Yoshi Dual Stacks (on a K2)

[Stocky]

Again Yoshi come up with something a bit different.

All that extra money you pay for the name must go into some R&D :D

They make these for all sorts of things including carbies for the oilers.

They are very compicated.

These particular ones are made for the K5/6 GSXR1000.

They are not a straight fit to a K2 but it can be done with a bit of custom machining of the middle throttle bodies.


Haven't tried them yet but I'm optimistic they'll be a little better than the Factory Pro kit I had in there as the cams and rpm I run seem to like really short stacks.

http://www.streetfighters.com.au/forum/upload/55285882459154.JPG
http://www.streetfighters.com.au/forum/upload/55285882477617.JPG

As a result the Factory Pro "Tunners Kit" is for sale $400


http://www.streetfighters.com.au/forum/upload/55285882437389.JPG

[WATEVR]

alright i will look like a dumb arse and ask WTF do they do?

[trx900]

hi stocky I might be interested in those would you be able measure the inside diameter of the stacks thanks

[gibbo]

Be fucked if I know what they do either but they look [:p]

Velocity stacks ain't they?

Old competition Trumpies used to have'em standard. They streamline incoming air into the carbs, giving higher air velocity through the carbs. Jap 4's have 'still air' boxes, which have a similarish (but much reduced) effect.

[dazz]

yeah, basically, different lengths alter intake speed and amount of turbulence into combustion chamber.

On 2000-2005 GSXR/Busa's the short 750 trumpets, pair valve mod, air filter and gear pos sensor are great for freeing up the engine. The kit above is an advanced tuning kit for engines that require more intricate adjustment when chasing small time increments on the track.

[Stocky]

Yes they are Velocity Stacks.

As a rule of thumb , long ones make good low end power and short ones make good top end power.

This is because of a tuned lenght. It's about sound waves in the inlet tract.

The Dual stack gives a resonance for 2 lenghts at the same time. Long and short.

So you kinda get your cake and eat it too.

Make sense ?

The Factory Pro kit has a tonne of different lenghts so you can tune the lenght to suit.

I'm away for a couple of days so I can't measure sorry.

I'll check as soon as I get home but I think they are about 50mm in the Factory Pro ones and 52mm in the Yoshi ones.

[Gulity by Association]

Hi Stocky -
RE stack ID:
The Factory Pro stacks are 45.3mm ID. I tried larger ID and I tried smaller ID and about 45 to 46 ID was the ID that gave the best "intensity" and "strength" of powerband in the upper midrange and didn't hurt the peak number or lowend. The 45.3mm ID is more equal to the primary butterfly diameter, which is probably the better definer of the "best" ID than the bellmouth ID.
Note that the Factory Pro adapter rubbers even feature a "tongue" that "stuffs" the upper part of the bellmouth to overcome the "too large" stock throttle body.
I've tried "dual" and "stepped" stacks in the past (similar to the Yosh stacks) and ended up concluding that, if you attempt to have "two" tuned lengths, you lose more than 50%(!!) of the wave "strength" at both "tuned lengths" and they just didn't produce as much improved power in a particular usable range.
All that's on a stock engined bike with stock cams, but I don't think that a "cammed" engine would be much different (on the 1000 Suz).
Recently, we compared a set of "50mm" ID stacks on a Hayabusa vs. the 45.3mm ID stacks. The 50mm ID stacks did very little as compared to stock and the 45.3's gained over 6 in the upper midrange.
As far as stacks go, the dual stack concept has been around as long as the week that they found out that intake tract length made a HP difference. Just about every pro tuner who can also fabricate that I know has experimented.

People have a very simplistic idea of how stacks work - but there's about 4 other factors in the design that will make or break how even all the same length stack works. You'll find people who don't know that all having some opinion about good or bad stack design, even though they don't really know.
For example, "too gentle" of an inlet radius kills potential power improvements in a defined range.

The USA Yosh guys are pretty damn good and the US team is, I would say, the toughest US team to beat in roadracing, but, They DO, at times buy and use OUR parts over what Yosh Japan sends.
Referal from them? Ask Jon Lau, Yosh USA VP or Rich Doan (he used to work for me) or Don Sakakura on the USA RR team.
Anyhow, since I don't really know about the Yosh stacks of your bike, did you dyno it (under a load), yet. You have to be really careful to dyno under load (not a simple 4th gear "sweep") to get these new high hp bikes to reach proper internal combustion chamber temps - or the dyno results will be "on the dyno only" vs. real world conditions (which have great amounts of load at high speed).

In good cheer and with best regards from rainy northern California,

Marc

Marc Salvisberg
Factory Pro Tuning
Over 35 years of Tuning experience

[Stocky]

Marc, thanks for the reply.

Great to see you on the forum.

I will get to the dyno as soon as I can.

I expect to see a mid range top end gain (some loss of 4000-6000rpm) from the dual stacks just going by the ass dyno.

I'll spend some time (and money) to test them properly.

I understand what you are saying and agree with your logic and testing.

I actually have a "tunners kit" of yours.

I had it on before the Dual Stacks.

My motivation for going to the dual stacks was lenght.

I went shorter and shorter with the Factory Pro ones and got more and more power (everywhere)

The Dual Stacks are shorter again.

I wonder if you could make me 2 stacks that are basically flush.

Then I could run the really short ones in the middle and the flush ones on the outside. I think this could be even better than the shortest Factory Pro setup and better than the Yoshi ones.

I'm thinking REALLY short. Bascially the bit that clips into the rubber and the bell mouth spilling straight over the top , almost flat on the floor of the air box.

I've still got this......


http://www.streetfighters.com.au/forum/upload/71358042037389.jpg

[Stocky]

I'd love to try these in the middle.
http://www.streetfighters.com.au/forum/upload/71358042014889.jpg


And then a Factory Pro version of these on the outside...

http://www.streetfighters.com.au/forum/upload/7135804202684.jpg


What do you recon Marc ?

Or do I just bandsaw the long ones off and have them welded back together really short [:p]

[Gulity by Association]

Hi Stocky -

Looks like your cam might be pretty advanced on the intake side and that would explain why you need really short stacks. I'm just guessing on that.

Is that "wrong"? No... It's just that the stacks and the cam timing have to work together or they make less power.

So - either you move the cams to match the intake tract length or you move the stacks to match the intake cam.

I'm guessing that you have 2 21mm stacks as your shortest Factory Pro stacks?

So..... lesseeee, here.....
Even "shorter"....

I have some 15mm stacks (15mm above the airbox floor), but that's still 15mm.

To go a bit past you having "some" flare inside the airbox, maybe try cutting the stock rubber stacks just above the upper "lock lip" and sanding a radius into them - that'll be about the shortest you can get.

If you still haven't lost any or enough midrange... to gain some peak hp (I'm guessing again), then you'll just have to retard the intake cam a couple degrees.

That's what I would do next (if you were asking :-)

DynoCam!
http://70.141.63.105:8080/image1

Marc

[barknmad]

Thanks Stocky and Marc for a really informative thread. Learn't a bit here. 8^)

[Stocky]

Marc,

Yes the Inlet cam is advanced.

As I go shorter with the stacks I get more and more mid range. I don't really gain top end except it doesn't nose over any more. It kinda holds it's peak better all the way to the limiter.



I have 15mm stacks, these are the ones I want to run in the middle.

I'll chuck 2 of the 60mm ones in the lathe tonight and make them "flat"

See if this is better than the Yoshi setup.

I did try the 15mm ones with the outer 2 flush like I have now and it was ok but not as good in the mid range as the Yoshi ones.
I always kinda wanted to run all Factory Pro ones (for the restriction in the top) but it hadn't occured to me to modify a long one until I replied to this thread.

Thanks for the idea ;)

[Gix11]

Hey Marc. Top information mate. A privelige to have you aboard. Have a look around the site and see if anything is of interest to you. Cheers.

[Hillsy]

Yeah - welcome aboard Marc - got one of your carb kits and an advancer for my ZX9. Your tuning settings that came with the jet kit were close to spot on (I didn't expect that, actually). Muchos Gracious

[Deano]

gday Mark.

also got one of you kits in my gsxr1100w with 38mm 750 carbs. I also found your recommended settings spot on.

welcome aboard mate.

[Gulity by Association]

WHATEVR -
Try this link to show how velocity stack "length" works.
http://www.factorypro.com/tech/velocity_stack_how_what_why.htm
The more little guys that get trapped in the engine, the more power the engine will produce.
Marc