ESE's works engine tuner

[wobbly]

To show you what the tube in the rear cone actually does ( when the diffuser is shortened to get the TL equivalent ) here is the
Ex port pressure traces from the Baseline, and the Long Tube rear.
Note the height of superposition, the pressure ratio at BDC,and the height and shape of the return pulse in relation to EPC.
Now you can see why the fabulous idea makes less power everywhere - except in the inventors head.

[Larry Wiechman]

Good stuff, Wobbly!
What causes the higher pressure ratio peak after EPO?

[wobbly]

With the rear cone extended out by a tube, the reflection from the initial part of the area reduction is reduced, thus the lower
max pressure ratio, then there is a period of no reflection whilst the wave travels down the tube.
Lastly we have the weak return wave from the final part of the rear cone, but its too late in the cycle as the Ex has closed.
The sim is like the dyno, it tells no lies unless you tell lies to it ( or yourself more importantly ).

But - when EPO we have residual pressure sitting at the port face, then the piston cracks open and the pressure wave from the combustion process starts to travel down the duct.
I have the sim pressure recording at the bore edge, so what you are seeing is the pressure ratio rising as the piston decends, then the pressure at the port dropping as the expanding wave moves
away down the header.
Finally the diffuser starts its negative pressure ratio action, sucking on the transfers as the piston dwells at BDC.

[breezy]

wobbly, if a bike came to you with an exhaust as shown in your dyno graph, could it be made to work by changing the programable ignition ?

[wobbly]

If you look at the graph where I compared the baseline pipe to a 50mm longer proper pipe you see that the longer new one
did exactly as it should - make a heap more mid power, less peak but a wider spread under the curve.
I did note that the longer pipe was detonating in the mid range, again completely as expected due to me not having optimised the timing to suit
the big increase in low speed power.
So the longer pipe could be made to work even better with a bit of time spent chasing the TubMax numbers, but the pipe with the tube in the rear cone
is simply never going to work anywhere near as well,no matter what ignition timing it is given.
At lower speeds the rear cone does widen the return pulse bandwidth, but that achieves nothing as the return pulse is not timed correctly anyway.
At peak and beyond, the return pulse is lower in amplitude, and the delayed extra kick from the last part of the cone is so late it does nothing,due to its action happening when the piston has
closed the port.
All I did to create the longer pipe was add 25mm to the diffuser, and 25mm to the rear cone - even that isnt optimised at all, as the ports are set to be working best around 1000 rpm
higher than the pipe, so all in all the whole concept of the tube extension is flawed and wont be setting any new benchmarks for power now or in the future.
Dumb then dumber is the short answer - forget this shite give me something interesting to analyse.

[RomeuPT]

Wob, I think I post this question before, but not in real terms.

Could any engine get the best from a pretty big strong tail cone but at the same time having the last part of diffuser angle the sharpest and the inicial diffuser very shallow, thinking about charge lost because of bad port design. Would a taper mid section have anything to this, what usualy happens in the pressure simulator with a taper mid section?

Saying the TZ750 didn't make more power with more then a 108mm belly made me thinking about banshee, mostly of the aftermarket pipes have no more then 105mm max belly diameter, I found the banshee ports reasonable and always thinked the pipes are that way to make the engine power band proper for the terrain but I am not sure.

[wobbly]

The sharp rear cone will pump up the peak number at the expense of powerband width, and yes the diffuser shape you describe will help crap ports
as it wont be pulling a big depression before bdc and cause the loop to short circuit early in the cycle.
Taper mids are just a way of balancing how much diffuser "power " you want vs the effectiveness of the rear cone.
The taper is so small, it in itself has no real effect on the pressure ratios in the sim.
Remember as Frits said there is only a finite energy available, and a taper belly is one way of twisting around where that energy is used to achieve a particular end goal.
Banshee ports are "not bad " but suffer from old fashioned axial angles - the B ports are angled up sharply.
The A ports are quite flat and dont like a very strong diffuser action, but for sure they are better than an old TZ750 layout that has a very wide and flat A port.
There are some quite fat Banshee pipes like Shearer inframes, and these do work alot better than the skinny things I have also seen.

[TZ350]

"O" ringed head and studs, doweled head but .... but it nipped up on the dyno ... even with the jammed rings it still made near 9.5 hp .

[TZ350]

Very slowly plodding through. I'm not far into the (ESE thread) thing, still reading 5 year old posts, but wondering how "TZ350" made out with his experiments on cylinder cooling. I've always thought that the front wheel of any motorcycle is a terrible obstruction to engine cooling, and that big ugly air ducts would be the solution (for air-cooled barrels anyway).

I Also think you can help the situation a bit by welding some cooling fins to the first several inches of the exhaust header-pipe, right after the mounting flange. As we all know, the megaphone section of the expansion chamber draws some fresh air/fuel charge some distance into it, and this is then crammed back into the cylinder at exhaust-closing by the positive return wave from the baffle cone (in Seattle, in the first days of expansion chambers, we boatracers called them "bounce-pipes.). This column of air/fuel picks up heat while it is in the exhaust tract; I'm guessing it would pick up less of this heat if the header-pipe had cooling fins.

I did this, welded some cooling fins to the header pipes, on my '76 Yamah RD400C when I made a new exhaust system. But I did no before-and-after testing of that feature in isolation. I don't race it, and ride it like an old lady (I'm old, I never raced bikes, only boats, and I don't mind a splash but don't want to crash), so can't tell you anything about the practical effect of the fins, sorry.

Actually, there is some evidence seemingly supporting my idea, from the sled (snowmobile) racers (who have some interesting 2-stroke tech, if you want to check that out). When the pipes on a sled get hit by a big load of snow, they cool off, the wave-speed slows, and they go out-of-tune until the snow melts off.

Same thing can happen with racing outboards. The sled guys sought to prevent this by wrapping their pipes with thermal-insulating wraps. They soon found that it was best to leave the first several inches of the header-pipe uncovered, no thermo-tape, because of what I'm talking about, an over-heated slug of air-fuel getting shoved back into the cylinder.

Thanks for the tips and the example from your own work and relating the experience of the snow sleds, I am encouraged by the idea.



I too think a lot of heat enters the cooling system from inside the exhaust duct and on my latest air cooled motor I am building, I plan on fitting a finned copper (or alloy) spigot that goes as far back into the exhaust duct as possible and which has cooling finn's on the outside.

The spigot will be a loose fit in the exhaust duct to cut down on heat transfer from the spigot to the cylinder and by using a small forced air fan and duct directing cooling air over the spigot finns it might be possible to keep the initial header-pipe section cooler and also reduce the heat uptake into the rest of the cylinder.

Air scoops and ducting will be part of the picture too.

[Yow Ling]

Thanks for the tips and the example from your own work and relating the experience of the snow sleds, I am encouraged by the idea.



I too think a lot of heat enters the cooling system from inside the exhaust duct and on my latest air cooled motor I am building, I plan on fitting a finned copper (or alloy) spigot that goes as far back into the exhaust duct as possible and which has cooling finn's on the outside.

The spigot will be a loose fit in the exhaust duct to cut down on heat transfer from the spigot to the cylinder and by using a small forced air fan and duct directing cooling air over the spigot finns it might be possible to keep the initial header-pipe section cooler and also reduce the heat uptake into the rest of the cylinder.

Air scoops and ducting will be part of the picture too.

Wouldn't it be easier to water cool it ?

[husaberg]

Dumb then dumber is the short answer - forget this shite give me something interesting to analyse.

Fair enough Robinson did the sums for I think it was bantams in 56X50.6 54x54.5 and something like 52x58.
From memory the long stroke came out on top but he seemed not to account for the ft/min from memory.
using the sim how does it play out with everything equally stressed out..........

[wobbly]

Dont need to spend hours trying to get the numbers to work in the sim
The short stroker is capable of mechanically going to 15,500 @ 26M/Sec but the port STA is simply unable of supporting any power up there.
Yamaha tried forever to make it happen, but finally gave in with a square engine and won the 250 title with Olivier Jaques around 2000.
Going the other way the 52 by 58.5 is able to generate the STA needed but with the longer stroke is only capable of 13500 rpm absolute peak rpm
whereas the square engine runs out at 14500 when stressed to 26M/sec mean piston speed, as has been proven to be reliable with an Aprilia.
The extra 1000 rpm would easily blow away an equally tuned setup simply due to the gearing torque available for an equal terminal speed.

[Cheesy]

Thanks for the tips and the example from your own work and relating the experience of the snow sleds, I am encouraged by the idea.



I too think a lot of heat enters the cooling system from inside the exhaust duct and on my latest air cooled motor I am building, I plan on fitting a finned copper (or alloy) spigot that goes as far back into the exhaust duct as possible and which has cooling finn's on the outside.

The spigot will be a loose fit in the exhaust duct to cut down on heat transfer from the spigot to the cylinder and by using a small forced air fan and duct directing cooling air over the spigot finns it might be possible to keep the initial header-pipe section cooler and also reduce the heat uptake into the rest of the cylinder.

Air scoops and ducting will be part of the picture too.

Since most engineering is adapting other peoples ideas it may be worth getting a Mazda 13B housing to have a look at. They have an insert in the exhaust port to reduce heat transfer from the exhaust to the aluminium, Im not sure what it is made of but it is hard as hell

[TZ350]

Wouldn't it be easier to water cool it ?

Absolutely ...



Good girl Cinderella Water Cooling.



Bad StepMother, Air Cooling, harder work but much more exciting and possibly rewarding for the adventurous.



Maybe Air Cooling is like Diana and the "Race of the Golden Apples", many have tried and failed, so what chance an old soldier with a limp.

The challenge, risk and possible reward from the air cooled's extra CC's, and the possibility of 40+hp if we get it right, makes Air Cooling attractive.

So if you want an easy life and don't want to race Diana, then don't, but I am going to try my hand.

[TZ350]

Since most engineering is adapting other peoples ideas it may be worth getting a Mazda 13B housing to have a look at. They have an insert in the exhaust port to reduce heat transfer from the exhaust to the aluminium, Im not sure what it is made of but it is hard as hell

Good tip and I will check it out. But unlike a 2T the 4T's exhaust is gone never to be seen again, so I imagine the hard thermal shield in the rotary is about shielding and mechanical reliability however hot the shield gets.

But some fresh charge is drawn into the 2T's exhaust header before being pushed back into the cylinder. And we don't want to heat this fresh charge if we can help it. So a 2T's shield ideally needs to shield the cylinder without getting to hot itself.