![]() ![]() ![]() When it comes to velocity stack lengths you have rob power from somewhere else to gain in where you want it. 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. I read the Factory Pro literature, and bought into it, and felt like I didn't get what I paid for. ![]() 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. That's understandable.Ī velocity stack is little more than a fluted length of tube. Most of those things are chosen for emissions controls and ease of manufacture. We're talking about velocity stack lengths here, not exhaust systems, port sizes, injectors sizes, compression ratios, piston crowns, cam profiles, and so on. 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. 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? 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. 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. 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. 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. 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. To get the best benefits of altered intake tract lengths, for sure cam timing and exhaust lengths should match it. ![]() Sounds like everyone here is pretty correct (except the Triumph dude :wink: ), as with most engine tuning mods you get a 'rob peter to pay paul' effect. If for the track, maybe but onlt combined with a whole heap of other mods. Many manafacturers tune their bikes with the airbox as part of the system. If not connecting to an air box then expect reduced engine life. Often velocity stacks have large bell mouths which preclude connection to the stock air box. It could be that the motor would benifit more from a bigger inlet valves, different cams, larger carbs or remapped fuel injection. The limiting factor may not be the intake runners if the inlet track and valves are flowing maximum. 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. They enhance the pressure pulses in the inlet tract to boost cylinder filling and hence torque but only at a relatively narrow rev range. 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. As with the other 2 posts, it is mostly a waste of time unless you are after the last bit of power. ![]()
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