ESE's works engine tuner

[Frits Overmars]

There is a relationship between how wide you make a port, and how gradually it should widen in order to keep the ring healthy.
With a good ring, 70% chordal of the bore is the optimum width. If you make it any wider, the widening has to be so gradual that you loose surface area at the top, where it counts most, because that's the area that opens first and stays open the longest.
The drawing below shows that with too wide a port you have to sacrifice the yellow areas at the top. But sacrificing those areas costs blowdown angle.area. That red port may have more open area, but not where it counts, at the top; the blue port is better.

[Frits Overmars]

Unless you keep the revs really low, a single exhaust port with a 70% chordal width does not give sufficient blowdown time.area, but because of the reason I explained above, making the port wider will be even worse. You will either have to use a bridge, add auxiliary exhaust ports, or raise the timing of the single port to well above the 190° that is optimal for pipe resonance.

The Aprilia cylinder is extreme in that respect: the middle exhaust port is 38 mm wide (older versions were 40 mm wide) and there are huge auxiliaries but even so the middle port is raised to 196° and then it gets a large radius at the top. The radius makes it difficult to measure the timing but if you shove a piston ring in the bore until you can just see light between the ring and the bore, you will find an exhaust timing of 202°. Don't try this at home, unless you want your engine to produce its maximum power at a mean piston speed of 23.6 m/s. But then your transfer time.area will probably be insufficient. And you know: if you raise the transfers, that will eat into the blowdown time.area.

Why does Aprilia use an exhaust timing that is too high for optimum resonance? It is a compromise: any lower, and the maximum torque will rise, but the reduced blowdown time.area will cause an early torque collapse and the product of torque times revs (yes, that's power) will be lower.

[wobbly]

The Rotax 24/33 rear cone was dropped in Superkart racing when I discovered that a single 28* made more power on the dyno.
This led to the development of the so called Silverstone pipes that we made when I worked for JL when he was still in England.
These won dozens of World and Euro titles.
I have spent days of dyno time testing multi angle rear cones, and have always been able to achieve the same or better power with a single rear of the right angle.
In many cases the sim likes a sharp rear cone, but in reality its no better.
Seems to me that the main reasons you got better power with the modified pipe, was down to a gradual front nozzle, stinger nozzle, and a way shorter tuned length.

[TZ350]

The cylinder is extreme in that respect: the middle exhaust port is 38 mm wide (older versions were 40 mm wide) and there are huge auxiliaries but even so the middle port is raised to 196° and then it gets a large radius at the top. The radius makes it difficult to measure the timing but if you shove a piston ring in the bore until you can just see light between the ring and the bore, you will find an exhaust timing of 202°.

I would be very interested in the Aprilias port STA numbers.

[Yow Ling]

How does this gearbox work? It a 1968 Jamathi, looks like an 8 speed but doesnt have the usual selector drum, forks etc.
Is the method of operation similar to the new seamless hondas? Can you shine any light on this Frits?

[husaberg]

The good news is that y'all did think about it, and that is what I hoped to accomplish.
Husaberg is right: 'the ports will serve to remove heat from the cylinder'. But then he spoils it by saying: 'the cooling system will...be cooling the transfers'.
Koba seems more cautious. And he is right too. Heat transfer: yes. But from where to where?
'Cooling fins' is a misleading expression, deliberately in this case, because I tried to set you on the wrong foot. I should have called them by their scientific name: heat exchangers....
The cylinder material will always be hotter than the fresh charge in the transfer ducts. So these 'internal fins' will cool the cylinder to the detriment of the charge density. Not good for power....

What did you think of the 1958 Clarke engine Frits.
Wob had seen one. In CHCH of all places.

I understood you were playing devils advocate a little bit there......... What i was attempting......
(more than a little clumsily no doubt English is my first language yet you write it better than I do. This speaks volumes about me, as it is, probably you third Language of a about 6!)
.....to say was with too many ports on an AC cylinder there would be so little contact area with the fins and cylinder bore and in effect the fins will be only cooling the transfers rather than the cylinder.
ergo the transfers will be then cooling the cylinder. Which as you infer is not that clever.
Isn't that what you were saying anyway or have i missed it again ? Don't worry
It wouldn't be the first time I have been extremely wrong. Just ask my lady She can supply a limitless array of examples.

I seem to remember something about how the crankcase should be cooled first (Prof Cramp i think) He also said F1 cars were far more advanced with their cooling systems too than GP bikes.

But how hot does a crankcase get on a racing two stroke? I must admit to never checking them, but my sons ktm50 is very hot. Too hot to touch comfortably.
Which I assumed was mostly a result of heat transfer from the slipper clutch? The oil is hot enough to burn you. Trust me I figured that the hard way.
This must be killing HP.

Remembering your pipe shielding pics awhile back. I realize it could have a large effect on power with inefficient cooling system.
Then why don't we see 2 stage cooling systems with a separate system for crankcases and one for the hotter bits Cylinder and Head.
Possibly with a kind of air gap or thermal barrier gap between to minimise heat transfer to the charge in the transfers maybe.
Or do we have them but I do not see them? inside the engine and all that? or are they there anyway because the modern two stokes transfers do seem to poke out
and i spent far to much time playing with old shitters.

Should the people that are using spacers beneath cylinders be using a plastic spacer (rather than an Alloy one to minimise heat transfer or are std gaskets on a AC cylinder an effective barrier?

What would be the optimum for efficient running of each part be?

Crankcase and charge (I guess just above icing) not really practical i guess as it will be heated as it compresses anyway.
Cylinder (another total guess 70-90 degrees C) it would have to be cool enough to minimise distortion and hot enough to minimise wear.
Even temps around the cylinder walls to I guess.Which your FOR cylinder would achieve.
The Head hotter as Wob said on one part and cooler on the other whoops i forget where I will have to look back and see?

The Starmaker shape was stolen from diesel tech, but as it shrouded the squish from the main body of mixture in the chamber, it was doomed from the onset.
The material is aluminium bronze, I would use beryllium bronze if cost wasn't an issue, the stock head itself I machined away to suit the insert.
In this case we attack all the relevant issues involved, with small detail tricks.
The squish band has a very highly heat conductive bronze surface that runs cool and keeps the end gases from overheating and thus forming radicals that lead to thermal runaway - deto.
Bronze inserted "rings" only do 1/2 the job as they have a heat joint barrier no matter how well fitted they are.
The one piece insert is far stronger than plain aluminium in such a big bore, thus the water can be run much closer to the places its needed, in the squish area , and around the plug threads, reducing thermal hysteresis.
And lastly, the chamber only is coated with a clear ceramic heat reflective, that retains the high temp in the chamber as the combustion gases are expanding.
Creating more gas expansion is the holy grail to pushing the piston down harder , with less wasted heat into the water - on the other side of the insert.
Same with the piston - only the chamber area is coated, if you coat the whole piston, the heat reflective surface becomes hotter than the raw piston underneath, again this will create deto in he squish band area.

I must admit that mid rant I started conjuring up some way to make use of the 50's sodium filled (Manx Norton amongst others) valve technology in another way.
They (the Sodium filled Valves) were superseded by better materials that could stand the thermal loads, but moving around the heat in a way like they did to increase in a way the area. To dissipate the heat i wonder..........?
Sorry if that is an overwhelming array of questions and probably more than a few gross generalizations there Fits

[Grumph]

How does this gearbox work? It a 1968 Jamathi, looks like an 8 speed but doesnt have the usual selector drum, forks etc.
Is the method of operation similar to the new seamless hondas? Can you shine any light on this Frits?

Around that period there was a lot of interest in boxes with the gears on the mainshaft all fixed - usually splined - and the layshaft all free. Engagement was by a shaft up the center of the layshaft either with dogs on or pushing balls out to engage each free gear as required. The Lotus "queerbox" as used in F1 was of this type and at least one continental maker did a replacement box for things like Manx Nortons too. Saves space on the shafts but you still need to pull the engagement rod out the side....

[TZ350]

The squish band has a very highly heat conductive bronze surface that runs cool and keeps the end gases from overheating and thus forming radicals that lead to thermal runaway - deto.

Hmmmmm I just love that detonation supressing copper squish come head cooling fin on my air cooled.



The copper head fin on my current engine comes right into the chamber and forms the squish band, copper being a much better conductor of heat than aluminium I expect the squish area runs cooler than it would have done with the std head.

And lastly, the chamber only is coated with a clear ceramic heat reflective, that retains the high temp in the chamber as the combustion gases are expanding.
Creating more gas expansion is the holy grail to pushing the piston down harder , with less wasted heat into the water - on the other side of the insert.
Same with the piston - only the chamber area is coated, if you coat the whole piston, the heat reflective surface becomes hotter than the raw piston underneath, again this will create deto in he squish band area.

I would very much like to know more about this clear ceramic and where I can get it, as I would like to try it on my all copper combustion chamber head (copper spray coated 1.5mm thick).



The copper was for sheding wast heat from the combustion area and transporting it to the outer fins to be dissipated. As copper transfers heat quicker than alloy I hoped for a cooler running combustion chamber shell.

The problem was that the copper discolured, so instead of being a good heat reflector it became a heat absorber. I am hoping that the clear ceramic will reflect heat and protect the copper and keep it shiny.

I have also found that if I use a std GP125 composit head gasket between the barrel and copper head gasket fin thing the head runs much much cooler, maybe 60 deg near the plug, with the barrel at about 100-130 between the top fins and 200 near the exhaust port area (lazer heat gun).

[bucketracer]

Then why don't we see 2 stage cooling systems with a separate system for crankcases and one for the hotter bits Cylinder and Head. Possibly with a kind of air gap or thermal barrier gap between to minimise heat transfer to the charge .....?

This is not quite what your talking about but close, this is the way DKW did it with their air cooled engine, also notice the short exhaust port duct that minimizes heat take up from the hot exhaust gas.

Generous case finning, short exhaust tract, crank case separated from bottom end and the roots of the clyinder head fins are all centered on the combustion chamber, unlike the Suzuki head where the heat has to travel further before getting to a fin. Even if they both have the same fin area the Suzuki's combustion chamber will run hotter than the DKW for the same power output because of the Suzuki's longer thermal path. TeeZee posted about this before complete with graphs and pics.

[Frits Overmars]

I would be very interested in the Aprilias port STA numbers.

STA stands for Specific Time.Area. STA depends on rpm: the higher the revs, the shorter the ports are open per revolution. So I can only give you STA numbers if you specify for what rpm you wish to know them.
It's like this: a cylinder has port windows with a certain width and certain distances from the cylinder top plane to port roof and port floor. You can only express the window dimensions in millimeters and square millimeters (or in other funny length and area units that english-speaking folk still use).
Put this cylinder on an engine with a crankshaft with a certain stroke and a certain conrod length. Now you can also express the window dimensions in crankshaft degrees.

Now we can look at the angle.area concept (the point between angle and area indicates a multiplication; I make a point of writing it like this )
Let us assume a port window is 1 mm wide. Turn the crankshaft until the window is on the verge of opening. Its open area is still zero.
Then turn the crankshaft 1° further. Let's say the piston descends 0.5 mm, so the open window area is 0.5 mm height * 1 mm width = 0.5 mm² , and it has been open for 1°; that yields an angle.area of 1° times 0.5 mm² = 0.5 °mm².
Then turn the crankshaft 1° further again. That first 0.5 mm² open area has now been open during 2°; and as the piston has descended some more, there is now some additional open window area that has been open for 1°. Multiply all those pieces of open window area with the number of crankshaft degrees they have been open, all the way from initial port opening till port closing, and you get the total angle.area of the port.
But for gas flow it does not matter during how many crank degrees an area has been open; what matters is the number of seconds it has been open. That is where engine rpm comes into play: twice the revs means half the time; angle.area divided by rpm is time.area. And if you divide time.area by the cubic capacity of the cylinder that has to be filled (or emptied), you have specific time.area.
You may have noticed that in previous posts I sometimes talked about angle.area, and sometimes about time.area. And hopefully now you understand why. When I talk about an engine, I use angle.area. When I talk about a running engine, I use time.area.
O, TZ350, before I forget: here is what you have been asking for:

[Frits Overmars]

How does this gearbox work? It a 1968 Jamathi, looks like an 8 speed but doesnt have the usual selector drum, forks etc. Is the method of operation similar to the new seamless hondas? Can you shine any light on this Frits?

Counting to nine can't be that difficult... The selector mechanism is under the engine.

[husaberg]

Counting to nine can't be that difficult... The selector mechanism is under the engine.

The original 8 plus err.. 1 gearbox pic Yow Ling posted has what looks like a set of Bevel gears at the rear underneath is this an ancillary drive (IE Pump) or part of a earlier design? of the gear selector mechanism.

[Frits Overmars]

What did you think of the 1958 Clarke engine Frits.

Doesn't ring a bell.

What i was attempting to say was with too many ports on an AC cylinder there would be so little contact area with the fins and cylinder bore and in effect the fins will be only cooling the transfers rather than the cylinder. ergo the transfers will be then cooling the cylinder. Which as you infer is not that clever. Isn't that what you were saying anyway or have i missed it again ?

No, that is not what I was saying. But I missed your point too; only now do I understand it. I was not talking about the 'real' cooling fins but about all the separating material with the accordingly large total surface area that you get between 11 ports.

why don't we see 2 stage cooling systems with a separate system for crankcases and one for the hotter bits Cylinder and Head.

You would have to find a place for a second radiator, about as big as the one we've already got.

Possibly with a kind of air gap or thermal barrier gap between to minimise heat transfer to the charge in the transfers maybe. Or do we have them but I do not see them? inside the engine and all that?

You apparantly missed the inside view of the Aprilia 250-engine I showed recently.

Should the people that are using spacers beneath cylinders be using a plastic spacer (rather than an Alloy one to minimise heat transfer or are std gaskets on a AC cylinder an effective barrier?

AC cylinders are not suited for racing; not since the 80's of the previous century. Sorry Bucketeers, but that's the way it is.

What would be the optimum for efficient running of each part be? Crankcase and charge (I guess just above icing) not really practical i guess as it will be heated as it compresses anyway.

All the more reason to cool as much as you can. Just above icing would be great for power.

The Head hotter as Wob said on one part and cooler on the other

I usually agree with Wob, but not on this one: hot heads induce detonation.

Sorry if that is an overwhelming array of questions

Sometimes it takes over an hour to answer one question. So I guess you've had your share of answers up until christmas 2016....

[gamma500]

There is a relationship between how wide you make a port, and how gradually it should widen in order to keep the ring healthy.
With a good ring, 70% chordal of the bore is the optimum width. If you make it any wider, the widening has to be so gradual that you loose surface area at the top, where it counts most, because that's the area that opens first and stays open the longest.
The drawing below shows that with too wide a port you have to sacrifice the yellow areas at the top. But sacrificing those areas costs blowdown angle.area. That red port may have more open area, but not where it counts, at the top; the blue port is better.

In the pic you posted, would that blue port make engine peakier, because of the sharper exhaust pulse?

[husaberg]

Doesn't ring a bell.No, that is not what I was saying. But I missed your point too; only now do I understand it. I was not talking about the 'real' cooling fins but about all the separating material with the accordingly large total surface area that you get between 11 ports. You would have to find a place for a second radiator, about as big as the one we've already got.You apparantly missed the inside view of the Aprilia 250-engine I showed recently.AC cylinders are not suited for racing; not since the 80's of the previous century. Sorry Bucketeers, but that's the way it is.All the more reason to cool as much as you can. Just above icing would be great for power.I usually agree with Wob, but not on this one: hot heads induce detonation.Sometimes it takes over an hour to answer one question. So I guess you've had your share of answers up until christmas 2016....

I see what you mean with the Aprilia engine cooling now

I hope that they won't have banned the 2 stroke before then.
Although my son would be able to ride it by then.

Wob informed me today that there is a new arrival from overseas currently being processed though in customs so maybe it will be ready by October i hope.
A baby Girl. Vanessa.

ps this err...liquid cooling you speak of. Do you think it will catch on.
Seems a bit high tech.
Oh well put me down for one of those to then Wob.

The Clarke engine is below 1959


.http://www.rearenginekarts.com/clark engine.htm