Topic: Self made Hi-Po parts

[gschuld]

Brent,

Yes, they have only 45 and 70mm stack lengths.  I was hoping for something a tad shorter.

George

[bwaller]

I will ask around the pits at Mosport this weekend George. At least you have an offer from Ric.

[gschuld]

I’ll give Riccardo’s stacks a try for sure.  I’m thinking of alternative arrangements to test with on the dyno along with the standard 45mm and 70mm stacks.  Say a 25mm to 35mm length stack made for the cr26-33 carbs.  Then it’s a matter of interchangeable secondary stacks(I could make them separately). I could try different sizes and positions.

George

[scunny]

for a self taught garage mechanic. what is the theory behind the double stack ?
Always prepared to learn.
cheers scunny

[scottly]

Please post back-to-back dyno tests of the double stacks vs the single stacks.

I will, super curious about the end results!

Before producing more parts, you really should verify results.

[Rod]

I'd be interested to know more about the science of the double stack (if there is any), from what I can see it's not being used anywhere at the cutting edge of motorsport (correct me if I'm wrong) which probably tells you all you need to know. Having read the http://www.bikebros.co.jp/vb/sports/sfeat/yoshimura-carburetor-en article, I can't help thinking that it's simply a Yoshi bolt-on for the show ponies - also disappointed to see in the article that Yoshi claim credit for inventing the 4-1 exhaust, not only did Dave Degans (Dresda) probably get there before Pops in terms of racing bikes, European single seater racing cars were using 4-1 in the 60's if not earlier, and not just F1 but even in the junior classes like F3  - e.g. the off the shelf Brabham F3 BT21 produced from 1966 was offered with three different headers from the factory: a 4-into-2-into-1, a 4-into-1, and an "up and over". So if a company can claim the intellectual property for inventing something as significant as the 4-1 exhaust when they clearly didn't, how much can one trust the veracity of the claimed power increases for their double stacks? Personally, I'd be wanting to see some verifiable data before I opened my wallet.

[Tintop]

The basic theory behind the double stack is that it allows for improved air flow over a wider range of rpm.  Long stacks improve low / mid range torque, short ones high rpm flow.  It's like having a variable length intake.  From my perspective the keys are finding the length that produces the best torque numbers, and having a short portion that smooths flow (eg a round profile).  You won't see them used on modern race cars because variable intakes, and valve timing accomplish the same thing.

[livefast_dieold]

Welcome back, everyone :-)

A quick heads-up. So basically in order to get quantity discount I've to order at least 100 pieces :-(
So the end price per piece is going to be approx. 40 €.

Anyhow, I've been thinking how to improve the design, I can make the stack larger to the point of almost touching each other, and there will be a stack for cylinder 1 & 3 and one for cylinder 2 & 4.
From previous design, the intake area will be 18% larger this way. I've also increased the space between the lower stack and upper stack by 1 mm (now total distance between the two stack is 3 mm).








I'll start manufacturing one complete set to check if everything is fine, hopefully being able to check performance improvement on the dyno to see if it actually works before manufacturing the sets for anyone else :-)

[gschuld]

Looking good Riccardo.

Bummer on the pricing quote😏

George

[livefast_dieold]

Brent,

Yes, they have only 45 and 70mm stack lengths.  I was hoping for something a tad shorter.

George

If you want I can easily adapt the original design I've already copied to the desired length

[Captain]

 You might be interested in how it was done on our install. The lower stack has an internal passage for the air jets (slots in the underside) and this allows for a deeper and more effective elliptical curve entry shape.  Yours appears to be not so pronounced and this may not be as effective.

[Tintop]

You might be interested in how it was done on our install. The lower stack has an internal passage for the air jets (slots in the underside) and this allows for a deeper and more effective elliptical curve entry shape.  Yours appears to be not so pronounced and this may not be as effective.

Beautifully simple and elegant solution to the air jets Captain, not surprised though.   It was your more rounded base I thought would preform better given my Weber experience.  Seems it did.

[livefast_dieold]

You might be interested in how it was done on our install. The lower stack has an internal passage for the air jets (slots in the underside) and this allows for a deeper and more effective elliptical curve entry shape.  Yours appears to be not so pronounced and this may not be as effective.

Interesting, looking at your pictures I was actually wondering how you tackled this.
Anyhow, I prefered basically to copy the original stack base, here a couple of close-ups:





I've highlighted the curvature to get a better sense of it: it's a perfect elipse :-)

[Tintop]

You might be interested in how it was done on our install. The lower stack has an internal passage for the air jets (slots in the underside) and this allows for a deeper and more effective elliptical curve entry shape.  Yours appears to be not so pronounced and this may not be as effective.

Interesting, looking at your pictures I was actually wondering how you tackled this.
Anyhow, I prefered basically to copy the original stack base, here a couple of close-ups:
I've highlighted the curvature to get a better sense of it: it's a perfect ellipse :-)

It is the continued curve past 90* that is the key in Captain's base.  Air is being pulled into the stack from almost 180* (behind the opening), so the sharp edge will disturb the air flow.  That said unless your seeking that last once of power like Captain, the difference will be negligible.

[gschuld]

Riccardo,

Thanks for showing the entry radius more clearly.  That’s really nice.👍

Captains slotted vent built into the stack is genius and must have been a chore to lay out.   How much that full wrap around entry matters in the end is a good question.

George

[gschuld]

FWIW...

George

[livefast_dieold]

Thanks for showing the entry radius more clearly.  That’s really nice.👍

Captains slotted vent built into the stack is genius and must have been a chore to lay out.   How much that full wrap around entry matters in the end is a good question.

George

I've based most on my design from this proportions:



obviously there's not enough space to have a bell mouth diameter that is 2.13 times larger than intake, and the "return radious" required for optimal performance is really minimum. More technical information on this on the pdf attached

[turboguzzi]

I'd be interested to know more about the science of the double stack (if there is any), from what I can see it's not being used anywhere at the cutting edge of motorsport (correct me if I'm wrong) which probably tells you all you need to know.

kawaski fitted them to the 2009 zx6r.... i got a set form ebay just out of curiosity, ended up fitting them my GPZ550 racer, but have no before/after data, bike runs ok
Kawi fitted new double-bore intake funnels that are a simpler form of the variable-length intakes on Yamaha sportbikes. These velocity stacks have inlets at two different (but static) heights, with the taller inlet boosting midrange power while the short stack maximizes top-end production.

[livefast_dieold]

They have arrived!!! Boy oh boy do they look pretty :-)
I hope they are as functional as they look good!







The only bummer is that the lateral slicing probably wasn't needed. The gap should have been 1 mm based on my calculations, but it ended up being 5 mm. I don't know if it's a stupid mistake while measuring carbs centre distance, or if there is actually a few mm difference among different carburettors racks, as at my mechanic there were 3 sets of CR for CB750 and maybe they are not exactly the same. Anyhow it's an easy fix :-)

[Medyo Bastos]

Those look great, let us know how they work


Sent from my iPhone using Tapatalk

[gschuld]

They do look nice.   

George

[livefast_dieold]

The only bummer is that the lateral slicing probably wasn't needed. The gap should have been 1 mm based on my calculations, but it ended up being 5 mm. I don't know if it's a stupid mistake while measuring carbs centre distance, or if there is actually a few mm difference among different carburettors racks, as at my mechanic there were 3 sets of CR for CB750 and maybe they are not exactly the same. Anyhow it's an easy fix :-)

update on this: one of the CR racks had the 1-2 and 3-4 spacing at 21 mm, the other two of 25 mm

[gschuld]

The only bummer is that the lateral slicing probably wasn't needed. The gap should have been 1 mm based on my calculations, but it ended up being 5 mm. I don't know if it's a stupid mistake while measuring carbs centre distance, or if there is actually a few mm difference among different carburettors racks, as at my mechanic there were 3 sets of CR for CB750 and maybe they are not exactly the same. Anyhow it's an easy fix :-)

update on this: one of the CR racks had the 1-2 and 3-4 spacing at 21 mm, the other two of 25 mm

I believe the factory spacing is 77-80-77

George

[livefast_dieold]

The only bummer is that the lateral slicing probably wasn't needed. The gap should have been 1 mm based on my calculations, but it ended up being 5 mm. I don't know if it's a stupid mistake while measuring carbs centre distance, or if there is actually a few mm difference among different carburettors racks, as at my mechanic there were 3 sets of CR for CB750 and maybe they are not exactly the same. Anyhow it's an easy fix :-)

update on this: one of the CR racks had the 1-2 and 3-4 spacing at 21 mm, the other two of 25 mm

I believe the factory spacing is 77-80-77

George

yes, I measured 75/76 (25 is in between). The rack that has 21 (so 71) had F2 intake rubbers on them, maybe for later models it was narrowed