Topic: new style stacks

[turboguzzi]

currently running my CR29's without stacks, simply because that's how they came....

but, just by chance, came across the last issue of PB mag and it shows very interesting new yoshi stacks.

they are split into a long and short parts and together give an effect similar to the motorized variable length stacks of the R1 and MV agusta. i.e. better filling BOTH at low and high revs.

They could be simple to make, what do you say guys?


sorry for the size of the pics, they off the yoshi online catlaog

[turboguzzi]

and kawasaki is putting them stock in the zx6

[MRieck]

 Those Yosh stacks look very nice TG......being Yoshimura I'm sure they are very, very expensive too (not that I've ever been afraid to spend money on bike stuff).

[mlinder]

So, wait...

There are two stacks, one shorter and one longer, with the longer having a smaller radius (but larger unobstructed total intake area)... which allows the air to be pulled in from the outside of the long stack at lower speeds, but as engine speed increases, the vacuum becomes greater, and the pressure, velocity and venturi effect become great enough that most of the air is pulled in from the longer stack?
Am I on the right track here?

[turboguzzi]

I feel that it is the other way round......

kind of at low revs the long tract gives the gas mass inertia effect while at high revs, the carb can pull air also form the gap and not be chocked by the long stack.

tricky, but if Kawasaki is adopting the thing, then there must be something here

want to try this on my racer, seems that there ar e a lot of variables to play with... primary stack length, secondary length and gap between them

another simple factor here could be that the inner cone simply "straightens" the flow around the inner lip of the shorter stack , avoiding turbolence

[bucky katt]

the harley folks have had something like that for a couple of years now. theyre supposed to give better rideability throughout the rpm range i believe.

[turboguzzi]

would be nice to see some samples of those HD things, my short online research only brought this embarrassing, fake, "double stack" kit, LOL

its interesting that I havent been able to pinpoint the theory behind it anywhere. all the sites just copy paste the kawi press release that it increases bot mid and high rpm power

yes, sure, but how?

[tinyrobot]

Here is an article about them from Superbike UK:

http://www.superbike.co.uk/products/exhausts/superbike_news_of_tasty_new_Yoshimura_kit_parts_fromJapan_news_85453.html

[kos]

Poor mans version of electronic controlled variable inlet length  stacks, that is all the rage in all race bikes in World Superbike and Moto GP and even some current street bikes.

Nothing new, just a different day...


KOS

[sangyo soichiro]

This may be a silly question to those with a lot of experience with velocity stacks, but how do they filter the air?  I've seen some with things that look like covers (I assume the 'covers' are the filters), but I don't see anything on the ones in the above pictures that looks like a filtration device. 

So how do they filter the air?

[Sam Green Racing]

 It's a Performance issue, why do you want to slow down the air flow with filters.

Sam.

[turboguzzi]

This may be a silly question to those with a lot of experience with velocity stacks, but how do they filter the air?  I've seen some with things that look like covers (I assume the 'covers' are the filters), but I don't see anything on the ones in the above pictures that looks like a filtration device. 

So how do they filter the air?

Most vintage racers run wihtout filtering in name of power, but


the ZX6R in question has those velocity stacks AND they are positioned inside a fully filtered airbox, the air filtering is done at the box's entry

Sam, current models have very precisely sized airboxes (for optimal wave resonance) and actually make LESS power without them. I am pretty sure our sohc's would benefit from a well designed airbox, but most likely it'll be too big to fit between the carbs and the rear down tubes.

[Rod]

TG - re bellmouths, I found a link to the article I mentioned in one of your other threads. The author (Prof Blair) was involved for many years with Queens Uni Belfast, he and his students prepared some indecently quick racing bikes on a very low budget.

http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf

[turboguzzi]

hi rod

 I actually posted that link in another stacks thread.....

Shame that its only a stack shape analysis based on steady flow and doesnt cover length vs bore issues.

TG

[MRieck]

This may be a silly question to those with a lot of experience with velocity stacks, but how do they filter the air?  I've seen some with things that look like covers (I assume the 'covers' are the filters), but I don't see anything on the ones in the above pictures that looks like a filtration device. 

So how do they filter the air?

Most vintage racers run wihtout filtering in name of power, but


the ZX6R in question has those velocity stacks AND they are positioned inside a fully filtered airbox, the air filtering is done at the box's entry

Sam, current models have very precisely sized airboxes (for optimal wave resonance) and actually make LESS power without them. I am pretty sure our sohc's would benefit from a well designed airbox, but most likely it'll be too big to fit between the carbs and the rear down tubes.

You are right TG. I've said this before

[kayaker43]

I also agree with the airbox size comment, I usually run pods and always noticed the stock airbox gives more low/mid range torque. I wonder if its a simple calculation to optimize airbox volume to a certain RPM? I'm thinking a given volume is most effective at one primary resonant frequency but there's probably also secondary harmonics? Modern airboxes are pretty large, that may be an attempt to regain some low RPM torque in a highly tuned engine?

It would be fun to dyno an engine while connected to a variable volume chamber. I suspect the volume can only be truly optimized for one rpm range.

Lets see,.. we want variable cam timing, variable exhaust and intake tract length, and variable airbox volume. Oh what the hell,. lets throw in a brain and a beating heart,.... 

[turboguzzi]

OK, so it's a poor man's variable length system? suits me fine and should be OK for vintage racing rules too me thinks.

Guys, as soon as I have time I am going to give it a try, already have an idea how to build this around the CR's.

Mike, Kayaker, as we agree on airbox = good, gotta ask you, have you ever tried building a bigger one for a sohc?

TG

[kayaker43]

At least on the 550, I'm not sure how you could fit one any bigger than stock?

You could always run the stock box minus the filter? My SV650 is extremely sensitive to small changes in the airbox inlet size, so that may be a tuning variable too?

[MRieck]

At least on the 550, I'm not sure how you could fit one any bigger than stock?

You could always run the stock box minus the filter? My SV650 is extremely sensitive to small changes in the airbox inlet size, so that may be a tuning variable too?

I agree....you really need a perimeter frame design to start with.

[Kemp]

Wonder if you could use the stock airbox on the 550 and eliminate the std air filter and the restrictive top cap/screen cover. Use the entire volume. The smaller airbox section that connects the four carbs to the bigger filter element chamber would act as a sort of harmonic restriction possibly giving us back the soft control for the low end torque delivery while the the larger volume of the filter chamber would give us a "big" volume air chamber. To filter we could use the least restrictive filter screen material (maybe something from a motocross bike) across the entire top of the filter element box. To adjust flow even more we could put another thin rectangle of filter material at an angle across the opening between the two chambers. The filter material would need to be very porous to allow almost unrestricted flow yet it would calm and stabilize flow. The second filter would slow/stabilize flow again and provide final protection for the motor. No engineer so I don't know what I'm talking about but the flat spot that pods deliver is a real issue with the small 550 mtrs. The alternative, unrestricted bell mouths, are too risky as eventually you will ruin your street mtrs top end with out filtration of some sort.

[Pinhead]

FWIW the stock CB650 airbox has velocity stacks on the ends of the carb boots inside the plenum...

[mystic_1]

FWIW the stock CB650 airbox has velocity stacks on the ends of the carb boots inside the plenum...

Same with the 750.

mystic_1

[kayaker43]

The 550 also has short rubber stacks built in. You can jet out the flat spot when running pods, but you still lose some grunt compared to the airbox.

[turboguzzi]

in modern superstock people run with filters and put down big power, its just that they have VERY large filter area so restriction is fairly low.

Kayaker, I'm very far from stock, planning this for my very modified racer, with the keihin 29CR's on short stubs there seems to be room for making both the stacks and an airbox. Mike, second option is to build the box AROUND the rear downtubes.....

if anyone got any info/formulas on airbox design and sizing, I'd love to hear.

TG

[MRieck]

in modern superstock people run with filters and put down big power, its just that they have VERY large filter area so restriction is fairly low.

Kayaker, I'm very far from stock, planning this for my very modified racer, with the keihin 29CR's on short stubs there seems to be room for making both the stacks and an airbox. Mike, second option is to build the box AROUND the rear downtubes.....

if anyone got any info/formulas on airbox design and sizing, I'd love to hear.

TG

OK then....I'll think about it TG......and stack set up too.

[mystic_1]

if anyone got any info/formulas on airbox design and sizing, I'd love to hear.

I've been reading up on helmholtz resonators lately.

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

http://www.saltmine.org.uk/randy/airboxdesign.html

http://www.thunderproducts.com/AirboxesDynotech.htm

mystic_1

[kos]

In a very early attempt at an airbox, the original CB750 SOHC Hondas had a rather small airbox.  If one looks at the internals of the OEM air intake system on these bikes, air enters bottom of box, travels thru the filter into the open area on top , then is transmitted into the plastic air funnels (velocity stacks) and on into the engine.  I used these funnels only on, our production roadracer that I raced along with Gary Nixon with great results. Seam's like Honda did some testing/design work on these stacks. Don't throw the stacks away when you strip the airbox off...give them a try.

BTW....Nixon won Superbike race in Mod Ohio on this Historic Production bike.
KOS

[voxonda]

I defenitely agree on the OEM stacks, have used them for years and the bikes always ran great on them. On closed circuits that is, no filtration.

[Bill/BentON Racing]

Same stacks I ran on CB590.Worked real well and inexpensive!,Bill

[turboguzzi]

shame the stock rubbers will not fit my Keihin CR29's...

Made a quick measurement today and it looks like I could fit a 4000 c.c. airbox without much trouble,

I recall reading that current superbikes have a 10,000 c.c. liter airboxes. So 4000 cc is not quite the 1:10 ratio of displacement to box volume that sounds right, but is not that far off either.

Taking with a very experienced sidecar racing mechanic and rider (did GP's) he said that the first big gain would be from the carbs not sucking hot and turbulent air.

[Bill/BentON Racing]

Well that makes sense,keep us posted.Bill