Do You Run Velocity Stacks?

Discussion in 'Triumph General Discussion' started by billyrideslow, Feb 13, 2019.

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  1. billyrideslow

    billyrideslow Member

    Nov 20, 2018
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    I've recently added some to my 2006 Bonnie and it's really made a big difference.

    I was wondering who else has tried these and what they discovered.


    velocitystacks.png
     
  2. R_1000

    R_1000 First Class Member

    Sep 2, 2016
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    I had them on my previous bike R1 but had to also modify the airbox and custom map on the dyno. Didn't see any noticeable difference after ditching all that money. Maybe a little better midrange. If I had to do it again, I will go the gearing route ;)

    Maybe different engines and tunes responds well towards the stacks
     
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  3. Callumity

    Callumity Elite Member

    Feb 25, 2017
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    https://www.triumphtwinpower.com/triumph-twin-air-filters.php

    On balance the carbed bikes seem better with the airbox in place but baffle removed and free flowing filter. Velocity stacks and pod filters can be iffy in cross winds but for many it is the minimalist look so very much a matter of taste over raw performance. Airbox retention seems to help mid range torque characteristics more than WOT horsepower.
     
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  4. billyrideslow

    billyrideslow Member

    Nov 20, 2018
    26
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    san diego
    #4 billyrideslow, Feb 13, 2019
    Last edited: Feb 15, 2019
    Thanks for your responses. Was wondering if what I experience was an anomaly or is it factual.

    At lower RPM I don't notice any difference, but at higher RPM's the bike starts to scream. I've re-map rev limiter, but rarely go above 7,000. I did change main jet from 1.40mm to 1.60mm to help feed her and made minor changes to pilot and needle.

    The sound is insane at the higher revs and she now sounds threatening.

    She's my commuter bike and because of where I ride, it's a constant race off the line. I like it, it's fun.
     
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  5. Tricky-Dicky

    Tricky-Dicky Crème de la Crème

    Dec 12, 2016
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    Velocity stacks will if nothing else is changed will slightly weaken the mixture and as most EFI systems are mapped slightly rich so you may notice a slight difference/improvement, the same apply's to carbs but to a slightly lesser degree although at WOT stacks will improve flow on carbed engines.
     
  6. billyrideslow

    billyrideslow Member

    Nov 20, 2018
    26
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    I based the design on mopar velocity stacks used on muscle cars. The idea is to get more oxygen into the cylinder which occurs at higher rpm. This is typically associated with the wider carburetor position. I did put in a larger main jet to compensate for greater air flow.

    Not sure what EFI would do but hoped it would remap based on oxygen sensor. I didn't have this problem because the bike has a carburetor.

    I don't have access to a dyno so had to use a long hill by my house. Before the velocity stacks I struggled in 4th gear. Now, it's 5th gear and I'm holding her back.
     
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  7. Tricky-Dicky

    Tricky-Dicky Crème de la Crème

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    EFI will not adjust..at least not on a Triumph as O2 sensor feedback stops at around 1500 rpm, on some later model cars that uses wide-band O2 full time are capable of readjusting for intake and exhaust modifications.

    I am surprised you needed a larger main jet unless the original filters was very restrictive...only trouble with stacks is they can suck in all kinds of debris.
     
  8. Callumity

    Callumity Elite Member

    Feb 25, 2017
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    If you think of your engine as an air pump, opening the inlet side will only achieve what an equal opening of the exhaust permits. What pipes are you running? The standard items are pretty restrictive.....
     
  9. billyrideslow

    billyrideslow Member

    Nov 20, 2018
    26
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    #9 billyrideslow, Feb 13, 2019
    Last edited: Feb 15, 2019
    I'm running diesel cross over pipes from monster exhausts. She pumps well.

    I incremented main jet size checking the plug for blackness. Seems to be about right, but this is seat of pants tuning. I had a larger one in there and she seemed to be drowning and went down to the 1.60mm. There's no black soot forming in the exhaust pipes. It seems to start ok on cold mornings. I've tried many options.

    screenshot_1031.png

    I've been monitoring dirt accumulation and haven't found any effects. She's tarnishing up from gas like normal. I ride her on the street and won't take her down a dirt road. Surprised at how clean they stay. Now, this isn't for everyone and I pamper her.

    screenshot_1032.png
     
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  10. Tricky-Dicky

    Tricky-Dicky Crème de la Crème

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    Larger main jets will only effect the last 1/4 of throttle and WOT openings it has no effect on the rest so tuning by just main jet will not have any effect on lower openings and cruse.

    And if your tuning by plug colour you need to cur the engine at the throttle opening your trying to adjust otherwise you get an incorrect reading.

    If you want to change the mixture at other load points you need to mainly alter the needle position first and then if needed change the needle jet.

    Also i meant that stacks will be prone to drawing in things like insects and dust
    but this goes through the engine and not the fuel system.
     
  11. billyrideslow

    billyrideslow Member

    Nov 20, 2018
    26
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    #11 billyrideslow, Feb 14, 2019
    Last edited: Feb 16, 2019
    Thanks for your input, it's rare to find someone with your knowledge and for me having this type of conversation, I'm enjoying it.

    I have changed the needle settings to help midrange. I guess if you're increasing the flow rate, then adding a little more gas across the range is a good idea. Checking for brown plugs seems to be working, nothing white or black. All I'm trying to do is beat the guy next to me. Not that I'm racing.

    She's got close to 60k miles on her and I was worried about the valve seats. But she's not losing compression and the valves aren't needing adjustment.

    I'm wanting to pull the head off and rebuild it. At the same time I was going to mill the head and increase the compression ratio. The engine seems like it can handle it. Clutch is slipping in 2nd gear and need to add stiffer springs to help it engage. I hate letting off the gas so the clutch will engage. I find myself pushing the hand grip trying to relax the cable.

    Anyway, she's my favorite bike right now and gets a lot of my attention. I do ride her a lot and like tinkering with motors.

    If you're ever in southern california, look me up I'd like to meet you in person.
     
  12. billyrideslow

    billyrideslow Member

    Nov 20, 2018
    26
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    san diego
    #13 billyrideslow, Feb 15, 2019
    Last edited: Feb 16, 2019
    Great read, thank you.

    I've read the CVK manual for Harleys but not the triumph variant. The triumph version is very informative. One thing I now realize is that I need a thruxton needle.

    I made a mistake in main jet size. Stock was 1.40mm and I'm at 1.60mm now, the pilot is .45mm.

    I can confirm that opening things up liberates a triumph carbureted bike.

    I'm her 3rd owner, bought her with 18k miles on her. I would classify her as a basket case and got her cheap. Figured out the problem, and have never looked back. I love the styling of the motor and had to have one.

    Your document made reference to an amal carburetor and read through that documentation as well, guess what......a velocity stack #37.

    screenshot_1035.png

    I designed the velocity stack that's on my bike and there is some science behind the design. It's not just a funnel. Ok, maybe it's a fancy funnel but there are some fluid dynamic considerations in the design.

    I'll work up some of my ideas and post'm. It'd be good to have someone check my math.
     
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  13. Tricky-Dicky

    Tricky-Dicky Crème de la Crème

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    I actually run big velocity stacks and filters on my Trident didn't actually notice any change when i added the filters so that was a bonus not that its about performance anyway i built it as a cruiser anyway.

    [​IMG]
     
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  14. billyrideslow

    billyrideslow Member

    Nov 20, 2018
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    cruiser my ass! that's a rocket.

    screenshot_1036.png

    Thanks for your photo
     
  15. billyrideslow

    billyrideslow Member

    Nov 20, 2018
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    #16 billyrideslow, Feb 15, 2019
    Last edited: Feb 15, 2019
    I really like the aluminum side covers on your bike. Not sure why the bonneville america has so much chrome. Does the world think we americans like chrome, bling & shiny stuff on our bikes?
     
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  16. Tricky-Dicky

    Tricky-Dicky Crème de la Crème

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    Try riding a hard-tail like a rocket.;)



    [​IMG]
     
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  17. billyrideslow

    billyrideslow Member

    Nov 20, 2018
    26
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    #18 billyrideslow, Feb 15, 2019
    Last edited: Feb 16, 2019
    I'd could totally ride her like a rocket and have a blast.

    I think we could drink beer together.

    Thank you, she's really nice
     
  18. Tricky-Dicky

    Tricky-Dicky Crème de la Crème

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    Thanks fella, I'm sure you could on US roads........but around here the best i could manage is 30 on the B roads and 60 on the A roads....unless you want spinal surgery,;) and besides the bike is 44 years old and I'm a fair bit more...but I'm sure we could enjoy a pint or three together.:)
     
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  19. Rocker

    Rocker Elite Member
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    May 1, 2016
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    Velocity stacks allow the fuel mixture to straighten out so as to enter the cylinder without swirling I read somewhere to optimum length (can't remember where) so I run my Triton (T140 powered) around 250mm (10 inches) from end of stack to valve head this can also be achieved by longer inlets which I run 35mm longer than stock to get to the 250mm length:)
     
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