers, true duals and no(?) converters, you may have a lean fuel mixture situation beyond what the stock computer can handle. I think Superchips is not an option on '04 4.7's either. Anyway, Magnaflow now makes x-pipes, as well as y-pipes. www.magnaflow.com
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josh
Dodge Dakota
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4/30/2007
23:11:59
| RE: should i add an x-pipe?
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yes i still have the stock cats in place...if magnaflow makes x-pipes, would a muffler shop be able to make one just as good?
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slowdakota97
Dodge Dakota
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5/03/2007
13:36:22
| RE: should i add an x-pipe?
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you should check out spintechmufflers.com they have an X pipe for the 4.7 i believe. I know they have them for the 5.2 and 5.9's I just installed an entire catless x pipe system from them and it fit almost perfect. it would probably be your best and easiest solution.
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Josh
Dodge Dakota
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5/03/2007
14:25:14
| RE: should i add an x-pipe?
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It's the pipe diameter. 2-1/4" pipe is too big for duals.
To maintain the scavenging (exhaust gas flow velocity), the pipes should be 1-1/2" to 1-3/4" diameter.
For both streams together, 2-1/4" pipe is right for the rest of the pipe behind the collector.
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Kota Kid
Dodge Dakota
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5/04/2007
18:00:49
|  RE: should i add an x-pipe?
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2 1/4 too big are you nuts?! Mine has the true dual 2 1/2in setup from spintech and my mpg didn't go anywhere and power went up big time!
Oh yeah and 2 1/4in pipe is not the best size for single exhaust 3in is, it will also sound worse with 2 1/4 instead of 3in. 3in pipe has much more deep of a sound than 2 1/4.
He11 on my friends Monte Carlo grand stock race car with a 2bbl 305 ,with stock vortec heads, we run 3in true duals for max power.
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Josh
Dodge Dakota
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5/04/2007
21:48:43
| RE: should i add an x-pipe?
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"...and power went up big time!"
Show us the dyno results.
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Kota Kid
Dodge Dakota
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5/05/2007
17:01:42
| RE: should i add an x-pipe?
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Show me a dyno i don't have to pay to use!
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Manny
Dodge Dakota
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5/05/2007
19:52:48
| RE: should i add an x-pipe?
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Then your statement "...and power went up big time!" is merely conjecture.
Josh is not nuts. His points about exhaust pipe diameter are valid within the context of the reasons he gave about maintaining flow velocity in a 4.7L engine's exhaust system.
The original post from another Josh has concerns about losing flow velocity with large diameter pipes subsequent to change to dual exhaust. Second Josh just told him why.
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Kota Kid
Dodge Dakota
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5/05/2007
22:08:51
| RE: should i add an x-pipe?
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Ok if small pipes are so good then explain to me why no performance car or truck out there uses 1 1/2in exhaust pipes? Or why dragsters that are required by class rules to have an exhaust system and/or mufflers use at least 3in pipes? Or why Nascars use 3 1/2in flattened pipes instead of 1 1/2in pipes that wouldn't need to be flattened for ground clearence issues?
Do you seriously think that taking 4 pipes, per side, that measure 1 5/8in each and trying to stuff all of them into a single pipe thats only 1/8 of an inch bigger than one of the 4 header pipes is a good idea?
And as far as my truck gaining power when i installed the true dual setup i can tell you how i can prove i am right. You come to eastern Virginia reinstall my stock exhaust, pay the dyno rental fee, reinstall the true dual exhaust and pay the dyno fee again. If you are willing to do that i am willing to let you do it. I don't have the money to dyno my truck at $175 a run around here before and after every mod that i do but if you will pay for me i would love to see the results!
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Kota Kid
Dodge Dakota
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5/05/2007
22:16:09
| RE: should i add an x-pipe?
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My Honda 400ex has a 1 3/4in exhaust pipe and only one cylinder! Does your logic mean that if i put a 1/2 in exhaust pipe on it i would gain power? I mean if 1 1/2in pipe is good for half a V8 than surely 1/2 in pipe is more than big enough for a much smaller single cyl engine!
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capone
Dodge Dakota
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5/05/2007
23:42:29
| RE: should i add an x-pipe?
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Somehow I knew you drove a honda...
Anyways, it depends on the engine and what you're trying to do.
Switching to true duals (or anything better than stock) will give
you better power. Just because you have bigger pipes than him
and felt more power doesn't mean that you're getting more
power than him. There is an ideal size for the amount of air
moving through the engine. All the cars you mentioned have
completely different motors pushing completely different
amounts of exhaust. Why do high performance cars have huge
exhaust? More air moving through = more fuel being burned =
more power = high performance car = bigger exhaust. There is
your logic for you. Opening up the exhaust effects
backpressure. Lower backpressure creates horsepower, and
while opening it up further it may create more you'll lose low
end torque. Pushing it too far will just be bad all together. You
should pay to have your truck dynoed, you may not be making
the power you hope you are.
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Josh
Dodge Dakota
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5/05/2007
23:51:19
| RE: should i add an x-pipe?
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Hey throttle back a bit there, junior.
The other Josh asked about perceived reduction of power because of loss of scavenging effect due to larger relative exhaust pipe size.
"Ok if small pipes are so good then explain to me why no performance car or truck out there uses 1 1/2in exhaust pipes? Or why dragsters that are required by class rules to have an exhaust system and/or mufflers use at least 3in pipes? Or why Nascars use 3 1/2in flattened pipes...."
His pickup is not a "performance vehicle", a dragster or a Nascar. It's a pickup.
"Do you seriously think that taking 4 pipes, per side, that measure 1 5/8in each and trying to stuff all of them into a single pipe thats only 1/8 of an inch bigger than one of the 4 header pipes is a good idea?"
Never said it was a good idea. I only said what diameter pipes I believe work best on a 4.7L Dodge engine for best exhaust gas flow velocity (scavenging), based on exhaust gas volume at different RPM vs flow rates of various pipe diameters and pulse propagation at different exhaust system lengths. That information was gathered as research for a planned set of custom long tube headers and exhaust system for my own 4.7L Dakota.
"And as far as my truck gaining power when i installed the true dual setup i can tell you how i can prove i am right. You come to eastern Virginia reinstall my stock exhaust, pay the dyno rental fee, reinstall the true dual exhaust and pay the dyno fee again. If you are willing to do that i am willing to let you do it. I don't have the money to dyno my truck at $175 a run around here before and after every mod that i do but if you will pay for me i would love to see the results!"
Can't help you with that. I'm on the other side of the map.
"My Honda 400ex has a 1 3/4in exhaust pipe and only one cylinder! Does your logic mean that if i put a 1/2 in exhaust pipe on it i would gain power? I mean if 1 1/2in pipe is good for half a V8 than surely 1/2 in pipe is more than big enough for a much smaller single cyl engine!"
Staying on subject, the overall length of the exhaust system also has a great deal to do with scavenging. How long is your Honda's exhaust system compared to the length of the Dakota's exhaust system.
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Kowalski
GenIII
5/06/2007
09:38:07
| RE: should i add an x-pipe?
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While exhaust velocity is very imortant for scaveging, I think the sizes Josh has recomended are small for a 4.7. There was no noticable power loss when I put a 3" single system on mine; and I'd think 2 1/4" should be a good size for dual exhaust for that motor.
Lead, follow, or get out of the way
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Kota Kid
Dodge Dakota
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5/06/2007
14:53:46
| RE: should i add an x-pipe?
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Thank you Kowalski!
I've got a question though if all you are trying to do is make your truck louder without affecting the stock driveability why go through all the trouble and money to have a true dual setup installed? You can get a cat-back system far cheaper that is easier to install that won't affect things like gas mileage.
Now don't get me wrong i'm not saying to go out and put a 4in true dual system on your truck and expect a power gain. I know there are limits to the size of the pipe, but there is no way in he11 you are going to convince me that a 1 3/4in pipe will flow better than a 2 1/2. I don't care how fast the air moves through the pipes if you try to shove it through a straw it is going to take more effort or in this case POWER!
Oh yeah, capone i don't drive a Honda i ride a Honda! Its an atv not a civic. I wouldn't own a japanese car if you gave me one!
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capone
Dodge Dakota
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5/06/2007
17:45:40
| RE: should i add an x-pipe?
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I hereby retract my honda comment ;)
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GraphiteDak
GenIII
5/06/2007
21:25:48
| RE: should i add an x-pipe?
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I don't think my oversized dual exhaust hurt my power enough to notice. It will still rip the tires from a dead stop being a QC 4X4 and all... That's pretty good. No x pipe either.
I may try an H-Pipe one of these days. But maybe not.
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Dusty
Dodge Dakota
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5/07/2007
18:20:17
|  RE: should i add an x-pipe?
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I agree that dual 2.5" is too big. I have consistant track times (in 4wd) before the 2.5" duals I was cutting 2.2 60's. After the dual I was getting 2.3's 60's. Lost torque. I'm debating whether to go back and do it all over again with 2 1/4" or just try to make the little 4.7 breath more...
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josh
Dodge Dakota
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5/07/2007
22:11:12
| RE: should i add an x-pipe?
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thanks for all of the feedback. but one thing that is still bugging me...i dont have anything to advance the timing and still have the stock cams. if i change the cams will that help the mpg IF i use the stock H.O. cams or the KRC h.o. cams. the stockers are cheaper but the KRC website states that with the proper setup( gears, converter, pcm flash and t-body) that their cams make 33 or more horses and 66 plus ft.lbs. since i cant flash my pcm would i still notice a difference or just be wasting my $$$?
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01Motorsport
Dodge Dakota
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5/07/2007
22:43:09
| RE: should i add an x-pipe?
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The neat thing about the HO cams is the peak torque around 3400 rpm, a real plus the heavier your Dakota is. '03 and '04 already have the "HO" intake manifold OEM. I have HO cams and 2 1/4" duals exiting a Flowmaster 70. A dyno run last month yielded 286 rear wheel torque (WITH the clutch fan). I couldn't be happier.
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Db4life78
Dodge Dakota
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5/08/2007
12:39:46
| RE: should i add an x-pipe?
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To tell you all the truth, in the context that Josh was speaking he is correct for the most part. If you break it down to the simplest terms it looks like this Q = V x A, where Q is the flow rate, V is the velocity of the flow and A is the area of the pipe. You can do the math to see how much more you are really flowing if you hold the velocity constant, which is what he as talking about maintaining. We could get into the calculus involved with this but I don't know that many people that like calculus. There is a balance point that is hit as to the optimal size to be used, beyond that it is pointless and even detrimental. Besides you can do all the math you want and calculate all the losses to figure your theoretical whp, but the only way to know for sure is to dyno it, and until then put up or shut up.
KotaKid you are right the smaller pipe flows will be less than a larger pipe, although the flow velocities will be less, and that is what was being brought up by Josh, so he is right, you will have higher velocities for a smaller diameter pipe.
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