ESE's works engine tuner

[wobbly]

So this is where we get differing perceptions on what is possible.
In the current fastest 125 engines on the planet I get the roof of the duct TIG welded and then its re machined on a 6 axis Rottler CNC designed for cutting 4T head ports.
Costs an absolute fortune to gain about 1 Hp in 50.
And in so many projects I simply couldn't count , I have counterbored the Exhaust duct then pressed in and welded an insert to be able to reduce the exit diameter.
Both are " easy " if you are trying to achieve the best result.

[F5 Dave]

If it had pedals, we didn't get it. No need for our rules.

(OK a friend has a solex somewhere). But all the 50s we git worth mentioning were the std non pedal, non restricted versions. At least my frame of reference the 80s.

We got A50, RD50, MB or MT50, GT50. Then RG50. Then a few exotics like RZ50, TZR50, Derbi,
Aprilia. But those weren't official imports.
I think it was the mid 90s before you couldn't put your learner arse on an RGV250 so pedallies weren't a thing.

Maybe you could ride a scooter on a car licence. Too far back.

[TZ350]

.


Is there no winning with this thing!!!! Now that I have found a way to stop it shaking its cylinder hold down nuts loose. It has started cracking its cylinder. Crack runs between two cylinder studs and right through the transfer duct.

[Grumph]

As long as it's not an air leak - and the liner is still intact and in place - keep going.
There's a process used to make porous castings good which involves using epoxy under vacuum.
Wouldn't surprise me if someone in Auckland can do it if it becomes necessary. Neil would know.

BTW : What was the solution with the nuts ?

[TZ350]

As long as it's not an air leak - and the liner is still intact and in place - keep going. There's a process used to make porous castings good which involves using epoxy under vacuum. Wouldn't surprise me if someone in Auckland can do it if it becomes necessary. Neil would know.BTW : What was the solution with the nuts ?

Thanks for the epoxy idea. I had not thought of that but I have some experience with vacuum impregnating magnet coils, so might be worth a try. But there are holes and the transfer port edge has distorted. I might get it welded and then finish it off by vacuum epoxying it.

Nordlock washers were the solution.

[aljaxon]

So this is where we get differing perceptions on what is possible.
In the current fastest 125 engines on the planet I get the roof of the duct TIG welded and then its re machined on a 6 axis Rottler CNC designed for cutting 4T head ports.
Costs an absolute fortune to gain about 1 Hp in 50.
And in so many projects I simply couldn't count , I have counterbored the Exhaust duct then pressed in and welded an insert to be able to reduce the exit diameter.
Both are " easy " if you are trying to achieve the best result.

wobbly on that 50v i did not want to alter the cylinder. i wanted it to look standard.

but on this latest puch project i have indeed welded up the duct and machined it so the diameter matches perfectly with your ducts converging 1.5 x bore bit. i even got a cone section at the correct diameter and flatten it slightly oval so as to machine the cylinder outlet to have the same ovality. and then the rest or the 1.5 duct goes back to circular.


i considered doing what you did - counter boring and fitting an insert but there would have been a step somewhere or gaps at the sides where the port diverges more than the insert that would have needed welding (cant do ac welding)

unless i really go overboard on the insert outside diameter.... penny just dropped.

btw this is me being silent.

[aljaxon]

Yeah, that text might steer you in the wrong direction, Al. I had nothing to do with it and for all I know neither has Wobbly.

frits i think you need to grasp that sometimes it appears i am not listening. i am listening, but sometimes i dont understand.
and so if i focus on things i do understand and conveniently ignore those i dont it makes me look like i am reading what i want to read.

its not through ignorance, (well it is in some meanings of the word as in not aware). i am not ignoring you but some stuff just stalls in my brain.
i am struggling to take a lot of this on board

i cannot understand the difference between a pipe designed for blowdown area and one for the ports actual area and if my blowdown are is effective diameter 18mm as opposed to actual 25mm how i use the 18mm in pipe design.

so much for me staying silent.

[aljaxon]

If it had pedals, we didn't get it. No need for our rules.

(OK a friend has a solex somewhere). But all the 50s we git worth mentioning were the std non pedal, non restricted versions. At least my frame of reference the 80s.

We got A50, RD50, MB or MT50, GT50. Then RG50. Then a few exotics like RZ50, TZR50, Derbi,
Aprilia. But those weren't official imports.
I think it was the mid 90s before you couldn't put your learner arse on an RGV250 so pedallies weren't a thing.

Maybe you could ride a scooter on a car licence. Too far back.

sounds a lott better than uk

my time was the 70's -50 cc with pedals (no honda c50) until 17, then a 250 on L plates then pass your test (10 minute piece or proverbial) and then ride anything. it changed around 1978 with mopeds restricted to 35mph and 125 the limit until you passed your test. and there was a time limit so this now expensive test £500? sent a lot of prospective bikers off the road to buy cars.

[Frits Overmars]

what ive found with your FOS is that to derive at D1 you calculate Lmax and X but the figure doesnt always match up with what the cylinders actual diameter is. and there is no deviation on that.
sometimes the cylinder cannot be altered if you wanted to keep the period header attachment circular nut.
all i ever wanted was a way around that discrepancy in diameters but i never got one from you.

Al, it would be a shame if our paths parted in this way. But the aspect in which the FOS exhaust concept distinguishes itself most from other concepts is the determination of the initial diameters. And if those are too large in an existing cylinder, you have just two options: throw it away or apply an insert, like Wobbly just wrote. In almost all cylinders you can do that without changing their outer appearance.

Looking back at my contributions I found this picture of a KTM 50SX cylinder with a clearly oversized standard diameter, and of the same cylinder with an insert.
This picture is over ten years old and I posted it in KiwiBiker, Pit-Lane, Facebook and four other forums, so there has been ample opportunity to find it.
I know it's nearly impossible to check everywhere, but you must realize that it's totally impossible for me to tell every questioner where to find the answer to every question.
That is your own responsibility.
​Keep asking questions, but also do your own research so you won't have to repeat every mistake I and others have made in the past.

[aljaxon]

thanks for that frits, of course you are inundated with questions from all angles and thats one of the reasons i repeated the same question thinking you may not have seen it. you should have told me to go and play with diesels engines instead....

ive read everything in your files. even tried one of the dutch ones using google translate.

i am going to splash out on an ac welder (only got dc atm) so i am not hindered anymore by big holes.

[Condyn]

You can weld aluminum using a dc tig with the flux coated aluminum sticks.

There is no magical calculator or formula for making the best pipe possible in the field. You have to test dozens of designs. The dyno/sim only does part of the work. I have pipes that dyno like shit, but hoard trophies on race day via the dynamics posed by the specific application. Start rolling cones

[palezu]

Hello fellow 2-stroke sufferers,
I want to do a report of my High Power 50cc project after some 2 years of trials and tribulations.
In 2021 I cast this 50cc watercooled cylinder from cast iron (the sewing machine, some may remember).
It was supposed to be a record breaker. I based the radial transfer angles on Frits' MB40 transfer angle picture: https://servimg.com/view/19023519/1#
The axial angles were 20*(A), 10*(B) and 55 for C. (Now that I look at this again, I realize that the axial angles in Frits' concept are much different...doh.)
The inner wall is a "generous" bulge without much thought put into it. The transfer entries are also not much thought, I just drew something that roughly resembled Frits' MB40 cylinder.
The cylinder is mounted to AM6 engine using a 15mm thick spacer plate which is probably very unideal. The transfer ducts are very short.

The exhaust duct is a normal 3-part, with wobbly's 1.5*bore length and restricted outlet area. The duct is water cooled on the top side completely. The auxiliary ducts are very long and quite slim, later I shortened the bridges quite a lot.
Main exhaust port floor is 3mm above BDC.
I made a lot of errors with the exhaust port design. At first I made it too low and the timing was only about 185 degrees. This was because I had thought that a properly designed auxiliary duct would flow so well that
the cylinder would easily surpass a typical power of a stud-compromised triple exhaust even with a low timing.
I made the auxiliary windows quite small, there was a lot of room to enlarge them. Then I made the outlet about 75% of the port effective area, but since the cylinder ports were already small, the outlet area ended up being equivalent to only a 20mm round port which was way too small.

On the first tests the cylinder was about as weak as a unported stock AM6 cylinder with a general powerpipe. My pipe is made with Blair's formulas, designed power peak at 14000, belly diameter 82mm, tuned length 710mm. At first only about 8hp at the rear wheel and not much revs.

First major improvement came from raising the exhaust port to 198 degrees and enlarging the auxiliaries. Peak power didn't improve much but I got way more usable range on high rpm. Second major improvement was again from the exhaust area, by enlarging the duct and header diameter from 22mm to 25mm brought some 2.5hp more power. Record power is now 12.5hp at 12800 measured on rear wheel. With some fine adjustment and a new piston ring I think it could do close to 13. But still that is nothing. This cylinder design is ought to give 18+ rear wheel horses when you think of all the ideas that have been read from this forum and implemented.

In addition to those mods I have also tried almost everything else possible. I have tried compression ratios of 15:1 and 13.5:1 with maybe only a slight improvement on rpm range and less power. I have tried 53% and 40% squish ratio, squish gap from 0.4 to 0.65mm and different ignition timing without much improvement to speak of.
Porting the cases for a more direct reed flow path. Different reed valve. Much stiffer petals. Different manufacturer carburetor. Basically only loses power or there is only a very slight improvement. My last trial was the crankcase compression. Changed the compression from 1.19 to 1.23 with a 45cc stuffer. The crankcase volume at TDC is 266cc by the way. Crankcase compression did nothing, only lost power on powerband beginning.

Current tail restriction is 15mm. I also tried to make a completely different looking exhaust with a 20mm fatter belly and about 30mm shorter TL. Even this was a failure, there was noticeably less peak power but the rpm range was pretty much identical.

I still have some hope of getting a bit more by enlarging the exhaust duct further. Apparently the 75% rule doesn't seem to work in a 50cc cylinder. At least I can assure it doesn't work if the cylinder ports are even a little bit on the small side.

But I would be surprised if enlarging the duct a bit more would give more than 1hp. It may be the case that the FOS-MB40 transfer concept does not work in a 50cc cylinder, or then I have done something wrong. Many people think that it is the missing B duct hooks that cause it but I really doubt that. 2strokestuffing had already tried to add the hooks and it didn't seem to do much at all. (but he too had a badly restricted exhaust channel which probably hinders all other changes). I have also tried to choke the B ducts with 3D printed plugs but didn't get a breakthrough. Funnily enough, adding a plug which reduced the entry area to maybe 15% of the original, in only the LEFT B duct, didn't make any difference to the power curve. Adding plugs to both ducts reduced power a lot.

Description for pictures:

1. cores in the mould. The water flow is so that cold water enters the cylinder head from the C port side and flows out above the exhaust duct. The engine stays remarkably cool under driving conditions with a standard Derbi moped radiator, which I think may be an indication of the effectiveness of the "reversed" water flow heat transfer. Or then it is just due to low power.
2. transfer duct top view
3. B duct side profile. The duct is modeled in the cad as if the cylinder bore was 36mm for core making reasons. The 2mm straight part is bored out.
4. Cylinder with some machining done
5. Cylinder adapter plate in the cases. There is also a resin-silicone-mess crankcase stuffer there which failed miserably later.
6. Exhaust port after raising it to 198(main port, aux is a bit lower)

One friend has an AM6 engine with an original single exhaust port Minarelli cylinder, another guy ported that cylinder and the bike pushed out 12.4hp to the rear wheel, so my cylinder is clearly failed. I am desperate to get more power next year but haven't yet made up my mind what to do next . Maybe a new cylinder but what to change?

[wobbly]

Here is a few ideas for you.
Years ago I did an RG50 Gamma based engine in EngMod shooting for 20Hp @ 13500 on AvGas.
The TL was 738 with an 80% duct exit of 23mm as this wasnt changed from stock, the stinger nozzle was 13.7mm and the mid was 106mm.
Porting was simply a scaled down RS125 Honda as it had a T port and the axial angles turned out to be exactly as Frits later produced drawing suggested.

Case compression was 1.3 , as anything bigger than this with reeds is doomed to failure , only a Rotary Valve engine would be happy at a big 1.23 ratio.
Big cases over 1.3 ratio need very thin reeds to match the Helmholtz forcing frequency mid powerband , and of course they then flutter like hell and destroy themselves in protest.
It had a VF3 from a KX85 in it - too big really but it was the best I could find at the time and it fitted easily enough with some welding on the case and cylinder.

This engine made 17.6 Hp @ 13600 sprocket power - so all but exactly the simulation crank power that was predicted.
It could have made more at higher rpm but using the stock gearbox the rev drops were to large to expect a bigger bmep to work effectively.
Bottom line is that if everything is matched correctly in EngMod the result is as expected , every time.

EDIT - having the Exhaust duct 3mm above BDC has been dyno tested and proven to work in full noise 125 engines - no one to my knowledge has been any higher and proven the concept on a dyno.

[palezu]

Regarding the case compression. I am thinking that I should have seen an improvement by changing it into the right direction but there was a major loss about 1000rpm before peak power. The 45cc (47.6cc) stuffer reduced the TDC volume by 15%. Feels like the change should be apparent.
Or maybe the choice of reeds is now wrong. Before the case stuffing I had softer reeds(didn't measure) and then changed to 0.4mm (and lost a lot of midrange but gained a little top). After case stuffing I still have the thick reeds. Maybe the softer reeds would work better now. It is tiring, seems there is always a possibility that one change is ruined by another...

[wobbly]

Well its the old story of bullshit in = bullshit out. When you are miles away from optimum and take a step in the right direction there are no rules that
say that improvement will do anything to help.
When you have a whole string of sub optimum choices the chances of getter anything meaningful with a single change are close to zero.
I have 10 disappointments on the dyno most days , if one tiny thing works without needing 3 other changes to regain synergy I'm over the moon with joy.