If You Think Pole Breathers Are Enough.....

[mikesx]

I wanted solid data on air supply for my motor so I rigged up a manometer to take some measurements and was surprised. For the first test I capped my hood breather arrangement and used only pole tubes. 1 is completely empty the other has all the cable ran in it. I latched down the hood and a couple of quick brapp-ups revealed about 1" w.c.

 

[mikesx]

I did a second test with hood breather cap removed.

Yielded no movement.

 

[mikesx]

Is 2”w.c. enough to affect jetting ?

 

[Harbor]

Nice test data.. pretty cool. So I have rrp poll tubes and 2 hood breathers tubes just as large. Was gonna say I am good but my engine is larger so I guess I'll have to do my own test.. thanks for posting

 

[Christian_83]

YES! finally! have been thinking about this for a while, but havent got to do it my self.
A few years back a guy had a 1100cc Lenzi superjet style ski, with no hood breathers, you could feel it on the hood, it sucked the hood down

 

[mikesx]

Nice test data.. pretty cool. So I have rrp poll tubes and 2 hood breathers tubes just as large. Was gonna say I am good but my engine is larger so I guess I'll have to do my own test.. thanks for posting

When I fired motor up the first time I was impressed by intake suction (4mil 898). I began doubting my breather tube calcs so I had to know. The flat part of breather is 5.5"x1.5" and the spigot connection for hose is 2.5" id ( had to really stretch the fernco on there so I know it was sealed). I don't have enough tuning experience to know if 2”w.c. would affect jetting, but I reason it could give you fits. Can any of the tuning gurus chime in?

 

[waxhead]

Im not sure it will effect the jetting so much as the carbs are vented to the same atmosphere as the carbs , under the hood. will it effect power, yes big time

 

[mikesx]

Im not sure it will effect the jetting so much as the carbs are vented to the same atmosphere as the carbs , under the hood. will it effect power, yes big time

Trying wrap head around this. If carbs are getting “ less” air, wouldn’t that put u in a rich condition?

 

[mikesx]

Im not sure it will effect the jetting so much as the carbs are vented to the same atmosphere as the carbs , under the hood. will it effect power, yes big time

Or are u saying carbs are jetted for strangled inlet? That all tuning was done at that atmosphere. If I calculated right I think 1” wc= less than 1000’ of elevation.

 

[PeteK]

Interesting read!

 

[Breese08SJ]

Assuming that the zip ties are 1" apart your picture looks like 2" WC. 1" down on Left and 1" up on Right. Reference " h" in attached pic.
Just an FYI not trying to be a d!ck

 

[mikesx]

Assuming that the zip ties are 1" apart your picture looks like 2" WC. 1" down on Left and 1" up on Right. Reference " h" in attached pic.
Just an FYI not trying to be a d!ck

Zip ties are exactly 1” apart. Good eye! It was 99 in that shade and I was getting pretty confused. Friggin melting down over possibly not making breather big enough. The second test calmed me down. But you are right ,2” w.c.

 

[Harbor]

Friggin melting down over not making breather big enough.

For what it's worth, my +8 mil 865 ran just fine thru just rrp poll tubes and
Your set up has more air then that with your 3 vents

 

[Baja 252]

Interesting read and subject. I don't have any scientific data, but here is my experience.

We have Rickter XFS with a 1000cc Dasa and a RRP pole set-up. With the ski out of water on the trailer and the hood sitting on the ski not latched, I slipped 4 fingers under the rear of the hood. This let in a ton of extra air around the rear of the hood because of the rear of the hood being held up about 3/4" by my fingers. We started the ski and blipped the throttle and the hood sucked down so fast and hard it didn't just suck the hood down on my fingers it smashed them so hard it hurt!
We did the test several times and same result each time, the harder we blipped the gas the harder it smashed our fingers. I can only imaging what it's like on the water under full throttle.
This winter we added a 3.5" hole in the hood with the RRP hood scoop and a 3.5" hose. Now doing the same test it barely pulls the hood down on our fingers. On the water the power definitely feel stronger. Surprisingly the effect on jetting by the extra air didn't really change anything, plugs and piston tops look the same before and after.

Our 1100 SXR did the exact same thing with the stock hood. Adding a RRP pole to that ski had the same results.

IMO for the best results a large cc engine in a AM hull need more air than just a RRP pole set-up can provide. Same goes for a factory hull with a larger than stock engine.

 

[Quinc]

@Jr. @wmazz

 

[CARBONX2]

My testing on a 1200 has found the need for 4 x 2,5" inlet pipes, but I have no breathers from the pole. If your hood is being sucked down, for your engine it is like riding at a higher altitude(reduced air density). Make sure inlets from outside into hood baffle area are big enough. Also check your filters, the low profile ones are a restriction(put a vacuum gauge on the primer fitting to check difference between filters and no filters. Do all testing with ski strapped to trailer in the water, you can then pull WOT for a few seconds to get readings/effects on hood. Length of tubes also affect air inlet resistance - Resistance Factor = Length / (Diameter x Diameter x Diameter x Diameter x Diameter)

 

[KMN]

I'd say any of the competition hulls with 1200's the riders have 6 tubes. My XFS has 4 2.5" tubes in the hood plus 2 pole breathers. The DVX has 4 2.5" tubes plus the smaller Xscream pole breather tubes. My buddy ShamSpeed and I have noticed there is quite a lot of potential in opening up the breathers.

 

[waxhead]

Trying wrap head around this. If carbs are getting “ less” air, wouldn’t that put u in a rich condition?

If you had a restrictive air-cleaner then yes, But the carbs are in the same environment so the pressure on the diaphragm is also reduced. This would lean it out, carbs are self compensating to a certain point. It will just flow less and make less power.

 

[mikesx]

If you had a restrictive air-cleaner then yes, But the carbs are in the same environment so the pressure on the diaphragm is also reduced. This would lean it out, carbs are self compensating to a certain point. It will just flow less and make less power.

That makes a lot of sense. Diaphragm, self regulating, the carb is also a regulator. Just like a SCUBA regulator that compensates at different depths. Loss of power will come from the fact it has compensated from “ less” air + fuel. Thanks Wax !

 

[Jr.]

An engine is an air pump. It will only make power for the available air it can pull. If you restrict the incoming air, you will restrict the power to be made . The engine will waste energy fighting for air. One of the very first things I do when I start a new tuning project is ck for avail air intake. In an ideal world, you will have 10-20% excess intake avail.
As we all know, this is not the case with a lot of todays aftermarket hulls. Competition boats run multiple large breathers to extract every last bit of avail power. The rec/ freeride world not so much. You need to find a balance between enough air, and minimal water intrusion. So tuning suffers. In my experience, jetting is effected by restricted airflow. However, not to the degree you would expect. Engines tend to run fuel rich, due to Oxy poor environments.
Im sure the next series of questions will be about calculating needed air for any given motor? Sure, you can do all the CFM calcs at given rpm vs breather tube sizes vs engine compartment volumes. Unfortunately, I dont have time for that! I just use a simple Manometer at both hood intake and pole breather entrance to see where I'm at and add accordingly. Kudo’s to the OP for his water tube! Like your way of thinking!