ESE's works engine tuner

[andreas]

Also, the 70/75% recommendation is not universal. I think it would be less on such a big bore. Or relieve the port.

[wobbly]

Two things I can see need attention.
The Ex port STA is too big - fill in the bottom corner radi and narrow the width to reduce the area below TPO. This will help big time with short circuiting from the A ports,
and increase the blowdown velocity.
Secondly why are you running all the transfers at the same height , that scavenging regime was abandond by everyone over 30 years ago.
Running normal stagger ie boost port lowest favours a broader power range , ideal for something without a PV , if its top end and overev you are looking for then the A port lowest is the go
as per Aprilia - but that was just as much needed to be able to increase the Aux Ex ports area as well , not relevant here.

[wax]

From looking at your port drawing, without dimensions, it is hard to tell whether the engine will live. But anyway, an exhaust port with a shape that is safe for the piston ring and with a width of 75% of the bore, will give less, not more, blowdown time.area than a 70%-wide safe port.
A 75%-wide port requires bigger corner radii to keep the piston ring alive, which reduces the uppermost parts of the blowdown area (the yellow areas in the left-hand drawing) that are the most important because they are open for the longest time.
The right-hand drawing can help you establish the safe shape for any exhaust port, assuming good quality steel piston rings.
Attachment 347584 Attachment 347583

Thank you Frits I can put that into the software and change it about

[wax]

Two things I can see need attention.
The Ex port STA is too big - fill in the bottom corner radi and narrow the width to reduce the area below TPO. This will help big time with short circuiting from the A ports,
and increase the blowdown velocity.
Secondly why are you running all the transfers at the same height , that scavenging regime was abandond by everyone over 30 years ago.
Running normal stagger ie boost port lowest favours a broader power range , ideal for something without a PV , if its top end and overev you are looking for then the A port lowest is the go
as per Aprilia - but that was just as much needed to be able to increase the Aux Ex ports area as well , not relevant here.

Thanks Wobbly
I can stagger the ports easy enough as I have to rasie the transfers anyway. They are down at 116 at the moment. Is a stagger normmaly about 2 degrees of duration
IN regard to the exhaust port I will see what I can do in regards to that as its pretty much set in this cylinder and I am trying to avoid pulling the sleeves out to weld up the cylidner. Yes its a case iron sleeve cylinder. old school. Can you actually get epoxy that wil live in a exhaust port ??

[wobbly]

For normal stagger the durations are around 132 129 126.
A port axial at 25* , B port at 12* , Boost at 55*.
Check the Ex duct exit area also , general rule is 90% of the port effective ie Chordal area X Cosine of the roof down angle - but thats shown in EngMod anyway.

[wax]

For normal stagger the durations are around 132 129 126.
A port axial at 25* , B port at 12* , Boost at 55*.
Check the Ex duct exit area also , general rule is 90% of the port effective ie Chordal area X Cosine of the roof down angle - but thats shown in EngMod anyway.

Thanks I will work all that out and post the sta up here when its done. Thanks guys

[Condyn]

Are the crank shields commonly observed on case reeds absolutely necessary? As previously mentioned, I removed reed blocks from an existing engine and am welding them to another. I have angled them axially towards the transfer ducts.

[wobbly]

The case shields , and the question about the reed box duct exit area are sort of the same question but with slightly differing reasons for the answer.
In the kart engines , the crank rotation is radially opposing the incoming flow , so the shields do two things.

Lifting the floor , and thus reducing the exit area , and also reducing the effect of the crank spin.
The pic of the Vortex DJT is a good example , where the reed block is very short and has a steep angle , so they have lifted the floor to form the shields and dropped the roof to reduce what would have
been a huge area increase past the petal ends.

In a normal engine with a case reed and the crank is spinning with the incoming flow - the floor ramps over the crank help to reduce the area change , but also push the flow upward toward the transfer duct entries.
This can be enhanced as well by a big difference in petal stiffnes , the top reeds ( and backups ) being much softer to bias flow exiting the block upward as well.

[Condyn]

Thanks as always Wobbly. I wish I would have been sucked into the two stroke pit 10 years ago as I am sure I force everyone to repeat themselves.
The varying petal thickness flow control is interesting and I will take note to experiment with that.

[husaberg]

You're right Philou. Below you'll find the Aprilia RSA pipe, codename Tubo102, once more.
The pipe in your above drawing is probably an early Rotax pipe, maybe model VSK150 or thereabouts, from before 1990, or a derivative thereof.
The partly visible logo on the right of your drawing belongs to Gazzaniga, an Italian producer of underwear who ran a 125cc GP racing team around 1990 with my friend Dolph van der Woude as designer/constructor. Dolph can probably tell us more about your drawing if he happens to drop in.
Attachment 347579Attachment 347578

Some of the pipes done at Rotax in the early days of the 256 and 128 had some quite different designs, alot of which I had never seen before.
Yes I think that is VSK 150 - I always wondered what VSK represented, or who actually did the new designs at Rotax back then.
This pipe if I remember correctly we used as a basis at JL, when trying to get the same power out of fully blown manufacture, except the first thing I changed was to a single rear cone.
We were sick of making the 180* U-turn for the front pipe on the Tandem twin for Superkarts.
Making that part front U part blown worked, but we could never get equal power by doing the rest . Hand made cones were always better.

I found these in stuff I posted before, the first one I assumed was the pipe in the first quote .
but it's not....
the second in the second attachment I thought was from a 256? that Frits had in the Frits files.
the others are all named. The last is the Honda KTM pipe for comparison.plus the FGrits rules of thumbs for plugging dykes
From memory there were two versions Frits posted in the Frits files of the Tubo 102 which I assumed were a front and rear pipe?

[TZ350]

[wax]

OK Here is it changed around
I was a little confused on the perfect exhaust port shape. It locks me in at about 95 hp but that will have to do.
Im going to try the piston opening the very bottom of the exhaust port as you suggested Wob
Thanks Guys for all the input, This is the engine by the way

[Muhr]

Hello
It is impressive how many dimensions a gear can have ...
Is there anyone who can answer regarding whether RSA's bevel gear on the balance shaft only has a press fit?

[Wos]

OK Here is it changed around
I was a little confused on the perfect exhaust port shape. It locks me in at about 95 hp but that will have to do.
Im going to try the piston opening the very bottom of the exhaust port as you suggested Wob
Thanks Guys for all the input, This is the engine by the way

Think your sketch Shows not max possible blowdown area

Have a second look at frits advice...in blowdown area the right and left sidewalls of the duct are vertical

[Wos]

OK Here is it changed around
I was a little confused on the perfect exhaust port shape. It locks me in at about 95 hp but that will have to do.
Im going to try the piston opening the very bottom of the exhaust port as you suggested Wob
Thanks Guys for all the input, This is the engine by the way

Think your sketch Shows not max possible blowdown area

Have a second look at frits advice...in blowdown area the right and left sidewalls of the duct are vertical