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

    AIRFLOW "X IC /Gibson/MC1"

    AIRFLOW Work

    X IC
    Gibson Exhaust
    TDR for GPRXP

    More airflow work, this time I got my hands on some nice toys. Thanks to forum members BeachBum0286 and Mrbtd for supplying me with the following…

    - X IC setup from a 08 RXP-X, including the OEM rubber pipes
    - 08 Exhaust pipe and waterbox
    - Gibson exhaust setup
    - TDR Waterbox with Riva Blue pipe
    - OEM Yamaha GPR Exhaust with Sound Suppression

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

    *** The numbers below represent AIRFLOW ONLY...They DO NOT represent any numbers in regards to EXHAUST HEAT, WATER INJECTION, or BOTH.....ALSO, it represents ANY 4TEC motor (N/A, non-IC SC'd, SC'd) that is spinning at roughly 6000 RPM, and does reflect any other modifications such as external IC, air intake, SC upgrades, etc....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...

    08 RXP/T-X IC w/OEM Rubber Hose

    This unit is straight out of a 08 RXP-X, which is the same unit on an RXT-X. This unit is also the 2nd Generation IC that is offered by Riva through the online store…

    The backpressure (BP) measured at the flow rate of .460 (6000rpm) show the X IC with a BP of 7.5 in/water by itself, and 9.8 in/water with the OEM rubber tubes installed. In the graph below, you can see how it rates up next to the previous generation (1G) Riva IC…Crunch the numbers, and the X unit is 87% more restrictive than the 1G unit, but only requires a 15% bump in motor speed to create the same flow rate…

    Physically, the units are WAY different. The only thing they have in common is they are both aluminum, and are being used in PWC…THAT’S IT…Physical size shows about a measured 75% wider CORE, which leads to more surface area for cooling, thus a more restrictive path.

    This would explain why general response is that the 2G unit is not as responsive as the 1G. But the size (CORE layout excluded) would suggest a more efficient unit for cooling.

    Gibson Exhaust

    Turbulent, is the best way to describe the output of this unit. Because of the internal makeup and baffle setup, despite being a straight through design, showed a lot of turbulence on the bench. Previous waterboxes were a smooth, consistent flow. The Gibson setup created a loud hissing sound, which means turbulence, which means backpressure.

    The measured BP of the Gibson setup was 11.5 in/water. The trimmed Jpipe had to be used in this session, and the flow of that was 8.0 in/water (normal Jpipe untrimmed is 7.5”). When combined as a unit the BP is 15.0 in/water. Below is the comparison between a Gibson setup, GreenBox, and a typical shorty waterbox with standard thru-hull pipe…

    *** The above info can be seen here...

    This setup puts it right in the middle of a Shorty Waterbox and Greenbox for total combined package, only to be edged out if the other two are incorporating a FLARED tip on the Jpipe.

    TDR Waterbox/Yamaha OEM Exhaust

    These numbers are based on the items typically used for building a conversion GPRXP exhaust system. Included in the system is the same trimmed Jpipe from above, along with a TDR waterbox, a Riva Blue exhaust tube, and some other parts of an entire OEM Yamaha 2-stroke exhaust system (see pics)…

    The TDR box is WIDE OPEN, its BP numbers are the lowest we have ever seen, only to be closely matched by the OEM waterbox from Yamaha. The TDR flowed an AMAZING 3.0 in/water, while the OEM box came close at 3.6 in/water.

    From testing we know that a standard Jpipe will flow 7.5”, while a FLARED unit will flow as low as 4.5”. YET a trimmed pipe will flow 8.0”, just a little more than a stock unit, BUT it is needed to be like this because of the tightness of mounting. Well, when a Jpipe is combines with a waterbox the combination usually yields a larger number. Not in this case, where the addition of the TDR box actually acts like one FLARE, and total BP for the combo is 7.0 in/water. When combined with the Blue Riva pipe, and the OEM outlet, total system BP is 7.6 in/water…The OEM complete system just beats it out, combos/numbers below…

    If anyone has any questions, feel free to PM me or post here...

    -- Danny

    ***** 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

  2. #2
    speedskixp's Avatar
    Join Date
    Feb 2008
    venice fl.
    Great info! Thanks Danny!

  3. #3
    Nonstop, all day, everyday. 01xdime's Avatar
    Join Date
    Aug 2005
    Pasadena, MD
    Wow, now thats pretty nice databaseof flow info. Great work Danny!

  4. #4
    800AMSOIL4U's Avatar
    Join Date
    Aug 2006
    Morgan Hill, CA
    Thanks for all the work and to those who let you use the items.

  5. #5
    West Texas RXP skoepp's Avatar
    Join Date
    Oct 2007
    west texas
    Good Work Danny!

  6. #6
    cheatin' piston popper addicted's Avatar
    Join Date
    Jul 2006
    north jersey
    Amazing work Danny

    so if the 08 straight pipe flowed 5.4" and the yamaha 2 stroke exhaust flowed 7.3" would it be accurate to say that the combo that I'm unning on my coversion is roughly the sum of those 2 for a total of 12.7"?

    And thanks to those that provided the parts necessary for these tests.

  7. #7
    mrbtd's Avatar
    Join Date
    Jul 2005
    Lindenhurst, Illinois, United States
    Few quesitons...

    On the GPRXP....The tuning box is the large black box that had the white stuff on it right ? If so we call it a Sound Suppresion box.

    It looks like even with the Sound Suppresion box the flow numbers are the same as the GH shorty set up ? From what I have read this is a good gain over the OEM set up.

    Obviously there is a huge size difference with the Yamaha OEM box - Does the size have anything to do with sound or performance ?

  8. #8
    Ride Hard! aha's Avatar
    Join Date
    Jul 2005
    Covina, Ca
    Wow great job Danny! Crazy info!!

    Its a shame that TDR dont make a waterbox that works with a rear exhaust on a RXP/RXT/GXT, I think that would be the absolute killer setup

  9. #9
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas
    excellent information Danny

  10. #10
    beachbum0286's Avatar
    Join Date
    Sep 2007
    Brigantine NJ
    Great work Danny!! Got any ideas as to how to mod the X water box yet?

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