Hi,

I have tuned a lot of 2-strokes engines over the years, but now i have been without for like 7 years due to family.
I wonder if i should ever start having fun with this again.
If so it need to be extreame, it was pretty extreame last time as i was able to get a Suzuki ts50x to run at 135-140km/h with a 66cc cylinder.

So basicly I will list my tips and tricks here, and maby any1 can fill in other tips/tricks and formulas which can aid in tuning 2 strokes. Either it be purely mechanical or chemical, products or experience or fresh ideas

So basicly what i did last:

Aligning piston with ports, matching cylinder head and cylinder head design and usage of off-center-piston-rod-placement:
I made sure every port in the cylinder opened fully. On the type of cylinder i used(Charmo 47mm, cheap thing xD) it actually missed 3mm to fully open.
I did this first by making a 3mm copper plate to keep underneath cylinder, then i measured and cut my cylinder from top so it would align perfect with piston in TDC (TopDeadCenter).
But i wanted to implement a trick i knew about from before:
* Not having centerplaced rod connection in piston can be used to increase the direct power transfered between piston and crankshaft due to the angle of the rod becomming more effective right after explotion.
this actually has an reather extreame benefit on torque. I knew that Malossi 47mm pistons for ts50x does gain this benefit by put them in with the indication/flow arrow pointing towards the intake.
So i put a Malossi 47mm piston(46,95mm) in my 47mm charmo cylinder, and ofc i needed to check that the piston ring meet itself at a relevant location where it dont open(like if that split was in the exhaust or intake port).
This also gives quite a free width to choose on exhaust port.

The Malossi piston has 1mm lower compression height, and also the cone difference from outer to inner part of piston was 2mm instead of 3mm.
This freely gave me another trick/benefit:
* Hemi Design, combined with regular 2 stroke design on cylinderhead.
Due to the difference i now used 3 x bottom zeal's instead of the 3mm thick copper plate. My cylinderhead was shaped for the charmo pistons cone. and since malossi has lesser cone/dome i would now make 0,4mm squish closest to cylinderwall, meanwhile 0,7mm closest to the combustion chamber.
Instead of the overall 0,6mm squish clearance charmo piston had.
This makes the squishband more effective squize the "unused" gas which are used to cool the cylinderehad to avoid self detonation. In this way u will squize a large potion of this gas into the combustion chamber and will therefore cool more due to circlulation/movement, as well as a large part of it will join the explotion.

Better cooling is always better, also on performance:
Thanks to this design i increased the effect of another trick, cooler gas gives stronger explotion:
* Lowering the flamefront speed. Every explotion has a flamefront, but infront of this flamefront there is a pressure wave. By lowering the flamefront speed u give more time to build greater pressure, and everything explode way stronger the better pressure there is. So the longer time pressure can build prior to flamefront catching up, the more power.
* Avoid self detonation. When self detonation appears, its actually acting like a chemical reaction which strips metal of molecyles. If bad it burns hole true the piston, it also early will pick appart the metall, so it looks like some1 hit it with something pointy(dont know the english name of the tool lol)

Reducing speed of flamefront is done by cooling down as good as possible.
I did learn a new "trick" after making my cylinderhead which is called "zingh-tracks". Theese Zingh Tracks are basicly several triangle cut from outer area of squishband, and towards the spark plug.Going deeper as closer to sparkplug/combustion chamber. I wish i would plan for this earlier so that i could min/max my cylinder head even further. Zingh tracks are supposed to do such that u spend less gas, increase the burning% and engine running cooler. It also allow 1 bigger dynamic compression(compression above exhaust port). From 9:1 into 10:1.
Anyway, ideally I would make a 3hybrid of the builds. A mix of regular 2stroke cylinder head & hemi design with Zingh tracks with 10:1 compression where extra volume given by the triangle cuts are included. Its supposed to give more effect etc even by just adding the tracks and there actually increasing the volume a little...
As you might would guess this cool's better, use more of the fuel in the cylinder head and ofc lower the flamefront speed further.

I know 1 more trick to lower flamefront speed, but that will be included later under water injection.
- Also be aware that you should not make/modify cylinderhead before you are done with cylinder and its ports.

I guess its time for some pictures.
Some picture of preparing/matching the cylinder with the cylinder head and piston:


Porting the cylinder:
Cylinder ports are on theese kind of cylinder to small for effect, as well as they are not well made which can actually hurt the piston. So we need to modify them.

Here we need to think about several things, such as:
- How high do they need to be, we use duration of ⁰ pr crankshaft rotation to know how long they need to stay open. And then calc how many millimeter from cylinde top area they gonna have its roof. Intake port we messure too its floor, and then we also need to know piston height.
- How wide CAN they be, what distance between.
- Which shape they should have. Which area of the ports are most effective.
- Blowdown
- How should the channels be
- Flow (not just ammount, we need to regulate speed and pressure, depending what we want to happen)

How its put together, just to explain around formulas etc.


We start with Height of ports/Duration:
1. We did already raise our ports be an massive ammount of 3mm due to the heightening of the entire cylinder / 1mm lower compression heigh of piston.
2. We need to match everything. What exhaust system can we use, and which RPM does that work best on. (consider our stroke and rod lenght). We need to know how big carbourator we can fit.
We need to know how much metal housing there is to work with inside the cylinder, as well as the cylinder head. We need enought remaining for cooling.
We follow a table which will be inlcuded in next picture to make sure ports works at the same area, and we match the blowdown which needs to be within 30-35⁰.

Duration (D) of exhaust ports and transfer ports calculation:
D = (180-ARCCOS((T^2+R^2)/(2*R*T))*180/Pi)*2
Where:
R = Half stroke lenght
L = Rod Lenght
C = Dead Clearance in TDC
E = Distance from cylinder top area to roof of port
T = R+L+C-E
(I use Te for Exaust, Ts for transfers, Tb for boosterports, and likewise Ee, Es, Eb).

Duration (D) of intake port:
D = (ARCCOS((P^2+R^2)/(2*R*P))*180/Pi)*2
Where:
P = =R+L+H+C-F
H = Piston Height
F = Distance from cylinder top area to floor of port

They can also be calulated in seconds open:
=D/(RPM*6)

Blowdown (BD) :
Should be between 30 and 35⁰. Based on personal feeling 30 is more for a even drag on the RPM curve, and 35 is more for top peak RPM setups. I use 32,6⁰.
This is the most effective area of the exhaust port, the time it has to do its job prior to transfer ports open.
BD = (De-Dt)/2
Where:
De = Duration Exhaust port
Dt = Duration Transfer port

Recommended Carbourator Size:
0,8 factor if reedvalve intake, 0,9 factor if piston intake.
I have a parelell reeedvalve and piston intake, i think its called boyesen when both work in paralell. Anyway, thats why i choose to use 0,85.
=0,85*SQRT(PeakRPM*(DisplacementVolume/1000))
(remember, PeakRPM is where its most effective, not how high it CAN go... Use the table on picture below)

Areal of cylinder:
=Pi*(D/2)^2
D = Diameter here.

Displacement/volume of cylinder:
=A*S/1000
Where:
A = Areal
S = Stroke

How many ml or cc (they are 1:1) of volume do you need above piston to reach a wanted dynamic compression:
You can do this several ways...

The percent way of finding ml/cc over piston when piston in TDC :
=CC*(Volume% above piston/100)/(Cmp-1)
Where:
CC = Total Volume/Displacement of cylinder
Cmp = Wanted compression, forexample 9
Volume% above piston = 100-(De/360*100)
De = Duration Exhaust port

Static Compression:
=(CC+Cml)/CC
Where:
CC = Total Displacement of cylinder
Cml = Milliliter or Displacement above Piston when piston in TDC.

Volume/Displacement over exhaust port:
=1*(Pi/4)*(D^2)*(Es-C)/1000
Where:
D = Diameter Cylinder
Es = Distance from cylinder top area to roof of exhaust port
C = Dead Clearance in TDC

Measured Dynamic Compression:
=(Vts+Vtdc)/Vtdc
Where:
VTs = Trapped Swept Volume (volume above exhaust port)
Vtdc = Volume above piston when piston is in TDC (Top Dead Center)

Crankshaft Casing Compression:
(CCC+CC) / CCC
Where:
CCC = CrankCaseCubick (measured in cc or ml)
CC = Displacement Volume

We end this here and add pictures, had issues so needed to post prior to done:



This post was edited by gel87 on Jan 19 2022 11:04am

Width of ports & channels, Flow and flow angles:

Transfer channels:
As shown on the awsome paint made picture in last post we want ports to point into the cylinder at correct angles.
This is first to make sure we loose as little as possible of our fuel/gas out the exhaust port. And then second priorities is to route it as close to the spark plug as possible.
The roof of transferports should point 90 degreas into the cylinder due to the piston beeing curved/domed on top. Meanwhile often the boostports are angeled upwards due to the fact those are further behind and will latest give flow to the combustion chamber.
To clarify the boostports are the 2 closests transferports to the intake. Theese have the longest route. So they are often angeled upwards, and even higher than the other transfers to have a little earlier start. Some are cut right into the intake port, but that is only possible if reedvalve is placed before this point.
(not possible on my cylinder)
Anyway, the drawing shows the angles which they are to enter the cylinder.

The width of the transfer channels should not be overdone. Usually i more or less just keep the original size here. Because a small channel will have a higher gas speed, meanwhile a wider channel wil have a bigger pressure, yet slower gas speed.
I build my engines with rather high RPM, due to I gain higher power this way. So i want my transfer channels to be able to quickly transfer gas from below my piston, to the combustion chamber above my piston. I do however make sure they have the correct angles and plan the route all the way from the start to the deliver point. And i also make sure they have optimal entrance, as well as they need to have smaller areal than their exit(the port itself). This is due to somehting called Inertia effect.

Inertia effect:
When a flow comes from a small channel, then suddenly enter a wide open space(like inside the cylinder itself) it will make a constant break in speed/flow at exiting the small channel into the big volume. This is due to what i just told with width = Slow, small = Speed. So we actually regulate the speed of the gas several times inside the cylinder by this easy prinsiple..
Which is why people destroy the effect of the cylinder when they make channels so big u can live inside them xD
This prevents the gas from just beeing flushed out the exhaust port. And instead of designed correct stop around the spark plug area.
(ofc some leakage will happen, but the 2 stroke exhaust sytem will fix this later).

Inntake channel:
Ideally u want to start the same size as ur carbourator, and then graduatly increase until u have the same areal on ur intake channel as ur intake port. If ur setup is like mine then you also graduatly widen up towards the reedvalve.

Finesse of the channel walls:
The flow follow the outer walls of the channels. This is with everything, even electricity running true a wire.
In the middle there is less flow.
This actually makes the surface of theese walls have great importance.
You must NEVER polish intake and transfer channels. What happens then is that gasdrops condens and sticks in the intake and graduatly plug it.
You may polish exhaust, but its not like there is much to gather there between a fine surface and a polish one, there will however be less exhaust oil/waste sticking if polished.
The transfer ports, and espesially intake port should have the same surface roughtness as a #250 sandpaper would give, and ideally it should make tiny lines which lays at 60 degreas. This is such that it will swirls the flow carefully(some little turbulence) and blending the gas better for a cleaner explotion in the end. Which will burn ur fuel more effective.(more power and less gas waste) If done correct it wont affect the flow, but it will blend the gasmix better.

The cylinder should also have 60 degrease angeled stripes(much finer ones) to better oil the piston with 2 stroke oil blended via pump or direct in gasoline.

The shape of the exhaust shoud ofc start at the width of exhaust port and graduatly become the side of the exhaust manifoild/system.

In general a round corner/wall/bridge has better flow than a sharper one.

Picture:

Exhaust system:

I have looooads of exhaust calculations in excel. But the exhaust calculations i did not do myself, i just copied that part from some1 else.
And i dont understand all. Im able to make cones for exhaust building, with sizes, match it on a the combined curves etc. But then some guy say that its better to have an even shorter exhaust system. etc etc... So i will just give some general hints and no formulas.

The exhaust system has 2 functions:
1. Remove the exhaust from the cylinder.
2. Push back spilled gas from cylinder, back into the cylinder just prior to piston closing the port.

Baiscly:
The first part of the exhaust system should be a little wider than the end part. This is due to we want some pressure in the first part, meanwhile in the last part we just want to get rid of the exhaust as fast as possible.
There are most likely numbers for this:

Ideal header diameter:
CC = Displacement or Cubics
=2*SQRT((0,00085*MaxRPM*CC)/Pi)

Min 9inch stinger:
=2*SQRT((((CC-50)/50)*52+92)*(1+((MaxRPM-9000)/1500)*0,12)/Pi)

Max 9inch stinger:
=2*SQRT((((CC-50)/50)*107+174)*(1+((MaxRPM-9000)/1500)*0,12)/Pi)

There are also for 4,5 inch stinger, and 18 inch stinger.
But i fear i have messed up formulas a little by putting some direct numbers, and i will have to crosscheck etc. THere is also for max belly area and cones and diameter increase and lenghts etc.. But it will require further investigation for me...

So we do it simple:
Find an exhaust system that you know works around the RPM u have most effect on and that u can fit.
Just remember if u have shorter rod and stroke it will work at a higher RPM on ur engine...

Other tricks:
To increase the pressure of the soundwaves that press ur gas back into the cylinder u can add heatwrap around the exhaust system.
To increase pressure will also help to drive a turbo better. Copper filled or alu filled wrap is best and should be watered prior to montage.

Resonance:
By allowing the exhaust system to move/vibrate freely it will by it self find its ideal resonance, which will increaser ur effect and espesially make the exhaust system fit a wider RPM band than if not.

I have to end writing atm now... But i will write more later.

Here u can see a picture of my exhaust system. It it mounted so it stays on, but by a small flat-iron and 2 feathers in front it vibrates freely to find its ideal resonance:

Some small info i forgot, im on phone now so will just add a few info in text.

Transfer flow:
What makes Flow is ofc differential pressure, so when people dig too big channels in their transfers this is part of the crankcase volume and will lower the differentional pressure.

Piston adding Flow effectiveness:
Some Pistons have small hollowing on the sides to "quickstart" the Flow. When this part passes the transferport it will start to move the gas a little. And stuff that is already moving in the right direction is way easier to transport more effective. They also have an added cooling effect on the cylinder wall and piston wall. On some builds there are even holes true the Pistons intake side to take shortcuts from crankcase to boosters. This will not work for me, since i dont have a reedvalve in front of inntake. So i have to be extra carefull on the inntake side.

However my paralell inntake has several positive effects:
It can move inntake gas faster, once i increased from 16mm to 26mm diameter it has almost a direct line to both intake port and reedvalve. Since inntake channel is not part of the crankcase volum i also get better differential pressure.

I have cutted some of the lenght of my piston skirts.
I cutted 5mm on inntake side skirt to allow for 179 degreas opening duration if intake port as well as 4mm on exhaust port side to even up. This also makes my piston weigh less and it Will therefore be easier to achieve higher rpm.

Ofc the weight difference on both sides + the shorter lenght of piston will be a little roughter on the piston and cylinder walls, but it has worked great for me.

What i did not mention earlier was that the off-center-piston-rod-pin also has a little extra roughness to my cylinder and piston walls, but not much. I dont have any issues with it.

If the weight difference on piston, and the offcenter-piston-rod-placement works against each other, or Even out each other i have not looked into(when it comes to roughness on cylinder wall) . The off center i read about in Graham bells 2 stroke tuning book, meanwhile putting in theese excact Pistons with reverse Flow direction i knew of before, but that book helped me understand why.

People think principle like off center Pistons Rod connections, lowering flame front speed etc helps negitable... This is wrong. The effect are insane.
I have experimented with just the reverse mounted piston as an example. The difference is night and day. The difference you feel i would say compare to the difference between driving a 80hp car and a 130hp car if both weigh the same.
What happened in my excact experience was:
A guy had a 66cc malossiy cylinder, a somewhat not optimal exhaust system and a 21mm carbourator. His moped went like 75-80km/h. It felt weak, it could not wheely in a normal matter at all, and was really weak uphill.
I remounted hos piston with Flow direction arrow reversed. The moped now went 90-95km/h. It could weelie on 2nd gear with just gas and a little drag in the stearing, as well as it was strong up hill.

This is more effective in lower and mid register, than on top rpm, but the problem he had prior was that it was just overall to weak.

This post was edited by gel87 on Jan 19 2022 06:54pm

well. i have absolutely zero knowledge about these, but its a fun guide so to speak

Thanks

Im nearly done with what i did all those years ago, and can then start on the plan further which are more excotic.

I will first conclude my first setup.

Ignition:
For ignition i used HPI ignition. At the time those did not have EL-power/charge coils for the local wiring. It was only for ignition. I now notice they have with included charge coils for lights and such. (i stript my moped for all those wires and the battery.)
It basicly conclude a innerotor drive with high effect ignition coil and CDI, which are programmable with storage for up to 8 curves but with 2 active curve changed between with a selector switch. 1 high rpm and 1 low rpm curve. I used the low rpm curve.
I also forgot the interface cable/unit, so im just using the standard curve which works great for me.
www.hpi.be

Tool's for porting:
http://www.ccspecialtytool.com/

Reedvalve:
There aint to much on the market for theese. I use a regular "tuning edition" which has carbon flaps. And i make sure the benders stops the flaps at 8mm opening. I have match ported this to the cylinder.
There do exists fiber versions, with the name boyesen reeds, which are split in 1 small overlapping 1 bigger flaps, but i was not able to fit those.. There might be versions that fits. I have also heard u can buy and cut them out urself.

Strenghtening of motorblock:
The TS50X is a good old quality engine(except for 1998 to 2001 models who used crappy steal quality etc, avoid those xD)
Its balanced until 16k RPM, and are known to last without problems. Every kind of "strengtened/tuning" parts there is availeble is always weaker quality than the original part in this scenario.
However they are not delivered with high effect from factory, there exists something of a 7 or 8 HP engine in japan with somehting called E21 cylinder if i remember name correct, this is also delivered with 6 gears.
Meanwhile in eu and norway we use something called E49 cylinder if i remember correct, which constists of a 2,5HP setup with 5 gears.
They have a pretty weak clutch. So i strengtened this by using a RM80 77-79 model clutch, with strengtened clutchspring from a very old 120 or 125cc rm model, and 4 x ts50x lamells. (i could fit 5 if i used RM80 or RMX50 lamells).
As for gearing i just took the 6 drive gear's from a RMX50 engine. If u take all the correct parts this fits perfect in ts50x engine block as well. So now i have 6 gears.
The ratio of 1 and 6 of RMX gears are the same as 1 and 5 on ts50x.

Ts50x ratio:
1st = 12-38
2nd = 17-33
3rd = 21-29
4th = 24-26
5th = 26-24

RMX50 ratio:
1st = 12-38
2nd = 17-34
3rd = 18-27
4th = 23-28
5th = 24-25
6th = 26-24

Primear ratio in engine is:
19-73

Sprocket ratio i use is:
14-54

I do have a fully usable calculator, but there was 1 part i did not know formula for, which maby some1 knows? Its how much increased speed a wider tire will give. I used a factor and a pickup table to get this correct and crosschecked with a calculator already existing.
However, this is the part where a wide tire will stright and become a bigger circle and will there have more speed at same RPM. If any1 know this formula i would be very glad to know ;D



I will also add the formulas for:
Piston acceleration and speed, and also power on rod connector:

RPM in Radians/sec (Rs) = RPM*2*PI()/60
degreased clockwise from top = 90 (at least with me)
which is in radians(Rc) = 90*2*PI()/360
Piston speed in m/s(Ps) = Stroke/(1000*2)*Rs*SIN(Rc)
Piston speed in Km/h = PistonSpeedInMeterPrSec * 3,6
Piston acceleration in m/s2 (Pacc) = (Rs^2)*Stroke/(2*1000)*SIN(Rc)
Weight of rod connector in gram (Wg) = lets assume 120
Weight of piston in gram (Wp) = lets assume 140
Torque on lower rod connector point in Newton(Lrod) = (Wg+Wp)/1000*Pacc ----> In KG: =Lrod*0,1019716
Torgue on upper crosspin(Urod) = Wp/1000*Pacc ---> In KG: =Urod*0,1019716





Conclusion:
Improvments:
* Matching ports to piston height = Gain 3mm height of ports, and albility to perfectionize the dead clearance from scratch. = Better combustion, higher torque and less fuel used, customizable squish. The stock squish on theese cylinders are terrible above 1mm.
* Porting all the ports to work with max effect around 14,5k RPM = A fine RPM to match with carbourator and exhaust sytem, as well as high so high power output possible.
* Making ideal shape of all ports, and increasing flow direction a little away from exhaust on the 2 closest transfers, as well as improving flow, entrance and strengtening the innertia effect.
* Smooth and correct finnish on inntake walls, for better mix of the gas = Better combustion % which is more power and less fuel requirement.
* Using an off-center-crosspin-connector = Increase effective angle of rod right after combustion and therefore also increasing torque by a lot.
* Custom make cylinderhead, with mix of hemi and stock 2stroke design, with optimal squish and 9,5:1 dynamic compression, with added octane booster in fuel = Less fuel usage, WAY more torque, better burning%, more power in general.
* Free vibration exhaust system, optimal for 14k+ rpm on my stroke and rod lenght, which finds its ideal resonance due to free vibration = More effect and way wider RPM range.
* Digital ignition who can ignite clean up to 17k RPM or furter (yes i get 17k rpm on it), which choose a good preignite based on RPM, instead of the original one who have only 1 presetted preignition point.
* From 16 to 26mm carbourator, to fit the required size.
* Slowing down flamefront speed increase power by quite a lot!

All in all this give an quite unicue 2 stroker who is made for top RPM, but thanks to torque increasing tactics like off-center-rodconnector, digital ignition, custom made cylinder head, free floating exhaust system actually works extreamly well at really low RPM as well. So its actually really strong all the way from 6k rpm to 17k rpm. Meanwhile it feels like 3 different "kicks" one at 6k, one at 9k and one inzane at 13-14k...

Next post will be about my further plans, theese are plans i have had for almost a decade soon xD And I do have the most of the parts.
It include stuff like:
- Turbo + EFI kit programmed for turbo + all the utility (MBE motorsport)
- Maby, custom adjustable cylinderhead which adjust with/for turbo pressure.
- Water Injection Kit
- Zingh + Hemi + Stock hybrid cylinder head.
- Filling of crank with light/ruff plastic or smt to increase crankcase compression.
- Strenghtening certain important frame parts.

This post was edited by gel87 on Jan 20 2022 11:33am

James May is that you?

Who is James May?

There was a little break in the updated, however i figured i could draw the important part in 3d to easier have volume calculations and such.

So i started with 360 fusion last day, never tried before. But now im done with crank + connection Rod + crosspin + piston + cylinder wall(without the ports so far) and a ugly top gasket/seal in alu. Im able to rotate the crank such that piston and all moves correct.

Next part will be to make to cylinder head with correct shape and volume included with the singh tracks for a 10:1 dynamic compression.

Ofc i will have to Split the cylinder and cylinder head in 2, so i can take away 1 part and have a a crosscut check of piston opening ports etc

When i get good in this program i can make the entire frame, and at least engine outer block, as well exhaust system etc and make sure turbo and relevant parts dont crash.

Ofc if this really becomes interesting and i get good enough in the program i can draw the entire moped with gearing, clutch, carb, saddle, steering wheel, etc etc and calculate tension/compression and all kind of stuff xD i have 2 frames, and 8 or 9 motors and several cases with just motor parts so i can meassure easy xD

congratulations you are hacking it