2 stroke expansion chamber outlet bleed pipe and port plugging pressure explained E5

Explaining the functions of the 2 stroke expansion chamber outlet stinger or bleed pipe.
The function of exhaust back pressure to port plugging.
Intake timing factors into the expansion chamber pressure.
Freeware 2 Stroke Expansion Chamber Exhaust calculator program
Download at birdcagesoft.com
(Page link on sidebar at site)
#2Stroke #ExpansionChamber

[@copisetic1104]

Stinger diameter and length affects the piston temperatures also. To small of a stinger will narrow power bands and damage pistons. I have used high speed pressure/temperature sensors in various expansion chamber locations to get critical pressure and temperature data for fine tuning pipes and ports. Prof. Blair was really good at using P/T sensors. That’s what got me started.

[@johnmundt2017]

when i was racing karts in the mid 80s there were many chamber choices available. everybody had there favorites and had there flex length for each one.there were aluminum one made in san diego CA they were called bozo pipes with a welded bozo clown on the back. some would rap there pipes. i saved all of mine and now im going to dig them up and do some math and see if my favorite agrees with what reality is do some reverse math. this going to be fun thanks for these vids keep up the good work

[@AuMechanic]

I messed with Karting in the 90's, we didn't have a lot of pipe choices here in Aus. But going from making pipes for bikes the Kart pipes were revealing in the differences between them and bike pipes.

[@The1badxj]

thanks for making these 2 stroke pipe videos, learning new stuff is fun, going to take a whack at building some pipes for my 30.5 1/5th scale engine.

[@AuMechanic]

Ive got a series on building pipes and equations involved in a playlist and Ill have a freeware pipe calc software up soon.

[@hammer32953295]

Hi don't know if your still active, I'm trying to figure something out, have made my own pipe, a mid range nice long pipe, had a curved stinger 180 Deg and slip on can, looked rubbish and was awkward, so cut it off and made a silencer, it's the same length as the stinger but now has the center section missing with a perforated pipe around it and a bigger pipe again around that, I'm hoping it will act like a stinger with length, but can't find enough info on the net to confirm, Pipe is a test pipe so will be cut and remade a few time, as it's my first scratch built pipe

[@michelem.1461]

Hi I've just discovered this channel and I'm loving it. Can you make a video with the explanation of strange types of chambers like chain saw's, old karts, street bike (with diaphrams) ecc.?

[@AuMechanic]

Hi Michele, glad you like the info. i will do a video on odd types of pipes, was going to cover that a bit in pipe building tips but also found a pile of old pics of Kart pipes that are worthy of mention, ones with sliding internal baffle cones etc. Kart pipe makers have been at the forefront of creative expansion chamber design for a long time thinking well outside of the box to see what might be gained.

[@KB_Joys]

Hello yes im looking for information about a belly stinger. Dimensions, length, placement, etc. I have a jog 50 pipe and thinking about adding header length as well. I intend to put this on an 85cc motorized bicycle engine, thank you

[@shroomskunk]

Would it be best to put a side exit stinger also slightly ahead of the baffle cone center like the internal stinger install?

[@kaneto88]

AuMechanic , I have an idea and would like to ask you do you think it can work. The idea is instead of typical stinger to use a lot of small holes in the belly area venting to a hollow chamber (with adjustable outlet) built around the pipe.

[@AuMechanic]

Hi You do not need a stinger at the rear of the pipe, that is just a gas bleed off method for the pipe, some very old Karting pipes had some unusual methods of bleeding off. Some had like a big can on the end of the baffle cone with no stinger at all, the can had bleed holes in it or one on the side of the can and some baffles to muffle noise. I would not use perforation in the belly section, rather to the rear of it then the middle. There are some kart pipes that have a perforated baffle cone with a very short outlet pipe that is to the side of it.

[@shanepipkin4041]

a 66 cc 2 stroke is it wise to drill a 1/16 hole before muffler for back pressure do to epa regulated without carb tune?

[@tinolino58]

Sachs 503 with 55ccm Ok, ich have only a mild resonance in my newly designed exhaust compared roba standard 28/70 cigarre. At 5000 rpm I feel much less power. Top end is a bit faster. Instead of 62 now 66kmh. I will modify my short 40/15mm stinger with a reverse pipe back into the reflector. I go for 70mm long and 14.2mm diameter. Any additional suggestions? 🙄

[@nazrinsyafiq6770]

Hello sir... My i ask u something.. To get more higher rpm... What is the suitable stingger need tu apply..? big and long stingger or short stingger but still big diameter? Can u explain to me?

[@AuMechanic]

Hi Nazrin The RPM range of the pipe is determined by the "tuned length" of the whole pipe, see the latest series on how to build an expansion chamber shows how to calculate that. The outlet pipe length and diameter determines how much back pressure the whole chamber has, a outlet pipe diameter of a given size causes a certain amount of restriction, if you make the outlet pipe shorter then it will cause less restriction which would be the same as slight increasing the diameter of it. This is covered in some more detail in the last video "How to Design a Two Stroke Expansion Chamber Performance Exhaust - Step 7"

[@Fumacenta2tempos]

Man, so this internal lenght of stinger, is the same as if the stinger would be totally outside? If it is 5cm inside and 10cm outside, is the same as 15cm outside?

[@AuMechanic]

To the operation of the pipe it is the same thing. The outlet pipe is a bleed off outlet to maintain some back pressure which also reduces spilling of fresh charge from the cylinder. That some of the outlet pipe is located inside the pipe makes no difference to that function.

[@Fumacenta2tempos]

@@AuMechanic thanks man, i loved your channel

[@Fumacenta2tempos]

@@AuMechanic do you know that proportion, that says the header must be 34% of the total length, and the header plus the diffuser must be 68%? The total length I mean is header+diffuser+cilinder+reflector. It makes sense to you?

[@johnirvine3346]

I need to move the outlet forward on my expansion chamber to shorten the overall length. What is the range where I can locate the outlet? Thank you!

[@AuMechanic]

You can push the stinger pipe inside the expansion chamber, according to "Jennings" the best position (no effect to power) is with the inside end of the pipe forward of half the full convergent length of the baffle cone.

[@LoweSpeedFab]

Hey Mate to calculate the mean point of reflection. Do you measure the “theoretical intersection point “of the baffle cone then run a center line to The widest point of the cone and half it ? Iv built my own pipe and it was rather loud iv used the method above and went 1 inch beyond my mean point of reflection with my stinger (same calculated length). and didn’t notice any sound difference. Is it typically a noticeable difference?

[@AuMechanic]

Hi Jacob Using Gordon Jennings pipe equations (Two Stroke Tuners Handbook) yes that mean reflection point is half the centre length of the full theoretical cone length. Equation is base radius X cotangent of half the angle of convergence to get the full length of the theoretical cone, then halve that. Pushing the pipe forward of that as Jennings specifies wont reduce / muffle the sound level of the pipe it only reduces the sharp peak of the sound a bit. Keep in mind that sharp peak is highly directional so you probably wont not notice any difference unless you were behind it. As Jennings notes it is more in the interest of with noise regulations.

[@LoweSpeedFab]

Thanks mate iv watched back on some videos i took of it running with the standard stinger vs the internal and as you stated rewatching the videos there is a less “sharp” note which sort of makes it seem less “loud”. Thanks for the reply mate really appreciate the detail you put into your videos they definitely inspired me to have a go at making one myself. I sent you picture of my bike and the pipe i made via Instagram if your interested in a look

[@AuMechanic]

Cheers Ill check it out I'm doing a free software pipe calculator that will be ready in about a week or two using Prof Gordon Blairs equations from 1996, Jennings equations are back from around 1970's

[@LoweSpeedFab]

I used a basic pipe calculator based on Blairs calculations. Im not sure how accurate this one is but im sure it will get me in the ball park and a much better pipe then the standard boxy muffler. Ill be sure to check yours out for my next pipe.

[@LoweSpeedFab]

Hey mate one more question thanks for replying to the previous. If i am to add a muffler will this have any effect to the tuned length? Or is it simply an addition. And if there is an effect is there some sort of calculation that can find a point of compromise for example i take 3 inchs of stinger of for 8 inches of less effective perferated tube straight through glass pack muffler the retains the same pressure in the system ? Or does it just not work like that. Thanks

[@wideopen125]

Thanks for the informative videos, love the blue dot tutorial. Just a quick question - On a KDX200 hybrid I had to cut 1" off the stinger to get the tail pipe to fit the frame mounts. (FMF Gold series main pipe, FMF Powercore tail pipe). The bike doesn't have the top end I would expect, no over rev, shuts off after the strong mid range hit. Could I have affected the power with the stinger cut? I'm obviously looking into other factors like carb and timing. I don't have any previous knowledge as to how the engine used to run.

[@AuMechanic]

An inch off the very end of the outlet pipe would not make a difference, at least would not cause the issue you have.

[@jpvalve]

did you figure it out yet? sounds to me like you might be running too lean, or rich cant really tell without seeing/hearing how it falls flat but it could also be that the kdx looks to me to be a enduro/trail bike and they tend to have been factoryported for more midrange torque than top end power so if you are comparing to race tuned mx bike its gonna seem to fall flat without massive spike

[@wideopen125]

@@jpvalve Thanks yeah I know what you mean, but the KDX is known for a snappy top end. I think I might have found the issue, but haven't ridden it yet to check. The reed valve insert (plastic stuffer with oval hole) was off an older KDX and hole was centred. The later manifold hole is offset, so they weren't lined up. And possiblt not fully sealed.

[@nimbusnimbus.IV.]

I never had any issues with stinger length, the diameter is another story.

[@marthamryglod291]

Kdx200 have that type of power anyway. An aftermarket exhaust amplifies low/mid improvements for tight wood riding.

[@dustinbailey9548]

I'm looking at replacing the muffler in my 2 stroke snomobile with a straight pipe, can that affect performance?

[@AuMechanic]

The smallest stricture of the pipe is "normally" the end that is in the chamber and so long as you are not changing that then there may be no loss in performance. You will have to try it and see.

[@sinurbia]

Hello. I have a question regarding a 2 stroke pipe tune, in this field its about the stinger length. So I welded up a silencer to my stinger and they both have the same diameter but when I went for a test run, I got a massive amount of bottom end pull and the higher revs were sort of gutless. Do you know what could be causing this? Can you give some tips? Many thanks.

[@AuMechanic]

Hi Nitrow Covered outlet pipes in this vidoe kzbin.info/www/bejne/pGakp3pjnampj5o The bleed rate of the outlet is a factor of diameter and length, they are fixed to one another, so if you make a tube longer it will have to be a larger diameter to bleed gas at the same rate. Too small power has been pushed down in the range due to the plugging effect increased at lower RPM, at higher RPM to the degree exhaust is pushed back into the cylinder killing top end, and scorching and potentially detonating the piston if you keep it up. Id suggest the mufflers you got are a little on the small side. Designing a pipe you can factor in the muffler to calcs, but adding one after market its a bit late to do that. Since it'd be too hard to upsize the stinger diameter it's be easier to try some mufflers with a bit more room in them such that they don't restrict the stinger. Another possibility is if you get a bit happy on the welder and there is a bead line inside the pipe choking it down. Maybe shine a torch down the end and look at your weld spot from the inside to see if its smooth inside.. Hope that helps, Ill be doing more on pipe diameters in next video.

[@sinurbia]

I did happen to find a bead sitting in the stinger, I just didn't think it would make such a big impact on performance.

[@AuMechanic]

The ID of the stinger is critical. For example where the outlet pipe figure is around 0.7 times the size of the ex port, a difference of 0.69 to 0.71 times the size of the port will have an effect. As its a small pipe any slag or over bead inside it will change the ID by a decent percentage and as you can see it by those figures a small change will have some bearing on the stinger outlet. The header likewise, not the same concern as the stinger pipe but like the stinger those are the two parts of the pipe the ID has to be free of any protrusions. That said the mufflers may still be a bit small, perhaps use a joiner tube over the OD of the stinger, just cut out the welded part so the stinger pipe end is clean, saw a split in the short joiner tube ends so you can clamp them to the muffler inlet tubes and try them out. If all is good you know it was the welds, if not good then you likely need to up size the mufflers for it.

[@sinurbia]

With all being stated, do you think a smaller exhaust port area/port duration would do any help in a situation like this? In case I remove the obstruction from the stinger, and the engine is behaving the same due to excess port plugging pressure, do you think having the port sealed earlier while having less port area will help cut down on at least some of the exhaust going back into the cylinder? I was thinking that this would create more of a bleeding process to prevent as much exhaust from re-entering.

[@AuMechanic]

In principle a smaller port area will offset the smaller stinger, but you would not do it for other reasons. One being a change to port area height wise will have a change on the port timing and tuned length values , secondly the belly diameter is also related to the same port area not just the outlet. If the pipe is made to suit those specs then you are de tuning it. Also comes down to the port timing you have and which end of the range that is at now. I should also mention, the problem you had is probably the pipe and since the addition of mufflers as all that was done, but other things can cause the same condition like slipped ignition timing and not limited to that, so be sure to check something else has not occurred during the period you added the mufflers before more cutting and welding.

[@wayneca2112]

Hi do you know anyone in Sydney that make 2 stroke expansion chambers for bikes as I need one built for my 1974 Beta 50cc bike thanks Wayne

[@AuMechanic]

No sorry I don't. Making custom 2 stroke pipes is a bit of a lost art. I have not made them for anyone commercially for decades, few are willing to pay the price it cost of making them.

[@marinelsubu2366]

You see it like this , it would be best to show it all in the CFD. " Two stroke stuffing " explains it much clearer and more colorful in just two minuts.

[@AuMechanic]

If you only want a brief explanation or animation that shows how expansion chambers work purely for general interest only then there are many of those on youtube but this channel is not one of them. This channel provides detailed tutorials on each component of the pipes and the equations used to design them to provide all technical detail required for those who want to actually design and build expansion chambers based on the scientific SAE published works of Professor Gordon Blair.