Jump to content
sansnombre

Intake Mod: Velocity Stack

Recommended Posts

sansnombre

I've done a lot of analysis on our FZ's intake system and along the way did an analysis on a possible intake mod of adding in a velocity stack to the outside of the airbox. The simulated change was a potential flow increase of up to 15% depending upon some variables. Not too bad potential, but that analysis was a very limited, static flow setup, just looking at the flow in the airbox. Nothing more. In short, this 15% increase would absolutely not be a 15% increase in actual, overall flowrate nor HP. It was a simplified assesment of whether it would help or not, and if helping, by how much. 15% was not too bad, but I didn't think it was worth the time to create it, and I didn't feel that it would actually increase perf by anything notable, if at all. Purely hypothetical.

 

But, I had a new 3D printer I was dialing in and thought WTF, let's create one. I made a prototype that was a single piece, but it necessitated removing all the bodywork and tilting up the tank to get to the rear screws, so I made into two parts. The bottom part is very similiar to the MWR top but has the internal section designed to accept the press-fit stack itself. This allows you to only remove the seat to access the screws (the rear ones are a challenge but doable with a very small ratchet) and you can fully put the bottom section on without removing anything else. The stack portion slides through the opening and is a press fit into the bottom section, clicking and popping into place. I plan to put a small amount of RTV or silicone seal in there to help keep it in place and seal it, but it doesn't really need it. It's solidly mounted with the press fit.

 

I used the recommended profile (ellipse based) but decided to make it a little shorter than optimal so it didn't go too close to the "roof" area of the intake volume. Still, it should definitely improve the smoothness of the flow, but I don't aniticipate anything else. This was more of a project to get the 3D printer ready to go . . . and for fun.

 

The pictures below show the stack PRIOR to being smoothed by being in an acetone environment, so it looks a little rough. The acetone gently melts and smooths the outer layer of the plastic and makes it shiny and smooth. It's actually being bathed as I write this.

 

Again, you can look up my analysis in two other posts and see what I found and a reference to this design change, so I won't go into it here. [ https://fz07.org/thread/7952/airbox-modification-simulation-testing-conclusion and https://fz07.org/thread/7684/intake-simulation-adding-velocity-stack  and https://fz07.org/thread/7851/prototype-intake-filter-external-airbox ] In short, no, I don't think it will have a change that is felt as I ride, but, yes, you might see some change on a dyno - you might see a slight shift of the peaks or maybe a very small uptick to the numbers in some section. But then again, you could see a decrease somewhere too, who knows? One day, I'll get it on the dyno with the two mods I've made thus far. Just for fun - I don't think anything other than slight could be hoped for.

 

And here it is . . .

 

VelocityStack (1).JPG

VelocityStack (2).JPG

VelocityStack (3).JPG

VelocityStack (4).JPG

VelocityStack (5).JPG

VelocityStack (6).JPG

VelocityStack (7).JPG

  • Like 1

Share this post


Link to post
Share on other sites
gregjet

Fantastic job, but flow through a non round hole is always problematic. Remember the max flow out of the box is the Xc area of ONE throttle body ( only one breaths at a time though they are close) so the hole only needs to be a bit larger than the ID throttle body to not restrict flow.

I reckon a round hole with the ID same as the width of the inside of the filter might be that best flow you can get under there, so there is at least a small area of smooth transition. But you design might be better . It needs a max flow test done. I'd be happy to use one your design shape as it is an improvement and looks good.

If acetone dissolves it, how is it with the fuel aromatics or is it just for a mould?

Still, great work and it will flow way better than the stock thing. Looks good . There are some real experimenters on this forum. The bike seems to attract the out of the boxes.

 

I agree an outside stack would be the go, but there ain't much space in there. Thought about a fair bit myself. Actual flow with a "Blair" stack  could be more than 15% at high volumes , if statics gives that figure. The total flow under the "tank" is pretty complex.

Edited by gregjet

Go forth and modify my son...go forth and modify...

Share this post


Link to post
Share on other sites
sansnombre

You're right on the "round vs. other" cross-section. The reference study I looked at says round is optimal, but square, if that's what you're flowing into, is not so bad. If you make it smaller then the opening (a smaller round exiting into the larger rect) then you also have to consider undesireable vortexes at the edges, but maybe an exit feature (smoothing the outflow) would help there. You prob can't tell, but I radiused the corners larger than the filter corners, but I supposed I can increase that. It would not be difficult to modify it so its opening was circular and exited through a shape that was closer to the opening. Hmmmm - might have to do a CFD and see what that does . . . 

 

I think I disagree on your concept of slightly larger than one cross-section - yes the two ducts flow out of sync, but you still are flowing into the airbox for the entire engine displacement at the same time. That is, flow for both chambers are constantly flowing into and throughout the airbox. They move together, but just exit alternatingly in small bites via one side or the other.

 

Good point about the aromatics - I hadn't thought of that. It's ABS, so I'll look it up to see if it's more robust beyond acetone. I chose this plastic because of the smoothing capabilities, but didn't think beyond that. If it's not ok, I have PET in house as well. Thanks for the heads up.

 

Not sure what a Blair stack is, haven't heard the term . . .

Share this post


Link to post
Share on other sites
gregjet

There is a superb paper by Dr Gordon Blair ( of motorcycle deity fame) on intake shape design. A touch tech for some, though  you won't have any trouble. Always worth keeping in the back of you mind when playing with intakes.

I figured that a smoothing exit would be necessary and have an idea in my head of the approx shape, but no drawing yet. The thing about 3d printing is you can do stuff like that. My initial experiment was done by hand in soft flexi foam. It was pretty rough but did flow a bit better ( dyno wise inference). There is no exit smoothing. Pic attached of the proto. It used to be on the forum but went the way of all things photobucket. Front foam is to try and keep engine heated air away as much as possible.

 

 

I had another thought that I also haven't dug into yet. If there is enough room in the airbox, to drop the whole filter lower down into the box to allow a better length stack. The stock filter is pretty small in terms of filter area. I suspect that's part of the reason the Hordbox is as successful as it is. Simply lower through filter velocities. Trouble is it will reduce the internal air volume and change the resonant frequency as well.

DSCN0974.JPG

Edited by gregjet
addition

Go forth and modify my son...go forth and modify...

Share this post


Link to post
Share on other sites
sansnombre

Silly me - the paper I was referencing WAS from Dr. Blair, so I guess I do know who he is.

 

In this case, I kinda think the change from rect to circular is an academic one, in that we both know it's a better design, but would it actually have any affect on the engine HP and perf. I think not, but certainly not enough to get back in there and modify and 3D print the design again. I guess I should have given the whole thing a little better thought initially and actually started with a circ design, either at the opening to ambient and/or as it terminates at the air filter. Or both.

 

But that would have begged the question of creating an exit feature to help the flow exit in the middle of the filter without swirling up and around inside the filter. Not a difficult thing to do - should have done it the first time.

 

The next design is blasted horn button. I have an idea of how to make a device that will attach around the handlebar and have a large lever that seats jus over the turn signal button. Much easier to activate.

 

Nice job on the cover above. I've never heard of the material you're using - how is it marketed? Hardware store stuff?

 

Cheers.

Share this post


Link to post
Share on other sites
gregjet

" I've never heard of the material you're using - how is it marketed? Hardware store stuff"

It is the same stuff they make the clip together soft foam floor mats out of. I use it to prototype all sorts of stuff. Not easy to work but not insanely difficult either. It is petrol and resin resistant, so has some advantages on motorcycles especially for making patterns. It would be great to use in a multi axis form cad device with simple rotary sandpaper type grinder as it doesn't clog easily and doesn't wear the tool much. Doesn't hand sand though.

Pretty much never use a horn button so it's is an area I don't usually consider, though I usually do end up moving the horn itself out of the way.


Go forth and modify my son...go forth and modify...

Share this post


Link to post
Share on other sites
nick13
On 9/24/2017 at 5:24 PM, sansnombre said:

The next design is blasted horn button. I have an idea of how to make a device that will attach around the handlebar and have a large lever that seats jus over the turn signal button. Much easier to activate.

 

Please do share... Let us know what's the idea there. Horn button location renders horn itself useless. I'm looking for relocation/substitution to that button too. Thanks.

 

Bedienteil_MT07_MG_6372_small.jpg

 

Bedienteil_MT07_MG_6363_small.jpg

Edited by nick13
  • Like 1

Share this post


Link to post
Share on other sites
sansnombre

I've never seen those before. Where are you getting those pictures? Interesting concept . . .

 

The connection of my concept and this one is the same, but it differs entirely on functionality. I'm going to wrap around the bar to secure it, just like they are. Then I have a lever that will actually depress the original horn button and extend between the directional switch and the high-beam switch. They'll be a big (but not intrusive to the functionality of the other buttons) thumb button that will actuate the horn button and be easier to access. Basically just atop the left/right symbols shown above.

 

Still working on it, but it's low priority at the moment - I'm also designing a spine retractor for a surgeon, and that's where my focus is at the moment. But this will happen - I hate the horn button, and have to find a solution. So in time, we'll have something.

 

Thanks for asking.

Edited by sansnombre
  • Like 1

Share this post


Link to post
Share on other sites
digitalsteve

It'd be great to see dyno runs for before and after.

Share this post


Link to post
Share on other sites
Grip it & Rip it
9 hours ago, sansnombre said:

I've never seen those before. Where are you getting those pictures? Interesting concept . . .

 

From this very forum:

 

 

  • Like 1

Share this post


Link to post
Share on other sites
r1limited

I am no scientist, I just understand what I understand.  A velocity stack is supposed to increase or decrease directed flow to the throttle bodies.  I may be wrong here, by this in itself increases or reduces the turbulence which causes atomization of air and gas.  In all of my references I have never seen a stack behind the air filter which is in front of the carbs.  IMO you are only increasing a volume into a airbox which will not effect turbulence in the the stock stacks.  I certainly believe in allowing an engine to breath, this is a great looking product and has a purpose, but I a personally doubtful it will benefit much.  IMO that stack should be attached to the bodies to the airbox.

But who am I? just a minion with an opinion.

Edited by r1limited

“Laws that forbid the carrying of arms disarm only those who are neither inclined nor determined to commit crimes.” --Thomas Jefferson quoting Cesare Beccaria

Share this post


Link to post
Share on other sites
sansnombre
11 hours ago, r1limited said:

I am no scientist, I just understand what I understand.  A velocity stack is supposed to increase or decrease directed flow to the throttle bodies.  I may be wrong here, by this in itself increases or reduces the turbulence which causes atomization of air and gas.  In all of my references I have never seen a stack behind the air filter which is in front of the carbs.  IMO you are only increasing a volume into a airbox which will not effect turbulence in the the stock stacks.  I certainly believe in allowing an engine to breath, this is a great looking product and has a purpose, but I a personally doubtful it will benefit much.  IMO that stack should be attached to the bodies to the airbox.

But who am I? just a minion with an opinion.

Generally a smoothed intake or exhaust decreases pressure losses by helping to optimize flow. I had to do a design once on a nuclear reactor structure that was being vented by three enormous fans. I had to select the fans such that we had adequate flow. Looking at the fan companies literature, they offered exhaust stacks (velocity stacks as the structure was vented to atmosphere), and this increased flow by a substantial margin. But I couldn't get my head around the concept. How could these devices at the end of the flow stream, external to the fans have any effect? And the answer was that it reduced the pressure loss as the flow exited the fans. So there was a lower pressure there that allowed a higher pressure differential internal to the fan resulting in an increased flow. Just showing that flow is complex and shaping it is a very important aspect of tuning.

 

You should re-read my post - I comment about the unlikely value of the stacks many times in increasing HP or torque. I also comment on how this activity was only to dial in a 3D printer, and not to increase performance of the engine. Your last comment about having stacks inside the airbox leading to the engine is also aligned with my thoughts and my previous analysis. Having larger, internal stacks also showed an increase in throughput. I have not gone into that design solely because it would be a huge PITA requiring removing the airbox from the bike and having to wrestle with the current fittings. Not worth it in time, but it would almost certainly show an increase of some nominal (perhaps negligible) value.

 

BUT, the CFD (computer-based simulation software) of this airbox with and without this external vel stack showed a ~15% gain in static throughput with the stack attached. So there is a possibility of a gain, but almost certainly negligible under this as a dynamic application.

 

As far as the idealized concept of whether it could increase throughput, I disagree with you. In concept, not having an aligned flow and allowing flow to come in directly lateral to the opening allows for sideways flow into the stream that effectively narrows the width of the stream (this is something called vena contracta). The purpose of the stack is to align the flow such that all lateral flow through the opening is removed and only aligned flow exists. Look at the attached picture; see how some effective width is lost because of lateral flow? Without a VS and having this lateral flow will narrow the effective opening into the filter. Enough to limit flow and have a negative effect on power? I don't think so with this MWR setup - it's basically wide open and is not causing a flow issue.

 

IF the flow is reduced significantly enough by the vena contracta to limit the required maximum throughput, then this velocity stack (VS) will help. But I don't think that's the case - I don't think with the MWR filter and the much larger opening AND the lateral flow somewhat limiting the throughput of a non-VS setup is limiting flow into the airbox. That is, the engine can draw as much as it can possibly draw with this setup, and giving it the ability to draw more by using the VS has no value. If we were using the OEM setup, then we DO have a limiting effective orifice (snorkel and smaller opening orifice) and increasing the potential throughput will help. In short, it's already opened up as much as is necessary, so opening it up more (increasing potential flow) will add nothing. Agreed.

 

That said, an engine is a dynamic animal, not limited to static conditions and flow. Lots of interesting phenomena in there with bouncing waves and compressed volumes, so it COULD do something, it's just unlikely. Here's something I found out when doing the original analysis - several tuners commented that they saw no additional increases in HP/torque by using the MWR cover in addition to the filter. So the radiused, and wide open addition didn't have any benefit . . . except with one particular exhaust. With that exhaust, there was an increase from this cover alone. Very small, but something. The point being that the dynamics of an engine is just that complex, and the interplay of these components is important, and having a VS on with that particular pipe might just do something as well. Don't think so, but who knows.

 

In the end, it was a project to dial in a 3d printer, not increase performance. That said, it would be interesting to put it on the dyno to see if it changes something . . . with that one particular pipe of course. ;-)

 

Cheers

maxresdefault.jpg

Share this post


Link to post
Share on other sites
r1limited

I built nuclear reactors for GE, 6 of them have my initials welded to them, all in all the Estimating the Airspeed Velocity of an Unladen Swallow depends on the counter weight of the injected harmonic balance dunt ya tink

 


“Laws that forbid the carrying of arms disarm only those who are neither inclined nor determined to commit crimes.” --Thomas Jefferson quoting Cesare Beccaria

Share this post


Link to post
Share on other sites
sansnombre

"Message for you, sir . . ."

 

- African or European?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.



×

Important Information

By using this site, you agree to our Terms of Use.