Topic: Dumb Question

[mlinder]

I want to buy velocity stacks.
What size do I need to specify for my k0 carbs?

[KB02]

Just measure the O.D. (Outside Diameter) of the air inlet side of the carbs and search for stacks to fit that size. (The Stack's I.D. (Inside Diameter) should be the same or there abouts)

And, the only dumb question is the one that isn't asked... 

[mlinder]

But... I thought most people have them slip INSIDE the carb intake throat... so as not to have a lip disturbing air flow where the stack meets the carb.....

[KB02]

Wouldn' that effect the air lines in the carbs? I'll admmit to having no knowledge of the K0 carbs, but my F1 and K8 have small air line right at the back of the carbs seem like they would be blocked off if something was inserted inside the opening.

Then again, I could be wrong.

[KB02]

There is this set on Ebay.

He doesn't mention any year, but it's worth asking, I guess.

[mlinder]

Sweet, thanks for the link!
I just ordered them.
I will be using them to try out my intake idea, http://www.sohc4.us/forums/index.php?topic=26342.msg271600#msg271600

[Geeto67]

The point of a velocity stack is to increase the air velocity entering the carb. I don't think smooth air matters as much (with carbs the more turbulent air you have going in the better fuel mixing you get) as how fast it is going in there and how the acoustic resonance is affecting it. This is a big difference from pods where there is usually a flat panel for the filter, and not a funnel like channel, which arrests the flow and does not help to increase intake velocity. Just so you know that this is not bunk, honda, ducati, and most other motorcycle mfgs have used this on their race bikes for 30 years, but I have never seen a factory race bike with pods.

the wrong bellmouth/ stack can actually slow intake velocity and rob you of precious hp. it is all about tuning intake length for chamber capacity. This is because a v-stack is basically a helmholtz resonator.

A Helmholtz resonator is an acoustic resonance chamber (as described by our plenum above) that modifies the acoustic frequency of a sound wave like a spring oscillating with a mass attached on the end.

you can calucuate it using the following equation:


where f = the rpm at which you get peak torque ( the natural frequency of pressure oscillations in the acoustic chamber ) , c = the speed of sound (= 340 m/sec.) , S = runner area, L = runner length, V = displacement per cylinder

A simplified version of this is using the Englemann formula for the above which also takes into account static CR of the engine:

RPM for peak torque =

642 x c x [ SQRT (S/[L x V] ) ] x [ SQRT { (CR-1)/ (CR+1) } ]


= 218,280 x [ SQRT (S/[L x V] ) ] x [ SQRT { (CR-1)/ (CR+1) } ]


I got these equations from this auto site on building v-stacked intake runners for honda car engines:

http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=471




 

[Bob Wessner]

It never ceases to amaze me what I can learn here. Now, how long will I remember it...?

[Geeto67]

It never ceases to amaze me what I can learn here. Now, how long will I remember it...?

here's another link for your noggin', becareful though lots of popups:

http://enaf1.tripod.com/teche.html#helm

[mlinder]

When you say 'runner area", do you mean the volumetric area of the stack, or the inner surface area of the stack?
In any case, wanna do the math for me?
I hate math.

[turboguzzi]

All the following is only MY opinion.

so just  a few points:

1. regardless of which V-stack theory you addere to (and there's more than one as you'll see), unless the V-stack creates a smooth passage into the nominal carb diameter, then I believe that you are waisting your time/money. look at how proper v-stacks like in original 29mm smoothbores are done and you'll see what I mean. stacks that simply attach to the external diameter instead of the air filter grommets are not going to do much. again, that's IMHO. The air bleeding holes are indeed a problem and proper V-stacks like those of an RS have a double sleeve and air passages between the trumpet and the internal bore before the step to feed them.

2. smooth air does matter as turbulence essentially reduces the effective carb bore flowing air at full speed. Properly designed V-stacks should reduce turbulence at the carb entrance.

3. last, resonance theory is just one way to approach V-stack calculation. another theory/school is that of maximizing use of the inertia of the moving air column. with the right valve overlap, right total inlet tract Length and diameter, the inertia of the fast moving air should keep on cramming mixture into the combustion chamber way after BDC. Not that I invented this theory, many tuners maintain that V-stack Length should go hand in hand with the chosen valve overlap.

4. But then, they sure look cool!

my two cents
TG

[mlinder]

I'm not overly concerned with their looks. They are going to be mostly covered, in any case.
This is just for a proof of concept setup.
As you confirmed for me, turboguzzi, if the stack doesn't mesh up nicely to the intake of the carb throat, it's pretty useless.
I have no trouble using some form of moldable, sandable substance on the inside of the stack to make a smooth transition from stack to carb throat, though.
Should be simple.

Take a look at the cross section of the (otherwise bad) design of a stack here, http://www.sohc4.us/forums/index.php?topic=26342.msg270048#msg270048
It's obvious to me that the transition should be smooth from ID of stack to ID of carb intake.

I will be working on making sure this is the case.

[Sam Green Racing]

Mark, I have a set that go over the outside of the carb throat but are the same size as the inside.
We had them custom made when we ran the stock carbs prior to the CRs.
I'm not sure if they are alloy or titanium, they don't weigh anything at all.
PM me if you're intrested.

Sam.

[mlinder]

Mark, I have a set that go over the outside of the carb throat but are the same size as the inside.
We had them custom made when we ran the stock carbs prior to the CRs.
I'm not sure if they are alloy or titanium, they don't weigh anything at all.
PM me if you're intrested.

Sam.

I'd be interested in taking a look at them, but likely could not afford them till next month.

[Sam Green Racing]

What sort of money was you thinking if you bought them elsewhere.
I think we only paid about £24 ($48) .
It's down to Chris how much he lets them go for, I'd take a guess at $30 plus postage, shouldn't be a lot as Like I said, they don't weigh much at all.

Sam.

[mlinder]

Ah, then I'm interested, but not till the 2nd of next month (payday!)

[turboguzzi]

seen your design, nice effort

my thoughts?

carb sticking into airbox is good, that's how they do it in superbikes

long stack, good for low down power, if that's what you want

shape looks wrong (like many other stacks...) should flare up more

look at the shape of the V-stack I designed according to formulas from the inventor of the Lectron carb.  you'll see ther also the double sleeve that fits over the carb mouth yet gives a smooth internal flow to the internal carb bore, like in smoothbore stacks

TG

[Sam Green Racing]

That is much the same as the ones we used turbo apart from, ours do not have the part that goes into the carb throat.

Sam.

[mlinder]

seen your design, nice effort

my thoughts?

carb sticking into airbox is good, that's how they do it in superbikes

long stack, good for low down power, if that's what you want

shape looks wrong (like many other stacks...) should flare up more

look at the shape of the V-stack I designed according to formulas from the inventor of the Lectron carb.  you'll see ther also the double sleeve that fits over the carb mouth yet gives a smooth internal flow to the internal carb bore, like in smoothbore stacks

TG

I like the design. Can't use the inner flange like that on the stock carbs, though.
I'm looking for high end power, actually. Hondaman game me some numbers for inlet length to help the 9k+ range... they were described as pretty long....
Will let you know how this goes.

Oh, 'nother question. Think I should do the back of the filter (the flat area facing backwards) in filter, or a solid?
Most of the cars and pods have a solid rear, or a top and bottom that are enclosed by the airbox itself.

[Sam Green Racing]

Mark / TG, The stacks on the superbikes only go into the airbox because they are pressureized by the ram air system, the ones I have are just open, as they were on the Daytona CR750s of the period. They are fully open.

Sam.

[mlinder]

Mark / TG, The stacks on the superbikes only go into the airbox because they are pressureized by the ram air system, the ones I have are just open, as they were on the Daytona CR750s of the period. They are fully open.

Sam.

Right, thats fine.
I'm going to be building a filter/housing for them though.

[Sam Green Racing]

I'll speak to Chris in the morning regards the price before he gets into work.
If all is OK, I'll get them out of the workshop and get the diementions and weights and post them here tomorrow night.
If all is OK with you, I'll post them to you Wednesday morning when I get off work.
You can send the money when you have it.

Sam.

[mlinder]

Great. The ones i just ordered, I may cut down. I'll need access to as many bits and pieces as possible for experimentation.

[mkramer1121]

I hate to open a can of worms, but I just don't see the point of running stacks on a non-race/drag bike.  If that's what you are going for, disregard the rest of this message.  Even with a screen, it just seems like you will be taking a lot more dirt into the engine on the street.  What happens in the rain?  The reason racers use them for the performance boost is because they are constantly tearing apart the engine between races.  I don't think they'd be that reliable on a street engine.

If anything, I'd say go with some foam pod style filters.  At least this way, the oil used to treat the filters traps more dust and road grime.  You still get the stack effect as well, as most pods have a velocity stack at the inlet.

[754]

Pull your Honda Factory stacks out of your airbox, try them to see if you like it.......no cost..