ESE's works engine tuner

[TZ350]

Be carefull about what you measure when considering transfer ducts.
In Engmod the duct is defined as follows - not what many would think.

Yes, I had wondered about that too, makes sense, thanks Wob.

[TZ350]

Page 1140 .....

TZ, Hp is not directly proportional to cylinder capacity in two-stroke engines. It actually follows a 2/3 rds power law.

Hence for a 70cc v's a 50cc at 24hp you have 24 * (70/50)^0.6667 = 24 * 1.251 = 30.0 hp for the 70

Basically hp is directly proportional to cylinder bore surface area - hence the reason over square 2 strokes are so poor.

I tried ceramic coated pistons some years ago and that's what they did , get hot and help detonation. I wonder about these modern metal sintering ( laser welding metal layer by layer ) apparently you can change the metal as the component is built up. A piston could start off aluminium alloy and end up with say a copper finish layer on top, flash chrome over that. Perhaps?

Absolutely. Aprilia GP piston heads were polished to a mirror shine; piston heads for four-stroke competition engines are sometimes chromed. I don't know whether this chroming can be done by selective laser melting, but chroming the piston head in the conventional way has given good results.
If you want to protect the piston from combustion heat, covering its head with a heat barrier is not the way to go because of the detonation this will cause.
The only safe way I can think of is to reflect the heat. That way it won't get into the piston material and as soon as the combustion is gone, so is that heat reflection; fresh mixture won't be heated.

Wobbly Re:Ignitech .. What's your take on this reported problem http://www.pit-lane.biz/t3652p20-2-s...cc-development > post no.2

There are several issues that I have worked thru to get the Ignitech to work its best.
Firstly is that they like low impedance coils - that is low DC resistance ( 0.2 ohm or less ) primary and a high inductance secondary.
The Suzuki RGV or Aprilia RS125/250 are the best common coils available, but I have used Crane PS92N cdi coils on Methanol burning Hydros where spark power is super important.
Stock Honda RS125/250 and CR250 coils are way too high resistance/low inductance to work well with this type of DC CDI.
Using both cdi to drive one coil doubles the effective energy available at the plug, and this is the way to get more power from say a RS125 Honda, especially if you swap out the coil.
Lastly using simply a battery alone isnt the go at all.
The voltage drops quickly under load with this setup, the DC CDIs work best when run with a battery that is being charged by the alternator at 14.2V continuously.
There is only one setup of MX rotor and stator that will drive sufficient current into an Ignitech for it to work best when using a cap instead of a battery.
The stator must have a 2 ohm winding and the rotor must be the later type with super strong magnets - you can feel them " clunk " over each pole as you rotate the rotor by hand.
You can see the voltage at the CDI drop ( on the computer screen ) during a dyno run - if the power supply isnt working as it should.
And as usual, the posts reveal that they werent using a resistor plug and cap as Seb4LO also pointed out, along with using the proper NGK race plugs.
So the spark would be all over the shop, not at the correct time to make power.
I dont know the exact calculation sequence the software uses, but I have found by trial and error that the best setup if possible,is to ensure that the addition of the base advance to the lobe duration
should be around the max advance used in the curve.
Having said that I have built several CR250 kart engines that have stock 6* of base and around 15* of lobe length, but the engine strobed exactly showing the 32* max advance as programmed.
And lastly I found that a lobe longer than around 20* length makes the calculations go haywire, and it will misfire badly at one rpm, then go perfectly well everywhere else.
There is a software button that says " wide lobe " and also one that says " no lobe length check ", but trying to translate from Czech what these actually do is impossible.
I simply cut the lobe length in 1/2 and it worked perfectly.

Answering the first question - you can use twinfire as I call it, dumping 2 cdi into 1 coil in a twin - by purchasing a DC CDI P4.
This has 4 cdi in one box ( twice the size ) and uses a rather older version of TCIP4 software, but does everything you would need.
You will need some serious power supply capability to keep that system from pulling down the voltage.
Im doing exactly that in the new TZ400 im building with two of the huge Crane coils.

Re the header dimensions, the reason for the latest configurations is to try and get the best, widest spread of lowest depression in the cylinder, from the diffuser sucking on the Ex port
around BDC.
Initially the diffuser is actually too close to the port at the bottom of the powerband, and the depression max is too early in the cycle ( transfers not fully open for best bulk flow )
Then into the overev the max depression point is too late, as the transfers are closing.
So the header end point can be moved around a little to tailor the shape, and peak intensity point where we want max depression in the cylinder for best power at a certain rpm.

Thanks Wob.

I have a DC CDI-P running for over a year now. Pretty nice. Hope that ignitech will update software or change the hardware to tune the spark plug energy, as seen it could increase top end power...

On header entrance as example, if I remember, NSR 125 exhaust round exit is 37, and exhaust header is 38. DTR 125 round exit leaves at 32mm and the header in a famous aftermarket exhaust is 33. I am wondering if this is the rule of thumb to follow, or if it would be better to go 1,5 or 2mm wider instead of just 1mm that is sometimes the tolerance needed to eleminate outward kinks. Maybe I will try to go with a 25mm lenght round transition from 32 to 34 for example without any kinks.

If is was oval, then I would be wheel advised

Sorry if I am posting too many hard questions.

Thanks

The twin fire setup does not add any voltage at the plug.
The two cdi output capacitors in parallel,simply doubles the available stored energy.
This translates into exactly the same arc over performance but increases the burn time duration, as the caps energy is drained into the ionised gap.
The only other way to increase burn length is to increase the inductance of the coil.
Using a PC based oscilloscope with an ignition analysis app,I saw the burn duration at x4 using twinfire and a Crane coil, over a standard single cdi and RS125 coil.

Re headers, at this stage the duct exit, and header entry I can only define in relation to the port effective area.
For a racing T port or tripple port setup the header should equal the whole effective area, and the duct exit = approx 75% of the area.
A CNC transition from oval to round makes the best connection between the two areas, with the oval width the same as the header diameter.

For a single racing Ex port ( that is - 72% and around 200* ) the duct exit and the header entry should both be around 90% of the Ex effective area.

Frits has pointed out, and I completely agree that the relationships should be based on the Blowdown capability, but that would need some time to find the correlation.

Wobbly!

We have talked over how important the blowdown and it's size are, but what about the blowdown's intensity? If the aux exhaust ports are opening later as the main exhaust port, the peak of the pression is smaller, meanwhile the blowdown lasts longer. Of course the STA is always the same.

In case of almost every race cylinder the aux exhaust ports are opening later, and this can be observed in systems with or whitout a power valve. In case of a T port the top edge radius is not 0, but pretty much bigger.

Is it important? Why don't we open the ports the widest possible? That way the ports could be positioned lower what would be optimal.

There are two factors in play with the tripple port setup.
You have drawn them correctly with 68% main port width, as this allows greater blowdown area to be gained via the aux ports.
Out at 72% that has proven to be approx the reliable max width, you loose some blowdown, and gain total area. ( not relevant at all ).
The problem is that even at 68% you cannot run a flat port roof with 8mm corner radi, as the ring life will be zero.

Secondly is that it has been proven in many dyno sessions that having all 3 ports open together looses power.
I can only explain this as a function of the fact that the effective duct length from the outer corners of the Aux is alot longer than that from the main port
mid point to the header.
Thus you get a smearing of the initial wave amplitude ( wider but lower intensity ) as it exits the cylinder into the duct during blowdown.
This reduces the effectiveness of the expansion phase, creating less depression around BDC, and less plugging efficiency as the piston closes the port.

It would appear that having a 68% main port opening first gives a good, high amplitude wave action in the pipe, then the Aux STA gets the blowdown pressure dropped as much as is possible prior to the Trans opening.

A few pages back was a drawing I did years ago of a T port with the outer edges higher than the mid point, thinking that this would ameliorate the duct length issue, but later
testing proved it didnt work well at all.
So by inferrence even lifting the Aux higher than the main wont fix this issue either in a 3 port.

I also believed what I had been told previously ,that large changes in initial diffuser angle would cause flow separation and massive turbulence due to choking.
I built a heap of pipes to come up with a new design for CR125 Moto in SKUSA racing.
One of the tests was to try a design similar to the older Aprilia, with a very steep diffuser directly after the header.
This pipe made good power, but i was sure that if I added a short 25mm section ( the length of a bend segment in the U bend ) between the header and the main diffuser, with
only 1/2 the angle change - it would make more power.
Sadly no free lunch, it was worse by a small margin - bugger, another wives tale down the dunny.
I went on to discover the relationship of best power production, to the shape of the depression waves amplitude around BDC - was super critical to where the main diffuser started.

Trombone pipe

I am very taken with the Trombones possibilities and after using EngMod2T to simulate it.

oh got that wrong more than usual.......
can't find the post either ROB but found these.........

[Martin1981]

Be carefull about what you measure when considering transfer ducts.
In Engmod the duct is defined as follows - not what many would think.

the centerline wobbly. of course. wouldn`t think anything else.

[F5 Dave]

Be carefull about what you measure when considering transfer ducts.
In Engmod the duct is defined as follows - not what many would think.

That would be a fail on my part, but it was easy to measure with the rubber to hand

[seattle smitty]

Wait a sec, back one page, Husaberg quotes Frits talking about crevice volumes, about nooks and crannies, and citing an engine that had 20mm spaces between crank bearings and seals that "acted as pneumatic dampers on the crankcase pressure fluctuation," etc..

Come on, you're also talking about opting for longer rods and flat-sided crank throws and substantially increasing total crankcase volume . . . which would appear to constitute a "pneumatic damper" so large that these crevices amount to nothing by comparison. If the ancient practice of crankcase-stuffing has been obsoleted by the enormous crankcase clearing action of modern expansion chambers, what's this about "pneumatic damping"?? Slow-witted members like me need extra explanation.

(Seems to me Dave's method of measuring port volume would have more validity than a centerline measurement {a difficult measurement to make accurately, isn't it?}, even if it doesn't work with the particular program . . . ).

[husaberg]

Wait a sec, back one page, Husaberg quotes Frits talking about crevice volumes, about nooks and crannies, and citing an engine that had 20mm spaces between crank bearings and seals that "acted as pneumatic dampers on the crankcase pressure fluctuation," etc..

Come on, you're also talking about opting for longer rods and flat-sided crank throws and substantially increasing total crankcase volume . . . which would appear to constitute a "pneumatic damper" so large that these crevices amount to nothing by comparison. If the ancient practice of crankcase-stuffing has been obsoleted by the enormous crankcase clearing action of modern expansion chambers, what's this about "pneumatic damping"?? Slow-witted members like me need extra explanation.

(Seems to me Dave's method of measuring port volume would have more validity than a centerline measurement {a difficult measurement to make accurately, isn't it?}, even if it doesn't work with the particular program . . . ).

The crevice Frits referred to was inaccessible next to the mains, thus was not easily accessible. (Likely just stayed where it was.) between the bearing and the seal
The volume between the webs had to be paddled through, with those pork chop flywheels paddling it around, which is a loss. when compared to a smooth crankshaft just slicing through it.
Friction loss is why there should be a minimum of 1mm clearance all around the crankshaft faces to alleviate the boundary friction shear?(I understand it can be larger but there is little to be gained from any larger clearances)
The most useful place for the large volume is in transfers and directly under the transfer's. Ie where it can be readily accessed and passed into the cylinder.
Remember The longer rod has other benefits such as dwell.
Of all the ports in a two stroke engine the transfers are open for the shortest duration.
It also proves space for a nice large port on a disk valve engine under the cylinder

Anyway My take on what has been said by others....
The more clever wity one's will be along later to fill in the gaps.

I seem to remember something along the lines of there was more than a revolutions worth of mixture just in the transfers alone.
It was around total of 650cc in the crankcase and transfers for the RSW125, 675cc for the RSA125, but most of it is near or in the transfers.

[fpayart]

Is that with a 22 or 24mm pin?

20 mm only

[seattle smitty]

The crevice Frits referred to was inaccessible next to the mains, thus was not easily accessible. (Likely just stayed where it was.) between the bearing and the seal.

I get that it was unusable A/F mixture (probably mostly oil anyway), but why is it any more of a "pneumatic dampener" than any of the rest of the volume (of the transfers, the volume under the piston, between the crank-wheels, all of it)?? Compared to the total volume, I'd think that whatever the theoretical effect is supposed to be (and what is that, again???), the actual effect of that itty bitty space would be undetectable. Wakaranai, so far.

[Muciek]

Question about carbs and airboxes.
Sorry for hijacking the thread but there is question that bothers me lately.
Is there any rule of thumb of minimal length carb face- airbox wall that's not restrictive to inlet? Looking few pages back we can see airbox of NSR300 (that one which sucked into little bird) and it's huge , on the other hand there is Aprilla airbox which looks like there is very little space between carb face and wall of airbox.

[richban]

Question about carbs and airboxes.
Sorry for hijacking the thread but there is question that bothers me lately.
Is there any rule of thumb of minimal length carb face- airbox wall that's not restrictive to inlet? Looking few pages back we can see airbox of NSR300 (that one which sucked into little bird) and it's huge , on the other hand there is Aprilla airbox which looks like there is very little space between carb face and wall of airbox.

If you don't have much room. The polystyrene and acetone method looks to be very simple and quick. Just carve a block polystyrene to the shape you need. Rap it in fibreglass. Then just pour in some acetone and watch the poly disappear. Boom! Custom air box. It will not be super pretty but it will work. If you want a pretty one then you could then turn the fibreglass box into a mould.

This is how I was planning to do my 300 ram air. Still not got around to it.

[TZ350]

Chambers RG50 full reed valve inlet conversion.



Plenty of openings into the crankcase and cylinder.



Curved flow guide to aid air flow around the bend in the inlet tract.

Also if the dyno does not like the carb with a curved inlet approach Chambers can go to a straight shot pumper carb setup without the curved manifold. so plenty of options that can be explored on the dyno.



My more conventional setup looks positively restricted by comparison.

[TZ350]

To get my reed valve inlet lower I cut the back out of the cylinder so the bottom edge of the reed block housing will seal on the crankcase.




Both motors will be filled in where the original case reed was.

[wobbly]

Did the work on the dyno at ZipKarts for testing seat proximity on the LH drive Superkart.
The 256 Rotax at full noise with a 300mm square alloy plate just 8mm from the carb face - no difference in power at all.

Re the RG reed conversion, many 50cc racers in Euro use 30mm HV Lectrons, you can run these very steep due to no pilot circuit in the front of the carb.
I have a SmartCarb on one as per the pic I posted before about the short intake.

[F5 Dave]

TZ, Well you've got two weeks till the GP, plenty of time.


I made my RZ airbox with polystyrene, with a smear of plaster over it. Took a little bit of time to melt & dig it out but all doable in a morning.

[wobbly]

What Frits refers to re the volumes " hidden " behind bearings, and more relevantly those volumes contained within flywheel balance holes
is that even in my minds eye I can see that there is no way that these volumes can " flow " from these cavities into the transfer duct entry area.
Thus all they do is expand or contract due to the varying pressure ratios experienced within the case - thus are " dampers " contributing nothing but
to increase the overall measured volume.

Re the centreline duct measurement, most people seem to think that the transfer duct length ends where the septum divider is, and this is usually situated at the case/cylinder deck line.
Whereas the real duct begins around the corner under the piston/cylinder cutout - quite a bit longer in length, and way bigger in volume.
This is obviously anecdotally true in that a ball nose radius on the cylinder edge at the beginning of this real duct entry, can and does increase power.