Hustler class ( Vinduro Buckets)

[diesel pig]

Looks like a EXup servo off a YZFR1?
https://partversal.co.uk/motodalysen/product/8126376

Yeah, That is what it is. After a quick e-bay search but be careful the prices are all over the place, some are low price unit, high shipping or high unit, low shipping. So hopefully there are some are low unit, Low shipping prices somewhere on e-bay.

[husaberg]

Yeah, That is what it is. After a quick e-bay search but be careful the prices are all over the place, some are low price unit, high shipping or high unit, low shipping. So hopefully there are some are low unit, Low shipping prices somewhere on e-bay.

Have you considered trying here?
While not as compact the WR250R has an EXup as do a lot of other Yamaha's normally first thing people do is biff these?

[diesel pig]

Have you considered trying here?
While not as compact the WR250R has an EXup as do a lot of other Yamaha's normally first thing people do is biff these?

I just liked how compact and tidy they are. When I do another power valve setup I will be looking for one.

[Flettner]

https://youtube.com/shorts/WgfU8sHdW...AnWXfbq-fJCXsz

[F5 Dave]

Think pa had one just like that on the farm.

[Flettner]

https://www.facebook.com/share/p/16b18uyFmK/

The water cooled, powervalve AG at Tar Hill vinduro recently.

[Flettner]

Off on a new tangent, 150cc twin supercharged fourstroke.

[F5 Dave]

The Devil take ya. Heresy!

[Flettner]

The AG in its latest guise. The powervalve has completely changed the power curve, no more hole between 6,000 to 7,000. So much easier to ride.
New cylinder head, 4mm exhaust dam, boost bottle retained, smaller exhaust restrictors at 2x 15.5mm, refined ignition and powervalve programmes.

[Flettner]

The supercharged fourstroke is off the table, EFI outlawed in our class and I'm not interested in a carburetor.

[diesel pig]

The AG in its latest guise. The powervalve has completely changed the power curve, no more hole between 6,000 to 7,000. So much easier to ride.
New cylinder head, 5mm exhaust dam, boost bottle retained, smaller exhaust restrictors at 2x 15.5mm, refined ignition and powervalve programmes.

So do the Exhaust restrictors make the tail pipe length and dim unimportant?

[F5 Dave]

Looks suitably grotty to not raise too much suspicion. Love your work.

[Flettner]

So do the Exhaust restrictors make the tail pipe length and dim unimportant?

Swap about inserts, makes tuning much easier. Rest of the system is if no consequence.

[diesel pig]

Swap about inserts, makes tuning much easier. Rest of the system is if no consequence.

I meant Diameter. Couldn't think how to spell it the other day. Good to know about the restrictors, I will start using them now I have a Lathe that can be easy to use different set tool angles.

[husaberg]

I meant Diameter. Couldn't think how to spell it the other day. Good to know about the restrictors, I will start using them now I have a Lathe that can be easy to use different set tool angles.

click on the arows for the pics and the posts around them

The exhaust exit "nozzle" was used first by Helmut Fath ( my hero ) when tuning for Honda where their V twin 250 had one stinger 150 long the other 450 long.
I have tested all manner of variations and the best is around 10mm of parallel nozzle and then 10mm of divergence to a stinger around 1.5mm bigger.
This reduces the effect of the waves bouncing up and down the stinger off atmosphere disrupting the rear cone waves.

The pipe vol/engine cc field in the pipe screen was added by Neels to the program when Frits noted that he had calculated this for the RSA - maybe he can elaborate on the relationship.
Note also that there is two fields for the length to end of header and length to end of diffuser.
I got Neels to add this as so few pipe designs are "correct" and its a pain to calculate all the time.The header end should be 30 to 32% and the diffuser should be 64 to 68%

TeeZee - really glad that you are looking at the STA numbers and realising that the sim is telling you what is needed - or not in many cases.
Getting all the elements of a design in harmony is what makes big power numbers.
I would try making the divergent header nozzle longer - very short ones can create shock waves and reduce the energy available to do positive "work" in the pipe.

Only Yamaha stuck with the wank flat roof scenario way after the use by date, and got their arses kicked for years in GP.
Till they finally bought a CNC controlled Jante machine from Czech, went square bore/stroke and using the 500 cylinders on the 250 easily won the champs in 2000 with Olivier Jaques.

The secondarys facing each other relatively flat will always collide, but the hooks rotate the flow under the boost as it exits the port ( easy to see with the tap water Jante trick),clearing out a big "dead" area
in front of the rear port.

All modern race engines have a nozzle restriction at the flange face, as big T ports and tripple Exhausts loose alot of velocity going into the header.
Rule of thumb is a 75% of the effective EX area at the flange.
Stepped oval duct into a round flange does work, but I have used a CNC oval to round transition in the spigot for years, as has Honda in A kit, and Aprilia factory engines, this works way better.
Here is a sim showing my new 400cc F3 engine, with and without the spigot nozzle.

The stinger nozzle effectively removes the stinger tube length from the equation - it was developed for Spencers NSR that had one stinger 150 long, the other was 450.
The nozzle is around 2 to 3mm smaller than the tube stinger .

Another good source for big ends is Thompson - I use these in KT100 crank rebuilds as the needles are already graded.
The rear cone nozzle in the old Honda manual is well out of date.
A later version was developed by Helmut Fath and was first used on Fast Freddys 250 where one stinger was 150 long the other was 450 long.
This better design has a short 10mm "nozzle" of the correct size to create the pressure restriction, then a short taper, up to a stinger tube approx 2mm bigger in diameter.
The bigger stinger and the reverse taper basically remove this resonant tube from the equation, and the stinger length becomes irrelevant.
Under normal conditions the wave action bouncing up and down the stinger ,off the open end to atmosphere, creates varying bad effects on the reverse cone waves.
The pic shows a section of one for F3 - 400.
Rear cone welds onto LH side, stinger pushes into RH side and welded as well.
Another side effect is that there is no welding ( dags) to affect the flow where the rear cone is attached to the tube.

Dont know about Loris and his anal action, but I was with Benson and the team at Cowes one year having diner on the corner, where Max had a new "girlfriend" that night.The next night the same "person" was on his lap,as a man.
Tell his new wife that one, and see if the bulge in the back of his pants is stronger than the one in front.

The backward angle of the port flank nearest the exhaust (the green line in your drawing) is important, but I agree that your duct is not a thing of beauty.
But the right-side duct, though it may look more attractive, is even worse. The backward angle of the green line may be somewhat exaggerated, but the blue line is not sufficiently angled backward, which will result in short-circuiting: fresh charge from the A-ports will make a U-turn and escape directly into the exhaust duct. And it will do so as soon as the transfer ports open, which means it will be too far down the exhaust pipe by the time the return pulse tries to shove escaped charge back into the cylinder.
I can only guess as to the purpose of such a design. Maybe it is not even a deliberate design but just the result of using existing casting cores for a new cylinder.
Or maybe the cylinder studs were in the way...

By the way, I appreciate you calling me Mr. Frits, but there is no need; just Frits will do fine .

Remember what I said about those simple calculations: they are only meant to help beginning tuners on their way and a lot of more or less important facors, like compression ratio, ignition timing, type of fuel, carburetter diameter, crankcase volume and angle*areas, are not taken into account.
In your example the important thing is that lower exhaust timings need bigger header diameters. But explaining why this is so, might be beyond the scope of this forum (and it would certainly be beyond the time I have at my disposal).
But come to think of it: the least I can do is post the same simple calculations here. Instead of all those factors I left out, I included one variable, the speed of sound. Starting with 550 m/s will get you in the right ballpark, after which you can vary this value according to your findings.
Final remark: the calculation of the tailpipe restrictor diameter is critical: you can only apply it to engines that are thermally sound. Air-cooled engines are not...