ESE's works engine tuner

[wobbly]

Again I am amazed at the technology ( or lack of it ) in these small RC engines.
Its been shown by tests done years ago that a downward angle of 25* of the Exhaust duct roof gives the best compromise of blowdown flow and duct velocity.
But in the previous post we have a duct pointing upward , surely that alone invalidates any comparison with any other layout considerations.

[teriks]

The side and rear exhaust engines we tested had either liners or standard closed transfers. Quickdraw once made crankcases for both types that differed only in the bolt pattern and cutout areas for the transfers. I have one of each type that are going into the proposed opposed piston engine. The ringless piston engines used in smaller models don't seem to have the same issues, but I'm not aware of anyone who has done careful test comparisons. Boaters use a variety if bent headers to run all types of exhausts. Below is the most extreme, a 180 degree header. I've run one of these engines and it was definitely more powerful than the older rear exhaust version. However, the one piece design of the new version was stiffer along with a bigger intake and other factors.

Lohring Miller

Attachment 347803 Attachment 347804

That recons, re. your tests of different cylinder directions.
Those pictures are of ringless engines, right? If not, the 180degree one should be pretty darn similar to the rear exhaust with regards to potential ring/exhaust port issues.

Again I am amazed at the technology ( or lack of it ) in these small RC engines.
Its been shown by tests done years ago that a downward angle of 25* of the Exhaust duct roof gives the best compromise of blowdown flow and duct velocity.
But in the previous post we have a duct pointing upward , surely that alone invalidates any comparison with any other layout considerations.

That duct for sure looks odd. Id guess its to avoid the huge flywheel, in that sense, for sure a side or front exhaust would be better.

There are some quite clever RC engines though, the MB Profi for one.
https://fiorimet.home.xs4all.nl/

[Frits Overmars]

There are some quite clever RC engines though, the MB Profi for one. https://fiorimet.home.xs4all.nl/

MB is the brand that brought me into contact with model engines. In the mid 1990s physicist Rob Metmemeijer approached me with the problem that the power curve of his 6,5cc two-stroke engines couldn't handle the power absorption curve of his propellers. Either the engine would not rev past the torque dip at 2/3 of max. torque rpm, or the propeller had to be so light that the engine revved way beyond its maximum power rpm. Rob had heard some whispers about exhaust power valves and I happened to have the drawings of the Cagiva 500-4 cylinder (a carbon-copy of the Yamaha YZR500 cylinder) at my fingertips.
Surprise: a few weeks later Rob showed me a running 6,5cc power valve engine. Now here was a guy that I would like to work with! However, I felt there had to be a more KISS-like solution for the torque dip problem, so after visiting a couple of F3D model pylon races to see what was needed, I came up with an exhaust pipe that is now universal in F3D.
The pipe was followed by a hardchromed sleeveless cylinder (for an engine without piston rings, hardchrome is just as good as nikasil) with teacup-shaped transfer ducts and my idea of port timings and scavenging angles. The engine also got ceramic crankshaft bearings. The result is the current MB40 Profi engine. The '40' stands for the 0.40 cubic inch cylinder capacity and Profi is the Ukrainian firm that takes care of the serial production (everybody wants an MB40) while Rob Metkemeijer still builds the prototpyes.

[TZ350]

[lohring]

A long time ago a model speed engine builder told me that piston to liner fit followed by head button design were the most important factors for high performance. The first is due to the big effect of friction in these small engines. The second is because compression along with the glow plug wire diameter sets the ignition timing. All the things we worry about in larger engines are nice refinements. Our 26 cc gasoline engines definitely benefit from better transfers and ports. Frits' design definitely helped the 6.5 cc engine, but the cruder designs of the Nelson 40, now sold by Aero Racing Engines, and Jett engines are still competitive.

Lohring Miller

[lohring]

MB is the brand that brought me into contact with model engines. In the mid 1990s physicist Rob Metmemeijer approached me with the problem that the power curve of his 6,5cc two-stroke engines couldn't handle the power absorption curve of his propellers. Either the engine would not rev past the torque dip at 2/3 of max. torque rpm, or the propeller had to be so light that the engine revved way beyond its maximum power rpm. Rob had heard some whispers about exhaust power valves and I happened to have the drawings of the Cagiva 500-4 cylinder (a carbon-copy of the Yamaha YZR500 cylinder) at my fingertips.
Surprise: a few weeks later Rob showed me a running 6,5cc power valve engine. Now here was a guy that I would like to work with! However, I felt there had to be a more KISS-like solution for the torque dip problem, so after visiting a couple of F3D model pylon races to see what was needed, I came up with an exhaust pipe that is now universal in F3D.
The pipe was followed by a hardchromed sleeveless cylinder (for an engine without piston rings, hardchrome is just as good as nikasil) with teacup-shaped transfer ducts and my idea of port timings and scavenging angles. The engine also got ceramic crankshaft bearings. The result is the current MB40 Profi engine. The '40' stands for the 0.40 cubic inch cylinder capacity and Profi is the Ukrainian firm that takes care of the serial production (everybody wants an MB40) while Rob Metkemeijer still builds the prototpyes.

Are you sure I didn't braze that pipe? I'm about that neat with my brazed joints. I like the pipe below for real power.

LOL

Lohring Miller

[teriks]

MB is the brand that brought me into contact with model engines. In the mid 1990s physicist Rob Metmemeijer approached me with the problem that the power curve of his 6,5cc two-stroke engines couldn't handle the power absorption curve of his propellers. Either the engine would not rev past the torque dip at 2/3 of max. torque rpm, or the propeller had to be so light that the engine revved way beyond its maximum power rpm. Rob had heard some whispers about exhaust power valves and I happened to have the drawings of the Cagiva 500-4 cylinder (a carbon-copy of the Yamaha YZR500 cylinder) at my fingertips.
Surprise: a few weeks later Rob showed me a running 6,5cc power valve engine. Now here was a guy that I would like to work with! However, I felt there had to be a more KISS-like solution for the torque dip problem, so after visiting a couple of F3D model pylon races to see what was needed, I came up with an exhaust pipe that is now universal in F3D.
The pipe was followed by a hardchromed sleeveless cylinder (for an engine without piston rings, hardchrome is just as good as nikasil) with teacup-shaped transfer ducts and my idea of port timings and scavenging angles. The engine also got ceramic crankshaft bearings. The result is the current MB40 Profi engine. The '40' stands for the 0.40 cubic inch cylinder capacity and Profi is the Ukrainian firm that takes care of the serial production (everybody wants an MB40) while Rob Metkemeijer still builds the prototpyes.

Rob is quite amazing, not only theoretically clever, but extremely efficient in the workshop!
That pipe of yours in not very easy to improve upon, that's for sure.

A long time ago a model speed engine builder told me that piston to liner fit followed by head button design were the most important factors for high performance. The first is due to the big effect of friction in these small engines. The second is because compression along with the glow plug wire diameter sets the ignition timing. All the things we worry about in larger engines are nice refinements. Our 26 cc gasoline engines definitely benefit from better transfers and ports. Frits' design definitely helped the 6.5 cc engine, but the cruder designs of the Nelson 40, now sold by Aero Racing Engines, and Jett engines are still competitive.
Lohring Miller

Actually neither Jett nor Nelson is competitive in F3d racing, since quite some time.
While there are some other interesting F3d engines, the MB is the only one really commercially available.

[Frits Overmars]

I like the pipe below for real power.

Shortly after the first appearance of my F3D pipe, competitors started to rumble about "the Fat Dutch Pipe", so we decided to give them something to rumble about: a picture of an F3D model plane with one of my 125cc dyno test pipes. Left yours truly, right Robbert van den Bosch, many times European F3D champion and some time after this photo was taken, also world champion.
When we first met, I asked him what he did for a living. He answered: "Bus driver". It turned out he was a Boeing 737-captain. His reaction: "Same job, but it pays better".

Rob is quite amazing, not only theoretically clever, but extremely efficient in the workshop!
That pipe of yours in not very easy to improve upon, that's for sure.
Actually neither Jett nor Nelson is competitive in F3d racing, since quite some time. While there are some other interesting F3d engines, the MB is the only one really commercially available.

Rob (below) is an amazing person indeed. His daytime playing field is acoustics, for example giving the Royal Albert Hall a once-over, that kind of level. He got into building model engines because he and his late brother Bert took part (and became world champion) in teamracing, another branch of model flying.
Teriks' remark, that the MB40 engine is the only commercially available F3D engine, requires some clarification. From Robs standpoint there is nothing commercial about it: he builds his engines purely to keep the sport going and there is no profit in it for him. Everybody can buy his engines, but active F3D competitors are given priority on the waiting list to keep their chances even.

[mikebmeehan]

Great work Thomas! You are an intelligent person!:

[JanBros]

bought a KDX200 but sadly there are 2 cracks between the exhaust ports on the left. I'm in doubt as to whether have them welded and replated or have it sleeved. if welded, will they weld it through and through and not leave parts of the crack that can grow again? and if they weld it through, I'm in doubt as to if it will not harm the flow if the weld protrudes, hardly being able to correct that.
I know the downsides off sleaving, but it 's just for having some off-road fun, not to ride it at max like a pro.

also first time I've seen a raised exhaust port on a standard cylinder from the early '90ies

[F5 Dave]

Yeah they had a strange rotating power valve to open that and the rack and pinion arrangement used to seize and strip the gears.

Change of needle was best improvement on mine.

[wobbly]

The plater here would vee the crack out , weld it up , bore and grind it back , and replate .
Easy job.

[JanBros]

The plater here would vee the crack out , weld it up , bore and grind it back , and replate .
Easy job.

no problem's welding through and through to avoid re-cracking ?

[wobbly]

A few cylinders are simply a bad design ( 4DP Yamaha TZ ) that crack no matter what , but the weld material is stronger than the cast alloy , so usually the weld is more reliable.

[husaberg]

no problem's welding through and through to avoid re-cracking ?

Closer to your home
https://www.kiwibiker.co.nz/forums/s...post1130610635