Fair weather rider
The technical questions are a bit too much for me, but the 72mm stroke lets them make a 300cc version just changing the cylinder bore, instead of having different cranks for the 250 and 300cc engines they keep all the bottom end equal across the two versions.Originally Posted by peewee
Gas Gas, TM and Husaberg do that, and KTM may as well do that "trick".
The rod length might be a compromise between ideal size and not to big that you end with the cylinder in the gas tank.
Moped rider
Just thank you for that thread! most interesting thread i ever read! Just one question: can anybody tell me where this chocky fish is available? i googled and can not find it. we only have chocky bananas available here in germany.
Weekend cruiser
Answer my self...
The more I think of it the easiest solution would be a resleeve etc etc...or make my own FOS cylinder from scratch.
Using any kind of putty will not work, even if TZ350 has shown the opposite in his ex-port.
Do as Wobs say and fit a reed valve to take care of the to high intake port and live with a to high transfer timing?
Or find that missing welder. Or both.
Crap, this was supposed to be a simple (low state of tune) engine just to have something running untill all crazy ideas can be put in to an other one.
Sorry for the rant, but its frustrating sometimes to know how bad i.e. a cylinder really is. EngMod2t prevents me from doing as "all others" and fit the parts and just ride the thing. Even for a simple engine.
Need to call that welder/brazer.
Hardcore Biker
Martin, thanks for keeping things in perspective here.
Peewee, it's not that I think the factories are "too stupid" to do something different. I'm just askin', same as you. The engineers weren't "stupid" in the mid-60's when everything had three intake ports, and nor were they ten years earlier when the engines were all cross-flows with deflector pistons. But they watch each other, and the state of the art changes by one outfit coming up with a new way of doing things that proves to be effective.
Have we reached the end-point of five-port (A's and B's and BP) 2-stroke development? As I read Jan Thiel, he seems to think so, that even with a clean-sheet design he couldn't do much more with a five-port engine, and that it would take a wholly new breakthrough design (like Frits' FOS) to get 2-stroke development going again. Personally, I'd like to find a little more power (outboards have no traction issue, and can hook up all the power you can find) from a five-port engine (Frits' 24/7 concept is very cool, but will surely be a bugger to get sized and tuned) before throwing in the towel and working on the FOS, which has too damned many exhaust pipes, Frits
Wobbly, I've gotta look for something . . . back in a minute, I hope.
Low personal B.M.E.P.
If you can't raise the bridge, lower the river...think outside the box. Taller piston ? longer rod ? Machine the case top face if you can't take more off the barrel.
No8 Wire Extraordinaire
After my bitching heating the epoxy made it flow better, just work quickly. Mikes bent steel idea had some merit too. You can spend forever inside these crappy 1978 MB100 ports.
Don't you look at my accountant.
He's the only one I've got.
Hardcore Biker
Wobbly, my teacher! Triumph! I actually found something! On P. 1023, Oct 23rd, Yow Ling in post #15336 offered "CFD Simulation of 2-Stroke Scavenging" and other goodies by C. Yang 3D. If you don't want to look, this was the sim with the cutaway cylinder that looked like it was running on tomato paste. There are some other nifty sims there, particularly one entitled, "Streamline," that might come close to showing what you are describing if I could just get the thing to run reeeeall sloooww. But I can't, so I have to take your word that the pinched corners of some of these ports appear not to drag down the adjacent A/F fllow. Makes no sense to me, but okaaayy . . . (still dubious).
(wobbly;1130805345]4T ports have been studied to death, and the best flowing examples have minimum turn to the valve axis and some have a flat floor giving a D shape to keep velocity up on the short turn.
(smitty) To keep velocity up, or to keep the flow attached and not turbulent? (probably saying the same thing)
(Wobbly) But as is described in the classical texts the CSA where the duct turns, is made bigger, and then necks back down to the venturi under the seat.
(smitty) Bigger CSA, PLUS a more flattened oval (or more-flattened D-shape, or more flattened rectangle-with-corner-radii) . . . right? This is half of what I'm getting at, as being (I thought) a better shape for the usual 2-stroke transfers as they make the sweeping turn.
(Wobbly) In a 2T we use the D concept on the short turn , but unlike a 4T where they are trying to get equal flow discharge radially thru the curtain area - and impart swirl, in a 2T we are trying to achieve different things.
Firstly is to keep the flow accelerating uniformly down the duct length, and secondly direct the flow uniformly so the discharge exits into the cylinder with NO swirl ie a coherent column.
Thus we cant use the expansion theory around the turn, . . . .
(smitty) "expansion theory"? . . . they want more CSA where the gas flow is taking a turn just so the flow rate will come out the same as in the straight sections of the port, right? wrong?
(Wobbly) . . . and IF the side walls were parallel at the exit then the best shape would be a rectangle to initiate and then preserve the columnar discharge shape.
But as is mostly the case, the front and rear walls converge radially, so the inner wall is best angled as an average of the two, and the square gets tipped over into a non parallel parallelogram ( whats that called ? ).
(smitty) FWIW, the non-parallel parallelogram is a non-symmetrical trapezoid. I thought I recalled it as a rhombus, but it seems they (rhombii? rhombera?) have to be symmetrical, where trapezoids do not. (I looked up quadrilaterals). Anyway . . . I sure wish I knew where/how to find that big-bore engine I referred to above, which evidently is or was a good performer, but differs a little from the more typical arrangement in your description, which I THINK I mostly get. Guys here have referred to the "hook" in the trailing edge of (what I think you are calling) the rear wall (Aprilia ports, I think), and I take it this is one way of getting the front and rear walls to "converge radially" (am I understanding you at all?).
(Wobbly) I have seen plenty of results from CNC anemometric flow visualising software, and have never seen any evidence that the flow in the corners of the ports is "lagging " behind due to excessive wall friction.
(smitty) This is where I wish I could run Yow LIng's sims in ultra slow motion, dang!
(Wobbly) So it would seem that the current techniques of linear area reduction increasing the velocity, and duct walls that initiate the radial flow directions early on . . .
(smitty) That last bit ("initiate early on") is part of what I question, and I don't see how it necessarily follows from the rest of what you've said. Taking four-stroke ports and runners, which as you said have had lots of development, they typically have a bunch of turns, entailing a bunch of shape-changes, from start to finish, even if we can ignore what they have to do to get around a valve head and impart swirl.
(Wobbly) . . . are the best compromise between raw flow numbers ( cfm ) Vs a high discharge coefficient with a coherent exit stream.
As always no free lunch.[/QUOTE]
(smitty) "discharge coefficient"? Just a dumb liberal arts major, y'know.
As always, I appreciate your kindly efforts and patience as you cast your pearls . . .
No8 Wire Extraordinaire
http://thetoastieproject.com/2013/07/15/chocolate-fish/ OTE=Martin1981;1130805850]Just thank you for that thread! most interesting thread i ever read! Just one question: can anybody tell me where this chocky fish is available? i googled and can not find it. we only have chocky bananas available here in germany.
ThE wonders of google. Results vary from country to country.
ahh crap i tried to post a link but tablet is a dog and i missed. At start of post
Don't you look at my accountant.
He's the only one I've got.
Weekend cruiser
Have done all that and yesterday I thought I hade it solved by using a different piston. But I was wrong.
Called my my welder and he will have a look. Think he will solve it just fine.
Thanks for the input and support though.
Hardcore Biker
frits it seems like one time you said if your FOS was upscaled to 125cc it would have even more power than rsa. do you have any predictions how much it would have ? if it was scaled even further to 250cc ?
Hardcore Biker
how you reckon this thing would fire. outside cylinders at the same time and middle cylinder 180* off ?
Forum whore
Being " just " an RZ with another tacked on one end it will be all 120 apart I suspect - easy to do with a jig as the crank isnt keyed
on the main axles.
Firing two together would be primary vibration balance suicide without a balance shaft.
Trust me I know, the BSL fired one end and the middle together, with 120 V angle and a balance shaft.
Very smooth, but busted cranks due to torsional twist, even taking the drive off between 2 & 3
Ive got a thing thats unique and new.To prove it I'll have the last laugh on you.Cause instead of one head I got two.And you know two heads are better than one.
No8 Wire Extraordinaire
Taking drive between 2&3?. Don't suppose you have pics of that?
Don't you look at my accountant.
He's the only one I've got.
Forum whore
The whole project would be futile if it would not outperform the RSA. From the point of view of the various angle.areas it should be able to rev about 20% higher than the RSA without running out of breath (and let's hope we can build a con rod bearing that will play along).
Estimating the scavenging efficiency is not so clear-cut. Of course I hope that it will reach the RSA's benchmark level (and sometimes I have wet dreams of beating the RSA's level thanks to a blowdown flow with less energy losses) but even if it loses 10%, I will still have a 10% power advantage.
Similar considerations should be valid when scaling the system up to 250 cc or whatever size you like.
Moped rider
I hope this system will work some day. but luc foekemas experience with it is not very encouraging yet.
https://www.facebook.com/notes/luc-f.../4080202582494
one thing i do not like so much.....2 pipes are needed. no KISS. Frits, luc seems not to be your very best friend or is it just a feeling?
WATCHA GONNA DO WHEN THE ULTIMATE WARRIOR AND HULK HOGAN DESTROY YOU!!!!
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