Single carb vs dual

[waxhead]

You gonna leave me hangin? You said niether side ever gets all 46mm of goodness. You then said air has mass and when the reed closes, all that mass isnt going to exit that side of the intake. Its basicly trapped there. So in effect your saying that the intake side solid with mass is causing all the 46mm goodness to go to the open reed side .... ?

Please quote me where i said it was solid. I said it has air has mass

I dont have the time to go through a full on physics lesson so do some research your self and let me know what you come up with

 

[BruceSki]

Crossover?

 

[badvinny]

Whats "hit the pipe" mean?

I feel a need to 'hit the pipe after reading all that!

 

[WB1994]

Please quote me where i said it was solid. I said it has air has mass

Therefore the air is backing up behind the reed cage and does not in fact stall and change direction and go down the other carb.

I never said that you said it was solid , If you read I say in my assumption your saying that the closed reed side is now in one way , solid. Now this is where you agree or dissagree and give a reasoning so I can understand and learn. Your hard to understand when you say all 46mm of goodness never goes fully to one side but cant give a simple explination to this moron. If one side is full of mass , where is all the 46mm of mass going? You said never fully to one side. But the other side is full of mass blocked off by reeds. With a shockwave thrown in for good measure.

 

[waxhead]

I'm starting to think your right and that a single carb is the go. You have convinced me

 

[WB1994]

Funny , Im running duals.

 

[waxhead]

You should go for a single

 

[WB1994]

Nah , I'd have to run 65mm to get as much as what dual 38's feed a single cylinder due to never getting the full 65mm goodness to one cylinder because the mass infront of the reed is trying to mygrate to the open side .

Im going to make clear lexan cases to watch both sets of reeds stay open at all times.

 

[waxhead]

Nah , I'd have to run 65mm to get as much as what dual 38's feed a single cylinder due to never getting the full 65mm goodness to one cylinder because the mass infront of the reed is trying to mygrate to the open side .

Im going to make clear lexan cases to watch both sets of reeds stay open at all times.

Yup. That's what I thought you would say.

 

[Lil Dick]

Soooo back to the thread stay with the dual 38s lol fair enough I got a guy going over the carbs think it's mainly just pop off


Sent from my iPhone using Tapatalk

 

[Half flip95]

I don't know of this is right but the way I'm imagining it is that assuming your front cyl reeds are closed and the rear cyl reeds are open and pulling air. Your "signal" is not a black hole that nothing can escape and the single carb manis have lots of empty space that the air can bounce around in and not go directly to the open reeds. Ie air has mass? Duals would be more effective because they are a straight shot with one direction of signal where as the single would be bouncing back and fourth causing some swirling of air? I look at how they port manifolds to get smoother direct flow and newer manifolds are designed to get the air in the cases as fast as possible. Maybe this was the thinking behind side draft manis but they just weren't practical in a ski? I really have no idea I just made all that up but it sounds plausible

 

[550/440]

http://www.1728.org/flowrate.htm

Using a velocity of 10 feet per second, these calculations were found (I don't know what the true velocity would be, nor do I know how to figure it out).

Single 38: 7.5940 cfm
Dual 38: 15.188 cfm
Single 48: 11.687 cfm

The very basic math suggests that dual 38s can flow more than a single 48. I'm sure there are 100's of other factors that will come into play. How many competitive skis do you see on the freestyle circuit running single carbs? How about on the racing circuit?

 

[lanmine657]

http://www.1728.org/flowrate.htm

Using a velocity of 10 feet per second, these calculations were found (I don't know what the true velocity would be, nor do I know how to figure it out).

Single 38: 7.5940 cfm
Dual 38: 15.188 cfm
Single 48: 11.687 cfm

The very basic math suggests that dual 38s can flow more than a single 48. I'm sure there are 100's of other factors that will come into play. How many competitive skis do you see on the freestyle circuit running single carbs? How about on the racing circuit?

A lot depends on case porting, a 61x platform will perform better with a single carb especially when reed stuffers are added, 62t and newr case porting are designed for dual setups, velocity in sometimes doesn't matter, it's more about matching intake with case porting

 

[Vumad]

You gonna leave me hangin? You said niether side ever gets all 46mm of goodness. You then said air has mass and when the reed closes, all that mass isnt going to exit that side of the intake. Its basicly trapped there. So in effect your saying that the intake side solid with mass is causing all the 46mm goodness to go to the open reed side .... ?

I'm not an expert on this subject, so someone correct me if I am wrong, but I believe I can help clear all of this up...

The assumption is that bigger is better. A single 46 brings more air and fuel into a motor than 2 single 38s, and since more is better, a 46 should work better.

More is better, but more depends on what is more. If we are talking about more efficiency, then more is better, but if we are simply talking about more volume alone, not necessarily.

The Yamaha 800, 1200, 1300 are side mounted with straight intake tracks. The seadoo 951 has straight intake tracks and the exhaust is on the same side as the intake. These configurations provide more efficient, less turbulent, airflow. The seadoo allows air to enter the left, travel rightwards and upwards, then back out the left, one smooth continuous flow.

Intakes on cases are not ported just for more volume. They are ported to provide a more direct intake track to the crank. This improves air flow, decreases turbulence and improve efficiency.

We all talk about porting, but polishing is also a factor. Actually, a port clean up and a polish, with no increases to port high or width can improve performance. It decreases air turbulence and allows for better exhaust flow. I believe no one will disagree with me that it would be foolish to port a motor and motor sleeve and leave the rest of the port with a finish match that of 40 grit sand paper. A larger port isn't better just because it is larger.



So, taking the conversation back to the discussion of dual vs single carbs, and the duals are better because they more efficiently deliver less volume.

The single 46 would provide more air and fuel, but with less carb signal, and more turbulence in the intake. It's not a question of how much air and fuel it pulls, but what it does with it. The turbulence and poor signal result in a very poor mixing of the fuel. We run richer than necessary to make up for poor mixing of the fuel.

A perfect example of this is my X2 (which matched specifications provided by other users with similar setups). My X2 using a single 44 had 150/120@32. With dual 44s, I'm running 122/117@21 (still getting it dialed in perfect). My performance has also increased. Lets say for arguement sake that the single delivers 100% of the air and fuel to both cylinders equally, we are giving much more fuel to each cylinder with the single than with duals. Why? Because the single is inefficient at mixing the fuel.

Dual carbs have a direct flow into the engine. They also provide that flow from an appropriate sized carb. They provide much more efficient air flow and fuel mixing. The result is increased efficiency. Perhaps if a single 46 provides more bottom than a dual 38s, it's time to increase to a set of dual 40s, 42s or 44s, and a proper tuning.

We've done 2 back to back tuning jobs recently (750 Bp and 750 SP). Single 44 replaced by dual 44s, and saw a minor - moderate improvement in power everywhere. And a dual 38s replaced by a single 44 which resulted in a minor changes on the bottom but a dramatic loss of top end power and increase in fuel consumption.



The statement made earlier about dual carbs being finicky early was silly. How many of us jump on a 20 year old B2 or GP760, that has never been tuned, just used annually, and it runs great? I'm sure plenty of us. Yes, dual carbs are harder to get tuned because there is twice the work, but keeping them that way is relative. Dual carbs give more performance, and minor changes in the carb will alter that performance. One cylinder may start to run a tad leaner / richer than the other. Singles on the other hand, the cylinders are always different, and you can't notice something that is not tuned right coming out of tune. It had cylinder miss match since day one. Duals simply set a higher expectation, and owners / tuners become disappointed when minor changes to internals result in mismatch that single carb owner would rave about.



If any of the above does not support the case, then how about very simple economics. Yamaha and kawasaki both changed from single 38mm carbs in 1995 to dual 38mm carbs in 1996. It can not be challenged that this configuration has a higher production cost. But wait, aren't these businesses trying to make money, why are they raising costs? Because the money is made in the competition. The duals make more power, and people buy more power. Single carbs went obsolete 20 years ago.

 

[WB1994]

They went with dual carbs because they went with couches because americans are fat and lazy and pin the throttle wide open all day long and its cheaper to stick on a second carb then warantee a motor. port timings changed and exhausts and cases. Not just carbs. All detuning for WOT runs on heavy couches. Detuning or idiotproofing. Before 96 people were sticking duals on a 61X. Tell me how well that worked. Sticking two carbs on something doesnt automaticaly make it better. There is a ton more pieces to the equasion on down the line all the way to the exhaust tube.

Its funny cause Ive tuned lots of motors and always found the dual carb guys having to go back to shore for a refil before the single carb guys. Ive run both and gotten better fuel consumption on singles. Weve also swapped riders in the surf to see if it was a heavy finger causing more fuel consumption and it wasnt.

Your stating alot of things that are assumptions there Vumad. Like how do you know if a single carb doesnt attomize as well as a dual? I can make an assumption too , like the fact that a dual carb is allways seeing a constant "on off " signal. The carb is performing and shutting down and performing multiple times a second. That condones better atomization than a carb getting a constant atmospheric preasure through it?

 

[Vumad]

Your stating alot of things that are assumptions there Vumad.

Fortunately for me, I started the post off by pointing out that I was mostly making deductions and assumptions. Go me.

They went with dual carbs because they went with couches because americans are fat and lazy and pin the throttle wide open all day long and its cheaper to stick on a second carb then warantee a motor. port timings changed and exhausts and cases. Not just carbs. All detuning for WOT runs on heavy couches. Detuning or idiotproofing. Before 96 people were sticking duals on a 61X. Tell me how well that worked. Sticking two carbs on something doesnt automaticaly make it better. There is a ton more pieces to the equasion on down the line all the way to the exhaust tube.

Haven't seen a XS or Dasa in a couch.

Before 96 people were sticking duals on a 61X. Tell me how well that worked.

And after 1996, people are sticking singles on 62T.

 

[WB1994]

Haven't seen a XS or Dasa in a couch.



And after 1996, people are sticking singles on 62T.

Congradulations , im confused.

 

[lanmine657]

I love all the equations and tech talk but usually what's on paper doesn't hold true in real world testing, yes there are many who still like big singles over big duals even with these newr bigger motors, no two boats will react the same to changes and that's why all of us have boxes of expensive parts on our workbenches

 

[waxhead]

I love all the equations and tech talk but usually what's on paper doesn't hold true in real world testing, yes there are many who still like big singles over big duals even with these newr bigger motors, no two boats will react the same to changes and that's why all of us have boxes of expensive parts on our workbenches

Plus some of the people in here don't seem to be bound by the same laws of physics as the rest of us

 

[naticen]

I believe turbulence would cause better atomization. Polishing intakes reduces torque in a lot of 4 stroke applications.

He's stating that DASA and XS aren't detuning for couch riders, but they still run duals. Not sure about the 61x, but I have a dual intake mani that came with a parts deal because he was getting out of the sport. He said he bought it because it was recommended by Art. I would think that means a 61x does well with duals. Obviously hearsay on my part.

Here's my dumb question of the day. Why can't you run a single carb on a 3 cylinder? You can run a single on a v6 four stroke.