Boysen port

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graham heise
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Boysen port

#1 Post by graham heise » Tue Dec 18, 2018 3:55 pm

Gday. I picked up some 31k cylinders that have been modified by someone beforehand. A passage ( boysen port) has been added from the inlet to the transfer. Also the 347cm has been changed. Just wondering what is the benefit of the extra port?

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graham heise
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Re: Boysen port

#2 Post by graham heise » Tue Dec 18, 2018 3:56 pm

Photo'sImageImageImage

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MK
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Re: Boysen port

#3 Post by MK » Tue Dec 18, 2018 5:23 pm

Nothing to worry about. They just add some extra hp's.
The 247 is just camouflage if you use them on a 250.
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Martin

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Re: Boysen port

#4 Post by Smoker » Tue Dec 18, 2018 5:41 pm

Why aren't these ports used on the RZ350 cylinders?

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Questo vecchio rz
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Re: Boysen port

#5 Post by Questo vecchio rz » Tue Dec 18, 2018 6:11 pm

Afternarket "Boyseen" ports,transfer additional mixture during the stroke.
When done right it aids performance.

Care must be taken NOT to weaken the cylinder, it can create ultra thin walls easily prone to failure.
Often builders will add material in order to strengthen the cylinder.
I have a 69.0 mm Tri-Z cylinder that has had the Factory Yamaha racing modification done, a Xtra boost port has been added, along with Harry Klemm portwork. It required Tig welding Xtra material. Motor is shockingly faster. Different machine though. There are a few Banshee tuners whom do this, with frankly proven great results. Jim Passions 11 port is one such example.

Aren't the cylinders 250cc YPVS cylinders to begin with ???
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JonW
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Re: Boysen port

#6 Post by JonW » Tue Dec 18, 2018 7:13 pm

Questo vecchio rz wrote: Tue Dec 18, 2018 6:11 pm
Aren't the cylinders 250cc YPVS cylinders to begin with ???
Not if they say '31K' on them, no one would change that.

I made up some '2's to go on my 350 cyls that had been doctored back in the day. :)

Yamaha put these posrts in the 51L 250 cylinders from the factory. All reports are that this is a great revvy and powerful engine.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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Re: Boysen port

#7 Post by Questo vecchio rz » Tue Dec 18, 2018 8:54 pm

Okay..thanks for that info. Never had 250s here in the states.
What had me guessing..was those ports look "cast" not done freehand by a individual....but I'm looking at a small pic on my phone.

On my Tri Z , the recomendation for the additional boost port and more aggressive port windows came directly from Yamaha Motor Co. It appears they knew what there doing by adding the additional 'boyseen" ports.
Banshee (Baja) race bike,+ 2 A Arms,L.E.Ds, Toomey, +4 stroker IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura rep.
85 custom Tri-Z
RZ/YZR bike(project)
86 VFR750 RC24 Merkel replica (project)
Royal Enfield Bullet 500

graham heise
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Re: Boysen port

#8 Post by graham heise » Wed Dec 19, 2018 6:25 am

thanks for the reply's. I'm aware of the added boyseen port on the 29l 250 cylinders and the better performance they have over other rz250 cylinders. Just made me wonder why this modification is not talked about or used more on a 350 cylinder if it adds some extra hp. Is this hp gain accross the rev range? does it create any dips or flat spots??
Another port could be added to the other side of the inlet to the opposing transfer, why not have 2?
Looking at the mod skilled hands have perfomed it and there is not much material left to the outside of cylinder. I suppose it is much easier to do on the 250 cylinder as the outside of cylinder is same dimensions as 350 but the cylinder sleeve is allot smaller with the 54mm bore. i am going to trace the port maps but from looking at the transfers, they have only been cleaned up, slighly enlarged and exhaust port raised slightly. The cylinder are still at 64mm and are in pretty decent shape. I will probable bore to 64.5mm run them and assess there performance.
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Re: Boysen port

#9 Post by JonW » Wed Dec 19, 2018 8:34 am

We spoke recently about this type of mod on 350 pistons on Norbos forum, have a look there for more info perhaps?

Oh and its not the 29L cylinder, its a 51L... the 29L is nothing special.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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Re: Boysen port

#10 Post by MK » Wed Dec 19, 2018 6:16 pm

Btw: Is it just on one side, not on both?
That'd be just half of the work done ...
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Martin

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Re: Boysen port

#11 Post by JonW » Wed Dec 19, 2018 7:16 pm

Martin this is Yamaha's work on the 51L cylinder:

Image
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

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OldTZracer
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Re: Boysen port

#12 Post by OldTZracer » Thu Dec 20, 2018 1:27 am

Back in the day, I saw drawings of the prototype 1UA cylinder spec with the these ports, as well as conical combustion chambers. Not sure why they didn't make it into production but like most things, I assume it was due to cost...
"...its a 2-stroke ya twit - Its supposed to smoke..."

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Re: Boysen port

#13 Post by JonW » Thu Dec 20, 2018 2:00 am

It makes sense that Yam considered this for the 1UA, it followed the 51L etc.

I would think a couple of things killed this:
1, Cost... you need to licence port tech like this
2, The RZ was a bit old hat by 86. TZRs were out and they were the next design phase, which included the 500 and the TDR etc.
80 XT500 Supermoto!
81 RD350LC Resto
82 RD421LC Hybrid
82 RD350LC decapitation project
82 RD250LC JDM '251LC' YPVS
83 RZ350 Resto
84 RZ500 Resto
85 RZ350 F1 Resto
86 RZ350 F2 Resto
86 RZ350 F2 Hybrid

Like Watches? www.PloProf.com & www.DeskDivers.com

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