ESE's works engine tuner

[dinamik2t]

Thanks for the time you took to analyze! That's really great info!

It's not like in reality things will be near the 'limit' as in the sim, but ok. I guess there are a lot of stuff concerning proper engine assembly & clearences to achieve those results. And then there is carb tuning ofcourse!
But.. in stroke we trust.

[husaberg]

Question why is the optimum configuration for a 2 stroke seemingly square bore and stroke. ie 54x54mm or 50x50mm.

What got me thinking about it was Wobs insistence that Vanessa be a Square motor around 50mmx50mm and the Final configuration of the Cagive V4 which was converted to 54x54.5mm in to improve midrange power.

Is it just the best trade off? ie port width vs height Combustion chamber dimensions.etc force area on piston heat loss etc.
Or is there more to it.

If someone was to modify say TZ's 56x50.6mmm 125 engine to 54x54mm and assuming all the port widths were kept in proportion to bore sizes was retained would there be the same top end power and more mid range? Theoretically speaking. I am assuming the engine is still within its mechanical limits with rpms of course.

Found this from Wob i knew it was somewhere. It answers a lot of my questions.

Scaling ports in a 2T is a complete waste of time, the STA numbers are different for every bore/stroke ratio, rpm and swept volume.
In general you want to keep as close to square as you can, as this maximizes the angle area available, and maximizes the safe rpm for the swept volume.
ie a 74 bore on a 58 stroke for 250cc will never make as much power as a 68 square 250 as the angle area of the ports is reduced way more than the short strokes ability to rev ( piston weight notwithstanding) and make power.
The roof angles for A,B,C were reversed years ago from your convention ie 25,8 ,55 , and the floor angles depend upon the inner turn radius size.
Scavenging patterns will be similar for similar bore/stroke ratios ie a 50 square, will be similar to a 75 square, IF the STA numbers are equalized for the max rpm achievable.
ie reving a 50 stroke 100 to only 12500 is nothing like reving a 125 Gp engine to 14500.
Bottom line is that to maximize power, the transfers will need to occupy ALL of the wall area not taken by the Exhaust, and once this is achieved then blowdown STA will ultimately set the power achievable.

Found this today Replica TZ anyone.
http://www.fondseca.com/index.php?ma...8743f63a4d4772
http://www.fondseca.com/index.php?ma...index&cPath=96


Here is below a couple of not so well known 3 cylinder 2 strokes.
No Honda's here. A ADM and not your normal Laverda triple either 1985
The pages look unreadable but they are clear when zoomed.

[wobbly]

As I said in the previous post we need to address two important factors in a 2T engine design.
Torque and rpm
It all comes down to Hp = Tq*RPM/5252.
Keep the torque constant and increase rpm by 10% and you get 10% more power.
Hard part is holding up the torque at the higher rpm level.
A short stroke will allow greater safe rpm, but the bore area needed to create the angle area needed, is limited more and more as you increase the piston size at the expense of stroke length.
The piston gets heavier as well, so ultimately the engine may not physically be able to rev to anything like what the stroke may allow.
Yamaha tried for years to fight Honda with a 56 bore size.The 250s failed miserably from Haradas win in 93 all the way up to 2000 when Jaques won easily on the new square engine derived from the 500.
The 125s won in 74 then never again.The short stroke 500s were useless except for the Rainey years, where he rode the wheels off the thing and Kennys bench was real deep.
The bottom line to all this is that the square engine has the best compromises of rpm capability Vs useful bore area.
Go short stroke and though you may be able to rev it, the scavenging is compromised by the bore availability.
With long stroke - the reverse happens.
This all assumes we are talking max power capability - 250cc MX is all longer stroke now as this favours torque production from low rpms,and the extra rpm capability of a square engine isnt needed to create peak power numbers.

[F5 Dave]

Wob, just looking at the hand drawn pipe in this list Frits posted (pijp 21) & looking at the stinger venturi; -it would tend to follow your rule of parallel section diffused out ~1.5mm larger, - the only thing I am confused about is the smallest diameter is ~23mm which is what I’d expect a conventional 125 stinger to be.

I thought the idea was to run a very short section at a smaller di than you’d run a conventional stinger mimicking the restriction of a longer pipe? So even though the drawing is exaggerated the diameter isn’t that small. I was expecting 21mm or something like that. Is it because the last baffle stage is steep? Or the requirement to get heat into the pipe can be produced by other means of ign & powerjet so stinger sizes have increased? It still seems odd. Or am I just wrong about the smaller than conventional size part?

[dmcca]

a question for Mental Trousers...

Is there any way to download or copy this entire thread in one go, attachments and all? Or possibly a way to make the printable version more than 40 pages per page and include the image thumbnails not just the URL?

Im heading away on holidays soon without net access and would love to take a copy of the whole thing to re-read

[F5 Dave]

Won't someone think of the children, cough I mean trees, Won't someone think of the trees.

either way most of the first 200 pages is lather & engine specific, although no one has accused anyone of being like Hitler (although maybe that did occur & I've forgotten). Mental won't read all threads so won't answer, perhaps a post in 'Site Stuff' thread.

[edit]
Ha, just for giggles I read the first page back in 2008. Post 5 for me & I'm probably still spouting nonsense.

[dmcca]

Won't someone think of the children, cough I mean trees, Won't someone think of the trees.

either way most of the first 200 pages is lather & engine specific, although no one has accused anyone of being like Hitler (although maybe that did occur & I've forgotten). Mental won't read all threads so won't answer, perhaps a post in 'Site Stuff' thread.

[edit]
Ha, just for giggles I read the first page back in 2008. Post 5 for me & I'm probably still spouting nonsense.

Thanks... dont worry the tree are safe... just want a copy in in word or pdf or whatever to go on the mini laptop

[Grumph]

from what i can see only the last couple of hundred pages are worth printing.
Out of curiosity I looked backatsome early pages and there's TZ wallowing in angst about air cooling a 125...justike a couple of pages back.

Fercrissake TZ - beg borrow or steal a copy of Irvings "Two stroke power units" and read wha he says about fan cooling....

As holiday reading though it beats Mills andBoon hands down.

[Buckets4Me]

Out of curiosity I looked backatsome early pages and there's TZ wallowing in angst about air cooling a 125...justike a couple of pages back.

.

the only difference seems to be the first time he was only making 19 h/p
and now he has nearly 30 h/p




They would make good bucket racers if they wanted to step up

[ac3_snow]

Quick question for all you wise ones out there. Should be a little more simple than what has been going on for the last month. Finally got around to trying to tap out the head studs which i ripped out two months ago. No worries except I also ripped out the one which I had previously tapped out to 10mm. Which is a slight delima as there is buggah all room left to go much bigger. So could I get it welded up and then re-drill it? or should I just devcon it back in....

as You can see in the pic I had a channel machined around the liner, to fit the head gasket/o-ring. This means there's not a whole lot of room around the studs.

[Henk]

Devon will likely go up in smoke. Main options are probably weld or helicoil.

[wobbly]

The stinger config in pipe 21 is exactly what is needed for a 125 making anything like 50 Hp.
I have been using CNC nozzles I had made over 10 years ago that are 23.2 at the smallest section specifically for the pipes I have built for karts that make around 50.
For a 125 down at 40 Hp then 22 is about right, as is used by the CR125 engines in SKUSA stock class,down at 30 Hp I would say 20 or 21 ( never built one, sorry)
It all comes down to the amount of air that is dumped into the pipe, and this is totally reflected in the Hp numbers - empirically these sizes work every time to generate the correct back pressure, without causing deto or finicky tuning issues..

[speedpro]

Which is why my pipe has a removeable end piece sandwiched between the end of the cone and the tailpipe. It is just a little piece of cone with a precise diameter nozzle. I tried one size then went up one and made more power on the dyno. Funny enough it felt better initially on the track with the smaller one.

[Frits Overmars]

Like below? Red is the exchangeable restrictor. Blue is its container, welded to the yellow endcone at the left. The yellow pipe at the right is the tailpipe (held in place by a spring) with a bigger diameter than the restrictor.

[speedpro]

Not as fancy. Mine has no venturi and is made from .8mm sheet. The two sizes I have were formed very tightly around the required size rod, welded, and then hammered with a rubber mallet. The end result is a perfect fit with a nice smooth finish. I might look at doing one with the venturi.