ESE's works engine tuner

[Pagi]

Woobly, Frits,

what do you think of the values?.......

[Grumph]

OK for Formula Libre .... tough for 'Historics'. Can we please have a simple analog thermal controlled main jet?

How about a separate slide for the air correction circuit - as Amal GP and TT and several other carbs.

Hugh Anderson reckoned to use the air control to get the small Suzukis up to temp and then stop them seizing once hot.

[Wos]

...like wobbly called it...are very delicious! 😉

To wobbly and frits...all others too

I ve been aiming a MSV of min 33 m/s at peak power (10 000 or 11 000 rpm) in our classic enduros aircooled racers...and we definitely recogniced that we need less ignition timing and that there is a limit where we gain no more power by ignition...

Is there a rule of thump if we improve the MSV further ...within the " rule of thump 1 % squish ".... to how much we can set ignition later?

Were we need less ignition timing?

Think if begin resonance is working earlier with high MSV .. . we can/ should reduce ignition timing earlier...

And after reaching resonance area???

Think MSV influence on ignition point getting smaller because we have better fuel charge?

Next free lunch please!

Thanks and Grüße!!!

Wolfgang

ps frits !

...jan schäffer is well known in germany..top ...not my direct friend...but i am impressed by his sucesses in simpson or liedolsheim races were we took part 20 years ago with Kreidler 😀

[wobbly]

A BiMetalic strip on the head opening and closing a tube connected to the air corrector inlet would be accurate and analogue

[wobbly]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

[Wos]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

Hey wobbly,

Tanks to you at nearly midnight here! 😉

Start point at 38 m/s at which rpm?

Power incerease realy?? This would be wooow!? 😀

Excuse my question... 😉 if i am right...that was never carified in special context here.. but very interesting point...😀 for a hobby 2 stroke addicted like me

Merci!

[Wos]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

Like ktm, yamaha and so on do today???

With a bevel 12 degree on pistons upper edge???

Dosnt that trap end gases in squish gap!?
Provocate detos?

Arnt they completely wrong? 🙃🤔

Only commercial thing of easier produdction???


Confused as i am!! ✋🤔🙃

[wobbly]

The squish band in the head should always be colinear with the piston , be it flat . radiused or conical, and as small a vertical clearance as is mechanically viable.
I can only give definitive guidance over what has been done in KZ racing over the last 4 homologation periods , that is 3+3+3+4 years.
initially there was domed with a bore tangent of 12* - next was a conical piston with a 7* rise , this was accompanied by higher axial transfer roof angles.
Then a 4* conic , again with increased transfer axial , lastly they used my design with a 4* conic changing to a 50% area flat top.
The last change was worth 0.5 to 1.5 Hp back to back on the same transfers.
A flat top looses around 1 Hp back to back against the latest setup, having to use a part spherical chamber design.

BUT , I have done testing previously where combustion volume and shape isnt limited ( 125 MX engines ) , and a flat top with a proper toroid shape , and more transfer axial is easily the best.
This shape has the least piston heat soak area , pulls the spark gap into the middle of the chamber , and also puts the initial expanding combustion bubble right in the firing line of the
turbulent eddies off the squishband edge , creating faster burn speed across the chamber.
This is analogous to advancing the ignition timing without the downside of pumping losses due to extra compression force when approaching TDC, after the gap has been ionized.
I would use this in a heartbeat for KZ , but the heads outer toroid shape traps air when cc checking per the rule book.

From all the testing I have done my setup of choice would be the flat top , with a piston edge radius , omitting the radius over the boost port or even better lifting the boost port floor well
above BDC to stop flow attaching to the radius and pulling it down toward the Exhaust exit , increasing short circuiting and ruining the scavenging pattern.

[Frits Overmars]

Woobly, Frits, what do you think of the values?

Acording to the port shape concept below the minimum safe vertical half-axis for a 74% wide elliptical port should be 17,7 % oif the cylinder bore.
Converting this ellipse to a multi-radius port (with the ELLIPSE program that you can find in my FOS software) gives corner radii of 11,4 % and a center radius of 67 % of the bore.
So your 12% corner radii are OK Pagi, but your 210 % top center radius is far too flat (your 50 % bottom center radius is OK though).

By the way, a 74% wide port with safe radii is no better than a 70% wide port that can have a larger center radius and smaller corner radii, offering more flow area on top, where it counts, because that is the area that is open for the longest time.

[Frits Overmars]

I have found 38M/s is a good start point of power increase vs not restricting overev too much.
But MSV calculations are just a guide as if done properly the piston will hit the head not long after peak useable rpm.
This ensures the least chance of deto , as with no end gases trapped in the squish , they cant detonate.

For me, Maximum Squish Velocities are not even a guide. Like Wobbly I prefer to make the squish gap as tight as is mechanically possible. I have never yet seen an MSV calculator that takes the dynamic stretch of a high-revving engine (about 1% of the stroke) into acoount and as a consequence their quoted MSV values make no sense at all.
Below you'll find a comparison of MSV values for the Aprilia RSA.
Without taking dynamic stretch into account the MSV would be 63,95 m/s. With 1% dynamic stretch the MSV appears to be 144,21 m/s. Some difference, isn't it?

[Pursang]

A BiMetalic strip on the head opening and closing a tube connected to the air corrector inlet would be accurate and analogue

Thanks wobbly, for that idea.

Carburetted Toyota's used lots of these for vacuum switching in various emissions control systems :


Different models/colours probably have different opening temps. One schematic I found said it was opening at 104 deg F. (40 C.)

Yamaha used this one in outboards:


Still Looking for an adjustable one (or one operating around 70C.)

[Wos]

Thank you wobbly 👍

"lastly they used my design with a 4* conic changing to a 50% area flat top"

Thats exactly what we do with flat top pistons from yz 125 yamaha or ktm with a steep bevel 12 degree of the piston axis...!!!!

Instead frontal colliding squish that partly eleminates energy
idea was to gain a force/ direction upwards to spark plug when squish is colliding in the middle of piston...

Little bit like frits concept with a domed one...

Second reason was to avoid a trap in squish, which the 12 degrees bevel without having its conterpart in head is!

Yes in stock there is a trap 🙃

3. Hard to do and proof the bevel in head beeing flush and parallel to piston

4. There has to be an energy loss / MSV loss with an angel of 78* in squish gap... 🤔



The yamaha has very steep a (35 degree) and b ports ( 25)

Ktm year 17 a is under 20 degree

Grüße! Wolfgang

[Pursang]

Bit more info on bimetal vacuum valves from a 4WD forum:

90925-05035 (violet) opens at 44°C (111°F) and closes at 30°C (86°F)
90925-05046 (pink) opens at 19°C (66°F) and closes at 5°C (41°F)

90925-05035 controls EGR, Primary Vacuum Advance and Evap.
90925-05046 controls the Choke Opener System.

90925-05047 (blue) was used in a broad range of applications from Corollas to 4-Runners, ~ ’87 – 94.
Picking one at random, it was used for the EGR systems on the 1988 MR2.
The FSM for that car states that the valve should open at 54°C (129°F) and close at 35°C (95°F).

[Flettner]

Nah, just run a disc valve motor, that way you can run efi without anyone anyone knowing. 😁

[Wos]

For me, Maximum Squish Velocities are not even a guide. Like Wobbly I prefer to make the squish gap as tight as is mechanically possible. I have never yet seen an MSV calculator that takes the dynamic stretch of a high-revving engine (about 1% of the stroke) into acoount and as a consequence their quoted MSV values make no sense at all.
Below you'll find a comparison of MSV values for the Aprilia RSA.
Without taking dynamic stretch into account the MSV would be 63,95 m/s. With 1% dynamic stretch the MSV appears to be 144,21 m/s. Some difference, isn't it?

Tanks Frits,

One of best things in life...are Kisses😛🥰... when piston kisses head...slighty an smooth😋👍😎

If i am right, rsa had 0,7 mm squish!?

This is more than 1%?

Reason?

Dont know the stretch of all involved parts at the yz 125 at 13000 in overrev... 0,7 works...no marks on piston... mayby next 0,65...

The only way to find minimum gap... seens to risk piston kissing head??? 😉🥰 ...😅🤣

Other ideas???


Tanks meister!

Grüße at all!


Wolfgang