Velocity stacks for bike carbs

[turabaka]

I was asking Cygnus about building or retrofitting a set of custom velocity stacks for my new Mikuni's, and we figured we'd just start posting up ideas outside of PM in an effort to get anyone interested involved.

For those that don't know, I've been running 34mm quad CV carbs on my car for a little over a year now.

http://i.imgur.com/N6lvo.jpg?1
http://i.imgur.com/vpwhN.jpg?1


While the current setup performs great, and gives excellent throttle response, they're just too small for the current motor work. I can feel them choking out at the top end.

so, I've decided to bump up to 40mm Mikunis from a Yamaha R1. I figure these should be more than enough carb for all of my current motor work and some extra.

However the problem is that the carb don't come with Velocity stacks like my old set, and the velocity stacks from the R1 are just really short and plastic.
Here's what the Mikunis look like.

http://i.imgur.com/Jntwj.jpg?1

What I'm hoping to do is find something that I can easily be removed. Similar to how the stock velocity stacks are installed. That way I can run pod filters on the street like I do currently, and just swap out to stacks whenever I go racing.

ideas? suggestions? questions or comments?

[cygnus x-1]

http://i.imgur.com/Jntwj.jpg?1

What I'm hoping to do is find something that I can easily be removed. Similar to how the stock velocity stacks are installed. That way I can run pod filters on the street like I do currently, and just swap out to stacks whenever I go racing.

ideas? suggestions? questions or comments?


So looks like the inlets are basically just open tube ends, no threaded holes for attaching flanges and such. Probably the easiest method would be to use rubber couplings with clamps like you did to attach the carbs to the manifold. The trick will be to find some stacks with exactly the right dimensions. What are the inner and outer diameters of the carb inlets? (the more precise you can measure these the better) Do the insides of the carb bores taper down at all or are they pretty much straight?

Do you want to leave the stacks on all the time and put the filter pods over the stacks or do you want to take the stacks off as well and just put on the filters? Unless the pods have some sort of radius on the inlet it would be better to put the filters over the stacks. How much room do you have between the carb inlets and the firewall or other obstructions? The A20 is a fairly low revving engine so making the intake system as long as possible will help out the low and midrange torque.

One possibility if you can't add much more length to the stacks is to make a sort of "donut", with a counterbore in the back that slips over the carb inlets. They could be permanently attached to the carbs with RTV or they could be slotted and clamped on with tube clamps. If the "donuts" had flat sides, some filter pods could be clamped on over the outside. Sort of like these but taller and with no holes:

http://www.extrudabody.com/catalog/AirHorn1md.JPG


I'll whip up a quicky model for illustration if this looks like a possible route to take.


C|

[itzdave]

there are quite a few companies that custom make them for dirtbikes and stuff. i remember seeing them when i was trying to get foam clamp-on filters for my dcoes(with stacks). cant remember the names but i can try to find out what filters i had and check some sites...

[turabaka]

I did find a company that makes aftermarket velocity stacks for the r1 carbs. They're roughly $300 though, and I'm just not willing to spend that on stacks. Especially when the carbs only cost me a whopping $67

Here's the aftermarket option currently made. They're made by factory pro
http://i.imgur.com/eNOK8.jpg

and here's what the stock stacks look like.
http://i.imgur.com/urJRe.jpg

There's a small notch on the end of the carb that you can't really see in the picture, and the stacks kind of clamp around that.

I measured the carbs, and the outside diameter of the tube is 45.75mm.
while the inside is roughly 41.90mm
Also the inside of the carb bore is perfectly straight to my eye. It doesn't appear to taper at all.

If it really comes to it, I guess I can run the stock stacks. I just don't think it would be that hard to cheaply make something similar to the factory pro style ones though.

[cygnus x-1]

I did find a company that makes aftermarket velocity stacks for the r1 carbs. They're roughly $300 though, and I'm just not willing to spend that on stacks. Especially when the carbs only cost me a whopping $67


If you look around you can get the FactoryPro stacks for less, but still $200+. Take a look at this:

http://www.ebay.com/itm/SINGLE-VELOCITY-STACK-CARB-FOR-WEBER-45-DCOE-CARBURETOR-PART-52840-001-/130592504040?pt=Motors_Car_Truck_Parts_Accessories&hash=item1e67eb78e8&vxp=mtr


These are $10 each. The OD is very close to the OD on your carb inlets so you could use some short rubber couplings and clamps for attachment. The ID is bigger than your carb inlets so you would need to bevel the inlets with a dremel or even a round file, but that's no big deal.

This is about the cheapest option you're going to find.


C|

[turabaka]

I like it.gonna go with those then, and post up pictures when they're all installed.

[cygnus x-1]

I like it.gonna go with those then, and post up pictures when they're all installed.


Excellent! :thumbup:

One thing I forgot to point out is that they're nearly 4 inches long, so you might have to chop the bottoms off a bit if they don't fit. You're going to want at least 1.5 inches or so of space between the stack inlets and the firewall for proper air flow.

So what do you have in mind for the filters? Will your old pod filters fit the new carbs?

C|

[turabaka]

Do you think it would be better to run pod filters like I am currently, or to run the filter screens they make for those weber stacks?

I was thinking maybe running these.

http://www.ebay.com/itm/WEBER-45-DCOE-MG-MGB-Austin-Aston-Toyota-BMW-Stack-Filters-/350549822463?hash=item519e65cbff&item=350549822463&pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr

[cygnus x-1]

Do you think it would be better to run pod filters like I am currently, or to run the filter screens they make for those weber stacks?

I was thinking maybe running these.

http://www.ebay.com/itm/WEBER-45-DCOE-MG-MGB-Austin-Aston-Toyota-BMW-Stack-Filters-/350549822463?hash=item519e65cbff&item=350549822463&pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr


The screens will restrict air flow less but the pods will filter out more particles. If the car is a race/show vehicle then the screens are probably fine. If you intend to drive it more often I would go with the pods.

C|

[Vanilla Sky]

I fail to see anything bad about the factory ones, other than them being plastic. Where do they fall in the affordability category? It seems like you might be able to buy stock ones for even less than those Weber stacks above.

I do like those screen filters, but I don't think I'd run them on the street. I do like having a screen on my intake, even on the track, though. Our Challenge car made 3 autocross runs and had all sorts of stuff make it into the air box. Our engine probably ate some of it, too.

[turabaka]

I fail to see anything bad about the factory ones, other than them being plastic. Where do they fall in the affordability category? It seems like you might be able to buy stock ones for even less than those Weber stacks above.

I do like those screen filters, but I don't think I'd run them on the street. I do like having a screen on my intake, even on the track, though. Our Challenge car made 3 autocross runs and had all sorts of stuff make it into the air box. Our engine probably ate some of it, too.

The stock ones are roughly the same price as the weber ones. I don't really see a problem with them either, I just kinda like the look of polished metal stacks on side draft carbs.

[cygnus x-1]

I fail to see anything bad about the factory ones, other than them being plastic. Where do they fall in the affordability category? It seems like you might be able to buy stock ones for even less than those Weber stacks above.

The factory stacks are not straight. It's hard to see in that picture but the opening is angled. You can find better pictures if you look around on ebay.




I do like those screen filters, but I don't think I'd run them on the street. I do like having a screen on my intake, even on the track, though. Our Challenge car made 3 autocross runs and had all sorts of stuff make it into the air box. Our engine probably ate some of it, too.

This is why I'm making an air box for my ITBs. I like the idea of not restricting air flow but getting crap in the engine is worse. The screens are a good idea for race use.


C|

[turabaka]

Just a little update. Finally got around to installing the DCOE weber stacks onto my Mikunis. They required a little bit of dremel work to get rid of the slight lip the carbs have, and to give a nice smooth transition from the stack to the carb, but I think they turned out pretty well

As you can see in the second picture there's a bit of a hole in the stack. I'm going to probably end up plugging it with some quicksteel and dremeling it nice and smooth. Aside from that though the stacks fit on nice and tight, and I'm not worried at all about them popping off.

http://i.imgur.com/WiLkh.jpg?1

http://i.imgur.com/2ISb7.jpg?1

[A20A1]

Looks great. The metal is very thin in that area, not much to grab onto. hope the quick steel doesn't come off and get ingested. I would just get some small rubber couplings to cover the gap, and a clamp to help squeeze it into the recessed grove, hopefully it wont leak.

[turabaka]

Looks great. I hope the quick steel doesn't come off and get ingested. I would just get some small rubber couplings to cover the gap, and a clamp to help squeeze it into the recessed grove.

sounds like a good plan actually. I might see what I can find.

[Vanilla Sky]

What about a wide rubber clamp that fits over the end? That would cover that hole and be more secure. The heat shrink hose clamps that Gates makes for big trucks work really well. They look pretty clean, too.

http://images.oreillyauto.com/parts/img/medium/gat/powergripsbclamp.jpg (http://www.oreillyauto.com/site/c/detail/GATU/32948/N0189.oap?ck=Search_N0189_-1_-1&pt=N0189&ppt=C0075)

Great minds do seem to think alike, eh?

[turabaka]

What about a wide rubber clamp that fits over the end? That would cover that hole and be more secure. The heat shrink hose clamps that Gates makes for big trucks work really well. They look pretty clean, too.

http://images.oreillyauto.com/parts/img/medium/gat/powergripsbclamp.jpg (http://www.oreillyauto.com/site/c/detail/GATU/32948/N0189.oap?ck=Search_N0189_-1_-1&pt=N0189&ppt=C0075)

Great minds do seem to think alike, eh?

That's actually what I was just looking into. McMaster-Carr has some stuff that's looking promising.

[Vanilla Sky]

Sure beats the hell out of old school hose with worm clamps.

[turabaka]

Sure beats the hell out of old school hose with worm clamps.

for sure. How big of a difference do you think it would make to get the heat shrink hose clamps versus just getting heat shrink tubing? Same difference in this instance?

[Vanilla Sky]

The hose clamps will grip harder and likely look cleaner. On the other hand, the Gates clamps are $5 each. Every time you pull the stacks, it would cost you $20 to use them. I'm sure there's an eBay knockoff by now, though.

[A20A1]

Wow never seen those before, looks perfect. Better then what I had in mind.

Just in case you chose the rubber and it didn't seal 100% I was going to suggest a small metal peg be squished between the clamp and coupling right above the hole to force the rubber into the groove better.
http://i23.photobucket.com/albums/b351/Wendy_girl/horn.png

[Hauntd ca3]

uni filter make oiled foam sock filters for dcoe/dhla style carbs.
thats what i have for my itb set up

[turabaka]

Wow never seen those before, looks perfect. Better then what I had in mind.

Just in case you chose the rubber and it didn't seal 100% I was going to suggest a small metal peg be squished between the clamp and coupling right above the hole to force the rubber into the groove better.
http://i23.photobucket.com/albums/b351/Wendy_girl/horn.png

eh. I see what you're getting at, but it seems a little overcomplicated. Even if it leaks slightly it shouldn't make a noticeable difference since it's pre-throttle plates.

[turabaka]

uni filter make oiled foam sock filters for dcoe/dhla style carbs.
thats what i have for my itb set up

These are the filters I ended up going with. they're just screens with a rubber boot made for the dcoe stacks.

http://i.imgur.com/KMnG6.jpg

[A20A1]

eh. I see what you're getting at, but it seems a little overcomplicated. Even if it leaks slightly it shouldn't make a noticeable difference since it's pre-throttle plates.

True true.

[cygnus x-1]

Those stacks are a good fit for those carbs. I can tell you from my own experience with ITBs though that if there is ANY possibility of something coming apart (due to vibration, thermal cycling, etc.) it WILL. Looking at how the horns are pressed over the flange on the carb, I think there is still some possibility for them to work loose from the flange because of the taper that's created as the end of the horns flares out to fit over the flange. Just adding a clamp of some sort may help or it may not. One way to address this if they do end up working loose would be to cut some very short slots in the end of the stack (shorter than the ones that are already there) to make some small "tabs" that you can bend in so that they lock onto the lip on the carb flange. Then when you add a clamp it will compress the tabs to keep them from bending back out, and cover all the slots so you can't see them.

So how much room will you have from the stacks to the firewall? Looks like not much unless you have a really short manifold.

C|

[A20A1]

Those stacks are a good fit for those carbs. I can tell you from my own experience with ITBs though that if there is ANY possibility of something coming apart (due to vibration, thermal cycling, etc.) it WILL. Looking at how the horns are pressed over the flange on the carb, I think there is still some possibility for them to work loose from the flange because of the taper that's created as the end of the horns flares out to fit over the flange. Just adding a clamp of some sort may help or it may not. One way to address this if they do end up working loose would be to cut some very short slots in the end of the stack (shorter than the ones that are already there) to make some small "tabs" that you can bend in so that they lock onto the lip on the carb flange. Then when you add a clamp it will compress the tabs to keep them from bending back out, and cover all the slots so you can't see them.

So how much room will you have from the stacks to the firewall? Looks like not much unless you have a really short manifold.

C|



I know the gap allows it to slip over the mouth of the carb w/tension, but it also allows air in which could help cool the joint keeping thermal expansion in check. yes/no?

http://i.imgur.com/eNOK8.jpg
This one has even more slots, it could just be for aesthetics, or to even out the tension, or to lessen the contact to the carb to keep the heat from transferring from the carb to the stacks. Or maybe a single hole caused the stacks to whistle at a certain RPM so they added more holes to get rid of the whistle.


Just curious about why the slit is so long that it allows air in and if it's really a good idea to seal it, other than to keep dust/dirt out.

[turabaka]

Those stacks are a good fit for those carbs. I can tell you from my own experience with ITBs though that if there is ANY possibility of something coming apart (due to vibration, thermal cycling, etc.) it WILL. Looking at how the horns are pressed over the flange on the carb, I think there is still some possibility for them to work loose from the flange because of the taper that's created as the end of the horns flares out to fit over the flange. Just adding a clamp of some sort may help or it may not. One way to address this if they do end up working loose would be to cut some very short slots in the end of the stack (shorter than the ones that are already there) to make some small "tabs" that you can bend in so that they lock onto the lip on the carb flange. Then when you add a clamp it will compress the tabs to keep them from bending back out, and cover all the slots so you can't see them.

So how much room will you have from the stacks to the firewall? Looks like not much unless you have a really short manifold.

C|

I'm not too worried about them popping off. I had to tap them on with a piece of wood and a mallet, so I'm guessing that with the shrink clamps they should be fine.

As far as clearance I'm going to cut into the wiper cowling and build a duct box for the carbs, so I should have plenty of clearance.

[turabaka]

Does anyone know if/where I can find articles or discussions on manifold runner length. Current carbs feel good with 6 inch runners, but I'd like to actually do the math this time around and figure out the best length to go with for nice and snappy throttle response without too much of a torque sacrifice.

[Vanilla Sky]

One of the Weber performance books I had discussed runner length and size fairly in-depth. I can't remember the title, and I had several of them that I read at one point. This one talked heavily about theory.

I'd seriously head over to the Grassroots Motorsports Forum (http://www.grassrootsmotorsports.com/forum) and post a "Learn Me" thread and make sure to specify that you're not a canoe. The collective knowledge there is absolutely staggering.

[turabaka]

What in the hell is a "canoe"? Lol.

Sounds like a plan though. When I get some time to sit down and think I'll head over there.

[Vanilla Sky]

It used to be the code word for spam before they had a report button. The GRM staff would search the site daily for that word, because it was something that no one would actually use.

[cygnus x-1]

I know the gap allows it to slip over the mouth of the carb w/tension, but it also allows air in which could help cool the joint keeping thermal expansion in check. yes/no?


The thermal expansion comment was mostly just a general statement, and probably wouldn't be an issue here. Where I had a problem was with trying to use a nylon insulating gasket between the manifold and head. It was mushy enough that the bolts would work loose as the engine heated up, causing uneven forces on the manifold, making it warp and hose up the alignment on the ITBs. It was a real mess.

In Turabaka's case I would be more worried about vibration.





http://i.imgur.com/eNOK8.jpg
This one has even more slots, it could just be for aesthetics, or to even out the tension, or to lessen the contact to the carb to keep the heat from transferring from the carb to the stacks. Or maybe a single hole caused the stacks to whistle at a certain RPM so they added more holes to get rid of the whistle.

Just curious about why the slit is so long that it allows air in and if it's really a good idea to seal it, other than to keep dust/dirt out.

Those do look odd. Not sure why they would be designed that way. On a bike these would be enclosed by an airbox no?




I'm not too worried about them popping off. I had to tap them on with a piece of wood and a mallet, so I'm guessing that with the shrink clamps they should be fine.

Yeah, might as well try it out first before making any further modifications.




As far as clearance I'm going to cut into the wiper cowling and build a duct box for the carbs, so I should have plenty of clearance.

Cool! I had the same idea! You'll get to it before I do though so I'm interested to see what you come up with.




Does anyone know if/where I can find articles or discussions on manifold runner length. Current carbs feel good wiwith inch runners, but I'd like to actually do the math this time around and figure out the best length to go with for nice and snappy throttle response without too much of a torque sacrifice.

Jenvey has some pretty good info:

http://www.jenvey.co.uk/jenvey/throttle-body-selection-with-jenvey-dynamics




It used to be the code word for spam before they had a report button. The GRM staff would search the site daily for that word, because it was something that no one would actually use.

Canoe. I like it. I''m going to start using that.


C|

[BITESIZE]

Holy shit Trevor, that's sick ass hell!!!!!!

[2ndGenGuy]

^^ You!

[mperaza]

It's been over a year about this project and looked promising. I would like to see the finished product

Pics please!

[turabaka]

It's been over a year about this project and looked promising. I would like to see the finished product

Pics please!

Project is coming along slowly. The motor just got rebuilt, and I'm in the process of putting it back together. Carbs are on, but not tuned properly yet. I'm currently switching over to megajolt, so the cars not running at the moment.

I've been spending a bunch of time lately working on my new daily driver, to make it reliable. Bought a porsche 944 in february, so the accord is sort of on the back burner.

I'll be working on the accord more soon, and will definitely post updates When I get it running again.

[2oodoor]

Ahh! Bumped ll
Great to see ya check in, 944 pics and project threads welcome too :)

[turabaka]

Ahh! Bumped ll
Great to see ya check in, 944 pics and project threads welcome too :)

I'll post some pictures of it sometime. It's pretty much just the usual 30 year old car maintanence. Wheel bearings. Struts/shocks, sway bar bushings, and ball joints.

[2ndGenGuy]

Wow yes, 944 thread NAO. Also more bike carbs!

[honda guy]

This is awsome! Let me know how they work and what was needed to make them work. I saw the pics of your old setup and it looked prity easy. Im wondering about throdle cables and everything else. Ive decided to keep my stock motor and build it up a bit and deffinetly like this setup.

[Jedup]

They only work good when your engine is wide open. Like when your 100mph on the highway You'll get horrible performance and if your knee is in front of it your pants will get sucked up and your engine will die. Run a regular air filter. I've learned this from experience