ESE's works engine tuner

[SwePatrick]

I can´t see the reason why one would like to aim more gasses in the rear of the cylinder against the exhaust?
As 'normal' with a hook, you got mainflow against eachother with the B ports.
And the hooks helps flip up the gasflow upwards to make it easier for the C port to lift it up.

[adegnes]

I can´t see the reason why one would like to aim more gasses in the rear of the cylinder against the exhaust?
As 'normal' with a hook, you got mainflow against eachother with the B ports.
And the hooks helps flip up the gasflow upwards to make it easier for the C port to lift it up.

But with slightly different wall angle as I mentioned maybe? Aim them more towards the C port to make up for the lost hook and make them less prone to shoot straight out the exhaust.

[teriks]

Pretty much exactly like this:

Well, a later design is not as radical on the B ports.
Is the newer design better? -I have no idea..

[peewee]

I would think that a B-port designed as Adeg is suggesting would cause less trapping efficiency. I would think that the port's speed would be on the high side causing more mixture to be lost to the Exh port, but then again on the reverse pulse from the pipe, the stronger stream may mix less with the exhaust and purity might go up? As Adeg has said, my common thinking has been proven wrong multiple times on these 2 -strokes.

Wobbly, you are saying that the port 'with NO hook' had better trapping efficiency?

a hook is like what honda did for so many years on dirt bikes. cr500 is good example. yamaha banshee is another. its old school and crappy but back then i guess nobody cared. i think what wobbly said is the radius back wall like most any modern cyl works much better than stone age honda hooks

[katinas]

After testing KTM SX 50, the results showed, that maybe rounded piston bigger radius (with sharp edge at C), requires little bit bigger ex. stinger area. Maybe is some coherence between radius and stinger dimensions, but we need more tests.

In theme about head inserts.
Very interesting, after our discussions about head insert alloy, last week I had call from one MX sixteen years girl's mother, to help about cracked VHM insert on their KTM SX 125, because before the last race she was leading in 125 class, just only boys around and new head can be arrive only after race.
Crack was in the middle of the sphere, aprox 20mm long, directly at water outlet side (sorry not made photo) and squash band with easy detonation sign. Made new insert from 2618A alloy
Last weekend girl won championship, first time in our country MX championship history.

[Ocean1]

Possible stupid question.

Isn't it likely that port shapes found optimal for small engines are not optimal for higher displacements?

How similar are the respective flow velocities? Are there likely to be differences related to boundary flow ratios?

Or are demonstrably ideal 50cc port details going to be able to plug directly into that CR500 with proportionately improved results?

[Frits Overmars]

After testing KTM SX 50, the results showed, that maybe rounded piston bigger radius (with sharp edge at C), requires little bit bigger ex. stinger area.
Maybe is some coherence between radius and stinger dimensions, but we need more tests.

Hopefully there is some coherence between radius and power, and there is definitely a coherence between power and restrictor size.

Isn't it likely that port shapes found optimal for small engines are not optimal for higher displacements?
How similar are the respective flow velocities? Are there likely to be differences related to boundary flow ratios?
Or are demonstrably ideal 50cc port details going to be able to plug directly into that CR500 with proportionately improved results?

I'd say that port shapes are scalable between engines with identical bore/stroke ratio and identical piston speed.
Boundary layers are not scalable, but this influence should be moderate, provided the dimension ratios between the big and the small engine are not extreme.
The proportions between a CR 500 and a 6,5 cc engine are extreme, but I expect that there'll be a reasonable scalabily between a CR500 and a 50 cc engine.
Which is not to say that you should try it: 50 cc-like tuning will turn a CR500 into an unrideable beast.

[katinas]

Hopefully there is some coherence between radius and power, and there is definitely a coherence between power and restrictor size.

Yes, with rounded piston on SX 50 first time engine overcome 14 hp and graph is higher everywhere in rpm range, but only after little bit bigger ex restrictor, not like with SX65/85 when roundness work immediately without any changes.
So, engine power, at some point with smaller restrictor, can be worse with rounded piston edge than with sharp.

[lohring]

Hopefully there is some coherence between radius and power, and there is definitely a coherence between power and restrictor size.

I'd say that port shapes are scalable between engines with identical bore/stroke ratio and identical piston speed.
Boundary layers are not scalable, but this influence should be moderate, provided the dimension ratios between the big and the small engine are not extreme.
The proportions between a CR 500 and a 6,5 cc engine are extreme, but I expect that there'll be a reasonable scalabily between a CR500 and a 50 cc engine.
Which is not to say that you should try it: 50 cc-like tuning will turn a CR500 into an unrideable beast.

I think friction effects, especially piston friction, overwhelm other considerations in really small engines. Except for Frits' design, most Schnuerle ported model engines have 2 or 3 transfer ports with the poorest passage designs. Maybe boundary layer effects are starting to restrict flow with the small passages in 5 transfer designs. Really small engines (as small as .01 cubic inch or .16 cc displacement) use an opposed exhaust with opposed transfers. Their success can be attributed to the high precision piston and cylinder manufacturing process.

Lohring Miller

[jonny quest]

https://m.youtube.com/watch?v=qQFx1jmgiic

Plasma spark hack

[adegnes]

https://m.youtube.com/watch?v=qQFx1jmgiic

Plasma spark hack

So basically a very small cap in parallel with the sparkplug, larger cap value makes it more "fierce".
Like a spark gap protection circuit.
Does it contain more energy though, or is it just sparking multiple times after each main event as the cap reaches high enough voltage?
Must add that I have no clue...

[F5 Dave]

. . .
The proportions between a CR 500 and a 6,5 cc engine are extreme, but I expect that there'll be a reasonable scalabily between a CR500 and a 50 cc engine.
Which is not to say that you should try it: 50 cc-like tuning will turn a CR500 into an unrideable beast.

You just know of course that a certain, rather large portion, of readers were breifly excited and entertaining this idea

Some longer than others.
Some mentally adding additional cylinder banks

[Ocean1]

I'd say that port shapes are scalable between engines with identical bore/stroke ratio and identical piston speed.
Boundary layers are not scalable, but this influence should be moderate, provided the dimension ratios between the big and the small engine are not extreme.
The proportions between a CR 500 and a 6,5 cc engine are extreme, but I expect that there'll be a reasonable scalabily between a CR500 and a 50 cc engine.
Which is not to say that you should try it: 50 cc-like tuning will turn a CR500 into an unrideable beast.

So, if capacity isn't constrained, is just another tuning variable within an open racing class then where is the likely optimum capacity point?

If any one of the current capacity limited racing classes had that constraint removed then what would the trend be? Towards slightly larger engines based on similar tuning factors because it's easy power with few comparative disadvantages, or towards significantly more capacity with all of it's associated mass issues and likely tuning discrepancies but hugely flexible power?

Or does that depend entirely on the track size and surface? Case in point: I think the difference between 250 and 400 MX lap times are negligible, more dependent on minor track variations than available power, and I think from track to track the respective advantages for each is close to 50/50.

[Ocean1]

You just know of course that a certain, rather large portion, of readers were breifly excited and entertaining this idea

Some longer than others.
Some mentally adding additional cylinder banks

But we're more excited by the intellectual exercise than the vulgar prospect of vast quantities of unseemly torque.

Aren't we?

[adegnes]

But we're more excited by the intellectual exercise than the vulgar prospect of vast quantities of unseemly torque.

Aren't we?

Indeed.
......