Expansion chamber exhaust

[harleyracer59]

Feb 27, 2020 7:35:48 GMT -5 ThaiGyro said:

What Harley refers to as "side bleed", is my stock. My trade. Bread and butter. I am now 63, but have been working "Center bleed", side or whatever, since 1975-ish.

They can be better balanced, if you get close the bleed port sweet spot. Even if off, they will self tune...but at a cost in rpm, torque, throttle response...You might not know, but it is just internal pipe flow dynamics.
When you pay crazy money for a big name pipe? Flow dynamics! You tune to it. More power? More sound? Better "feel"? They are all more quiet, due to internal wave balancing/neutering.

We did a dyno series on my '99 Mazda Miata. 1.8 liter, stock internals, except a programmable ECU. We did OEM exhaust, We did "sport headers". We put on a "Spec Miata" competition system to run SCCA. The results? Sound, primarily. So you know, the "spec Miata" headers, were IMO, sponsor money...lost 5 hp on the dyno to OEM stock. I did some flow research, and installed an OEM manifold header from a 2001 on my 1999. Plus 11.6 HP!

You must get the poo-gas out quickly and let it goooooo!
So play with your pipe by tuning to it...have fun!

  hey TG   on my home made side bleed I just  cut the 180 off the back of the chamber and moved it to the center of the chamber. drilled a hole and stuck it half way in so 90* was in chamber and 90* was out facing the silencer back.  are you saying in your post that even the location of where the side bleed enters the chamber effects the performance?  what about the direction of the side bleed inlet?  like 180* the silencer to facing forward.  or cutting 90* off of it  so the side bleed inlet us flush with the chamber wall?   ive ridden 5 different scooters before and after switching to side bleed chambers, and all 4 pulled longer and harder than their end bleed chambers they replaced.   2 were mlm, 1 was estori?, other 2 were my converted chambers. 
     I would love to get you and 190mech together and chat about exhausts and take notes.   there would be a wealth of knowledge to listen and learn.     what location would you consider the optimal location to insert the side bleed? in the middle or more forward or back in the chamber?   what would you consider best direction for side bleed inlet?  flush with chamber wall ot facing forward or towards the rear of the pipe?   I look forward to your reply.   

[2stroked]

harleyracer59 John(190Mech) has a thread here somewhere where he lays utter boat loads of pipe knowledge on us. I mean it's just invaluable. I'll see if I can find and link it after a while.

[harleyracer59]

Feb 28, 2020 18:03:27 GMT -5 2stroked said:

harleyracer59 John(190Mech) has a thread here somewhere where he lays utter boat loads of pipe knowledge on us. I mean it's just invaluable. I'll see if I can find and link it after a while.

  thanks and I know of the thread very well.  ive read though it atleast 5 times just trying to understand all the info that's there.  ive also talked with john privately about chambers and silencers and building these.  hes an awesome guy and will share or take the time to explain anything I have wanted to know.   we are lucky to have him on this forum.     

[2stroked]

Feb 28, 2020 22:43:25 GMT -5 harleyracer59 said:

Feb 28, 2020 18:03:27 GMT -5 2stroked said:

harleyracer59 John(190Mech) has a thread here somewhere where he lays utter boat loads of pipe knowledge on us. I mean it's just invaluable. I'll see if I can find and link it after a while.

  thanks and I know of the thread very well.  ive read though it atleast 5 times just trying to understand all the info that's there.  ive also talked with john privately about chambers and silencers and building these.  hes an awesome guy and will share or take the time to explain anything I have wanted to know.   we are lucky to have him on this forum.     

Damn straight he is. The Peace Pipe has its own star on the wall. The time and care John has taken and gave to explain, build and experiment with these pipes. Its priceless. 90% of what little I know about these pipes is due to him. He helped me walk through doing the math to get dimensions to build a pipe for my Beamer. Pages of equations, eachnof which will make you hair turn grey, fall out, and run away..

I've still got those equations, results, and the pattern I've drawn out. Without his help, I would have never been able to even get close to that far.

[ThaiGyro]

Harley, really John is the guru. He has helped me with my designs, by giving me pipe specs to shoot for...think about that as I try to answer your question above.

We, meaning my long ago guru, Rick Schell, ,found many things about center bleed pipes. Better mid range and a bit quieter, without giving up top end...but that is a longer story.

With that in mind, I used to have pipes made, (Couldn't weld wax in those days) the idea was to "bottom center" the stinger outlet. This was an assumption of perfect internal balance. In reality I cannot mathematically figure that. John probably can, or come very close.

Why I suggested that it doesn't truly matter...is that it will balance itself, pressure wave wise, just as any chamber will, but do it more better...or MO Betta, because it is in or near the middle of the belly cone. Rick said a few times, that he wished he could measure the pressure wave peaks and different rpms. Nice thought.

The other thing that I got from here...john (190mech or Vert?) was the notion of stinger orifices. Some call them "restrictors"...I am/we are using them as port balancers, with some fun results. Again, thinking about what I said about flow dynamic balancing and Rick knowing that perfect was a guess...my personal belief is that you can regulate that with a port tuning orifice.

The example I recall: For my Honda with 49cc, 10,000 rpm the various calculators come up with 16mm pipe stinger diameter. OK, so you build that and tune the carb and iggy to get the best results at a given rpm, like WOT. Now, my thoughts is...or was, we have build a few now...is that if you install, say a 20mm stinger pipe +/-, but install a restrictor...or better yet have a series of them, you can reduce fiddle time with the carb and get better drive or better top end with one pipe. NOT big, but another easy tuning point. We fabbed up 6 for my engine. Internally: 15.6; 15.8; 16.0; 16.2; 16.4 and 16.6, give or take the variation of the idiot with the drill...me) I used a small drill and then machining reamers.

On the Honda I cannot give a great account, as the engine was near dead and now truly is...however, we did a top end job on a KTM 65 SX, with a conventional stinger, but welded on a fatter external port to the stock pipe, with an 18mm ID spec and it kicked some serious ass. The rider was top 10 in his class, but could not control the power in tight corner exits. We spent a few hours at the track, just playing with restrictors/orifices and whammo! He dropped nearly a full two seconds on lap times. Same carb tuning, but some additional suspension tuning as well. I think it was actually less responsive in the tighties, but gave him confidence on exits. From sliding to hammering. He did best with a larger orifice, which lowered the internal pressure a tiny bit, but gave better top end. Fine tuning.

On a scooter? Shoot, who cares? I tune for mid range, but I am old. Any CVT is best at full throttle, then back off as needed. Well, maybe any 49cc. My Honda OEM style, loved 7000 rpm, before it died, it hated that rev range, but 8800 to 9200 was sweet!  I havde a diagram, if you are interested.  I think I found it here on the forum!  Not a simple part, but not hard to make.  It involves a taper from pipe to orifice, based on OD geometry...a maybe -16 degree taper to the orifice, which is a few mm long, then a +10 degree widening OD to the exit pipe.  It works.  The cool part is that you can easily build an exhaust sleeve to accept the orfice tube And hold it in place.  Just remove the stinger and muffler...pop and drop.

[ThaiGyro]

Geez! I nearly forgot.

Center bleed versus side bleed? Pipe dynamics with GAS FLOW should be little to no difference. The reason we always did bottom/center bleed was over-all flow dynamics. No Two stroke is a "single phase" gas flow. Hot, maybe...the gas and unburned oil are holding hands. However, when you both slow that mixture and cool it a bit, It becomes near two phase, meaning the light hydrocarbon gasses separate from the heavier unburned hydrocarbons.

That is TWO STROKE BLACK GOO. Soooo, we made our center bleed pipes on the bottom, where the goo can poo! On the side? No poo, just pipe accumulation and internal malformation, meaning reduced performance. Simple?

We thought that there was a better chance at 14,000 rpm that the goo-poo would be expelled better. On high speed tracks...no goo. Technical tracks were worse. We cleaned every race.

Ohhh, And we did see 400+ rpm better with our bottom/center bleed designs than a conventional pipe with no port mods. Just efficiency? I do not know.


I personally believe that the best spot for a center/side bleed is possibly not the center of the belly cone, but slightly aft of that.  That "looks" like where the pressure might be highest, based on geometry. Someone may have a real answer.  There are so many things happening in quick succession.  Mind boggling.  For you younger ones trying to learn?  Good on 'ya.


The middle is good enough for me.

[goodkat]

Can a mod gather the info here and put it in a sticky thread? This discussion is pure gold!!

[ThaiGyro]

Harleyracer59, Sorry for the delayed answer, was out for a few long days...

I did not yet answer your stinger question. Lost my files to a computer geek, who re-imaged my back-up. Six years down the cyber toilet.

I will try using this:



The pipe images above are just one of many designs, but give an nice view. The BUKU, above, is an RC car pipe that slides. I am not doing that...yet

The rear baffle is a built in muffler, like many street two strokes of yester-year. The "nipple" you see is actually the reversing cone. Square cone? Weird. The bleed pipe/stinger is not long and tilted to the front.

We have a few designs cooking, all of which angle to the rear, but no build in muffler. The top picture is common on a Euro scooter. Note: no belly section really. The description says low to mid power. The bottom shows the convergent cone with a belly. Better!

NOW...picture that pipe with no muffler section and the bleed pipe rear tilted. What we have done, so far is a few variations. One stinger port at the middle of the belly with a 20mm inward protrusion and with no protrusion. (They both need external reinforcement)

The next version is the same two combos with the exit being just after the belly convergent cone connection.

Lastly, as described briefly above, we have redone a few with the stinger tube being larger than the designed stinger ID, so can can insert one of our restrictor/orifices.

This is what I referred to as bottom bleed.  We may end up with an open or perforated  convergent cone to reduce the return wave disturbance, but am thinking it would be a banded annulus with the stinger in the annulus.  (Sorry, "annulus" is an area or space between two round surfaces.)  A fat spot that gathers the exhaust in this case.  I don't like that as much, a tad less efficient.

Second note:  Rear exit stingers are most common for good reasons...top end screaming.  The designs we are playing with are attempting to gain more mid-range torque, where we have gearing mods to assist in top end.  Street scooters.  My poor sad Gyro cannot do more than 32 mph/48 kph.  More power in the engine needed and some  CVT /tire combo that doesn't create so much drag.

When I can find or make better diagrams, I will post them.

[190mech]

Here is a pic of the quick change 'nozzle' that Frits Overmars posted elsewhere a while back;



Helmut Fath was the inventor of it way back when a multi cylinder road racer needed different length stingers,but the tuned length needed to be the same..

[ThaiGyro]

Mar 12, 2020 19:41:22 GMT -5 190mech said:

Here is a pic of the quick change 'nozzle' that Frits Overmars posted elsewhere a while back;


Yes!  That is what you sent me!  That is what we are using.   Even on a stock-ish pipe with enough diameter, this orifice works!


We make them cheap.  Thin copper tubes...fill with melted lead or aluminum...drill the orifice...taper the inlet...taper the outlet.


DONE!     I can say...our pipe designs are not fun to do.  However, when we get close, these restrictor/orifices are the shit!  You can carb tune AFTER!...miss tune?  Just swap an orifice...bigger a tad or smaller.  It is easier than pulling a carb.

By the way...BTW, whatever.  I call this an "orifice", because that it what it is.  In my engineering mind, a "restrictor" is a devise that is designed to create a limit.  In the oil business, we used RO's...restricting orifices to create a constant, given a constant need.  Might seem minor to you, but not to me.  We could change them at will.  Your poop-shoot, for example, is an orifice that is self adjusting...Nice, huh?

[SMALL CC TEK]

Yeah all the center bleed pipes i have had are a bit quieter than normal pipes . For some reason i never checked it but i think they run hotter than a normal pipe just my opinion ..Nothing wrong with that i could just feel the difference in heat ..I personally like the performance of a center bleed pipe better especially on small cc motors

[190mech]

Being a 2stroke junky and building pipes since the 70's,ALL of the badboy stuff(MX,Drag,Road Race,Speed Record)use conventional tail end pipes,none of the masters to this date mention the center bleed concept..Gordon Jennings had a good article on inverted stinger expansion chamber pipes waay back; www.bridgestonemotorcycle.com/documents/do_you_really6.pdf
Center bleed packages better on a lot of applications,perhaps thats why its still used...

[ThaiGyro]

As 190mech stated...nothing new. I was lucky enough in the late '70's and beyond, to run some single and twin 2T's at Boner ville. One Yamaha 125, similar to my own, but running my 6 speed box...stuffed case, big ass Lectrons, ran a one direction pass of 186 mph...the bike had more, but we broke everything...every day. We saw a 50cc do near 150!!

The pipes on that bike were adjustable, but not by us drivers. So if a failure...gloom or doom! THe engine cases in those days...were quite sponges. We tried to line them, coat them and reinforce seals....BOOM!

[nme]

Feb 23, 2020 18:18:56 GMT -5 190mech said:

If youve got stock port timing,squish,etc there is no use in getting an expansion chamber,start modding it then yeah,its a needed item for sure..Sorry no brands were given as a pipe design is very specific to what the build is...

Where does this information come from?

[190mech]

Gordon Jennings,A.Graham Bell,Helmut Fath,Jan Thiel,Wayne Wright..