ESE's works engine tuner

[F5 Dave]

so you will run a TPS on a splitter cable or whatever & anything less than full run a rtd curve. Would like to see how that goes.

[TZ350]

The more tec posts from the last ten pages.....

There are several options in lengthening a pipe. You can move the end cone, like on the above drawing, or you can lengthen the header, like on the trombone pipe.
The gas pressure generates a force that is proportional to the cross section area of the moving part and proportional to the pressure difference at either side of that area. For a moving end cone this force can be up to 4 times larger than for a sliding header. That is one reason to go for the trombone system rather than the moving cone system.

The second reason: say you wish to lengthen the total length of the pipe by 10 %. If you do it by moving the end cone, you will also enlarge the pipe volume by a little over 10 %.
But in a good pipe configuration the header length is about 1/3 of total pipe length, so in the trombone system, lengthening the pipe by 10 % will result in lengthening the header by about 30 %. That gives a far greater variation in the pipe's Helmholtz frequency than a 10 % volume change.

It is true that the length percentages of all pipe components should be in a rather fixed relation to each other. Varying the lengths of all components by the same percentage would be the theoretical optimum, but that is not feasible.
Lengthening the belly will disturb the optimum relations, as will lengthening the header. So the pipe in its lengthened version will not be the optimum for the low resonance rpm dictated by the length. But it will be a hell of a lot better than using an exhaust power valve that spoils the 180° effective exhaust timing, necessary for true resonance.
And a pipe shortened beyond its optimum may not show the optimum length relations between its components either, but it will be a lot more effective in overrev than artificially raising the exhaust gas temperature by retarding the ignition, or by weakening the mixture strenght through closing a power jet, which has the disadvantage that not all inhaled air is used for combustion.

I thought that closing the power jet after peak power only restored the proper air fuel ratio? And the over rev was extended because the exhaust gas was not being cooled by an over rich mixture.



I guess that's what happens when water injection changes the temperature of the exhaust gas, water injection looks like it would be a good idea if it was practical and didnt have any down sides.



I have simulated the Slippery pipe in EngMod2T before and was not that encouraged by the results but your explanation of the Trombone looks interesting and I will try that in EngMod now.



More good old engineering and design compromises to play with.



Do I understand this correctly, given sufficient blow down and exhaust STA an exhaust duration of 180 deg would be the optimum at any rpm?

Thanks Frits ..... gives me a bit more to think about.

The short answer is yes. But why is it that each time you people sit down for five minutes to write a question, I have to sit down for two hours to write an answer?

When the exhaust port opens, a pressure pulse starts moving through the exhaust pipe. It is reflected at the end cone and it should be back at the cylinder just before the exhaust port closes.
Next a part of this reflected pulse bounces off the partly-closed exhaust port and a residual pulse starts moving down the exhaust pipe. This residual pulse too is reflected by the end cone and starts moving back to the cylinder. Ideally it will arrive at the exhaust port just when the port opens again. Then the cylinder pressure and the pressure of the residual pulse combine their energy and the resulting pulse will be stronger than the pulse from the previous cycle. And the combined pulse from the next cycle will be stronger still, and so on; we have achieved true resonance.

Some may argue that we want a low pressure in the exhaust pipe when the port opens because then the spent gases will experience less resistance while leaving the cylinder. But that is not true. Gas flow depends on a pressure difference ratio. But once that ratio reaches 2, the flow velocity will reach Mach 1, the speed of sound. Raising the pressure difference any further will not raise the flow velocity any further.
The cylinder pressure at exhaust opening can be as high as 7 bar and the pressure of the reflected pulse will be about 2 bar. Thus the pressure ratio is well above 2, so lowering the pressure in the exhaust duct outside the cylinder will not do any good to the flow.

What has the exhaust timing got to do with the 'true resonance' I mentioned above?
The initial pulse starts moving at Exhaust Opening and it has to be back at Exhaust Closing, or a little earlier. This pulse travels with the speed of sound and its journey up and down the exhaust pipe will take t seconds.
The residual pulse starts moving at Exhaust Closing and it has to be back at the next Exhaust Opening. This pulse also travels with the speed of sound and its journey up and down the exhaust pipe will also take t seconds.
So from EO to EC takes t seconds and from EC to EO also takes t seconds. In English: the exhaust port should be open just as long as it should be closed.
Assuming that the crankshaft rotates with a uniform speed, this means that the crank angle during which the exhaust is open must be equal to the crank angle during which the port is closed. So both angles must be 180°.

I developed this line of thought some 40 years ago, but when I first published it in 1978 (in the motorcycle magazine Moto73 of which I was the technical editor) everybody called me crazy. Some people still do, but I got used to it .

Above I made a couple of assumptions. The crankshaft does not rotate with a uniform speed, but at high revs the deviation is negligible. In case you really want to know, I did the math for the Aprilia RSA125. At a nominal rpm of 13,000 the minimum rotation speed is 12970 rpm @ 107° after TDC and the maximum value is 13031 rpm @ 356° aTDC. What's more significant: the deviation in crankshaft position from truly uniform rotation is always less than 1°. So that really is negligible.

Second assumption: both the initial pulse and the residual pulse move with the speed of sound. Not true: the pulse pressures in exhaust waves are so high that acoustics rules do not apply any more. We are dealing with gas dynamics here and the stronger a pulse, the faster it moves. Since the residual pulse is weaker than the initial pulse, they move at different speeds. But we will leave this aside for now.

Third assumption: the initial pulse starts moving as soon as the exhaust port starts opening. More or less true, but we are not interested in the first weak appearance of the pulse; we want to know when the pulse reaches its maximum amplitude. And that requires a certain amount of open exhaust port area. It turns out that for our desired theoretical exhaust timing of 180° we will need a geometrical exhaust timing of about 190°, depending on the shape of the port: does it open gradually or does it open over its full width all at once.

The obvious question will be: why has the Aprilia RSA125 a geometrical exhaust timing of about 200°? True, at 190° the maximum torque value would be higher, but the engine would not want to rev because the blowdown time.area would be too small.
The 200° are a compromise: a bit less torque and a bit more revs; as long as the torque decline is smaller than the rpm rise, we gain horsepower.

That Dutch trombone pipe moved from +70 mm length to -20 mm length, so its effect was concentrated on the lower revs (although raising max.rpm from 14,500 to over 17,000 rpm was a welcome bonus).

The tech term for what Frits is describing is Superposition of the Ex pulse.
This is easily described in a sim, where a residual pressure ratio is seen sitting at the Ex port when it is opening.
The "new " pulse is added to this residual, and a very large pressure ratio exits down the duct to the header.
The larger the initial ratio, the larger the amplitude of the wave in the diffuser - this creates a deeper depression around BDC, and it is this that initiates the biggest mass flow
from the transfers.
The lower Ex timings of 190 and below create larger residual pressure ratios,over a wider band, and thus these work with a good pipe design to use "resonance" to increase band width and also peak power.
Big problem though is this whole concept is at odds with maximising blowdown to allow good peak power and more importantly, overev power.

The sim shows RGV100 making serious power with the superposition pulse going down the duct - off the scale.

Re the trombone pipe results you did sims for TeeZee.
Look carefully when you say it seems to affect the top end "more ".
At 9000 the lowest reading is 13 Hp, the highest reading is 17 Hp, thats an increase of 4 Hp, thats 31% more power in the bottom end, that then allows the thing to rev to 17,000.
Seems a not bad result.

Re the powerjet temp result you mentioned.
The effect of the solenoid powerjet is as you described - this I only discovered recently with a datalogger that I could set the sample rate of the EGT high enough to read the temps quick enough - along
with some exposed junction probes.
I was testing a RS125 on the dyno and it was making NO power past 12500, looking at the data you could see the egt drop from 640 C to 580 in around 400 rpm.
After fixing the fact some idiot had left out the rpm plug in the loom, the solenoid now switched on at 12200, and the temp stabilised at 650 past 12500 and the thing than reved out to 13500 +.
So the powerjet switching isnt making the mixture "lean"as such, it is simply maintaining the correct mixture, and thus the temp in the pipe.

http://www.epi-eng.com/piston_engine..._cup_to_f1.htm

http://www.epi-eng.com/piston_engine...y_contents.htm

Frits used the same example.
It would certainly help with useful overrev on tight tracks as well as when you have a wide ratio gearbox
Variable pipe lengths with length or temps
I came upon this today.

Husabergs post is worth a look.

Attachment 262505

130mm Trombone Header

After playing with EngMod2T for a bit I found that the interesting thing about the pipe elements needing to stay within certain percentage limits is that when you reduce the headers length, like in the Trombone arrangement the overall tuned length also reduces so the headers percentage of the overall length does not get out of balance as quickly as you might think.

Rob you could look at lifting the B,C transfers like Aprilia, and move the front of the Ex Boosts forward to gain more blowdown to suit, as the bridges
on each side of the Ex are wide - will heat up alot and expand out toward the piston - eek.

Here's the EngMod equivalent of Aprilia Tfrs. It a mix of RSA/RSW cylinder derived from Frits' info on durations and data from the whiteprints from his files. But don't take the radial angles to be 100% correct.

Attachment 262585Attachment 262586

As for the bridge between main & auxiliery exhaust. A couple of lubrication holes on the piston or a vertical lubrication band, like the aprilia piston below, would mess with the transfers??

Attachment 262587

The Aprilia has the B,C ports opening 1* before the A port.
So you could leave the A port at 116 and open the rest at 115.
This will of course drop the Bl STA, so to get it back you may as well reduce the bridge width to gain some area.
Reducing the area reduces the heat soak into the bridge,thus reducing the expansion.
But it also reduces the support area for the ring and piston.
You choose the compromise.
Having all 3 ports open together will lower the midrange power, so you could also lift the main port a little to get some stagger as well as widen the top of the Aux.

The purity in the ducts is a function of the fact that the port (s) that open first, flow last due to reverse flow of the blowdown pressure into those ducts.
Thus they will have more impurity than those that open later.
You cant change the fact that the excess blowdown has to go somewhere, you choose the scavenging pattern to get the STAs needed, and you live with the result.

As with most things we deal with there is two sides of a coin involved that leads to having to compromise.
A bridge with a smaller area/volume will expand less,but of course it also has less face area to support the piston/ring.
The ultimate expression of this is the Aprilia that uses as much area as possible to gain Blowdown STA.
The opposite is the CPI cylinders that have alot of material between the main port and tha Aux.
I needed alot of blowdown in the RZ400 cylinder to make 120CHp so the width has been halved,its just about to go on the dyno
with Wossner pistons using the same ovality as the 485 with wide bridges.
The new pistons have a cutaway above the pin that extends to the bore centerline, so I couldnt go any wider the other way.
So we shall see the effect immediately.

[TZ350]

More work on the triple port cylinder.



Ring ends just meet on the bridge between the boost and B transfer port. The other lines are so I can drill oilers for the bridge between the ex port and main transfers and make a port in the piston for the boost port.



Piston protrudes 1.2mm at TDC.



Lower cooling fin is 2mm thick.



Later on I plan on using a head gasket to thermally isolate the top copper cooling fin and head from the lower copper cooling fin and cylinder so the head can run cooler than the cylinder.



Checking the squish clearance, and yes its 0.8mm.



How the two copper cooling fins stack on the head leaving a (will be) polished alloy combustion chamber.

[TZ350]

Chambers bending up his main shock bracket, we have all the sophisticated tools like CNC folders.



Chambers is making a copy of a RS125 canterlever swing arm for his RG50.

[jasonu]

Chambers bending up his main shock bracket, we don't have a lot of sophisticated tools.



Chambers is making a copy of a RS125 canterlever swing arm for his RG50.

http://www.youtube.com/watch?v=oVOxa9I2Obs

In reference to the tasty beverage in the last pic

[worm13]

Attachment 262360Attachment 262361how much would you pay for this bit of rubbish? gt50

heres that photo I said I knew about and have one of a matching sidecar for it aswell

[crazy man]

heres that photo I said I knew about and have one of a matching sidecar for it aswell

the sidecar looks like it has a stinger t100 in it

[TZ350]

a couple of recent videos from the Dutch 50 cc scene.

http://www.youtube.com/watch?v=mvV4x...feature=relmfu

http://youtu.be/0odVzSgufjk

That Dutch trombone pipe moved from +70 mm length to -20 mm length, so its effect was concentrated on the lower revs (although raising max.rpm from 14,500 to over 17,000 rpm was a welcome bonus).

I have been looking at the Darcy RG500 pipe that peaks at 10,500 and simulating it with a Trombone header. By shortining the header 130mm It looks like I can get the power spread to extend out to 14K.



The total amount of power under the curve is much greater than I had before.

After we get the triple port and Pirana pipe testing out of the way I want to try my hand at one of these Trombone pipes. They look like the key to making an all conqering 2-Stroke.



The plan is to make a pipe that works well down low and then use the Trombone effect to get lots of extension of the working range. Not so much about peak hp numbers, that 2-Strokes can be good at but dramaticaly increasing the area under the power curve.

I need a Trombone section that can collapse 130mm, now there is the trick, how do I make that .....

[dinamik2t]

Have you given any thought on the setup yet?
The dutch racer has a backward facing cylinder and a straight pipe, which makes it quite "easy" to vary its length.
On a curved header it will be challenging to come up with an efficient moving system. I like it! :d

[TZ350]

Have you given any thought on the setup yet?

One possibility is to use one of those water cooled after market 50mm big bore kits you see advertised for scooters and fit it backwards on the GP cases and have a 100cc water cooled screemer.



Or I could make a pipe like this one, as there is plenty of room in front of the engine I could use the the first part of the pipe as the Trombone. Or even the vertical bit could slide in and out.



This is one of Speedpros pipes where the muffler comes forward instead of pointing out the back. Its pretty easy to see that if the back could pivot, the front Trombone section could move up and down easily with the pipe pivoting at the back.

[Yow Ling]

One possibility is to use one of those water cooled after market 50mm big bore kits you see advertised for scooters and fit it backwards on the GP cases and have a 100cc water cooled screemer.

Or I could send you a rz250 barrell they fit both ways on the gp cases, got a lifetime supply of them !

[TZ350]

A "Real Mans" dyno .....

First run 19.9 hp second run 23 hp.

Actually not to hard to make with a disk brake for an energy sink and a load cell to measure the torqe.

[husaberg]

I am sure some pics of the bikes or engines have been added before a British attempt at a prepackaged Rotax tandem twin TZ beater from the 80's made in both 250 and 350cc.

Lozza will be well aware of this When i was looking for pics his name pops up quite a few times.
One thing i have not picked up on is they had mirrored disks on at least one of the bikes.
I always thought the rear disked Derbi or Aprilia was strictly for packaging?

but was it mainly for a better transfer layout with more symmetry as well?
Possible advantages with the twin disk i can see include a symmetrical flow and the inlets would be smaller so less obtrusive to the transfers.
It should also possibly offer better drive-ability( it does of course fail the KISS test though.)
Frits I think posted a twin disk 50 done in the 70's.

The Kreidler engine shown by TZ350 was cutting edge technology in 1962, but I do not think any of you want to copy transfer passages that, together with twin rotary disks and a twelve-speed gearbox, produced all of 10 HP out of 50 cc.
In case you wonder: the transfer timing was 142°; the single exhaust was way over 200°. Don't try this at home....
Below are some more pictures of the same engine, showing the twin carbs and the screwed-in caps that gave access to the transfer ports for easy modification.
You can also see the hand-operated three-speed gearbox behind the foot-shifted four-speed box.

oh to fit the trombone pipe in why not tip the motor forward TZ it has advantages being a disk valve with the side sucker carb.
The gearbox breathing and oiling will need work and the ground clearance might suffer a bit.
and yes the selector will be a bit in the way not as neat as the Rumi which was a reverse cylindered design as well.

[wobbly]

That dyno run looks more like a Hitler gas chamber than a dyno cell.
With the header leaking like a sieve and the carb sucking dirty air, no way is anything repeatable going to happen.

[TZ350]

Here we go, a simple disk brake dyno.