HIGHER EXHAUST PORT, GOOD IDEA? How Exhaust Port Timing Affects Two Stroke Performance. 

This makes me want to tune my friends moped thats been sitting outside my garage for a few months

The. More you raise the exhaust port more blow down is created. Too much blow down is what kills the bottom end. So sometimes you have to increase transfer (raise transfer ports) timing as well to keep the right blowdown ratio.

I really appreciate you putting the time to educate us on the lesser known facts of two stroke engines. I mean anyone has the concept of switching the air filter for a "performance" one, changing gear ratios, different spark plug, etc. But this stuff is a bit more outside the box and very intriguing

This totally blows my mind especially when just used to big cc snowmobile engines

This brings back so many memories =D I love the Peugeot sp, 103 and this newer one you are working on. If only we had mobile phones back in the day when I was working on those moppets lol.

Thanks for the tutorial.

When is the video about changing your balancefactor coming? btw, love your videos. They're instructive, not too long nor short, and you explain everything so well, good job man! Keep up the good work! :)

Love your videos very informAtive you defenitely need a television channel I'd watch every saturday faithfully at breakfast

Very usefull info ! Thanks ! Will use this for my KR1S !

That is a good explanation of raising the exhaust port but what happens if you lower it. I have just resleeved a two stroke cylinder and I reduced the port timing from 190 to 185.5. This was done at the same time as widening the ext port to achieve more area than before. I was hoping this would result in a longer power stroke.

Very informative video. Thanks for you explanation

Great explanation! For those who dubt about i suggest learn about time/area and more specific on blowdown time-area, in your case your positive performance are an e sample of the possibile with clever way! Aniway Thank you to Walter kaaden from mz we know also That timing lesso Thank 180 does nt work perfectly with pipe tuning..

You probably don’t think so but your explanations are easily retainable!!! Give yourself more credit my good friend! Appreciate all the time, energy and funds that you put in for the channel!!

Very informative. Thank you 🙂

And on day 7 god invented the power valve

Thank you for the video. Very informative!!!

Good series of videos. I'm really enjoying it. Might also be worth noting that the volume above the exhaust port is a sealed chamber containing a huge explosion so earlier you open the exhaust port the earlier the pressure escapes into the exhaust. The force on the piston (and the work done) drops suddenly as soon as the exhaust port is open.

Great job with the videos

This is a great topic

On 200 degrees on a 125cc running methanol, Reverse fuel pressure with a readout, change the timing depending and reduce cooling with with tape on the radiator, and also start rich with jetting and work your way down. My 125cc engine dyno’d at 39.7hp in 1997. And also drop one of the piston rings (bottom one)

Alex, nice explain, lots of pen action, can't go wrong with pen action, well at least until the ink runs out. To add abit of info for you and AuMechanic (good basic chamber videos, thumbs up). When engines run, they don't run at a constant rotational speed all the time thru the cycle. So say your rpm meter is displaying 11000rpm, this is the mean rpm, measured at one point in the 360* rotation. If you were to measure the instantaneous crankshaft angular velocity (done with an encoder with the output quad'd to get the resolution down to 0.1-0.2*) on a single cylinder 2 stroke you'll find the instant varies from the mean by as much as +/- 250rpm, 500rpm P-P. The undervalue bottoms around exhaust port open which then gains rpm until the overvalue top just before BDC and then loses rpm back down to the undervalue at exP open. So its not possible to use simple maths for the time that the exP is open and closed and this has an effect on why the natural port duration for resonance usage is not 180* along with other factors involving the sonic wave speed in the pipe itself.

if there is one guy i take advice from, then it is from you sir. 👌

Thank you!

How about chain saw engines with no pipe. We raise the exhaust port ceiling, and lower the intake port. Then we cut about 1/8” from the bottom of the piston skirt. I wish I knew more. I port Husqvarna dirtbike vintage engines and they respond very well. Like your videos.

2:28 damn you convinced me

Good content.

Simply put 👌

With all the issues fuelling the spx with nitro, does the different fuel affect the resonance? As in it depending which fuel used burns/bangs faster or slower the petrol,, meaning faster or slower pulses etc etc

I've seen a few youtube vids on how a 2 stoke expansion chamber work, none of them give the full story! The actual way that they work is that when the port is uncovered a positive pressure wave travels down the pipe but when it reaches the diffuser section of the pipe due to a law of acoustics some of the wave is reflected back up the pipe with a negative sign (in other words a partial vacuum). This vacuum actually helps pull fresh charge up from the crankcase above the piston and even out into the exhaust). Not all of the initial wave was reflected back, some remains as a positive wave and travels along the pipe until it hits the baffle cone, it is then reflected back with the same positive sign, this wave pushes the fresh charge that was 'stored' in the exhaust back into the cylinder. Simples! The acoustic law is basically that a pressure wave (positive or negative) is reflected back as a wave of the opposite sign when it reaches the end of an open pipe. The diffuser is a 'sort of open pipe', not fully open. This is why the diffuser is important in an expansion chamber. The law also states that a pressure wave will be reflected with the same sign when it reaches the closed end of a pipe. The baffle cone is a cone and not a flat plate with a bleed hole in it in order to try to increase the RPM range that the pipe will stay in tune. (The diffuser cone(s) can be tuned in the same way. Steep baffles cone(s) mean that the wave amplitudes are high but the RPM range that the pipe will work is very narrow.

sir i wanna ask, if im using over bore cylinder 59mm to 61mm have power valve..exhaust port should be hi also? mean,adding more gasket for cylinder? ..how about the head,need adjustment?..need your help sir..

Hello thank you for your video's. What happens to performance when you block off the converging cone exit .... and re route the silencer pipe to the belly area instead. Thus a side exit bend to the silencer instead of conventional exit at rear of converging cone. Hope I made sense.

Have you ever seen a Agria 1700? This is a old kind of "Tractor" don't know the name in english. In german its called "Einachser". The Agria has an Hirth 250cc Engine 2 Stroke! They are racing in the dirt with these Agria's... maybe a Agria would be a perfect Project for you?

The biggest performance killer when raising the exhaust is loss of compression. Keep that in check and you probably won’t notice much difference between a couple degrees.

Excellent! So you could get a custom pipe to match for the added height though?

the only easy way to do this for me is wack another gasket between the barrel and bottom end, this will also raise my intake, what effects will this have? my motor is a yamaha kt100j (13hp) it revs to about 11280rpm, i managed to get it to compete with its destroked higher output cousin (kt100s) but i seem to run out of power at around 10800

Do you have an educational background in design? Because you're always spot on with your drawings and you always seem to know how to make helpful diagrams

If the pipe pulse (a sound wave) is released earlier (due to a raised ex port), than it has to come back to the piston earlier also, (not later), since the sound wave is a fairly stable speed, (depending on pipe temps). It's a good point that I had not put that much thought into though. But "your" second pulse (off the piston, which I have never seen before) has to be diminished in strength quite a bit. But that would not matter. Once the port opens again, (the big boom),--that little pulse is going nowhere. Sorry man.

I just put on a 60cc cylinder on my moped and the exhaust port is "too high", for me at least. It has no torque at all but from like 7 or 8000 rpm the hp is insane and its sketchy to ride. I would wish that it had a little more of both since the old 49cc one had all the torque...

This vid only explains half of what an expansion chamber does, the positive pressure wave that travels down the pipe is partially reflected by the defuser part of the chamber (the diverging cone part), it is reflected as a negative wave, in other words as a partial vacuum. When this vacuum reaches the exhaust port it helps pull fresh charge up from the crankcase via the transfer ports, it actually pulls fresh charge into the exhaust pipe. This fresh charge is rammed back into the cylinder by a positive pressure wave just before the exhaust port closes.

Port wide 1/2 mm up clean transforports new case bearings seal retainers these bicycle engine can get to 15,000 rpm now they have 92cc motorbike engines 52mm piston

Hello, I'm just getting into motorized bicycles and this vid brings a question to mind; is resonance a factor in the intake as well? Also, if so how is it different from the exhaust resonance as far as affecting performance?

Cool video bro !!! I got a old 250 with piston port set up I’m trying to get it running I put new piston rebuild the carb it’s trying to start but no luck what do u think is wrong

With a piston ring out of the bore what should the gap be? I'm asking because I am curious to know how much tension the ring should put onto the cylinder wall when inserted in the bore around the piston?

Hello guy! Does the exhaust manifold/flange length have any effect on resonance? If so, can anyone please tell me what the difference would be using a shorter and a longer one? Thanks in advance.

So can this contribute to a weak power band? if not, then what makes a power band sluggish?

Por favor subtitula tus videos al español! gracias!!

If the exhaust port timing is too high can this be corrected with retarding the ignition? My 85cc dirtbike pops when wot more than 2 seconds jetting is correct. 105 BBC kit installed

So many factors not addressed. Tune exhaust design, carburetor tune, boost ports, reed valve,piston port, rotary valve compression, ignition ignition

What do u think about dimpling port0ing? Intake? Exsaust ? Just like a Golf ball i did it to my race 2 stroke motor thinking it wqill helo admizing my oil gas mix what do u think?

hello.. sorry I am commenting on an old video.. People always discuss about raising and lowering the port and it will indeed change the power curve of an engine. what happened if we tweak the bottom part of the port, i.e making the port longer down the cylinder, but not changing the port timing. what will happened then? I hope you can explain it if you have this kindof experience. thank you.

In the book 2stroke tuning by hayes Its a good book Gr marvin

tip top top tip : the hotter the exhaust pipe/gas is the faster the sonic pulse travels wrap or ceramic coating helps with this how am i'm gonna get this to work on my outboard engine hmm i don't know yet :) but something has to happen

but leaving the tube long on the carburetor you gain torque for what you lose in expansion chamber so I don't think I would shorten the tube on the carburetor

Hi! Me and my friend building a peugeot fox for mopedcross. Do you have tips for porting the original 50cc?

I raised the exhaist port on my cylinder i was just wondering How will know when driving if ive raised the exhaust port to high.

QUESTION:: Does more blow down give more torc or top end. Does less blow down give more torc or top end. There is no videos out there saying what more or less blow down does

I have a cheap chinese cylinder kit on a cpi sm 50 (Taiwanese Minarelli am6 copy) I didn't run the kit before rebuilding the bike but the kit had a silly amount of poorly cast, rough material around the exhaust port so in chamfering it I was raising the exhaust port also. in the upper RPM's itll scream away, has a very narrow powerband and not much power in the lower rpms so the engine has to be worked all the time which makes town riding a chore. its almost like a yamaha dt125 with the powervalve pegged open but alot worse since the little 70cc has less power than a 125

Hi m8, i like your videos a lot, maybe you can give me a hint with my bike. I have a 2018 Aprilia RX50 with engine d50b0, i took off everything that is restricting it, i installed aftermarket cdi, leovince xfight exhaust, polini cp19 carb moded with different jets and now i have a proper piston wash with 49low jet; 90 mainjet; neddle 12/22 clip position 1 above midsection, airsal 74.2 bbk, i kept the stock air filter, malossi vl6 reeds kit, gears 11/50. I would like to get more torque in low band, i use it only on mud and forest, don't need speed too much.... I would appreciate any advice. Thanks

i raised the exhaust port on my motorised bike it doesn’t rev quite as hard now but i also don’t have an expansion chamber will it be better with an expansion chamber ?

If I extend the exhaust timing to be higher... (184deg to 190deg) what effect should it have on my carb jetting? Should it be richer? And which jets? All of them?

Are performance crankshafts worth it? Someone told me that performance crankshafts are as strong as oem crankshaft. How much can oem crankshaft take before breaking?

So are you say you should or shouldn't raise the exhaust port

Tell us more about time area and blow down :D

Can you tune the expansion chamber to gain more effect on lower revs at the cost of performance on the high end of the power spectrum?

I had my cylinder head ported "sport port" do I have to upjet?

So basically, if i increase the exhaust port, it would be best if i also design a new pipe to match the port?

Has anyone tried a variable length pipe on a two stroke? Can't easily lengthen a cone, but maybe a short telescopic straight part between the diffuser and the end cone?

In the age of no internet and RU-vid, I've learnt this with trial and error with my little 110cc bike and ruined many cylinder blocks along the way. I learnt that high is always better, but the problem is to find a matching sport exhaust to match it. None of the ones/aftermarket sold in the store would match it but found one old and beat up exhaust matching it perfectly. I did not know it had to do with resonance but now I understand why it's a pain to look for a matching exhaust. It easily hit 180kmh in a few seconds. I used it for drag

I much prefer to widen more than raise.

Sir, I need such a help. I want to ask about the port of such a cylinder, how can we increase the speed from its port. Please help me. Please tell me.

So raise the ex port, lower the compression you gain the 17600 rpm?

So i have a small 2 stroke. I just measured the exhaust port duration and it is a measly 160 degrees. Should i CuT dAt ShiET? seriously though, i want the engine to rev higher, its a single speed transmission and i want more top end.

Matters with resonance is that a large numbers of moped just can't use it due to configuration the moves the engine ... Exhaust that lift up with engine are bit fragile on tightened points, If you specifically could "find" them, most of times not allowed anymore on roads, And other point is to built parallelogramme balance system onto the moped, ... Which is not either allowed on roads ... Resonance cannot efficiently be used on exhaust with ajustable inclination the move the engine . So, hight exhaust without proper resonance that reduce the frequency bitrate usable is not a solution on most of case . Better look for exhaust port in three pieces two barrels and two smalls laterals ones . You will have a way more longlasting rings ... Endurance the engine sometimes has to be considered ... Once theorical power cannot runs for miles, how get a sense the work done ?

I want to buy a new Cylinder for my 2 stroke bike. Some have exhaust boosters and some dont. What are exhaust bosters?

Widen the port is power.... make it higher the rpm goes up.. u need a balance between the two....

Sometimes i feel like i'm a high exhaust port 😂

But is it good idea if my engine hasn't got expansion chamber? Thanks.

shorten the pipe was my first idea.

I knew about the first pulse but not the second one is this why the power-valve works well it it give the flexible power band. Also Why does EVERYTHING in your workshop not go rusty like mine did with a propane heater in there.

When i port my yamaha jog 50cc cylinder i notice that Higher exhaust port gives very very much power put makes it lot more rpm but with giannelli exhaust,190° exhaust port and 19mm carb i get 96km/h

Is it 190 degree is suitable port timing duration for all 2 stroke bike ?

Not exaust port, but injection port at high pressure making a sort of supercharging, you could inject a little amount of fuel and NOS mixed with special injectors that already exist ( the injector wich inject fuel and NOS mixed), do you undetstand what I said. They Are NOT exaust port puted higher, they are actually injection ports above the exaust line.

Also doesn't the raised exhaust port lower compression

i se the wawe a difrent way. i se it like a pressior wave and controll it with the last pipe before the silanser. the pressior wave has to resunance and have like a little pause ca 10 or 12 cm the port so you get a under presior at the port and a high pressior in the rest of the mufler . the higer the revs the more presior and ther is ver i detirmet the Ø of the last pipe and controll the pause to get max back presior and max wacoom at the port and newer loos all the presior in the mufler. ewrything you push back in the cylinder is free horses.

Walter kaaden!

So a higher exhaust port is better?

Higher exhaust for my dont ist the good idea and less if you don't have a gearbox

I want to increase performance of my Yamaha Dt125 ypvs so I want to know how can i change my ports...

I believe you are talking about what is know as back pressure?? Some back pressure is needed to stop fresh air and gas from escaping out the exhaust while the cylinder is taking in new mixture or CHARGING. To much BACK PRESSURE is NOT good OR to little. Your type of exhaust comes into play here does it not??

I get the theory but what happens with engines that do not have a tunned pipe, say a chainsaw motor has a small box silencer, do the pulses still return to the engine with this design?

Just going to hopefully add to the conversation: You can make hp but have the power band so narrow that in real life, the engine falls below the band when shifting. The bike will be very sluggish and won't win any races.

Hey bro do you work on engines? If it were to ship you mine. Its brand new just want to make it max out on rpm.its for a scooter project.

so basicaly the earlyer your port opens the longer the pipe needs to be,

Size doesnt matter but resonance. Thats not what she said!

You should make a 4StrokeStuffing channel !!

Longer exaust timing, likes longer exaust systems...

Too many things I don't agree with to get into. To start with the pulse speeds are not the same. Not even close. The temp of the exhaust gas when the port opens is higher. And much hotter. Anyway how about doing a video with insanely low Ex port durations and fun things you can do with them. Chambers work better with high exhaust port duration than they do with low ex port durations.

Port High = Half stroke? Stroke 50 mm/ port High 25mm.....

Go 200degree,, stop the nonsense ;) check drawings from Aprilia RSA cylinder.

Ifyou worked on 4strokes you wouldn't be spending so much *money*