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Velocity Stacks?

Discussion in 'Modifications and Projects' started by SHEPPO, Aug 3, 2008.

  1. G'day tech guru's.

    Has anyone played with after market velocity stacks, such as the factory pro units?

    I've head good things about them, and wondering if it's a worthy mod. About US$250+shipping for a set.

    I'm assuming altering the tune would be needed with a PC3 or similar, much the same as when upgrading exhaust systems and air filters??

    That's all.


  2. What type of bike have you got?

    mucking around with inlet runner length is pretty advanced tuning. You'd only go there after you'd got a lot of other things on the bike right first. Even then I doubt an off the shelf solution would be right for your setup.
  3. Unless it's an already known and researched improvement for your specific bike, you'll probably get more performance improvement (and a whole lot more fun) by spending the $250 on a racecraft course.
  4. As with the other 2 posts, it is mostly a waste of time unless you are after the last bit of power. As you may be aware, velocity stacks use the momentum of the moving air in these runners to force extra fuel air into the combustion chamber. They enhance the pressure pulses in the inlet tract to boost cylinder filling and hence torque but only at a relatively narrow rev range. The trick is to match the length of the runners with the usable rev range and this can take a bit of trial and error in many cases.
    The limiting factor may not be the intake runners if the inlet track and valves are flowing maximum. It could be that the motor would benifit more from a bigger inlet valves, different cams, larger carbs or remapped fuel injection. Often velocity stacks have large bell mouths which preclude connection to the stock air box. If not connecting to an air box then expect reduced engine life. Many manafacturers tune their bikes with the airbox as part of the system. If for the steet, not worth it. If for the track, maybe but onlt combined with a whole heap of other mods.


    Bob Moore
  5. Sheppo

    I can only say in my 2003 ZX6R I changed the outer intake trumpets to shorter ones, matching the original inner trumpets. They came out with 2 short, 2 long.

    Lost a reasonable amount on bottom end, but what I lost I gained at least that, I think even more on the top end. Was happy with the $30 odd investment, on a stock standard bike with stock exhaust.
  6. bike is 04/05 R1.

    velocity stacks are a set of 4, about twice the length (thus will improve low/mid rpm power) of the OEM plastic ones, and are said to increase mid range by 6-8hp, and roughly 2hp up top. also smoothening the power delivery from the before/after graphs i've seen.

    8ph for $230 is pretty good bang for buck. and considering the bang is in the streetable section of the rev-range, i see it as a worthy addition.
  7. If it does what it claims, but get it wrong and changing the length of inlet runners could cost you the same amount of power.

    Also keep in mind you don't get something for nothing. The stock length of runner would have been designed with one band of power in mind. From what you've written that is probably top end.

    Longer runners generally mean a peak torque lower in the rev range but it also means a loss of top end power.

    so long as the runners are designed for your engine (and specific year and australian model) then they will likely give a power increase in the bottom end. But don't believe them if they claim it also gives top end.
  8. Most all intake tracts I see on motorcycles are designed for one thing, to fit in teh available space.
    There are huge gains to be had....if you can make the room.
    The formula is pretty simple for working out intake runner lengths.

    Regards, Andrew.
  9. i've played with inlet lengths before, but with car motors.

    how i see it, a bike ridden mostly on the road needs a good mid range. the bike in question is 170+hp, that's way more than anyone needs on the street.

    if adding a set of longer velocity stacks will boost the midrange (making the bike more street-able), how is it a bad thing? even if it dropped a hp or two up top, i highly doubt anyone would know, since even in 1st gear it's loss of license for 12 months!
  10. Not saying it's a bad thing, just that there might be more fun ways to drop $250 and go faster :wink: .
  11. if you can name one mod that will give me 6-8hp for $250, i'm all ears :cool:

    there's not much on a modern sports bike that can be changed, cheaply, to give good rewards! especially once the usual pipe, filter 'n' tune have been done.
  12. Be careful of the claims. 6-8hp sounds like bunk. Seriously. A common complaint of the post '04 R1's is that they are down on midrange compared to most of the rest of the litre bikes. Top-end power is competitive.

    Now, ask yourself, given that this is fairly common knowledge, and pretty much every reviewer writes about it, and every rider experiences it, if added midrange was as easy as extending the velocity stacks then don't you think that Yamaha would have done it?

    I had ordered FactoryPro velocity stacks for my old 2000 Model R1. I had dyno graphs from before/after. I made an insignificant difference and actually added weight to the bike. Overall I considered it to be a waste of money.
  13. I am so god damn sick of hearing this sort of argument. Everyone from commodore drivers to bike riders think their machines are perfectly engineered right from factory. Factorys do things for reasons that dont suit everyone, from trying to please the majority, or chasing peak power, or saving $. I could name literally dozens of examples.

    Post your experiences, fine. But for fcuks sake keep this shit to yourself. Some of us have experienced positives in this area- yes, actually improving on factory setups. Myself included.

    I know i am only new here so I dont mean to cause offence, but I swear I am going to go nuts if I hear it one more time
  14. See this is why I ride a Triumph. They ARE perfectly engineered from the factory.
  15. Sounds like everyone here is pretty correct (except the Triumph dude :wink: :LOL: ), as with most engine tuning mods; you get a 'rob peter to pay paul' effect. To get the best benefits of altered intake tract lengths, for sure cam timing and exhaust lengths should match it. PLUS generally; where you shift power, you also need shift fuel, eg: a mod that gives more top end and less low down will require more fuel up top and less down low.

    Many times on the dyno, in the past, I have fitted shorter intake trumpets, bellmouths, stacks (call them what you like) and have gained 5hp up top and lost 8hp low down. So if you live in the top end (like on the race track), go for the shorter stacks but to get the most benefit, also shift the fuel. If you ride a litre bike, and you shift the power up top, be warned, there aren't many people that would NOT get SLOWER lap times.

    I agree with going with a longer intake tract length for the street on a big bike, maybe even a bump up in compression may give better midrange response also, although the modern sports bike has quite high compression already; you'd need to make sure it doesn't 'ping' its head off.

    I don't really believe that changing the intake length will give more lowdown AND topend, but maybe it is unmasking an inherent problem with the bike?

    If you want more lowdown & midrange, I say go for it; it's a cheap mod, I think we'd all be interested in the before & after dyno runs.
  16. If you want more power at usable speeds, get a whopping big rear sprocket. :)
  17. Why don't you just use a lower gear then? :LOL:
  18. Because then you can't boast, "It does wheelies in the first five gears!" :LOL:
  19. The 07/08 R1 has variable length intake stacks...... so I guess they have :grin:
  20. Get off your f*cking high horse Brad. We're talking about velocity stack lengths here, not exhaust systems, port sizes, injectors sizes, compression ratios, piston crowns, cam profiles, and so on. Most of those things are chosen for emissions controls and ease of manufacture. That's understandable.

    A velocity stack is little more than a fluted length of tube. If the manufacturer of a bike that's known to have a weak midrange in comparison to the competition could easily add ~10mm of length to some injection molded 10c rubber/plastic tube to gain 5-8hp in the mid-range without any sacrifice in top-end power, it would've been done.

    I read the Factory Pro literature, and bought into it, and felt like I didn't get what I paid for.

    Yes, most any factory engine can be easily improved, but in this specific instance, my prior experience is saying that it's a bunk claim. When it comes to velocity stack lengths you have rob power from somewhere else to gain in where you want it. Any manufacturer of parts that claims a net gain across the board is selling snake-oil.

    Just my 2c.