ESE's works engine tuner

[Mike Fisher]

I've just looked at Vrooam, is it the Factory or the Castor Blend you recommend, both seem to be descibed as having castor and synthetic components? I presently run Rock Oil Kart 100 which is a castor synthetic blend formulated for air cooled motors at 20:1 in a 370 Bultaco Astro used for short track, mainly 300m ovals. https://rockoil.co.uk/products/castor-kart-100/ I aim to gear to 9500rpm and to keep CHT under the plug washer to 215C.
Going right back to Gordon Jennings, in 1978, he ran tests on a PE250 that showed a power increse upto 15:1 with R40 thta is available here: https://vintagesleds.com/library/man.../oilpremix.pdf

[Frits Overmars]

The ignition curves for 2-stroke engines that I see here and there always start low in degrees, then rise steeply to +/-30 degrees and then drop back down at the start of the power band. Around max hp and rpm to 15° and from there further down. An almost flat curve of 15.5° is very different from the usual curve shape I describe above. Would that still be useful in practice?

Indeed, most ignition curves start with their timing close to TDC to avoid kickbacks or even running backwards when starting. Then they switch to as much as 30° before TDC in order to have a lengthy expansion phase between end of combustion and exhaust opening, so the exhaust gases have lost most of their energy by the time they enter the pipe. That way the pipe cannot mess up the scavenging quite so much at revs that are too low for its layout.
But there are other options. Yes, at 2/3 the rpm of max.torque all pipe pulses arrive too early, messing up the scavenging. But what happens even lower in the rpm band?
At 1/2 the rpm of max.torque both the suction pulse and the stuffing pulse arrive back at the cylinder before BDC. But after this, the exhaust port is still open for a long time, so a secondary suction pulse and a secondary stuffing pulse can still manage to arrive at the cylinder before the exhaust port closes. And these secondary pulses can do some good, so it may not hurt to keep some energy in the exhaust gases at these low revs, i.e. start combustion closer to the 15° before TDC-region.
This still does not answer the question about your flat-line ignition curve. I did notice one thing about it though: the burn duration in your EngMod screenshots is extremely short....

[Jan Van Hamme]

Indeed, most ignition curves start with their timing close to TDC to avoid kickbacks or even running backwards when starting. Then they switch to as much as 30° before TDC in order to have a lengthy expansion phase between end of combustion and exhaust opening, so the exhaust gases have lost most of their energy by the time they enter the pipe. That way the pipe cannot mess up the scavenging quite so much at revs that are too low for its layout.
But there are other options. Yes, at 2/3 the rpm of max.torque all pipe pulses arrive too early, messing up the scavenging. But what happens even lower in the rpm band?
At 1/2 the rpm of max.torque both the suction pulse and the stuffing pulse arrive back at the cylinder before BDC. But after this, the exhaust port is still open for a long time, so a secondary suction pulse and a secondary stuffing pulse can still manage to arrive at the cylinder before the exhaust port closes. And these secondary pulses can do some good, so it may not hurt to keep some energy in the exhaust gases at these low revs, i.e. start combustion closer to the 15° before TDC-region.
This still does not answer the question about your flat-line ignition curve. I did notice one thing about it though: the burn duration in your EngMod screenshots is extremely short....

Those duration values are my fault.
I will have engmod generate the vibe and combustion parameters itself and then enter all these calculated values and repeat the entire process of searching for max hp per +0.5 degrees.

[Wos]

So just to reiterate, yea all of the castor based oils work fine in pump gas, and yea they all make more power at 20:1.
Buckets , whatever, are no different.

Wobb!!

Soory... christmas days i read not verry carefully

Thank you so much for repeading!!!
Sounds the parts will lif very much longer


What are the diffreces in reading the spark plugs?
Castor blends readable?

Recogniced that motul variates from black to light grey colors when others, for example ravenol fullsynth ester do variations in brown...

Merci!! ��

Wolfgang

[wobbly]

Mike F - its the Factory version of Vrooam, I have not tested the other type as its not available here.
I really just don't get why you, with plenty of experience and intellect , tell me you are attempting to tune with a CHT, that tells you absolutely nothing except how hot the plug washer actually is.
As I have said a 1000 times EGT tells you exactly the state of combustion, and allows incredibly simple tuning for peak power with any Density Altitude to within 1 jet of deto, in any engine.
In the tests I did I started with a baseline of R40 at 16:1 as per Jennings, but the modern castor based mixes made more power with less oil at 20:1.

Re the ignition curve testing - when off the pipe the scavenging efficiency is crap so the combustible mixture is full of residuals thus the burn speed is much lower as is power.
With a bunch of advance this gives time to at least use what energy is in the fuel that is available, and the biggest upside is that throttle response is hugely improved.
Further up into the powerband a similar but reduced version of the same effect is in play, but then we have the downside of increasing losses due to compressing the rising pressure from the increasing burn speed,
thus less advance is needed.

The whole idea of advance manipulation is as Frits described, plus as the combustion " cleans up " then the point of maximum cylinder pressure needs to trend toward 15* ATDC for peak effective use
of the rising pressure pushing on the piston.
The other side of that coin is the optimum crossover of burn duration Vs compressing losses is 15* BTDC that we all know is where most well tuned ( ie the correct compression ratio for the fuel ) engines end up at peak power.

We have the exact scenario being asked about in the KZ engines, with a flat line ignition set at about 17* BTDC in stock form.
This requires a very short pipe ( 760mm ), as there is way to much advance past peak power.
When these engines are retuned for road racing say, then the pipe reverts to the normal 800 mm TL, and the ignition , that is now adjustable, does the normal 30* dropping to 15* at peak, then down to 10 or so in the overev.
This gives a huge increase in power everywhere ( peak power much the same ) - except if a bigger carb is added.

Wos, see my remarks to Mike above, I refuse to answer any questions re tuning by looking at plugs or pistons - except the burn line on fine wire ground electrodes, but even then the ignition timing
should have been well established on the dyno, long before looking at plugs at the track.

[Jan Van Hamme]

I did notice one thing about it though: the burn duration in your EngMod screenshots is extremely short....

I think that a fast combustion time achieved by the high squish speed, the 55% squish band and the transfer scavenging angles used is not a bad thing?
When I let Engmod generate the combustion parameters, those duration values are back in the same range as before.
I hope that i can assume that my Zeeltronic PDCI-15V with 100 mJ spark energy en high energy Zeeltronic coil ZK3550 can still pull the spark in that "gust of wind"?

[wobbly]

JVH, the issue with " high" MSV is that this is analogous to adding advance due to the increase in flame speed, but to prevent deto you have to pull timing out.
What is " high " - and I am suspicious of any build that has 55% SAR.

[Wos]

Called Maxima !!!
We are so exited wobb... how maxima smells

[Jan Van Hamme]

JVH, the issue with " high" MSV is that this is analogous to adding advance due to the increase in flame speed, but to prevent deto you have to pull timing out.
What is " high " - and I am suspicious of any build that has 55% SAR.

Wobbly,
How I arrived at that 55%:
I set the ignition to 15° at maximum HP engine speed.
I selected the stinger diameter at which the MACH value in the nozzle is around 0.9.
Then I set the compression so that there is no detonation.
And to get msv to 40m/s, I had to go up to 55% squishband.

I don't know how strong that "high" energy coil is myself. The term ‘high energy’ is on the packaging, but that doesn't really say much.
Perhaps those of you with extensive knowledge of materials and product experience know what that type is capable of.

[husaberg]

Hi is logging in issue with Neels (vannik) sorted?

[wobbly]

Just sent an email to Neels.