Topic: Velocity stacks????

[OLDHEAD]

i love the look of the stacks ive been thinking a lot about them -  but for what TT said about it - any one using stacks a while can chime in for or against - much appreciated

[shag nasty]

I have never had a problem with these stacks and getting them jetted correctly. for 69-76 carbs and stock motor I run 117.5 - 122.5 jets. On a matic motor with round top carbs it was 115 jets.

I have ran pods and bread boxes and they have a major problem that these stacks don't have and that is side drafting, when you get up to 50 or 60 mph with pods or bread box it is like all the air gets taken away from the carbs causing bogging and the motor acts almost like it is running out of gas.

as far as my experience with having the screens on the inside of the carbs or the out side it is not going to make that much difference unless you are racing your bike and come on who is going to race our bikes on a professional level.

I am after the looks of the velocity stacks and not so much on the performance that they were originally designed for.

I have ran my bike up over 100 with these stacks on it and felt like it still had a lot more to give.

[Retro Rocket]

I think what a lot of people don't realise is that our bikes come standard with velocity stack already, and in most cases will run better with the stock stacks and a good free flowing filter. Another down side to pods is rain and velocity stacks by themselves will just prematurely ware out your engine.....Fly screens on them don't help much..

Mick

[voxonda]

+1 on Mick,

Use the oem stacks on one of my replica's oem carb's('76), think they work better than anything I've tried sofar. But I only use it on track.

Rob

[wannabridin]

so what if we want the look and don't mind sacrificing some performance for a street bike?  i'm not going to have a high hp monster, just something i can rip on and drive it hard!  i mean if i can get better performance from the stock airbox w/ a k&n over stacks with a small filter inside the throat, then i'll do it, but i'd love stacks for the looks!!  hopefully steel dragon can elaborate on the ID of his pieces relative to the throat diameter...

[beveldrive]

Wow, this thread has run and run!
As I suggested at the start, a foam sock is a good compromise when it comes to filtering rampipes. In my experience better than a 'pod'.

Anyhow, I've just fitted my CRs and for a while I was gonna stick with just the ram pipes as supplied by Keihin. i figured that as the bike will not be a daily ride - what the hell, and I rarely ride on dusty roads. But in the end I fitted foam!
These are well clear of the ram pipe entry, and I'm hoping they will be rigid enough to resist the suck of the carbs. Time will tell

   

[voxonda]

On my first Cb750 I protected the engine by using the side panels of a K0, they cover the stacks. Have no better pic, this is from '78. Gee, still had hair back then and about 50 kg less.


Rob

[Retro Rocket]

I know there's not much room but i am going to make an insert for the airbox to make it bigger, I want it to go down and hit the top of the gearbox to increase its volume. I know TT doesn't think it will help but i also want to put some ram tubes {air intakes} into the filter section as well to supply more cooler air. This set up is common with modern sports bikes, so i thought i would give it a try.....

Mick

[Steel Dragon Performance]

Hey guys, sorry about the slow reply. About the inside diameter of our stacks, they are approximately 250 thousands bigger than the bore of the carb, which isn't much for the stock application. However, you also install a screen which disrupts air flow anyways, so that little bit of difference will not be noticed.

These stacks are designed for the average street built bikes. We have always had good replies on how it makes the bike run and we ourselves on our own personal bikes have had good results with proper jetting. If these were for a drag racing/street racing bike, then ,yes, you would want the inside diameter of the stack to match the carb. In this situation you would also not have a screen installed because the screen will cause restriction/interruption of the air flow. We have had custom orders for this type of application and had good feed back from them. Those kind of stacks also cost more due to the different thickness of stock we use and extra machining involved.

The reasoning for the screen is for the cafe/chopper/bobber builders who don't like to use inner fender guards or filters, will keep rocks and other debris from entering the carbs. For the stock application the screens will not filter fine dust but are good insurance that you don't suck a rock or a small child into your carbs lol .

With proper jetting we have had many customers say their bike ran better.

Thanks,
Mike

[Tintop]

so what if we want the look and don't mind sacrificing some performance for a street bike?  i'm not going to have a high hp monster, just something i can rip on and drive it hard!  i mean if i can get better performance from the stock airbox w/ a k&n over stacks with a small filter inside the throat, then i'll do it, but i'd love stacks for the looks!!  hopefully steel dragon can elaborate on the ID of his pieces relative to the throat diameter...

I have been speaking with Mike @ Steel Dragon about his stacks.  They have a step were the stack & carb meet. This then becomes the mounting collar.  As noted the stock intake is based around stacks.  30mm for the 500 & up to 76 550, 40mm for the 77/78, and 55mm for the 750.  Interesting to note that Honda supplied a longer stack than Keihin does with the CR's (50mm).


The photo above illistrates what I personally don't like about socks, they cover the entire stack.   That said, if you are using the stock ones, do you care.   Using Turboguzzi's PiperCross socks as an example - sock 100mm overall (filter material 15mm thick) / stack working length 55mm / mounting area 10/15mm, would yield an air space above the bell of ~15mm (100- (15+55+15) = ~15/20mm).  On a 550 you would have to shorten the sock because of the frame by about 15mm.  For my 550 I'm using x4 #2/3 stacks, to make fitting my filter simpler.

[TwoTired]

250 thousands?
That's a 1/4 inch step right at the carb mouth!  This isn't much?!?  By whose standards?  The stock "stack" is at least 200 thousands better!

With proper jetting we have had many customers say their bike ran better.

No offense, but this really means absolutely nothing in the scientific world, and is a pure marketing/sales ploy.
It's the same ploy oil manufacturers use to sell their brand oil, unsupported testimonials without quantifiable data to backup the claim.  Popular opinion does not ever trump the realities of physics or real test data collection.

The upshot is that these stacks are purely for a cosmetic "look", and NOT designed for a functional benefit or a performance improvement.  Yes, the engine will still run.  Whatever you put on (or in) for a filter will help save the engine from ingested particle wear but science says you will NOT get a velocity stack performance improvement.  Good luck with getting the jetting right at all street speeds!  (Or, a DYNO test result improvement!)

Wow....

[Steel Dragon Performance]

I apologize about the 250 thousandths, I meant to put .0250 thousandths. I'm not trying to make a sales pitch here, I'm just trying to answer the questions that you and some of the others have posted. Sorry if you feel this way but before you criticize something, maybe you should try it first. We have not made any claims to horsepower gains. We simply stated what others thought of our product.

Thanks,
Mike

[Retro Rocket]

I apologize about the 250 thousandths, I meant to put .0250 thousandths. I'm not trying to make a sales pitch here, I'm just trying to answer the questions that you and some of the others have posted. Sorry if you feel this way but before you criticize something, maybe you should try it first. We have not made any claims to horsepower gains. We simply stated what others thought of our product.

Thanks,
Mike

Not being picky here Mike but you did put the wrong number in your post and it was scrutinised accordingly. Just remember that there are some very smart guys on this forum, engineers and the like that will debunk any "myths" or simple untruths. not saying thats the case here. Any step in a velocity stack, no matter how small will interrupt the way that the stacks are designed to work which is providing a undisturbed flow of uninterrupted air.....simple as that.....

Mick

[Steel Dragon Performance]

We did mention a small step in my earlier post, and I do agree with it being a disturbance along with the screen as we mentioned earlier. From my own personal experience I have not noticed any problems from this small step. I will be flow testing these sometime in January and I will post the Data on here if you would like. Yes I do know it was a typing error and I apologize about that but I don't think it was necessary for TT to make sales pitch accusations. I do realize there are a lot of smart people on this site and I don't doubt that one bit.

[Retro Rocket]

We did mention a small step in my earlier post, and I do agree with it being a disturbance along with the screen as we mentioned earlier. From my own personal experience I have not noticed any problems from this small step. I will be flow testing these sometime in January and I will post the Data on here if you would like. Yes I do know it was a typing error and I apologize about that but I don't think it was necessary for TT to make sales pitch accusations. I do realize there are a lot of smart people on this site and I don't doubt that one bit.

I would love to see that data will you be using a coloured smoke so we can see exactly is going on?  Just wondering, why the small lip in the first place?

Mick

[Steel Dragon Performance]

My son will be testing these at the High Performance Engine Machining College where he is currently going to school, so I'm not sure what he will be using. That would be pretty cool though. As for the small lip, in order to keep the cost of the stacks down and affordable, we have to go with a different stock which is slightly bigger than the inner carb throat diameter. We can make them to fit perfect with no lip, but we have to use a thicker walled stock which costs a lot more $.

[Retro Rocket]

My son will be testing these at the High Performance Engine Machining College where he is currently going to school, so I'm not sure what he will be using. That would be pretty cool though. As for the small lip, in order to keep the cost of the stacks down and affordable, we have to go with a different stock which is slightly bigger than the inner carb throat diameter. We can make them to fit perfect with no lip, but we have to use a thicker walled stock which costs a lot more $.

So boring out the carb throat a touch would cure this and probably improve performance....

Thanks for the reply..

Mick

[Steel Dragon Performance]

Yea that would be an option, you could probably just lightly bevel the carb throat a little bit with sand paper or a hand dremel.

Thanks,
Mike

[TwoTired]

Well, since the tittle of this thread is Velocity stacks, I'll point out the difference between ones that actually work and ones that only "look" similar to real velocity stacks.  The reader can decide if looks are more important than function.  Or, if they really wish to know the difference between a facade and the real thing.

First stop is wikipedia:
http://en.wikipedia.org/wiki/Velocity_stack
This will give some of the basics to understand their real purpose.

Then, here are some pictures showing what they are supposed to do.
Pic 011 illustrates the functional goal.
Pic 012 gives some design guides to look for in a true velocity stack.

Note that the stock stacks lack the bell lip radius for a true, well designed V Stack.  But, it does a very good job of matching the carb bore inner diameter transition point.  See pic 015, it's the stock inlet stack for a Cb550, the CB750 stack aligns with the carb similarly.
Pic 030 shows a pretty well designed inlet with integral V stack.  I found this example at:
http://www.team-integra.net/sections/articles/showarticle.asp?ArticleID=471
It's for an Integra engine, but they have the math, physics, and dyno tests that show them to actually make a performance benefit.

If its just the "look" you want, regardless of function, just have a tinsmith knock out some aluminum bells to applique onto the side of the bike like Honda did with the 700SC.  See pic 033.   

Lastly, I maintain the no true Velocity Stack maintains its performance benefit if a filter is placed within or near its airflow guiding surfaces. 

Rock on!   

[Steel Dragon Performance]

If you go to our website and go under photo gallery,go to Jim's H1 Kawasaki stacks, you'll see that stack design that we make is very similar if not identical to your top picture showing the functions of a velocity stack. Sorry about not being able to post the pictures in the forum, I'm not sure how to do that. These stacks were bored out to fit the inner carb throat diameter exactly. They were made for Jim at TRA-CO Racing Engines CO in North Carolina. He has been testing velocity stacks and performance engines for years dealing with cars and other race applications. He was a very knowledgeable person and cool to talk to. As I posted earlier, I agree with any screen or filter interrupting air flow through the stack to a degree. However, that is the bike owner's choice depending on the application.

Thanks,
Mike

[TwoTired]

If you go to our website and go under photo gallery,go to Jim's H1 Kawasaki stacks, you'll see that stack design that we make is very similar if not identical to your top picture showing the functions of a velocity stack.

Sorry, have to disagree.  I don't see a 1/4" radius at the entry for any of the stacks you offer.  The stack draws air from all around the stack entrance.  An abrupt edge will create turbulence, unless the inlet air flow has very slow velocity.  The required radius has been cut in half for the H1 example.

Anyway, if I understand you correctly, for use on the SOHC4 carbs, one has to bore the inner diameter of the carbs, to get a flow match at the carb to stack interface.  Do you publish inner diameter specs?

[wookie]

Does anyone run the stacks that come with the Cr's?  From a performance standpoint, pods or stacks on Cr's? 

[beveldrive]

Yes.
See my earlier post

As has been said, and as I illustrated with the see-through airbox at the start of this thread,  the rampipe should ideally be situated in still air, with space all around the entry radius. My sock filters are a compromise, but due to their extended length, I'm hoping they will provide good flow. Time will tell.
The other reson I chose socks rather than pods was I just happened to have plenty of the filter material in my workshop - it was a no brainer.



Steve

[TwoTired]

the rampipe should ideally be situated in still air, with space all around the entry radius.

If you will allow me, I think the term you are looking for is unobstructed air, rather than still air, as "still air" implies no movement.

Cheers,

[wookie]

With all do respect i was looking for opinions based on experience.

"I'm hoping they will provide good flow. Time will tell."

Anyone else care to chime in.