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  1. #1
    Banned User
    Join Date
    Dec 2006
    Crest Hill, IL

    AIRFLOW Work (Kanaflex, Riva Rear, etc)

    AIRFLOW Air Intake Setups

    Systems flowed…

    - OEM system on common SC’d units
    - Riva Power Filter 3” Intake
    - Riva Rear Air Intake System
    - Kanaflex DIY system
    - R&D 4” SC Adapter

    For history on previous flow work, and reference as to the numbers, please click on this link…

    *** The numbers below represent AIRFLOW ONLY...They represent ANY 4TEC motor (N/A, non-IC SC'd, SC'd) that is spinning at roughly 6000 RPM, and does not reflect any other....Nor does it reflect airflow behavior above 6000 RPM, such as modded motors that spin at 8100-8600 RPM...BUT these numbers can predict what effect some mods will do at those air rates...


    For over a year now I have been trying to get all the components for typically used air intake systems. As they were made available to me I flowed them and held onto the information, waiting for the right time to post it as ONE POST. I finally got that chance, so THANK YOU to all members that help contribute over the past year.

    Testing on the Air Intake Systems is a lot different from the previous Exhaust/IC work I have done in the past. In those situations we were PUSHING air through the test items, and recorded the build up of back pressure……NOT IN THIS CASE.

    This time around we were working with a VACUUM situation, and numbers would be different.

    Imagine yourself breathing normally, but then attempt to breath through a straw. The resistance you feel is the restriction of the inlet hole size of the straw. You are forced to suck HARDER to get the same amount of air VOLUME needed to sustain a breath. Better yet, remember when you would try to drink a THICK MILKSHAKE and the straw would practically collapse on itself as you struggled to get anything up that straw!? Take that analogy as we attempt to flow these items.

    Since we are working in a VACUUM environment, the numbers make look small, relative to previous backpressure work. BUT their impact and calculations are measured the same.

    For comparison, the backpressure seen on exhaust work was measured in positive (+) inches, and the closer the number to ZERO the better…In a VACUUM environment, once ZERO is established, any resistance seen (like an intake) will result in a negative(-) number. Therefore the closer to ZERO is desired, and anything past ZERO and showing a positive(+) result is desired.

    Baseline test was first, so we figured that NO INTAKE at all on the SC inlet was about as GROUND ZERO as we could get.


    The OEM intake was in 4 parts…
    - Rubber neck
    - Plastic tube around engine
    - Rubber connector
    - Plastic box above fuel tank

    Each item flowed nicely individually, BUT the rubber connector that was used to connect the 2 plastic unit was an issue. It is a small rubber unit with about a 1.5” opening. This we knew was gonna cork the system up. Looking at the data below you can see that once the elbow and first plastic connection go in, vacuum is present. Its not until the rubber connector and last box are in until we get a baseline number, which in this case, is -4.85” in/vacuum…THAT is our baseline span, from -4.85” to ZERO.

    Riva Power 3”

    First up was the Riva Power 3” Setup, which was one of the first aftermarket air intake systems developed by Riva for the SC 4Tec motor. Utilizing a 3” formed plastic tube, and a K&N Air Filter w/ water resistant cover, this unit was a staple in many aftermarket intake systems…HOWEVER, over the past few years people have switched over to a custom made Kanaflex system that offers a more efficient setup that helps feed the large volumes of air the current larger aftermarket SC’s demand, all while being cost effective.

    The numbers seen for the Riva Power setup show that just the addition of the tube by itself shows a drop in flow, with a vacuum of -0.43”. HOWEVER, with the addition of the K&N Air Filter helps distribute the inlet area to produce a +0.19”. Installation of the protective filter element, used to reduce water intrusion, brings the flow down to ZERO…

    Riva REAR AIR

    This system comes in a few parts, but the focus is on the 3 main parts…
    - SC adapter
    - Black Plastic Snorkle
    - Protective Filter Element

    This unit is commonly used on the RXP platform ONLY. The benefits include drawing the coolest and freshest air from outside the engine compartment, which help benefit overall power production. Drawbacks are that it is more open to the outside that the other intake setups, and therefore is VERY susceptible to water injestion from just the slightest misdirected wave. To help reduce water injestion, Riva includes a protective filter element which helps keep debris out of the intake system, but can still pass water through on a HIGH DRAW from the SC…

    The numbers seen for the Riva REAR AIR were very impressive, but to a point. Just by placing the SC adapter on the bench (which is made ONLY for the Rear Air), flow INCREASED dramatically. With +1.45”, the adapter alone improved airflow. The addition of the black plastic snorkel reduced this number slightly, but was still impressive at +1.04”. But once we put the protective filter element in place, the numbers went down to a -2.29”.

    This reduction on flow is attributed only to the filter. The clean air that this unit is bringing into the SC is better than any air that can be brought into the engine compartment, BUT, the restrictiveness can be altered. The filter material can be swapped out for a less restrictive material, and airflow will increase. But a less restrictive material will increase the chance of water intrusion, which is already high because of the location of the inlet. Any modification of the element is to be done at the owners judgment.

    R&D Adapter/ Sno-BEND Adapter

    The R&D adapter is the answer to the aftermarket demand for a larger intake system This unit is to be combined when using a 4” Kanaflex hose system, to help the transition onto the SC housing. This unit is available in the Online Store…

    This unit posted similar results s the Riva adapter unit, with a flow of +1.39”. This unit is installed directly onto the SC housing, and allows for the 4” Kanaflex to be bolted directly to it. Simple and easy to use. The Kanaflex must come at the SC at a direct angle. This is usually of no issue, as this modification is also combined with several others that allow for extra room in the rear cavity of a 4TEC powered ski.

    If you would desire to have a system hug the motor like the Riva Power 3”, then look to the Sno-BEND setup. This system was designed by forum member SNOMAN, and is simple to construct. Using a 4-ply 4” to 3” 90 degree Reducer Elbow from and a 4” metal joiner from a local autoparts store (along with filter, info below), this setup allows for a smooth system that hugs the motor and can be attached to the Kanaflex tube in the same way. The Sno-BEND system flows +1.15”…

    Kanaflex w/ Spectre FIltre

    A Kanaflex system was developed over the years as an alternative to feed the SC more air to gain more power. When installed properly, a Kanaflex system is the most cost effective way to run a ski in any water condition while still maintaining the best opportunity to get the most power out of the motor SAFELY and EFFECTIVELY.

    Feeding the hull with more air is a simple issue to solve, and the more air you can get INTO the hull and directed towards the air filter, the more power you will make. Do a search on this forum for ways to get more air into the hull.

    Obtaining the proper Kanaflex, which is model version 620WD, can be found at several online suppliers. Depending on the ski, overall length will around 7-10 ft. depending on ski and mounting location/style. The following flow work was based upon a 7ft. section which is typically the length found on most RXP’s.

    As for a filter, the unit used is a simple Spectre Fabric style that was purchased at a local Autozone. A 4” metal adapter was also used, which is the same unit found in the Sno-BEND assembly.

    The data shows the flows for both setups, at different stages. Both setups flow positive numbers compared to no system at all, and both setups will provide ample air to any SC.

    If anyone has any questions, feel free to ask me.

    ***** Other airflow work is available in these threads...

    Manifold w/ IC setups (Piranha, Riva, XS)


    OEM IC

    Piranha/Riva IC and XS IC

    Rotax Racing IC


    GreenBox and Shorty Waterbox

    X Waterbox and Pipe

    OEM Waterbox and Full Size Gutted

    Gibson and X IC

  2. #2
    Hydrotoys's Avatar
    Join Date
    Jul 2005
    Mesa, AZ
    I think the only other thing I'd mention, is the spectre type cloth/paper filters, when they get sea-spray or any type of moisture, become quite a blockage. I'm pretty sure there is a 4" filter in Jerry's store that only has the flame arrester element on it, and no filter media. It fits the FX-HO I think.

    EDIT: Danny, anyway to get a number off the Spectre and spray it with just a water spray, or would that harm the test equipment?

  3. #3
    ou812's Avatar
    Join Date
    Jun 2006
    Very interesting! Good info!

    What about the kano flex setup without the filter attached like I have been running for a few years now (idea from water4fire). What was the flow without the filter? Just the outerwear is needed for water spray.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  4. #4
    EH Team Water Pig's Avatar
    Join Date
    Oct 2007
    St. Catharines, Ontario, CANADA

    AIRFLOW Air Intake Setups


    Nice work! Great information and presentation.
    Do you have any info on the stock RXP-X air intake?
    I think the X-stock is probably less restrictive than the earlier RXP's but not by a lot.
    Your thoughts?

  5. #5
    Good info Danny! Are you measuring pressure in inches of water column?
    Also, would the riva waterbox flow enough more than a stock gutted box that you would expect an rpm increase? If so how much would you estimate?



  6. #6
    SeaGoat's Avatar
    Join Date
    Jun 2008
    Jacksonville, N.C.
    Good work Danny. That's some very useful information right there. That need's to be stickied along with all the other flow work you've done so that it's an easy reference for all the newbies questions. Looks like I need to order some parts.

  7. #7
    superdave's Avatar
    Join Date
    Oct 2008
    Indianapolis, Indiana, United States
    We need to send you a Tornado to flow test

  8. #8
    SeaGoat's Avatar
    Join Date
    Jun 2008
    Jacksonville, N.C.
    Quote Originally Posted by ou812 View Post
    Very interesting! Good info!

    What about the kano flex setup without the filter attached like I have been running for a few years now (idea from water4fire). What was the flow without the filter? Just the outerwear is needed for water spray.
    7 ft. of kanaflex with the snowbend was +.64 and with the R&D adaptor was +.61.

  9. #9
    Chaserxp215's Avatar
    Join Date
    May 2008
    Grosse Pointe, MI
    nice work, thanks for the info.

  10. #10
    formerly Gold06RXP Turbo Nick's Avatar
    Join Date
    May 2007
    Dayton, OH
    Has anybody used something else on there Riva rear air besides the pre filter supplied w/ the kit? I may have to switch to the kanaflex after seeing these #s.

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