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  1. #1
    Member John Kiewicz's Avatar
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    Airbox mod for VFR800

    A few times I've read the recommendation to modify the airbox on a VFR800 by removing the rubber inlet snorkle and/or to drill out the rivets to remove the vacuum-actuated flapper gizmo.

    However, my question is this... does it actually improve performance or do people think that it improves performance? Has anybody ever truly answered this question?


  2. #2
    Member jobvfr's Avatar
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    Ahhhh... The great question: does it actually make the bike faster?
    I guess if you think it's faster then it must be! :)
    I've done the flapper mod and I doubt it made any difference at all. I left the snorkel because it seemed to prevent hot air from the front exhaust pipes getting pulled into the airbox.

    Putting more stickers on your fairing and a sweat-band on the brake res. add about 15hp too!
    Jobvfr

  3. #3
    Uber Guru CandyRedRC46's Avatar
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    the snorkel alone is worth about -.5 to 1 to 2 hp at different spots in the power band...
    and well the flapper opens up when up need it, so...
    youre looking at 2 hp max, a little more with a power commander with a tune...

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  4. #4
    Uber Guru CandyRedRC46's Avatar
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    here this is from veefer800canuck


    From: DynoWorks@aol.com [mailto:DynoWorks@aol.com]
    Sent: Monday, 29 March 1999 5:20 PM
    To: vfr@cs.wisc.edu
    Subject: 800 snorkel dyno test (mostly data)


    Hello list ...

    Had the opportunity to do a back to back dyno test on the VFR800. We'll let
    the numbers tell the story.

    Dynojet Model 150 Chassis Dynamometer
    Eastside Harley Davidson, Bellevue, Washington
    DYNORUN #1, baseline, 4th gear roll-on - 3-27-99, 3:17PM
    DYNORUN #5, no snorkel, 4th gear roll-on - 3-27-99, 3:22PM

    DYNORUN #1 DYNORUN #5
    RPM SAE hp SAE hp
    3500 28.3 28.8
    4000 32.1 31.7
    4500 35.4 35.4
    5000 39.8 40.3
    5500 45.2 46.1
    6000 54.4 55.3
    6500 62.6 63.2
    7000 69.6 69.9
    7500 75.6 75.5
    8000 81.1 information not available
    8500 86.6 87.1
    9000 90.0 91.0
    9500 91.6 92.7
    10000 93.2 93.8
    10500 92.9 94.2
    11000 90.3 91.6
    11500 88.8 89.6

    Magnifying the resolution of the 500 rpms nearest the hp peak follows

    10000 93.2 93.8
    10100 93.4 94.1
    10200 93.5 94.3
    10300 93.6 94.6
    10400 93.3 94.6
    10500 92.9 94.2

    Magnifying the resolution of the 1000 rpm range nearest torque peak follows

    RPM SAE ft-lb SAE ft-lb
    8100 53.4 53.3
    8200 53.4 53.4
    8300 53.6 53.6
    8400 53.6 53.7
    8500 53.5 53.8
    8600 53.4 53.8
    8700 53.2 53.7
    8800 53.0 53.6
    8900 52.8 53.4
    9000 52.5 53.1

    Testing conditions: 29.66 in.Hg. absolute barometric pressure, Vapor
    pressure .44 in. hg., ambient air temperature 49.5 deg. F. Partly cloudy.
    All stock '98VFR800FI, 3,273 miles.

    Subjective comment: Noticeably louder intake noise. Doesn't sound like a
    sewing machine anymore. Changes the character of the engine. Feels raw,
    sharper edged. I will be leaving the snorkel out for now.

    Wayne Chan, WMRRA/OMRRA #326

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  5. #5
    Uber Guru Meatloaf's Avatar
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    I wish I had stumbled upon this information before. I'd have ripped out the snorkel long ago. I was planning on doing all the "usual" mods when I get to my exhuast and dyno tune but will be ripping this out almost immediately.
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  6. #6
    Uber Guru CandyRedRC46's Avatar
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    lol its really only there for noise control...

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  7. #7
    Uber Guru John451's Avatar
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    I took mine out for 2000 miles then put it back in after feeling it softend low/midrange throttle response and a VFR riding friend advising me it's more likely for water to get into the airbox when riding distance in sustained torrential rain...Top end seemed a little faster and it sounded Unreal.

  8. #8
    Uber Guru CandyRedRC46's Avatar
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    If you want your low-end throttle response back, just actually tune the bike for having the snorkel and flapper out. As in get a Power Commander and have the air/fuel tuned for the added air that the bike is getting, you will wind up getting even more power, with no loss any where.
    Last edited by CandyRedRC46; 07-11-2013 at 05:15 AM.

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  9. #9
    Uber Guru Meatloaf's Avatar
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    Quote Originally Posted by CandyRedRC46 View Post
    lol its really only there for noise control...
    Even more of a reason to take it out... I love the sound of a low RPM roll to WOT in the upper gears. It almost sounds like a turbo spooling up. With all the other noise from the VFR's engine... it doesn't make too much sense to put that in and not deal with anything else. Kinda seems like putting a band aid on a compound fracture.

    It will be coming out before the next time I ride.
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  10. #10
    Uber Guru CandyRedRC46's Avatar
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    Honestly I couldn't stand the way the bike sounded stock, opening up the throttle under lower revs... Sounded comparable to lugging a Briggs & Stratton... Bur, now with all the mods I can roll the throttle open from as low as 3 grand and she sounds awesome.
    Last edited by CandyRedRC46; 07-11-2013 at 05:17 AM.

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  11. #11
    Uber Guru John451's Avatar
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    Quote Originally Posted by Meatloaf View Post
    it doesn't make too much sense to put that in and not deal with anything else.
    Horses for courses was just making a case against but agree it is a cheep harmless mod that's easily reversable so what the hay.

    While I have money for anything safety or maintenance unfortunately I'm on a strict budget for anything non essential like a PC2 and dyno time. Then again my catless, O2 sensorless Gen 5 '99 already has much better low end and mid range FI fueling stock than my old Gen 6 had so don't feel I'm missing out on anything. Sadly I'll just have to make do with GDC whine and Arrow Carbon end can music to keep my ears entertained at lower revs.

  12. #12
    Member jobvfr's Avatar
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    Very interesting dyno-info, if the insurance pays to fix my bike, I'll try it.
    Jobvfr

  13. #13
    Member John Kiewicz's Avatar
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    Good info on the airbox. And with that ... I have more questions!

    1. I also own a Honda CRF450X dirt bike. The hot mod is to open up the airbox by using a razor blade to cut the airbox.

    Thus, besides removing the rubber snorkel and/or the flapper assembly ... could you cut open a portion of the top of the VFR airbox so that there would be a direct opening above the air filter? You would retain the outer edges of the top portion of the airbox lid (to be able to clamp the filter tight to the lower airbox), but the center would be opened up.

    2. How much of a power gain is realized by eliminating the factory catalytic converter system? Does someone in the aftermarket make a pipe retrofit gizmo that simplifies the cat removal?

  14. #14
    Uber Guru Meatloaf's Avatar
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    Several have modded the airbox, some more radical than others. Usually they cut things open between the two openings and fab it into one large opening.

    As far as eliminating the cat, its hard to say. A few for sure, maybe more. Most can get 10hp or so out of the bike by getting rid of the cat, a new slip on, power commander, dyno tune, and some various other mods.
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  15. #15
    Uber Guru CandyRedRC46's Avatar
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    Quote Originally Posted by John Kiewicz View Post
    Good info on the airbox. And with that ... I have more questions!

    1. I also own a Honda CRF450X dirt bike. The hot mod is to open up the airbox by using a razor blade to cut the airbox.

    Thus, besides removing the rubber snorkel and/or the flapper assembly ... could you cut open a portion of the top of the VFR airbox so that there would be a direct opening above the air filter? You would retain the outer edges of the top portion of the airbox lid (to be able to clamp the filter tight to the lower airbox), but the center would be opened up.

    2. How much of a power gain is realized by eliminating the factory catalytic converter system? Does someone in the aftermarket make a pipe retrofit gizmo that simplifies the cat removal?
    1. There would be more benefit by finding an aftermarket filter that actually has the same surface area as stock and lifting the tank up a little to allow more air to actually reach the airbox.

    2. Not much... The best route is to get the 98-99 header or a motad header...




    Edit: Pipercross air filter has all the surface area of the oem filter.
    Last edited by CandyRedRC46; 07-11-2013 at 05:19 AM.

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  16. #16
    Member John Kiewicz's Avatar
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    CandyRedRC46,

    1. Is it safe to assume that the 98-99 header is for a year Interceptor that did not have a factory catalytic converter?

    2. Is the 98-99 header a direct bolt-on for a 2007 Interceptor?

    3. If the 98-99 is a direct bolt on, how much better would an aftermarket header system be versus a stock 98-99 header?

  17. #17
    booty prez

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    Quote Originally Posted by John Kiewicz View Post
    CandyRedRC46,

    1. Is it safe to assume that the 98-99 header is for a year Interceptor that did not have a factory catalytic converter?

    2. Is the 98-99 header a direct bolt-on for a 2007 Interceptor?

    3. If the 98-99 is a direct bolt on, how much better would an aftermarket header system be versus a stock 98-99 header?
    1. Yes, 98-99 year 5th gens did not have cats, starting in 2000, the bikes had cats and o2 sensors.

    2. Almost, you will need the 98-99 down pipes that go to the rear heads and a set of 98-99 gaskets for the joint between the downtubes and headers, but if you have these, they bolt right up. You will also need to get or make some o2 sensor elims.

    3. I do not know this.

    Shameless Plug - I have a set of 1999 headers (catless) with the down tubes that I am looking to sell. Will be on buy/sell forum shortly. You will be responsible for the gaskets but they can be found at bikebandit or servicehonda.

  18. #18
    Senior Member steven113's Avatar
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    Quote Originally Posted by Bweiss View Post
    1. Yes, 98-99 year 5th gens did not have cats, starting in 2000, the bikes had cats and o2 sensors.

    2. Almost, you will need the 98-99 down pipes that go to the rear heads and a set of 98-99 gaskets for the joint between the downtubes and headers, but if you have these, they bolt right up. You will also need to get or make some o2 sensor elims.

    3. I do not know this.

    Shameless Plug - I have a set of 1999 headers (catless) with the down tubes that I am looking to sell. Will be on buy/sell forum shortly. You will be responsible for the gaskets but they can be found at bikebandit or servicehonda.
    3. The aftermarket headers do not flow any better or worse than the stock 98-99 headers but delvic and motad makes their exausts out of stainless steel so they dont rust like the stock system. I chose the motads for my bike because my stock pipes had some crash damage. I am very impressed with the quality of the motad system, it was a perfect fit and makes the stock exaust look cheap in comparison.
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  19. #19
    Uber Guru CandyRedRC46's Avatar
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    A good option is getting the 98-99s and having them ceramic coated.
    Last edited by CandyRedRC46; 07-11-2013 at 05:19 AM.

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  20. #20
    Senior Member VFRBenny's Avatar
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    Quote Originally Posted by John Kiewicz View Post
    A few times I've read the recommendation to modify the airbox on a VFR800 by removing the rubber inlet snorkle and/or to drill out the rivets to remove the vacuum-actuated flapper gizmo.

    However, my question is this... does it actually improve performance or do people think that it improves performance? Has anybody ever truly answered this question?
    Mine feels much better and does pull much harder past 4500 rpm.


  21. #21
    Uber Guru CandyRedRC46's Avatar
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    Holy shit!!! Is that a gixxer engine swap kit?! lol
    Last edited by CandyRedRC46; 07-11-2013 at 05:19 AM.

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  22. #22
    Member John Kiewicz's Avatar
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    I understand the concept behind the Suzuki-spec airbox scoop, but would it really do anything? If it were exposed to the outside I would expect that it would grab (or direct) air ... but when mounted under the fuel tank/seat I don't see any potential for scooping. Wouldn't an open top (without scoop) work equally well or better ... with a whole lot less fabrication work needed?

    Also, if you were to run that fine Gixxer-issue ram-air airbox ... I would suggest a bit of overhaul by aerosol (as a flat black paint job is worth an extra two tenths in the quarter-mile).

  23. #23
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    So...I'm a little confused....what do you guys mean by the "down tubes that go to the rear heads?" I thought a header WAS the tubes that go to the heads?!?!?

  24. #24
    Senior Member steven113's Avatar
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    Quote Originally Posted by APEXLVR View Post
    So...I'm a little confused....what do you guys mean by the "down tubes that go to the rear heads?" I thought a header WAS the tubes that go to the heads?!?!?
    It is, The headers on a v4 must be slit into front and back sections. The down tubes are the indipendent header tubes for the rear two cylinders. They connect to the main header behind your rear brake lever.
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  25. #25
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    Interesting read that might apply here.

    RC51.org Dyno Chart & Tuning Basics page


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