ESE's works engine tuner

[wobbly]

Without making a comment on the actual effect of changes , what's going on with the weather correction for this software.
You have the difference between 19 to 25*C air temp and 0 to 60% humidity.
0 cant be correct , but is the air being corrected properly ?

[Peljhan]

Uh, I think I forgot to input weather data (correction factor) for red curve
Can't do it now, only when measuring. It is cheap software.

[wobbly]

Do you have a choice of Correction.

[41juergen]

@Wob: you mentioned some when that the distance of the spark plug tip to the piston shall be approx. 6 mm as shown in my sketch... is that valid for flat pistons as well for domed once or a setup with a straight angle/ flat dome?

[wobbly]

For a flat top I have been as close as 3.5mm , but only because the chamber was very small for Methanol.

[lodgernz]

For a flat top I have been as close as 3.5mm , but only because the chamber was very small for Methanol.

I always try to position the plug gap at the point where straight lines from the squish band meet.
Is that wrong?

[wobbly]

That works just fine for a dome , but of course cant be done with a flat top.
In that case its just a matter of juggling the toroid chamber shape and the spark gap position.
I dont know how much is too much as Ive never had a chance to test it properly , but I believe you can get the toroid roof too high , ie the plug boss down very low, and that this geometry may
affect the scavenging loop arriving from near the rear wall and travelling across the chamber.

[Peljhan]

Do you have a choice of Correction.

No, I can't even export it in excel or something else.
If we use only corrected blue and black curve, there is still missing complete power top on blue curve with new insert.

[dtenney]

Looking for a bit of help, please. Is there a standard or a formula for calculating the needed distance from the piston crown to the spark plug? This is for a square bore/stroke 85cc motor.

[Peljhan]

Looking for a bit of help, please. Is there a standard or a formula for calculating the needed distance from the piston crown to the spark plug? This is for a square bore/stroke 85cc motor.

I doubt you will find a formula for that. I had a gap lower than 1,5mm on 90cc (18hp) "square" aircooled engine. I was experimenting with head inserts and needed to put a 1,5mm shim under sparkplug in one instance to get more clearance. When I forgot to install a shim once, piston tuched the plug and engine didn't start. It was working fine with about 1,5mm gap, the only difference I saw was clear spot at the center of piston dome, but no detonations visible.

[jonny quest]

Thanks Frits



https://www.kiwibiker.co.nz/forums/s...post1130892885

Good catch Husa! No one had any information back then either!

[wobbly]

Peljhan , the factors in play to kill top end are MSV , that obviously has changed dramatically with the closing up of the clearance, compression , that should be the same cc
or finally maybe the head was deforming previously - as you said the new one was alot stronger.
In any case the instant result of any factor like this is a big drop in EGT - so you need to start logging this , as to get a real correlation between any two setups you should
be adjusting the jetting to hit a target egt number..
The fix is a reduction in ignition timing , past the point where the power graphs cross.

Re the plug position , the pointers for this exist in Jan finding that a flat roof " bathtub " chamber gave better power over a simple part spherical shape, that pulls the plug gap down closer to the piston.
Then we have the toroidal shape , that pulls the plug down even further , and testing I did showed this was absolutely the best for a flat top piston.
The only other factor as mentioned before was my feeling that having a very deep toroid roof , with a large plug boss intruding into the combustion space , may ideologically seem good for flame front positioning
but could in fact start to disrupt the scavenging loop flow.

[41juergen]

Thank's a lot for all the feedback!

[Wos]

Very very interesting Diskussion... answers about head, flat top, domed, distance plug...squish and the special influences😎 wow...😲

My next question

the angle of squish band to the head shape ending to ...for example " bathtube"...


Which is optimum " crossing" angle of both geometric " flow directions"?

Crossing 90 degree?... thats what i do🤔

or with flow from head in direction of squish?...angainst it🤔✋

Thanks for continuing exiting answers✌🥰

Wolfgang

[wobbly]

In my dyno testing of heads for a flat top piston I tried three geometries of chamber outer wall with the toroidal shape.
Each was optimized for ignition timing and best power egt.
First was a wall at the bowl edge of 90* that then formed a radius into the toroid roof shape.
This needed less ignition and a bigger jet , compared to the original flat roof semi tophat shape - background detonation level was considerably less , and power was up the front side nearly 0.5 Hp and around 1.5 Hp in overev.

Next was a radius all the way to the bowl edge that was 30* from vertical at the intersection.
This needed the same setup as above but made around 0.3 to 0.5 Hp more everywhere.

Last was a straight wall @ 60* up from horizontal , then forming the toroid roof radius - so the radiused roof was higher to achieve the same cc
This needed more ignition , and a smaller jet , but the power was much the same as the tophat example.

Squish and cc were all identical and had no radius on the squish/bowl edge , just the sharp corner broken with wet and dry.
I wish i now had the opportunity to try chamber shapes with the latest piston , having a conical squish , transitioning into a flat top with 50% bore area.
This is the shape I used in the BSL 500 , but only with a bathtub , as that is what Jan had found worked best at the time.