Exhaust pipe simulation.
https://www.youtube.com/watch?v=jaAE-Bq2lvo
CO

CO, I'm currently working with Dave (autobeta) and Neels (author of ENGMOD2T) on Engine and pipe designs for the Oddy and Pilot, Should be interesting :)

Meth

Wow I'd love to get my hands on those cone templates :)
Cone templates for stock and modified FL350 at 6700rpm powerband ;)
CO

Hey meth -- Yes I have seen some of those vids on youtube.
Ask those guys what they think of ultra high compression and water injection for a two stroke.
David Vizard did some work on this in the 70's on four stroke v8 engines for racing. There is a youtube video or two on it.
https://www.youtube.com/watch?v=jextyKc2UN4

Just thinking outside the box.
CO

CO, will do on the water injection. I have a fair amount of experience with water...water/methanol mix injection in turbo set ups. Good Stuff!

Right now I'm working on 2 brand new FL350 pipes, a rev pipe and torque pipe...and yes they are different. Then there's an FL400 performance pipe and CR500 conversion pipe. I'm also working on an FL350 Rotax performance pipe. Everything is moving along.

Other items on the list are numerous, a new FL350 cylinder...This will be a first... and other goodies :) Here's a few pipes for your viewing pleasure..

OH my and still air cooled
CO

Hey meth -- I'm looking at that pipe on the FL350 and I'm not sure if I like that design.
On the front cone there is a "steep step up".
This is a bit of a "reverse" cone so wouldn't it reflect part of the wave coming from the rear cone and therefore not push the charge back into the cylinder ?
CO

CO, no, the multi section (angle) diffuser is a common strategy in pipe design. There are guidelines established through much research including Blair's where the rational behind this is explained. Several of the OEMs actually introduced this in the early days of 2 stroke GP racing, which led to further investigation. The diffuser as a whole can be varied in several ways, yet still needs to fit within the theoretical calculations including: temp, id, length and angle.

If you look at a pic of one of the more popular FL350 pipes from the hey day, the "Kleem" pipe, you'll see the same strategy was used. As a side note that pipe was designed and made by power pros.
Take a look at the 4 pipes in the picture, all 4 pipes are for an FL350 and all 4 even though they look very different, have very close averaged dimensions. That said each pipe functions with a slightly different temperament then the other.

It's important to keep in mind the thermodynamic driven process that is going on in the system as a whole, then the design of the expansion chamber is such that you exploit that process.

Very interesting.
On my brothers machine the Engine is built. Has the "cats eyes" exhaust ports and 2 mm shaved off of the bottom of the cylinder. It also has a pipe that looks exactly like the pipe on the far left of that picture. It was made by bill's pipes and has that sticker on it.
Mine has the same style pipe made by DG pipes but it has a two piece longer inlet section coming from the head.
My brothers machine with the built Engine is way faster than my two stock machines but all three were the same until you hit 40mph. Then his machine just runs away. That "dyno" run data is posted on this site. I had an app on my phone and ran all three on our airport road. It's the one we used when I was a teen in the late 70's as our unofficial drag strip. We had white lines painted on the road back then but they're worn off now ----- Baahahahha.
Adnoh did a great job on the charts in that post.
CO

Edit: Anyone reading this post if you are interested, here is the post:
viewtopic.php?f=1&t=19752&hilit=dyno
CO

By the way I did build an actual dyno. Here is the thread if anyone wants to read it.
viewtopic.php?f=1&t=19665&hilit=dyno
The video link no longer works because I took down the vid from youtube but if anyone wants me to repost, I can do that for you.
CO

CO, great last post! Perfect example to look at pipe design. You can start with the general theoretical equation which tells us the general length a pipe should be, it uses exhaust duration, the speed of gas (at a certain temp) and the rpm of "peak" power. Lt= duration x SOG/Peak RPM where Lt is total length, duration is exhaust duration, SOG is speed of gas in the pipe and Peak RPM is the RPM the combination will make peak power.

There are many variations of the calculations utilized that break the total length into the theoretical sections of the expansion chamber: Header, diffuser, belly and baffle. These calculations can be manipulated to satisfy the systems intended use and spacial constraints. A simple visual of your pipe (DG, which is actually the pipe pictured on the far left, and your brothers pipe (which actually looks to be a Kleem, second to last on left..the rusty pipe) If you look at each section, they may/will differ tuned pipe by tuned pipe, but reverse calculations all lead back to the first. The 2 stage aggressive diffuser on my pipe is an example of this. Normal diffuser angles for Motocross are 7-8 degrees, normal angles for road racing are 8-9 degrees, each type of racing calls for specific power band ranges. Now take into account space limitations in the Oddy and by perverting the diffuser angles and lengths we can still design within calculations for intended peak rpm.

DG has a longer header (lead in pipe) and a semi-long less aggressive diffuser, building the pipe this way causes a longer strong evacuation of the spent exhaust charge and strong draw on the incoming charge. Now skip the belly for a moment and look at the baffle, it is long and has a slow tapered ending. This design actually doubles as baffle/semi-stinger in that the bleed of of pressure is slowed enough to enable the less aggressive baffle to send a good return wave and keep the fresh charge that the long header/ diffuser pull into the cylinder, stuffed in the cylinder. These design characteristics give a factory oddy Engine great low end power and infact brings the peak power rpm lower compared to the Kleem pipe, hence your brothers buggy moves out better as the rpms climb. In order to design/tune a pipe in this way demands the belly be of appropriate length to facilitate the primary and return waves cross where they need to for all of this to happen.

Now, your brothers pipe has a shorter header, a larger id diffuser a larger id belly and a shorter larger angle shorter baffle. Based on the above this pipe loves higher rpm and works better with modifications that support higher mass charge movement through the system and higher peak rpm utilization. When the Kleem pipes where sold (per Harry Kleem a couple weeks ago) they had higher engagement primary clutch springs included. This pipe shines when the Engine is twisted hard.

On your brothers machine, why was the decision made to cut the base of the cylinder down? Has the deck been cut at all? You mentioned the porting and exhaust eye brows, has the exhaust duration been changed other then cutting the cylinder base down?

1) I do not know why they decided to cut the base of the cylinder down.
I bought two of my machines in the USA and this was one of them. I have no history on the Engine or the machine.
All I know is that it is goddamn fast. The dyno runs at the airport proved it. It still pulls hard at 60mph. It loves rpm.

2) It does not appear the deck was cut.

3) I don't know if exhaust duration has been changed. But I doubt it. Looks stock except for those "eyebrows"/cats eyes.
When I first bought these machines I knew NOTHING about oddy's. I blew up this particular Engine 6 times before I figured it out. You will notice the beautiful smear of liquid aluminum on the cylinder in the pictures below.

4) In the pictures below you will see that the base was obviously cut down 2mm because the webbing on the cylinder base is noticeably smaller than the stock one on the left. It's the picture with the straight edge.
Also seen is the cats eyes (eye brows) exhaust port.

5) My brothers built Engine had 173 psi compression after the fresh rebuild
An Engine with my homemade head had 153 psi compression
My Engine had 140 psi compression

6) Once I switched to AVGAS all of my problems just disappeared.
It was like penicillin -- Insta cure. That's why I'm always yapping about it.
CO

Edit #1: I had to think about this for a while.
They cut down the cylinder base to gain intake timing (about 11 degrees based on my calculations). I may be wrong though on this theory.
I say you gain intake timing because the piston don't suck the reeds open until it goes up.
By lowering the jug you have lowered all exhaust, transfer and intake timing together.
BUT you gain on the intake timing 11 degrees because it opens sooner because the jug is lower.
Am I on smoke for thinking this way ???
CO

Hey meth: I know this is off topic here but you don't show up and comment very often anymore so thought I would throw it in before you disappear again.
I just remembered a question you had years ago when I made a homemade cylinder head.
I was cutting the combustion chamber with a homemade cutter made of high speed steel.
I think you said you tried that too but the cutter wandered.
Well that happened to me too but it was because of the pilot hole I drilled. I bet you made the same mistake.
What I found out was that you do NOT cut a pilot hole. Just plunge the cutter into the aluminum. It finds and holds it's own happy spot.
By the way that Engine still runs great and also has a welded piston in it (it was holed). We went out for a ride with it about a week ago.
Also of note is that this Engine still has 153 lbs compression, taken about a month ago.
Pics below.
CO

Is Professor Blair's work still relevant today, technologies evolve and change all the time?

Keep in mind I have not looked pipe design since the late 90's so admittedly I am 2 stroke expansion chamber stupid but I would think with the evolving power valves on the exhaust that change the exhaust port opening height on the fly some new discoveries may have been discovered during that time period that would apply to most all 2 strokes. Not even sure what new tech may have occurred since the power valves came out.

Four strokes has evolved so much my next jump would be to a 4 stroke like the Polaris ACE 570 or the current 875cc twin cylinder Engine.

Never be afraid to try something new with a 2 stroke pipe, remember the center bleed pipes that were made for the FL250 race engines they performed really well.

Hey Meth:
Work with me on this pipe theory of mine.

A lot of work has been done on pipes and pipe calculators but one of my theories concerns back pressure and time.

At very high rpm there isn't much time for the returning reflection wave to shove the fresh charge mixture entering the pipe back into the cylinder.
My theory is that it may be the actual exhaust pressure inside the pipe that prevents the fresh charge from even escaping in the first place and it may also be holding back some escaping exhaust if this pressure is too high. The pipe designs would obviously try to minimize this back pressure but there is no way in hell it is zero. I wonder what the real pressure in there is at 10,000 rpm.

This is a two fold problem.
If there is pressure in the exhaust pipe then there will be pressure in the crankcase and this will cause a reduced fresh charge from entering from the reeds and carb.
The vacuum from the piston going up would have to overcome this pressure BEFORE it can suck fresh charge through the reeds -------- no ??
So at higher rpm you are losing volume of fresh air/fuel.

So that tells me two things:
1) Auto adjustable stinger size on the fly or
2) Auto adjustable distance of the reflection cone to come closer to the exhaust port (impossible to do on an oddy).

The auto adjustable stinger would be easy.
CO

Don't forget to look at the picture above that answer one of the questions you had on why they cut down the base of the cylinder on my brothers built Engine.

Hope you come back to read this post.
CO

Edit: Oct 17th
Here is two videos I did recently on exhaust back pressure:
1) With muffler: https://www.youtube.com/watch?v=Q49ZWyxjBr4
2) Without muffler: https://www.youtube.com/watch?v=-mPiuWMOw6U
CO

CO! I didn't disappear, I have been balls to the way with everything, traveling, my sone got married, my 1 Shepherd needed surgery...It's been a crazy couple of weeks. I will read through the entries in this post and comment later tonight.