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I've got two questions, bear with my they're probably gonna be kind of noob-ish.

1) why can I buy a 35/35, 35/70, but not a 70/70? Im guessing it's because there isn't any room for the other 70. Well ok, kinda a second part of this one, which one do I want? Im more interested in acceleration, I mostly go between 25-60, and rarely go past 70-75. Which one will give me the most torque?

2) do these stacks change the RPMs at all? I think I read that with a slight increase in HP, there is a slight decrease in RPMs needed to go at a certain speed. Dunno if that makes sense, I don't know much about this myself.

So I'll try to rephrase that. Im just going to make up some numbers. Lets say my bike is going 70 mph, 6K RPMs and 50 HP (just random numbers). Now, I add the stacks, and lets say Im going 70 mph again, but the stacks add, say, 3 HP. Does that mean that I can be going 70 mph, with 50 HP, but a slightly slower RPM because the bike doesn't have to work as hard to get that HP? Maybe, -500 RPM?

Im curious about this because I would also like to make changes to the sprockets, maybe -1 in the front, dunno about the back yet. Again, my goal is more acceleration, just becasue I think it is fun :) But I guess changing the sprocket ratio will make my bike run at a slightly higer (say +500-750) RPM then normal, which is harder on the engine and a little harder on my wallet for gas. I figure that if the my stock bike runs at 6000 RPM, and I change the sprockets it'll run around 6600 RPM at the same speed, no good :( BUT if the V Stacks REDUCE the RPMs slightly, again say 500, will the combination of the two make my bike run at about normal RPMs, but more low end power? Again, assuming the Stacks actually reduce the RPMs slightly. Or, is this not possible?

I just want to do some interesting things to my bike, the sprocket, stacks, need a TRE and K&M filter. BTW, I don't think this'll turn my bike into some beast of a thing that'll too powerful to control, after all it is an SV, but I do have 5 seasons experience on this bike stock, so I think I can handle myself on it.
 

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Discussion Starter #103
As for the first question, yes you are completely correct in your assumption that 2 70mm trumpets would not fit within the confines of the air box. Although I have not yet received a degree in engineering I believe they have spent numerous hours researching these things and I see fit to simply take their word for it. If you're only looking for low end power you definitely want the 35/70 stacks. Those are the ones I have and I love them.

The second question is a bit more tricky but I'll take a crack at it. Velocity stacks are funnel shaped devices that when placed inline with the carbs/butterfly valves allow for a more even and organized air flow from the airbox into the engine. Its is here where the "hp" is gained. Feed the engine more air and you get more power. The downside of this is of course that more air equals more fuel.

To use your numbers as an example, your bike is going 70 mph at 6k with 50HP at the rear wheel. You park your bike, install the stacks and go along your merry way. Now, you have gained more HP, so your bike can accelerate back to 70mph in a more hurried manner. Horsepower as a unit is defined as work done over time and in the case of and engine can be expressed by the equation HP= 2pi*Torque*RPM/33000. This means that RPM and Horsepower are directly proportional and that increased HP means an increased RPM.

I likewise have some similar modifications to my bike as the ones listed in your post and I highly recommend these stacks. From the sounds of it you're just looking for something to push you back in the seat a little bit more then the stock motor and that's exactly what these did for me.
 

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For a while I couldn't figure out why there were not 70/70s, but then I saw the pics and i figured that must be the answer. Still seems weird, and I wonder what it does having two different legnths installed; but if so many people have gotten them I guess it's not a problem.

OK, so an increase in HP from the use of the stacks will also increase the RPMs, not decrease them? So will combining Velocity stacks, -1 tooth in the front, a TRE and getting rid of the snorkel make my bikes engine run at too high of RPMs, and maybe cause damage? If thats what will happen, I need to do some more thinking on this. Yes, I want to get my bike as much power as possible without spending a ton and putting the engines integrity at risk. I don't want an I4, can't afford a 1000 and porting the engine sounds cool, having an SV750; but that isn't cheap either and not the safest of mods it seems, but there are mixed opinions on that. Another thing to consider, much, much later when I've run out of things to do.




Also, I've been using this site to figure out what my speed/RPMs will be with stock teeth as well as custom teeth numbers. Im not too sure if I agree with the numbers (it only goes up to '05, I have an '07 but I doubt that matters much) as they don't match with what I get when I ride.
http://www.gearingcommander.com/
But, I haven't gone riding in a few months so I do forget a bit; plus I have stock guages which throw off the spedo but not in the same way this site is confusing me.

Anyway, it says that:
--Stock (15/44) 63 MPH @ 4500 RPMs, 75.6 MPH @ 5400 RPMs, 88.2 MPH @ 6300 RPMs
--Custom 1 (14/44) 58.8 MPH @ 4500 RPMs, 70.6 MPH @ 5400 RPMs, 82.3 MPH @ 6300 RPMs
--Custom 2 (14/47) 55.1 MPH @ 4500 RPMs, 66.1 MPH @ 5400 RPMs, 77.1 MPH @ 6300 RPMs

Of course I dunno if these numbers are from a stock spedo or a more accurate one.

I don't know if these numbers quite match up, and I don't remember what RPMs are safe to maintain while cruising on the freeway, though I don't really need to go much faster then 72 aside from occasional emergencies. Is 6000 or less generally ok for maintaining? If so, then even with the most extreme gearing ratio I can do roughly 73.5 MPH at 6000 RPM. Does that sound safe?

I might be better off making a new thread about this one though.

EDIT: Im thinking that site uses stock guages, and that if I were to swap them out for Vapor guages I wouldn't get the same numbers. Custom 2 is probably not safe and custom 1 MIGHT be ok; as I hear that stock guages are about 10% off. It would mean that (in custom 1) I would really be going 74.1 MPH at 6300 RPMs instead of 82.3, and likely 71 MPH @ 6000 RPMs.
 

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I wonder if these would help on an SV1000 as well, I think the airbox is the same, dont know if the throttle body holes are the same size though, I would expect them to be bigger but who knows.
 

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I bought the stacks in the group buy and honestly, I don't notice much difference if any at all. There may be a little more induction noise. I am running a SV1000 snorkel and a stock paper filter. I don't really feel any increase in power, even though my wallet is lighter. I never thought they were going to be some magic horsepower adder, I just felt like giving them a shot. I don't regret it.
 

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Discussion Starter #108
OK, so an increase in HP from the use of the stacks will also increase the RPMs, not decrease them?

Will combining Velocity stacks, -1 tooth in the front, a TRE and getting rid of the snorkel make my bikes engine run at too high of RPMs, and maybe cause damage?

Is 6000 or less generally ok for maintaining? If so, then even with the most extreme gearing ratio I can do roughly 73.5 MPH at 6000 RPM. Does that sound safe?
I edited for just the questions :)

Yes, you are correct. Adding the stacks results in an increase in HP and an increase in the RPM. Though a much slighter increase in RPM then I think you're expecting.

Currently on my bike I have the stacks, K&N filter, stock gearing, no snorkel and a TRE. Runs fine and I have no issues with it.

When the bike was designed it was more then enough durability to withstand RPM's in the 0-10K. If you want to take it up there every once and a while I see nothing wrong with that. 6K RPM and lower is fine for maintaining.

As for your numbers with that site... I used the same site and came up with my own. Just to demonstrate how changing things in the gearing effects the speed. Ranked in increasing speed


Custom 3 (14/44)
6th gear, 5400 RPM = 70.57mph

Custom 1 (15/46)
6th gear, 5400 RPM = 72.32mph

Stock (15/44)
6th gear, 5400 RPM = 75.61mph

Custom 2 (15/42)
6th gear, 5400 RPM = 79.21mph

Custom 4 (16/44)
6th gear, 5400 RPM = 80.85mph

Also worth mentioning is that you'll loose gas mileage when you change the gearing one way and gain it in the other.

Better gas mileage: Smaller rear or larger front
Worse gas mileage: Larger rear or bigger front
 

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Im not too concerned with the gas, I get about 55-60 as is. I wouldn't expect the loss in mileage to be huge, maybe 5? On a car that usually gets 25 that's pretty significant, on my bike I won't be too upset.

So, you notice a significant differece using the filter, snorkel (or lack there of), TRE and stack? That's pretty much what I want to do, plus lose one tooth in front. By the details you left, I don't think I'll need to worry too much about changing my ratio and taking my bike on the freeway.

Thanks for the input.
 

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To use your numbers as an example, your bike is going 70 mph at 6k with 50HP at the rear wheel. You park your bike, install the stacks and go along your merry way. Now, you have gained more HP, so your bike can accelerate back to 70mph in a more hurried manner. Horsepower as a unit is defined as work done over time and in the case of and engine can be expressed by the equation HP= 2pi*Torque*RPM/33000. This means that RPM and Horsepower are directly proportional and that increased HP means an increased RPM.
It's true that if you have more HP, you will be able to accelerate up to a given speed more quickly, but that's because you have more torque at a given RPM, not because more HP gives you more RPM. Boosting HP along with changing your gearing will take advantage of more available torque to get up to speed faster, go faster at lower engine revs, and have a faster top end... Why? Because of being able to power taller gears, not because of higher revs.

Problems arise when moving too far from the factory set-up, due to the amount of torque the drive train is designed to handle, and since the boost in available HP with this 'stack' type of air induction is most significant in higher air flows (higher revs), changing gearing too much will diminish the available power at lower revs.

I wouldn't change my sprockets for a two or three HP boost in the higher revs unless that's where I intended to run (I don't). Better would be a change in sixth gear ratio, but that might cost a little more than I'm willing to spend.

I wonder what a cost/benefit analysis would show for the boost a turbo charger would give... 8)

~Just my thoughts~
 

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Edited my late night post to make it more understandable in the daylight. 8)

Everyone understands that stacks are a passive compression booster, right? Somewhat less effective than Ram-air, and way down the scale from an active turbocharger.

But they look cool! 8)

Sent from my back pocket using Motorcycle App
 

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So you're saying that the stacks might reduce my RPMs? That's how I thought it worked, but I really have no idea.

I understand that it's possible to really stress the engine beyond what it can handle (porting the engine) but I would assume what I want to do isn't that bad, but again Im assuming. Like I stated before, I haven't done anything to the engine yet. I do plan on getting a better filter, maybe removing the snorkel (I took off my front fender, so maybe not a good idea), a TRE and of course these stacks. Add to that the sprockets, and something with the exhaust but I really don't know what to do with that exhaust just yet.
 

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So you're saying that the stacks might reduce my RPMs? That's how I thought it worked, but I really have no idea.

I understand that it's possible to really stress the engine beyond what it can handle (porting the engine) but I would assume what I want to do isn't that bad, but again Im assuming. Like I stated before, I haven't done anything to the engine yet. I do plan on getting a better filter, maybe removing the snorkel (I took off my front fender, so maybe not a good idea), a TRE and of course these stacks. Add to that the sprockets, and something with the exhaust but I really don't know what to do with that exhaust just yet.
No Doc, stacks won't change your RPMs, you control that by rolling your throttle. The stacks help generate more power, helping you go fast faster. Neither will they give you a higher top end (or higher RPMs), unless you make the final drive ratio taller by changing your sprockets. But, changing your sprockets for a higher top speed hurts your performance at lower revs, especially since stacks don't help much until the engine gets wound up.

So, I don't think adding stacks will help a whole heck of a lot, but I don't think they'll hurt anything either, except that helping one cylinder more than the other with 70/35 unbalanced stack configuration might not be such a great idea...
 

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No Doc, stacks won't change your RPMs, you control that by rolling your throttle. The stacks help generate more power, helping you go fast faster. Neither will they give you a higher top end (or higher RPMs), unless you make the final drive ratio taller by changing your sprockets. But, changing your sprockets for a higher top speed hurts your performance at lower revs, especially since stacks don't help much until the engine gets wound up.

So, I don't think adding stacks will help a whole heck of a lot, but I don't think they'll hurt anything either, except that helping one cylinder more than the other with 70/35 unbalanced stack configuration might not be such a great idea...
Ok, I just want to figure this all out. These stacks will give me (slightly) more HP, even at "normal" RPMs? Like, if I were to somehow make a perfectly 1/4 turn of the throttle stock, then do it again (perfectly) with the stacks my RPMs should stay the same, but the HP will be slightly higher? If so thats fine, pretty much what I want.

As far as changing the sprockets, Im actually more interested lowering my top speed, in order to increase my low end power and torque. I usually drive around 55 MPH, sometimes hitting 75 on the freeway. My only concern is that if I change the sprockets to fit this goal, how will that affect the engine? Removing one tooth in the front will probably make the bike permanently run at a higher RPM, regardless of speed or gear. I just wonder if this will be too hard on my bike, or as I've been told earlier in this thread, even running 6K RPM for an extended period of time isn't too bad for the SV.

I agree with what you said about using two different sized stacks, one of the reasons I haven't done this mod yet is because I don't get how using two different stacks can be okay for my engine, but Im no mechanic. But, if my RPMs are always high when accelerating, would the 35/35 be a better fit? Im guessing no, but again my goal is acceleration, 0-60 and then maybe a little from the 60-80 range just incase something goes down on the freeway.
 

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Ok, I just want to figure this all out. These stacks will give me (slightly) more HP, even at "normal" RPMs? Like, if I were to somehow make a perfectly 1/4 turn of the throttle stock, then do it again (perfectly) with the stacks my RPMs should stay the same, but the HP will be slightly higher? If so thats fine, pretty much what I want.

As far as changing the sprockets, Im actually more interested lowering my top speed, in order to increase my low end power and torque. I usually drive around 55 MPH, sometimes hitting 75 on the freeway. My only concern is that if I change the sprockets to fit this goal, how will that affect the engine? Removing one tooth in the front will probably make the bike permanently run at a higher RPM, regardless of speed or gear. I just wonder if this will be too hard on my bike, or as I've been told earlier in this thread, even running 6K RPM for an extended period of time isn't too bad for the SV.

I agree with what you said about using two different sized stacks, one of the reasons I haven't done this mod yet is because I don't get how using two different stacks can be okay for my engine, but Im no mechanic. But, if my RPMs are always high when accelerating, would the 35/35 be a better fit? Im guessing no, but again my goal is acceleration, 0-60 and then maybe a little from the 60-80 range just incase something goes down on the freeway.
Doc, Understanding how the presence or absence of these stacks affect your engine's efficiency at precisely metered fuel flows (precise throttle rotation) would require testing. Suffice it to say that if you ran your engine with stacks, it would produce slightly more horsepower than running it without them. I don't know how much more power, or when this would start to become effective, or even if you'd be able to notice, but I am confident that some additional power would be produced by their use... Unless your air filter leans things up too much. And, to get the most out of this mod, you might want to remap your ECU (with access to a dyno).

About riding at 6k... Many riders play between 6 and 9 or so... You won't hurt it at all riding at 6.
Just a note: It's not as exciting, but I find that riding between 3 and 5K (60 in 6th at 45k) gives me a 15% boost in mileage over the riding in the 6 to 9K range. You're going to take a real hit running 6 to 9 combined with running that smaller sprocket up front.

Regarding differences in the front and rear stacks, I remember reading somewhere that in order to compensate for the the rear cylinder running a bit hotter than the front, some riders run it slightly leaner, so maybe putting a taller stack on front wouldn't be a bad thing... But without knowing how well these stacks are tuned for this engine, I'm not at all sure how effective this would be. And if they fit, would using two 70s be better than one?

I'm afraid you're just going to have to test, test, test! 8)

Who makes these stacks?
 

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Anybody has dyno charts proving this?

Id buy it but it would be good to know some real numbers on OUR bike
 

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Sometimes somebody does it right on WikiPedia:

http://en.wikipedia.org/wiki/Velocity_stack

Or for too much information:

http://www.profblairandassociates.com/pdfs/Bellmouth.zip
+1
From the first reference
1. Allow smooth and even entry of air at high velocities into the intake tract with the flow stream adhering to the pipe walls.[citation needed]
2. Modify the dynamic tuning range of the intake tract by functioning as a resonating pipe which can adjust the frequency of pressure pulses, based on its length, within the tract.

Some people can explain things clearly with just a few words... 8)
 
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