B pipe routing/ tuning

[Ben34]

Do you follow the instructions from factory pipe for hose routing? Head to top of b pipe. Bottom of b pipe to pisser and stinger.

Or I also see people running head to bottom of b pipe. And top of b pipe to pisser and stinger.

Stick with the instructions? Also what is a good starting point on the screws? 701 dual cooling in a freestyle ski. 1/2 open on Botox screw? Thanks mod pipe btw

 

[Mike W]

I’ve always ran from back of the head to the bottom of the headpipe. Top of the headpipe to a pisser. Then a 3/8” “T” to the stinger with a 1/8” restrictor. An old needle and seat drilled out works perfect.

As far as the pipe, top and middle closed, and bottom open 1/4. I’m sure others can really get in the weeds on pipe tuning, but this works best on my ski. Stock ‘17 RN with just a pipe.

 

[john zigler]

I’ve always ran from back of the head to the bottom of the headpipe. Top of the headpipe to a pisser. Then a 3/8” “T” to the stinger with a 1/8” restrictor. An old needle and seat drilled out works perfect.

As far as the pipe, top and middle closed, and bottom open 1/4. I’m sure others can really get in the weeds on pipe tuning, but this works best on my ski. Stock ‘17 RN with just a pipe.

Same here....

 

[Ben34]

Curious as why they recommend it that way then.

 

[fastgtfairlane]

I set up all of my skis with 2 cooling lines. One feeds the engine and the other feeds the headpipe separately. I've found the pipe responds better with cooler water feeding the headpipe directly from the pump rather than being preheated from the engine first. I'll run a restrictor on the headpipe outlet to keep a little pressure on the headpipe to get a better spray pattern on the injector screws and use the outlet on the head to feed the stinger. I leave the bottom screw closed on the headpipe, middle open 1/4 turn and top 1/4 to 1/2 turn open and adjust pipe temp with top screw as needed.

My superfreak hull has 2- 1/2 inch lines coming from the pump. I used a 2 in/4 outlet manifold to plumb the cooling lines. 2-1/2 inlets, 4- 3/8 outlets. 2 feed the engine, 1 feeds the pipe, both go directly overboard and adjust Temps with restrictors, the 4ty line goes to the stinger of the chamber with an adjustable flow control valve. Definitely more complicated but allows more fine tuning for Temps of both the engine and pipe.

 

[john zigler]

Curious as why they recommend it that way then.

You CAN do it as Fact pipe describes in their instructions. I just prefer to fill the pipe from the bottom (Back of head pipe) as it pushes are out as it fills, and IMO water line routing is much cleaner/easier.

Fastfairlane has another good option as far as routing goes. Many times we also feed the pipe separately with cold water. His screw settings are different than ours but if it works for him / his set up that is good. You may have to tune for your set up, and goals. On a "Rec Ski" I personally prefer water restrictors over a flow control valve, only due to reliability and ease of use for the end customer.

 

[Dorny119]

I too run one line into the motor, and one into the bottom of the exhaust.

For the motor, the line separates via a "Y" fitting, and each cylinder gets a line in. Then, i have two exits in the head. They EACH go overboard, with equal length hose. I wanted to be sure I can see that each cyl is getting flow, and be sure they are equal pressure.

For my exhaust, I have the line coming into the bottom, out the top, T into FCV and Overboard. Three pissers total. I only started doing this late 2022. I have not played around with tuning the exhaust at all. This is where i have questions. I only just yesterday installed a new headpipe. It will be my first time with a headpipe that has turn-able screws lol.

I know the exhaust tuning world is complex. It's dynamic, and has many variables. Much of the info on the internet is contradicting to what I have experienced. For Example; the goal of the FCV is to keep the watebox empty at low RPM for quick throttle response. If that is true, then why did I gain INSANE bottom end hit when a piece of seaweed blocked my pisser one time (before i ever had a FCV). I was riding one day, and all the sudden my SJ (Stock with Limited Bpipe) was jumping out of the water with a crack of the throttle. I was amazed. I then noticed only a tiny spritz of water coming from my pisser due to seaweed. I dislodged the weed, and immediately lost that super fun bottom end hit. So, would the blockage in the pisser have caused MORE water to enter the waterbox? Sure enough I went on to make a restrictor of my own on the lathe, and installed it to keep that awesome bottom end hit. The drawback was a loss of top speed was drastic. This does make sense to me, because the waterbox must be so full at higher RPMs from the restriction, that there is poor exhaust flow.

So this whole concept confuses me about the info i see on the internet. Anyone care to elaborate on this? I also wonder what the science behind the Top, Middle, and Bottom screws are. I know it has to do with sound waves. But what's the principal? As a stubborn engineer, i have a hard time taking knowledge at face value, and have to understand it myself before i can accept it lol.

 

[DylanS]

Whatever Exhaust Wave Speed the Exhaust Wave returns at, to best "seal" the Cylinder Exhaust Port, will yield the best Cylinder Compression Pressure (BMEP).

More BMEP yields more Power.

By increasing or decreasing the Exhaust Wave Return Speed, the BMEP moves up or down the RPM Band.

By controlling the Cooling Water injected into the Exhaust, the Exhaust Wave Return Speed is controlled. Cooler Gas (more Water) is slower, Hotter Gas (less Water) is faster.

Cooler Slower Gas favors the 'Low End" of the RPM Band. Hotter Faster Gas favors the "Top End" of the RPM Band.

There is only one "Sweet Spot" BMEP for every Exhaust Return Speed (Temperature) and Exhaust Port Height. Find the RPM where you like the "Hit" by tweaking the Water Injection Screws.

It's all about "synching-up" (synchronizing) the Exhaust Return Wave to the proper Exhaust Port closing time. Research the Two Stroke Scavenging Effect also, where unburned Fuel gets pushed back into the Cylinders via the Head Pipe and Exhaust Manifold. Also known as the "Supercharging Effect". So in fact, the Exhaust Port is a two-way Passage.

The best improvement to this "Power Give & Take" seems to be Exhaust Power Valves which maintain a better Exhaust Port "Seal" for better BMEP along a wider RPM Range.

The Power Valve Blade will "retain" better dynamic Compression along the RPM range.

With no Power Valve Blade, the tall Exhaust Port results in weak or lost Compression at low RPMs because the Intake Mix can't be compressed until the Piston closes the bigger taller "leaking" Exhaust Port. Research "Cylinder/Piston Swept Volume".

At the end of the day, Two-Stroke Engine and Pipe Tuning is an Art more than a Science, as the Gas Dynamics are very complicated.

That's why Hands-On Experience beats Theory. Horsepower to Water wins every time.

Enter the Self-Taught Two-Stroke Wizard.

I too run one line into the motor, and one into the bottom of the exhaust.

For the motor, the line separates via a "Y" fitting, and each cylinder gets a line in. Then, i have two exits in the head. They EACH go overboard, with equal length hose. I wanted to be sure I can see that each cyl is getting flow, and be sure they are equal pressure.

For my exhaust, I have the line coming into the bottom, out the top, T into FCV and Overboard. Three pissers total. I only started doing this late 2022. I have not played around with tuning the exhaust at all. This is where i have questions. I only just yesterday installed a new headpipe. It will be my first time with a headpipe that has turn-able screws lol.

I know the exhaust tuning world is complex. It's dynamic, and has many variables. Much of the info on the internet is contradicting to what I have experienced. For Example; the goal of the FCV is to keep the watebox empty at low RPM for quick throttle response. If that is true, then why did I gain INSANE bottom end hit when a piece of seaweed blocked my pisser one time (before i ever had a FCV). I was riding one day, and all the sudden my SJ (Stock with Limited Bpipe) was jumping out of the water with a crack of the throttle. I was amazed. I then noticed only a tiny spritz of water coming from my pisser due to seaweed. I dislodged the weed, and immediately lost that super fun bottom end hit. So, would the blockage in the pisser have caused MORE water to enter the waterbox? Sure enough I went on to make a restrictor of my own on the lathe, and installed it to keep that awesome bottom end hit. The drawback was a loss of top speed was drastic. This does make sense to me, because the waterbox must be so full at higher RPMs from the restriction, that there is poor exhaust flow.

So this whole concept confuses me about the info i see on the internet. Anyone care to elaborate on this? I also wonder what the science behind the Top, Middle, and Bottom screws are. I know it has to do with sound waves. But what's the principal? As a stubborn engineer, i have a hard time taking knowledge at face value, and have to understand it myself before i can accept it lol.

A FCV that’s on a line that runs directly to the water box is totally different than a line that runs to the stinger of a pipe. Reason you had so much bottom end hit is because you had so much more water coming out at the stinger effectively making it a “smaller” outlet and bringing out that low end punch. I do not run FCV’s unless it’s on a line feeding directly to the waterbox personally.
Waterbox is more or less empty at higher rpm, FCV’s help with keeping it from loading up at low rpm. Reason you lost top end is because you made your stinger smaller via forcing more water out down there.
FCV’s do not make nearly as much of a felt difference as you’d think but they do help when used properly.
Oh and you can also get these cool little fittings, it’s a strait thru fitting with a bolt in the center, that let you adjust how much water you let flow thru a line. Real nice for tuning.

 

[Dorny119]

Whatever Exhaust Wave Speed the Exhaust Wave returns at, to best "seal" the Cylinder Exhaust Port, will yield the best Cylinder Compression Pressure (BMEP).

More BMEP yields more Power.

By increasing or decreasing the Exhaust Wave Return Speed, the BMEP moves up or down the RPM Band.

By controlling the Cooling Water injected into the Exhaust, the Exhaust Wave Return Speed is controlled. Cooler Gas (more Water) is slower, Hotter Gas (less Water) is faster.

Cooler Slower Gas favors the 'Low End" of the RPM Band. Hotter Faster Gas favors the "Top End" of the RPM Band.

There is only one "Sweet Spot" BMEP for every Exhaust Return Speed (Temperature) and Exhaust Port Height. Find the RPM where you like the "Hit" by tweaking the Water Injection Screws.

It's all about "synching-up" (synchronizing) the Exhaust Return Wave to the proper Exhaust Port closing time. Research the Two Stroke Scavenging Effect also, where unburned Fuel gets pushed back into the Cylinders via the Head Pipe and Exhaust Manifold. Also known as the "Supercharging Effect". So in fact, the Exhaust Port is a two-way Passage.

The best improvement to this "Power Give & Take" seems to be Exhaust Power Valves which maintain a better Exhaust Port "Seal" for better BMEP along a wider RPM Range.

The Power Valve Blade will "retain" better dynamic Compression along the RPM range.

With no Power Valve Blade, the tall Exhaust Port results in weak or lost Compression at low RPMs because the Intake Mix can't be compressed until the Piston closes the bigger taller "leaking" Exhaust Port. Research "Cylinder/Piston Swept Volume".

At the end of the day, Two-Stroke Engine and Pipe Tuning is an Art more than a Science, as the Gas Dynamics are very complicated.

That's why Hands-On Experience beats Theory. Horsepower to Water wins every time.

Enter the Self-Taught Two-Stroke Wizard.

A FCV that’s on a line that runs directly to the water box is totally different than a line that runs to the stinger of a pipe. Reason you had so much bottom end hit is because you had so much more water coming out at the stinger effectively making it a “smaller” outlet and bringing out that low end punch. I do not run FCV’s unless it’s on a line feeding directly to the waterbox personally.
Waterbox is more or less empty at higher rpm, FCV’s help with keeping it from loading up at low rpm. Reason you lost top end is because you made your stinger smaller via forcing more water out down there.
FCV’s do not make nearly as much of a felt difference as you’d think but they do help when used properly.
Oh and you can also get these cool little fittings, it’s a strait thru fitting with a bolt in the center, that let you adjust how much water you let flow thru a line. Real nice for tuning.

Thank you JC. Nice reply! Thanks for reading my long winded comment. Your reply helps alot. I wonder if the top vs bottom screws differ in water temp because the bottom is closest to the water supply, and the top screw is water that has run through the pipe already. So, bottom = cool water which may mean less required water, and top = warm water, which may mean more required water (to keep the exhaust at the desired temp).

Dylan, ok yea the smaller outlet thing you mentioned makes sense. Interesting. Thanks!

 

[kevbo]

Superjet style mufflers suck water off the bottom of the box at full throttle.. The FCV is there to stop extra water from entering and filling up the muffler at part throttle. All thats happening in the head pipe is a VERY tiny amount of cooling water leaking inside. Factory Pipe confused riders by giving them a choice of where the leak happens and a screw to turn.