ESE's works engine tuner

[Frits Overmars]

Hi, I've made it this far with the transfer ports and exhaust.
The C-port and inlet port are the next step.
Does anyone have any comments, tips, or suggestions for improvements to the duct shape, B-hook, or other suggestions?
Footprint of the crankcase original Yamaha RD125LC-10W to all scavenging angles FOS concept.

Jan, with the exhaust duct shape in your drawings you are leaving a lot of blowdown flow on the table. The pictures below may show what I mean.
Never mind the center bridge and the auxiliary exhaust ports in my pics (although it would be good if you could accommodate these).

[Jan Van Hamme]

[QUOTE=Frits Overmars;1131239985]Jan, with the exhaust duct shape in your drawings you are leaving a lot of blowdown flow on the table. The pictures below may show what I mean.
Never mind the center bridge and the auxiliary exhaust ports in my pics (although it would be good if you could accommodate these).

Beste Frits, bedankt voor de aanbeveling.
Ik had die 2 tekeningen al zien staan in uw tips en tricks op onedrive.
Ik dacht, verkeerd dus, dat dit enkel bedoeld was voor uitlaatpoorten met een brugje.

Wat dat brugje betreft...de zuiger die ik ga gebruiken is een Wössner voor een YZ125. Die heeft 2 gaatjes van 1mm in de zuigerwand om de uitlaatbrug te koelen.
Omdat ik gelezen heb van Jan Thiel dat ALLE centrale brugjes op termijn breken, wou ik liever geen uitlaatbrug tekenen.
Als men die gaatjes aan beide zijden afschuint (soevereint) kunnen ze blijvend opgevuld worden met JB Weld extreme heat zei me iemand waarvan ik het blindelings van geloof.
Daarom dacht ik de gewone enkele uitlaatpoort te gebruiken.

Toch een brugje in de uitlaat maken zou dit opvullen elimineren maar hoe breed en hoe diep maak je zo een brugje in de uitlaat/poort zodat het zo lang mogelijk standhoud voor het breekt of scheurt?
Brugje ook wat terugslijpen maar hoever en welke vorm?
.…Die vlakke YZ125 zuiger heeft een schuin vlak van 12° aan de rand. Ik zou dit kunnen wegdraaien naar dome. Maar dan heb ik maar maximum een tangentiële hoek van 4°.
De bodems van de A en B poorten ook 4° (voor dome) of 12° maken dan? Dome zal wel het beste zijn maar is 4° dan niet weinig?

Ik zit momenteel al voorbij de BMEP 13,5. Voor jou is dat peanuts maar voor mij en mijn standaard RD125LC versnellingsbakje en motorconstructie is meer blowdown en transferoppervakte en dus vermogen misschien gegarandeerd breuk?
Ik weet dat niet en kan dat niet echt inschatten.
Meer blowdown door extra auxiliaire uitlaatpoorten (bredere totale uitlaatpoort)… gaat dat geen frontpower en of powerbandbreedte kosten?
Er staan me ongetwijfeld nog enkele slapeloze nachten te wachten om uw goede raad in mijn hoofd te verwerken en te proberen analyseren.

Hartelijk bedankt voor uw vorige en verdere antwoorden en uw tijd.
Groeten Jan



Dear Frits, thanks for the recommendation.
I had already seen those two drawings in your tips and tricks on OneDrive.
I thought, wrongly, that this was only meant for exhaust ports with a bridge.

Regarding that bridge... the piston I'm going to use is a Wössner for a YZ125. It has two 1mm holes in the piston wall to cool the exhaust bridge.
Because I've read from Jan Thiel that ALL central bridges break eventually, I preferred not to draw an exhaust bridge.
If those holes are beveled on both sides, they can be permanently filled with JB Weld Extreme Heat, someone told me, and I blindly believe it.
That's why I thought about using the standard single exhaust port.

Making a bridge in the exhaust would eliminate this filling, but how wide and deep do you make such a bridge in the exhaust/port so that it lasts as long as possible before it breaks or tears?
Grind the bridge back a bit, but how far and what shape?
...That flat YZ125 piston has a 12° slant on the edge. I could turn it down to a dome. But then I'd only have a maximum tangential angle of 4°.
Should the bottoms of the A and B ports also be 4° (for the dome) or 12°? A dome would probably be best, but isn't 4° a small amount?

I'm currently already past the BMEP 13.5. That's peanuts for you, but for me and my standard RD125LC gearbox and engine design, more blowdown and transfer surface area, and therefore power, perhaps guaranteed to break?
I don't know and can't really estimate.
More blowdown due to additional auxiliary exhaust ports (wider total exhaust port)... won't that cost front-end power and/or power bandwidth?

I'm sure I'll have a few more sleepless nights ahead of me as I process and analyze your valuable advice.

Thank you so much for your previous and subsequent replies and your time.
Regards, Jan

[Frits Overmars]

I would definitely not make a central bridge in the exhaust. But judging by your drawings, there are no cylinder studs in the way, so you could make auxiliary exhaust ports.
These will give you so much blowdown angle.area that the exhaust timing does not need to be excessively high, which is good for bottom power.
I am familiar with the flat Yamaha pistons with a 12° slant. I would not modify them (but I would prefer to use a different piston brand).
The axial angles of the transfer ducts should be equal to their roof angles, about 25° for the A-ports and about 12° for the B-ports, but only where they transition into the cylinder bore, so while the port roofs have a certain flat part, make the lengths of the flat part of the bottoms zero. This also helps in making the inner radii of the transfer ducts as large as possible.

A BMEP of 13,5 is impressive. I never held an RD125LC cylinder in my hands, but I am somewhat familiar with the RD350LC and my biggest concern would be the cooling. I felt that there was water everywhere, except where it was needed...

[Jan Van Hamme]

I would definitely not make a central bridge in the exhaust. But judging by your drawings, there are no cylinder studs in the way, so you could make auxiliary exhaust ports.
These will give you so much blowdown angle.area that the exhaust timing does not need to be excessively high, which is good for bottom power.
I am familiar with the flat Yamaha pistons with a 12° slant. I would not modify them (but I would prefer to use a different piston brand).
The axial angles of the transfer ducts should be equal to their roof angles, about 25° for the A-ports and about 12° for the B-ports, but only where they transition into the cylinder bore, so while the port roofs have a certain flat part, make the lengths of the flat part of the bottoms zero. This also helps in making the inner radii of the transfer ducts as large as possible.

A BMEP of 13,5 is impressive. I never held an RD125LC cylinder in my hands, but I am somewhat familiar with the RD350LC and my biggest concern would be the cooling. I felt that there was water everywhere, except where it was needed...

These are the dimensions as I drew them. So at the A port it should also be 22° at the bottom?
For cooling, I wonder if it would be useful to draw cooling fins internally in the cooling channels of the printed cylinder.