Dual 2.5" vs Single 3" exhaust
#1223219
04/27/12 08:55 PM
04/27/12 08:55 PM
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Joined: Nov 2011
Posts: 2,154 Its a TRAP!
DARTH V8Я
OP
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OP
Oh No!! I just had a moron attack!
Joined: Nov 2011
Posts: 2,154
Its a TRAP!
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So, which would make more horsepower/torque in both peak and 'under the curve' in a typical NA smallblock? Right now I'm leaning towards a single 3" in my application, but if need be I could squeeze in a dual 2.5" exhaust. Thanks.
When it takes more than a sweet mullet to prove you rule at the trailer park..
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Re: Dual 2.5" vs Single 3" exhaust
[Re: WO23Coronet]
#1223221
04/27/12 11:12 PM
04/27/12 11:12 PM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
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Marysville, O-H-I-O
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the dual system will give you the best of both worlds. your pipes will be small enough to keep velocity/scavenging up at lower RPM for better torque, but by having 2 pipes, you can still get high RPM flow out of them.
2 2.5" pipes have a lot more cross sectional area and flow potential than a single 3" pipe.
but, for a truck (assuming that's what this is on since your asking about duals vs single) it can sometimes be tricky routing a true dual system, especially if it's a newer truck where the tank hangs inside the frame rail, in front of the rear axle, forcing your driver side exhaust to cross over to the passenger side.
how "big" is your engine? a single 3" system will still support a TON of Hp. my engine is only lightly modded, and put down 300 hp to the wheels, I do not feel like my exhaust is the limiting factor, or anywhere near choking me down yet. my exhaust will flow more than my heads will
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Re: Dual 2.5" vs Single 3" exhaust
[Re: DARTH V8Я]
#1223224
04/28/12 09:32 AM
04/28/12 09:32 AM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
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Too Many Posts
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Marysville, O-H-I-O
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with properly sized headers that go into a single 3" system, you'll easilly make 400 crank hp. My Dakota has the worst headers on the market on them. $120 "shortys" that bolt to the factory down pipes...they are marginally better than the stock manifolds, especially since they are about as compact as the factory manifolds. it then flow through some 2" pipe that dumps into a 3" single run that's about 5 feet long.
I put 295 hp and 330 tq to the wheels, so that's up around the 375-400 ball-park on crank hp, and Like I said, my heads are what's holding me back now, not my exhaust.
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Re: Dual 2.5" vs Single 3" exhaust
[Re: 70Cuda383]
#1223225
04/28/12 10:17 AM
04/28/12 10:17 AM
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Joined: Feb 2009
Posts: 773 Crofton, Ky.
rattler
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super stock
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Crofton, Ky.
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I'll give you the numbers to compare. A set of dual 2 1/2 pipes have a combined surface area of 9.8175 inches, while a single 3 inch pipe has a surface area of 7.0686 inches. Thats quite a bit of difference.
1957 Dodge truck, Snakeskin Green with a little stroker motor. 1964 Plymouth Savoy wagon ( my new project)
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Re: Dual 2.5" vs Single 3" exhaust
[Re: HotRodDave]
#1223230
04/28/12 04:43 PM
04/28/12 04:43 PM
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Joined: Oct 2003
Posts: 21,345 Marysville, O-H-I-O
70Cuda383
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Too Many Posts
Joined: Oct 2003
Posts: 21,345
Marysville, O-H-I-O
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Quote:
Quote:
I'll give you the numbers to compare. A set of dual 2 1/2 pipes have a combined surface area of 9.8175 inches, while a single 3 inch pipe has a surface area of 7.0686 inches. Thats quite a bit of difference.
I think you mean cross sectional area not surface area. Those duals have a ton more surface area in the pipes to create friction witch resists flow. Also because the cross section is so much higher in the duals it loses velocity. If you had two exhaust systems of equal cross section then the single would make more power. The single would also be more balanced and scavenge better, sort of like an X pipe but it don't seperate back appart. A single exhaust with an equal cross section will have more velocity, flow and HP. Your examples are not equal though.
All that is true. dual pipes will have MUCH more surface area inside the pipe, creating more boundary layer turbulance/friction and resistance to flow.
a dual 2 1/8" pipe is about equal in cross sectional area to a single 3" pipe.
I would think the dual 2.125" system would have more low end torque, and still maintain the same higher RPM hp of the single 3" system.
I've always read that smaller pipes will have more velocity, more torque, but will not support high RPM flow requirements. Especially with header primary sizes.
if a smaller primary size gives more low end torque/scavenging because of the increased velocity of the flow, but will become "stuffed up" and not support high RPM hp, then why would that not apply to the full system?
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Re: Dual 2.5" vs Single 3" exhaust
[Re: DARTH V8Я]
#1223232
04/29/12 12:40 AM
04/29/12 12:40 AM
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Joined: Sep 2003
Posts: 1,168 Vancouver, WA
MoparMarq
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Joined: Sep 2003
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Vancouver, WA
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Quote:
I think the reason is becouse fluids follow a different set of rules then gasses in terms of flow. By that I mean fluids produce more friction then gasses.
False. As far as the engineering is concerned, the same equations apply for fluid mechanics. Fluid in these terms can be a liquid or a gas. The difference in this case was touched on by HotRodDave in his use of the term "surface area". All other things being equal, two pipes of the same "cross section area" would be sized at about 71% of the diameter of a single pipe (1 / square root of 2). Nearest real world comparo is single 3" vs. dual 2-1/4". In theoretical terms, the dual exhaust (at 71% diameter, or 2.14") will have 1.4 times the "surface area" (the outside of the pipe) for heat loss to the atmosphere prior to exiting the tailpipe. Heat loss slows velocity. This makes the comparison between given cross section area size pipes a comparison between apples and oranges.
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Re: Dual 2.5" vs Single 3" exhaust
[Re: Tom Hand]
#1223235
04/29/12 01:20 PM
04/29/12 01:20 PM
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Joined: Jan 2005
Posts: 12,419 Kalispell Mt.
HotRodDave
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Kalispell Mt.
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Then why not run 8 single exhaust systems Headers are takeing advantage of tuneing, collectors are also needed for this tuneing, the rest of the exhaust system is primarily dealing with just flow. If you understand what is really going on with a tuned length header/collector you will understand why they are run together... the piston forces exhaust out in one big "lump" really fast, this "lump" goes flying past the end of the pipe of the next pipe in the firing order, as that mass of exhaust flies past the other pipe the inertia it has pulls a vaccume on the adjacent pipe, if that pipe is just about to dump the exhaust then the first lump will help pull it out of that pipe, it is the venturi effect. In a normal V8 there is an un even firing order from side to side so you get two lumps really close together, this is where the X pipe comes in, or the old fashioned less effective H pipe. It allows that big supper lump to bleed from one side to the other and allows scavenging from one side to the other, now the ultimate exhaust would be to join the two pipes into one at just the right time for the two big lumps to help pull each other out the entire length of the pipe in a single exhaust configuration. After a certain point in the system there is gonna be no significant tuneing effect and simply raw flow numbers are gonna make the most HP and a single pipe with the same cross section as a dual system will flow more, then it becomes a matter of packageing the system and most cars will have a hard time fitting a single 3.5 inch pipe with out dragging the ground or bending it too tight, this is the only reason dual exhaust became popular for high power machines. A dual system has more heat loss due to surface area than an equal cross section single and heat loss costs HP also. Now there is gonna come a point where simply raw flow rules supreme even over scavenging but that is top fuel territory (not even nascar or F1) where 8 single exhaust pipes rule but even then they still tune with the primary lengths instead of just running the exhaust right out of the head. Here is how scavenging works http://www.youtube.com/watch?v=pzhM9e5ZpbASee how he lets his breath pull more air to fill the bag with one breath instead of the 6 or 8 individual breaths, that is like how one exhaust "breath" from one cylinder pulls on the next one to better empty the cylinder and if you can get the cylinder more empty then you can pull in more A/F on the intake stroke and make more power. The pipes by them self would never make as much power if they were not able to pull their neighbors exhaust and by running duals you are limiting there ability to help there neighbor.
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Re: Dual 2.5" vs Single 3" exhaust
[Re: HotRodDave]
#1223236
04/29/12 01:54 PM
04/29/12 01:54 PM
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Joined: Jul 2007
Posts: 271 MO, USA
Tom Hand
enthusiast
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enthusiast
Joined: Jul 2007
Posts: 271
MO, USA
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For sure HotRod Dave you are right on about the tuning but in fact, at the muffler, heat loss gains power. Heat loss brings with it a loss of gas volume and that helps the muffler work a bit easier and this is what you want for good silencing. Obviously, we are both talking about different ends of the system and I agree about scavenging. Headers and good exhaust systems depend upon it to get fresh air in after getting exhausted air out. If any others want to see what new cars have on them to get good silencing and performance, check out new Honda and Toyotas. These have split pipes after the axle and run two very large volume mufflers. Exhaust is such cool science. Tom
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