ESE's works engine tuner

[F5 Dave]

Its slim pickings in Taumarunui now the cafe at the end is gone.

[jonny quest]

I swear I remember reading a post by Jan or Frits in the Aprilia Pit Lane thread commenting that having piston below transfer floors was best for power, i just can't find it anymore.

[peewee]

i dont recall them saying its good to have the piston below trans floors but i remember jan saying he saw good results by raising the exh floor. possibly thats what your thinking of

[F5 Dave]

And that having a step in the transfer floor (too low) was bad and a gap (floor too high) was bad for piston cooling.

[Frits Overmars]

it wouldn't be too hard to fit a thin divider, maybe. With a divided port you may simply be able to block off the upper portion when desired though that doesn't achieve engine throttling. It would increase blowdown when desired.

Like you say, it's no good for throttling, so at the moment it's no good for me. But apart from that, putting a curved divider in a curved duct may well improve the flow.
Because of inertia, gas flow through a curve concentrates against the outer wall; the pressure at the outer wall is higher than at the inner wall. This pressure difference causes cross flow turbulence, therefore flow resistance. This resistance is proportional to the ratio between the outer radius and the inner radius of a curve
(this is one of the reasons for wanting the largest possible inner radius in a transfer duct).

Let's look at an example: a curved duct with an outer radius of 30 mm and an inner radius of 10 mm. The radius ratio is 30/10 = 3.
Now we put a curved divider with a radius of 20 mm in the middle of that bend, so we will effectively have two curved ducts laying one on top of the other.
The radius ratio of the outer duct is 30/20 = 1.5 and the radius ratio of the inner duct is 20/10 = 2. Both have become less turbulent than the original single duct;
it more than outweighs the small loss of cross flow area caused by the divider's thickness and the wall friction which has about doubled, but which is small compared to the turbulent losses anyway.

Now you may wonder why we don't put even more than one divider in a curved duct. Well, we do, sometimes. Take a look at the airconditioning ducting in large buildings. From the outside you hardly see any curves; you see square angles. But inside there are series of curved dividers: less flow resistance, less need for power-guzzling fans and less turbulence-induced noise.
Now all you need to do is put curved steel dividers in the sand cores of the transfer ducts before you cast your cylinder .

[kel]

A very happy 65th birthday Mr TZ350. Congratulations you are now entitled to a gold card! (a subsidised public transport plan for senior citizens )
Have a great day Rob, see you tomorrow.

[F5 Dave]

Yeah happy birthday Rob.

[TZ350]

Yep, thanks ... I have been hanging out for my Gold card and free MNZ race licence, it is letter from the Queen next ...

[Bert]

Happy birthday Rob.
It will be great to catch up this weekend.


So the drinks are on you tonight.

[TZ350]

Happy birthday Rob.
It will be great to catch up this weekend.


So the drinks are on you tonight.

Yep as much as you can drink ... Beersies all round.

[Frits Overmars]

A blend of oygen and hydrogen atoms? We've got enough H2O over here, I don't really fancy drinking H2O2, and I don't think we can brew anything else from H and O. Nevertheless, happy birthday mate. Enjoy your Gold Card .

[breezy]

I've been doing some sketching based on the comma idea. I can be done, but I haven't yet figured out where to put the actuator linkages. These would get in the way of the coolant passages that don't show up on the sketches, so I'm not done thinking yet.
The lowered yellow comma reduces the transfer timing from 130° to 60°. That is an 80% reduction in area and a 91% reduction in angle.area, which should be good for idling at about 2000 rpm.
The second picture shows how the lowered yellow comma fits nicely between the transfer duct sidewalls and the piston.
The blue comma on the left disappears into the transfer roof when it's completely up, but it will show some leakage at intermediate positions. I think I can live with that.

Frits, with the exhaust ports sitting directly above all transfer ports and with what looks like a very small area of metal seperating them, wouldnt this cause problems from the exhaust gas heat, detonation, at worst, or heating up the fresh charge in the transfer ports. I would think the water cooling path to keep all this cool would have to be really targeted and cricial else disaster....

[Lucas M]

Hello, It´s me again,
Thank you for your reply.

Lucas - here are some guides that will let you see where to start.
The pipe lengths should be around 32% from piston to header end, and 66% from piston to diffuser end.
Having 50mm added to the header will for sure make the lengths all wrong.
The cylinder duct exit should be 75% of the total effective Ex port area, and the header start should be 100%, with an oval duct ( plus ears )
to promote Aux blowdown flow - with a smooth transition in the spigot from oval to round.
The rear wall of the Aux Ex is way too shallow, the exit radial angle should be to bore centre, with a pocket turn into the duct.
There is going to be a blowdown mismatch in the STA numbers at 190/130 , can you widen the B port without getting into the ring pins.
Also I can see that the B port is angled up sharply, this needs the roof ground flatter to say 10*, then epoxy the A port roof to 25*.
With no powervalve you should have the A port highest, then staggered down to B and C like a Honda RS.
Can you fit a programmable.
Having a 50cc make peak at 11500 means the pipe and ports are not matched, to use the rev potential of the little engines stroke.

Wobbly, you are right by giving me the percentages for exhaust lengths. Never calculated it, but now I can say, my header is too long, about 6%. Without lengthen the header, my exhaust fits nearly 100% with Frits rule of thumb.
The rear wall of the Aux Ex IS way too shallow, unfortunately there is not infinite space behind for good flow, because of the studs. Same for widen the b ports, but I will do what I can.
11500rpm is too low for racing, I realize this in every race. Around 12500rpm would be nice.
You earlier wrote something about the staggered ports like Honda RS. Jan Thiel wrote regarding to the Aprilia RS cylinder with power valve, open the b ports earlier gave a bit more power in low revs. What´s the knowledge behind staggering like Honda? (You wrote something about that in post #3259 of this thread)

That German forum might be just the thing for you, Lucas, because it mainly concentrates on your machine brand: Simson.
It's not an open forum, but what you can do is this: the power graph you posted shows a phone number. Dial it and ask for LuKas ().
He is one of the forum administrators. If you can convince him that you will be an asset to the forum, he may let you in.

One more thing: on 31 January the annual Tunerbattle takes place in Zwickau. It's a test bench competition for Simson tuners. Lukas can tell you all about it.
And one day before, on friday 30 January, many members of this german forum will meet in Zwickau and get drunk talk two-stroke. I'll probably be there too.
Maybe you can gate-crash . In fact I'm sure you can, because none of us knows all members by face. Just drop in. But don't tell them I told you.

Frits, I was expecting it´s the two strokes forum but I was hoping it would be an open forum. I know Lukas, but my thought is, these 2-stroke wizards will rather stay among themselves. The Tunerbattle in Jan 31st is already circled in my calendar.

[wobbly]

Flow divider plates do work very well - I did this on several Jatski setups where the carbs sat vertically and the manifold was a steep angle
into the reed valve on the side of the engine.
This was done to get the intake length correct, and there was no room sideways inside the hull.
The thin plate split the carb flow area in 1/2 ( well not quite as I offset the divider to try and bias some more flow on the short turn side - the
flow bench pitot probe said it worked wonders in cfm and velocity ) and ended up as the same thickness as the divider in the VF3 reeds.
I dont know exactly how much power this created, but adding 50mm to the intake length in EngMod said it was worth 4 Hp per cylinder of the twin, and
the whole mod setup made another 12 Hp at peak rpm at the crank.
The same idea works wonders on engines where the intake manifold is severely bent, upwards or sideways.
Dividing the inlet in 1/2 helps to equalise the flow entering the case,and along with staggered reed backups this bumps up power every time.

Re port stagger - the Aprilia has a powervalve plus full digital control of the ignition and powerjets.
In any engine - like KZ2 for example with no powervalve and a straight line ignition, the high A port with staggered lower B and C gives much wider powerband width
especially down low where the pipe is only just starting to work.
The high B port scenario was developed solely to enable much bigger Aux Ex port sizing above a low A port, as was need to give the very high peak and overev power numbers.
The powervalve and ignition took care of the midrange power.

[TZ350]

Hello, It´s me again, Frits, I was expecting it´s the two strokes forum but I was hoping it would be an open forum. I know Lukas, but my thought is, these 2-stroke wizards will rather stay among themselves.

Your project is very interesting, I would love to see more pictures and details of your work posted here as it progresses.