The only good thing that the Boyesen reeds taught us was that the " stuffer " between the manifold exit and the reed tip exit was developed on
a flow bench to keep the flow area ( and thus the velocity ) virtually constant.
The stuffer takes into account that the reed width is generally alot wider than the entry diameter, and coincidentally the vertical height is reducing as the flow approaches the tips.
Filling in the sides with a well shaped stuffer insert keeps the area constant and directs the flow such that all the petals are opened equally by the same velocity.
What Boyesen did do was to direct the flow around the turn correctly to try and equalise the tip lifts.
One thing you need to realise though is that there is just as much positive pressure ratio developed on the intake side of the petals, from the sonic tuning of the intake length, as there
is a negative pressure ratio pulling flow thru from the case.
Here is an example of the very best setup I have done for the 30mm carb on a KZ2 - 125 engine.
This flows around 12% more air on a bench and makes around 1 1/2 Hp more than stock at peak, and near on 4 Hp at 14,000.
It divides the flow into 4 quadrants feeding each petal equally with the CNC insert,plus the plastic stuffer keeps the area constant right into the reed V.
Wobbly.
Stuffer looks very neat. What's your thoughts on it in a rotax max kart engine ?
In an old 125 TM125MX I did for open karts the crank only had 0.5mm clearance within the case.
I machined the side faces and the OD of the crank pocket to make it 1.5mm and at the same time removed 5mm from the reed face.
This got the case volume back to where it was.
Reducing the boundary layer friction by doing this was worth 0.5 to 1 Hp at the sprocket.
Never had the chance to do a back to back on a RV but every fast one I have seen has some sort of patterned cut on both faces.
I did once have the faces treated with a PTFE piston coating on a 20,000 rpm RV engine and this reduced the disc and case wear to nil.
Thanks for the insight. How much clearance is typically used on the disc of a race RV engine? Unfortunately, I have yet to get my hands on one. As far as I understand, the disc is typically allowed to float a little. And at the end points of the disc travel, how far away from the side wall faces will it be (or does it have to be), then?
we might expect you to be the last person to say this, Frits!... You came up with the 24/7 concept; shouldn't that render all of this effort unnecessary?
In the long run: yes, I think so. But there are many people here working on rotary inlets and for them it is simpler to carry on than to switch to 24/7.
On the other hand, if you are already working on a reed valve engine, converting it to 24/7 is much simpler than converting a rotary valve engine.
And finally I am in a position that I don't need to push everyone into 24/7; it's already on the move: http://www.kiwibiker.co.nz/forums/sh...post1130808805
Originally Posted by seattle smitty
I'm wondering if you have found in testing that as elegantly simple the 24/7 intake is as a concept, maybe it turns out to be a very hard thing to tune in practice. My uneducated guess is that your swing-away valve method of creating a 24/7 intake might make it hard to get the carburetor to work across the whole rpm range.
That was my initial fear too, Smitty. That was one of the reasons I was so keen on dropping the carburettor and switching to fuel injection. But the Modena tests have shown that a single carburettor can handle the switch from a closed to an open 24/7 inlet without any problems. And Modena have also got a conventional reedvalve kart engine running quite nicely on injection so they know what they should be looking for.
I liked the idea of splitting the job between two carbs, one primary carb (over a reedblock) that's drawing all the time, and a second carb (over the 24/7 intake tract) that is only open when the pipe goes to work. Maybe a little more complex mechanically, but maybe simpler to tune?
No maybe's about it: more complex and more difficult to tune. Are you sure that deep in your heart you're not a double-overhead camshaft man, Smitty?
Originally Posted by Haufen
How much clearance is typically used on the disc of a race RV engine? As far as I understand, the disc is typically allowed to float a little. And at the end points of the disc travel, how far away from the side wall faces will it be (or does it have to be), then?
Clearance should be about 0,4 mm. And the disk should be able to float until it rests against either side of the disk chamber. That makes setting it up a whole lot easier.
Remember the 12-speed twin-disk Kreidlers? They had both disks pressed onto the crankshaft. Getting them well-sealing yet friction-free was a nightmare.
I'll ignore the abuse, but what is the engine in the photo?
Can you tell us about the results so far with the 24/7 kart engine? Are they blowing over backwards? Piling up the asphalt in folds behind the tires? Slowing the rotation of the earth?
I'll ignore the abuse, but what is the engine in the photo?
Aprilia APB: the engine with which Max Biaggi won four 250cc world championships between 1991 and 1996.
Originally Posted by seattle smitty
Can you tell us about the results so far with the 24/7 kart engine? Are they blowing over backwards? Piling up the asphalt in folds behind the tires? Slowing the rotation of the earth?
I have the RV clearance at 0.5mm, close to what Frits stated.Using the Clykro drive makes this real easy as I said, the pinion can float along with the RV fixed to its shaft.
The reed stuffer went thru many stages and it quickly became clear that moving the splitters up close to the carb entry would overly restrict the already
small area from the 30mm carb - as they need a good rounded leading edge to reduce turbulence.
In the end after hours on the flow bench, having a longer vertical split with extra width and shape to the stuffer down the sides gave the best flow
and you could see that the reeds were being lifted symmetrically across their width.
Previously the outer tips were nowhere near as open as the inners, ie the reed was twisted across its width, more of an issue I would say in this wide 4 petal design.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Just to clarify.
Rotary valve clearance. We you say Frits recommends 0.4mm
& Wobbly you have set it at 0.5mm
Clearance would be all around the disc ( ie both sides & O/D )
Or are you both talking end float
Cheers
I have 1mm clearance per side on the OD and yes we are both talking 0.5/0.4 total end float of the valve from face to face.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
can someone give a quick explanation of the pros and cons of a solid vs hollow crank pin ? ordered a hollow pin because thats all i could find for the particular application but a solid pin showed up. if its better ill keep it, if not ill send it back and keep looking
The solid pin will be heavier and obviously this affects the balance ie it will make the factor lower.
Hollow pins do have one issue though and that is if the press fit is designed correctly for a solid pin then the fit will then be insufficient.
Hollow pins need more interference, as they crush - loosing some of their OD as they enter the hole..
The fit must be correct for the hollow pin for another reason - as the do crush, then if the press is too heavy the pin will "barrel " down
at the ends where they enter the wheel, and this is bad for the rollers as then the pin isnt parallel.
What size do you need.
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
Originally Posted by wobbly
The only good thing that the Boyesen reeds taught us was that the " stuffer " between the manifold exit and the reed tip exit was developed on
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