ESE's works engine tuner

[DSE]

DSE, I assume that your 'jumper' is what Wobbly calls his 'ski jump', the hump at the bottom of the exhaust duct. And yes, is there is such a hump, cooling it will be good.

Wobbly already commented on your exhaust drawings, so I will concentrate on your transfers. Contrary to what you have drawn, the A-ports should have larger axial angles than the B-ports. You may want to take a look at the 'leaning tower of Pisa' story below for both the axial and radial angles.

I also noticed that the inner radii in your transfer ducts, indicated with Ri, can be made be way larger than they are now; see the constant-radius inner radius in the A-duct drawing below.
Attachment 356682Attachment 356683 Attachment 356684

Mr. Overmars, I apologize to you for the incorrectly worded question.
I did not convey the essence in detail, I wanted to ask you about the cooling of the jumper in the exhaust duct of the cylinder.
In the photo of the 3D model of the cylinder, I made the appropriate sections to make this cooling channel visible. In fact, it won't be possible to get such a channel in the cylinder casting, so I thought about making it by drilling.
This is a cylinder of a go-kart engine, with a volume of 193 cubic centimeters.
This is just an example, since he is one of....the ones I did.
The models of the gas distribution channels that I listed above are the engine that I want to make, with a cylinder displacement of 250.
The stroke of the piston is 65 mm, the cylinder diameter is 69.5 mm.
I read about the Leaning Tower of Pisa carefully. Conclusions will follow.
I've taken into account your comments on the geometry of the channels, and I'll redo the 3D models over the weekend.

[DSE]

DSE, here is a quick sketch of my meaning.
I have tested the low boost port floor, with and without a hole in the piston.
With this system, the EGT is always lower ( due to more lost charge out the Exhaust, from the boost port ) and leaning it down does not gain back the power.
In the KZ engines we have been as high as 685*C EGT running C12 in the USA and have never had issues with the piston crown overheating.
We always have timing edge deto, well before the piston dome is in trouble , and that is with 50+ sprocket Hp.

Thank you, I read it carefully. There is something to think about.

[DSE]

DSE, here is a quick sketch of my meaning.
I have tested the low boost port floor, with and without a hole in the piston.
With this system, the EGT is always lower ( due to more lost charge out the Exhaust, from the boost port ) and leaning it down does not gain back the power.
In the KZ engines we have been as high as 685*C EGT running C12 in the USA and have never had issues with the piston crown overheating.
We always have timing edge deto, well before the piston dome is in trouble , and that is with 50+ sprocket Hp.

How do you track it?

[wobbly]

DSE, we have the best power EGT and the RAD from the test on the dyno.
Its easy to track the EGT, up to the point with one jet leaner , the temp does not increase.
That is the deto limit.

[DSE]

I use thermocouples, type K. The ones I made myself, the cases.

[wobbly]

Exposed tip ? , 3X bore from piston face ? tip on centerline of the header ?

[Frits Overmars]

I did not convey the essence in detail, I wanted to ask you about the cooling of the jumper in the exhaust duct of the cylinder.
In the photo of the 3D model of the cylinder, I made the appropriate sections to make this cooling channel visible. In fact, it won't be possible to get such a channel in the cylinder casting, so I thought about making it by drilling.

DSE, from your above post I gather that by ‘jumper’ you don't mean Wobbly's ‘ski jump’, but the center bridge in a T-shaped exhaust port. As Wobbly already pointed out, such a center bridge is not desirable. But if it is there anyway, it is certainly a good idea to cool it internally. Casting an internal cooling channel is indeed impossible (unless your name is Neil Hintz), but drilling is quite feasible.
Honda did this in their last NSR250 factory cylinders. I would love to show you the photos I have (and don't ask how I got them) but unfortunately me and my archive are currently not in the same country.

[DSE]

Exposed tip ? , 3X bore from piston face ? tip on centerline of the header ?

Actually, here is a thermocouple with a "hot junction".
Then I give it to the laboratory for verification.
Some spikes of up to 600 degrees Celsius are accurate. There is an error of 700 and 800, by 2 degrees.
Then I put it in a shrink tube, warm it up, and mount the plug.
I'm dressing the case.
Done.
Some buildings, however, are about 15 years old, maybe more ... it doesn't matter in principle.
The tip of the thermocouple sticks out in the large window, and purging takes place through the round hole.
I put it in the center of the collector section, 120 mm from the sleeve mirror.
That's about it.
(p.s. - . I really didn't quite understand about the 3 holes...maybe I missed something. I almost forgot, these thermocouples are for working on the stand) )

[wobbly]

The distance from the piston face to the position of the EGT probe in the header, should be three times the bore diameter ( square bore/stroke ).
That is a very strange method of shrouding the thermocouple tip, why is that even necessary?
The best EGT probes I have been using for over 10 years are Stingers from Exhaust Gas Technologies in USA - they have a 3 year guarantee, and are only around $70 USD .
I have bought literally hundreds of them for race customers, and never had a failure - the junction is completely exposed to get the fastest response time for data logging
on the dyno or at the track.

[koenich]

may i ask which engine are you using? do you have some pics and some dyno curves?

We always race in short and slow circuits so I've been forced to privilege relatively low rpm usage, having peak power at 12700 with a nice overrev and some hp earlier in the power range, but I'm happy for the torque figures we see, 11,4 Nm at 12400 at the wheel is a good result after just 2 races and a couple of dyno runs.

Derbi EBS with Bidalot cylinder - 19 HP and 10 Nm with peak HP around 13.500 1/min (at the wheel on a conservative Dynojet).

Well done with your cylinder - looks amazing, especially with the low revs! However, why not rev further to be able to gear shorter? If you gear for similar vmax your wheel force will increase...?

[DSE]

DSE, from your above post I gather that by ‘jumper’ you don't mean Wobbly's ‘ski jump’, but the center bridge in a T-shaped exhaust port. As Wobbly already pointed out, such a center bridge is not desirable. But if it is there anyway, it is certainly a good idea to cool it internally. Casting an internal cooling channel is indeed impossible (unless your name is Neil Hintz), but drilling is quite feasible.
Honda did this in their last NSR250 factory cylinders. I would love to show you the photos I have (and don't ask how I got them) but unfortunately me and my archive are currently not in the same country.

Mr. Frits, please take a look at these channel cross-section sketches.
Is it possible to consider such an interpretation of the cross sections of the purge channel profiles?

With the graduation channel, I'll probably work with the sketches before starting to build 3D models, and of course I'll show the result.
It probably wouldn't be a bad idea to attach a profile of the piston bottom, I didn't think about it right away.
I'm laying the piston with a sphere with a radius of 360 mm and a compression height of 30.5 mm.

I stopped at a connecting rod with an inter-center distance of 129 mm. At least this size seemed to me more optimal in terms of calculating lateral forces.... Well, what will happen with gas exchange and filling, it will probably have to be evaluated only in bench tests.
The engine is still being drawn and is in the stage of sketches and layouts.

[Frank S.]

Hi DSE,
just a small remark, Mr Overmars prefers to be called Frits😁
Keep on designing your personal 2T Engine and keep us informed🤗

Regards

[DSE]

Hi DSE,
just a small remark, Mr Overmars prefers to be called Frits😁
Keep on designing your personal 2T Engine and keep us informed🤗

Regards

It's clear. thank you.

[Gradella23]

Derbi EBS with Bidalot cylinder - 19 HP and 10 Nm with peak HP around 13.500 1/min (at the wheel on a conservative Dynojet).

Well done with your cylinder - looks amazing, especially with the low revs! However, why not rev further to be able to gear shorter? If you gear for similar vmax your wheel force will increase...?

we weren't able to find the right match with the original cagiva gear spacing, so we always lacked the right timing in super slow corners.. this low revs config helped us covering this problem.
anyway we'll develop some more during the off season to gain something revving higher.

in the coming weeks i'll have a pair of derbi (but euro3) cylinders to begin playing with. I want to finally develop a credible alternative to the very good bidalot kit.

[Frits Overmars]

Mr. Frits, please take a look at these channel cross-section sketches.
Is it possible to consider such an interpretation of the cross sections of the purge channel profiles?
With the graduation channel, I'll probably work with the sketches before starting to build 3D models, and of course I'll show the result.
It probably wouldn't be a bad idea to attach a profile of the piston bottom, I didn't think about it right away.
I'm laying the piston with a sphere with a radius of 360 mm and a compression height of 30.5 mm.
I stopped at a connecting rod with an inter-center distance of 129 mm. At least this size seemed to me more optimal in terms of calculating lateral forces.... Well, what will happen with gas exchange and filling, it will probably have to be evaluated only in bench tests.
The engine is still being drawn and is in the stage of sketches and layouts.

Thank you DSE. Yes, I prefer to be called just Frits, without the 'Mr' or even the 'Dr' that Germans seem to be so fond of.
And of course everybody is free to use the nickname he or she prefers on the internet, be you would make me happy if I could call you by your first name too.

Your posts raised a number of questions. And I guessed wrong with your 'jumper' so now I will simply ask instead of guess: what is a graduation channel?

Your engine has a 69,5 mm bore and a 65 mm stroke so it's definitely short-stroke which as you may know, is unfavorable for the specific angle.areas in a two-stroke engine.
Your 129 mm con rod length is less than twice the stroke. If I were free to design an engine, I'd use a rod/stroke ratio of 2,2 , so noticeably longer than you are planning to use.

You wrote that you studied the 'tower of Pisa' concept but it does not show in your drawings. Your axial transfer angles are steeper than the proposed values in my concept,
which is meant for a square bore/stroke engine. For your short-stroke engine those angles should be even smaller.

The most import radial transfer angle is the leading direction angle of the A-transfer port. Why make it 40° instead of 30° if you still enjoy the freedom of the designing stage?