Glowgeek

OK, everything you said makes sense to me. The only question that remains in my tiny brain is how that poyt sound develops merely from reversed exhaust gasses bouncing of the top of a closed exhaust valve. How much science would it take to understand that?

Cat 1

My Feedback: (1)

Got a quick tune run in - I'm close - Have to bump the jet size just slightly as I'm a bit of lean at the top wide open pulse... But it runs great... will probably try a bleed to raise the bottom of the curve a bit too - right now its acting just like the first few runs with the other "TBI" conversions..

1967brutus

The biggest part is the short period where the exhaust drwasw in air when the piston starts going down. That's the "poy" part... the "t" is the closing of the valve...

A bit a joke, but basically that basically is it.

1967brutus

I just stumbled on the vid in my normal YT feed. It runs brilliant. Top-end indeed needs a bit of work, and if you say that is due to a touch too small nozzle, I immediately believe you.
But idle and midrange are allready brilliant.
I have an idea for the airbleed: Would it be possible to place the airbleed in the barrel? Like where normally the LS needle adjuster is?
Because I was thinking, a conventional airbleed in the body will close off when the throttle is opened, causing a "bend" in the curve, but a lateral airbleed in the barrel will be open all the time, and will most likely result in a much smoother and easier adjustable curve...

I'ts just a thought....

Glowgeek

It's coming down to phonetics is it? Hehehe

The piston has moved down the cylinder approx 30° of crank rotation (1/6 of it's downward travel) before the exhaust valve fully closes, long after TDC, so it seems likely that at that point most all of the air entering the cylinder would be through a wide open intake valve, very little through a nearly closed off exhaust valve. The point I'm making is that I don't see how there would be enough velocity remaining in the exhaust tract to make the "P" sound in poyt.

Hmmmmm

1967brutus

Nope... because at idle, the throttle is closed... And that thorttle opening is less than 10% of the full valve opening... So there is barely anything coming in through there UNTIL the exhaust valve is closed and it HAS to come in through there....

But I was not even joking with the "Poy" being from air being sucked in through the exhaust: Put your finger in your mouth and pop it out sideways, and what you are doing is creating a part vacuum in your mouth, and the pop you hear when your finger comes out is not the sound of your finger coming out, but the sound of the air rushing in.

Glowgeek

Thanks for that chat Bert. My brain is smoking again.

Now for something more important than pops and poyts, my new ignition should be here today. I hope I'm not mistaken, that the first Rcexl CDI module was what caused running problems with my 200Ti. If the new CDI doesn't fix it then I have another problem. I'll have to find another glow twin to mount the first one on.

Raleighcopter

I just want to say...

The conversation today and especially the video is what this thread is all about. That other site is missing out.

1967brutus

Yeah... that thought has crossed my mind quite a few times since the move. Have to say, haven't regretted it for one minute.

We could use more traffic, but not willing to sacrifice that peacefulness here for more traffic there...

John_M_

Yes that is true, but the exhaust reversion pressure comes back across the combustion chamber when both valves are open for that brief period... its like opening a can of soda pop, it burps the pressure in the can.. the same happens with valve overlap... you get a small pressure release on the induction side, pushing fresh gases out the induction manifold as standoff, exhaust scavenging then pulls it back in... great for carburetor induction, but horrible for feedback EFi.

John_M_

Well its difficult to have a conversation, with so many differences in opinions, then you have the trollers that aren't particularly interested in the conversation, but more interested in provoking an necessary debate.

There's more watching than you realize, and probably will interact as this becomes more refined and successful conversions such as with Billy's post experience.

1967brutus

I guess you're right about that. Patience is the game.
As for the development and refinement, that's where you guys come in: my own engines all run and the planes fly, and it is hard to figure out refinements when things simply work.
So all I can say is, guys, keep up the good work and keep giving feedback.

John_M_

Well yes, but you guys were working on trying to get rid of the crap trap and other improvements, just keep moving forward.

1967brutus

Meanwhile:

Glowgeek

Fun project Bert.

Cat 1

My Feedback: (1)

Very nice!!!!!! Love the sound Bert...

Cat 1

My Feedback: (1)

OK fellas, Need some input... UP sized the jet (twice) and still lean on the top - The throttle is not "dead" with top end opening so I don't think the venturi is overly big and its smaller than stock... I am turning the Large 18x6 wide APC at 7300 rpm (1500ft pressure Alt). With the jet increase (now at .5mm) I am not able to richen to rpm drop and have "no headroom".. if I pull the throttle back 15% - I then can find a bit of tuning headroom.

I have straight pipe stacks and have a pressure nipple in each side - But i'm not getting any tank pressure - tried variations on the theme (blocking one side) but no dice. I am getting black oil into the Tubing up to the Syringe crap trap but no apparent movement when powering up. Im thinking that my pressure fittings are not capturing pressure and acting like static ports.

Other than that its running great - Added an air bleed (conventional) and it pulled the idle mix up and made it less sensitive.. Just have to find some room on the top .. I could keep jetting up but I think its more pressure related.. Im already "big" for comparative jet size - Just need a little more "push"

How is 7300 for Power on that wide APC Bert?

I am also watching temps with a small IR heat gun - #1 cylinder runs about 5-10 degrees cooler at high power but this cylinder does have a bit less Compression "POP" than the other - I think it slowly improving though...

John_M_

I thought it was larger than that... CDi boxes and plug leads are bigger than the engine. ... What was the piston ring fit like? tight?

Over on the other board there's another company developing a twin 6 v12, ( claims not to be affiliated with toyan ) same / similar design as toyan, it runs, but it needs work... he has two versions one better in design than the other.

John_M_

You won't get much pressure out of straight open ended pipes... you'll need a larger dia expansion chamber and then the exhaust exit should be the same ID as the header pipes, pressure tap in the expansion section... Or, if you take a look at how saito does their straight pipes on the 130 / 182 twins, they swage the tip down to reduce the exit dia to create some back pressure in the pipe, and then add a pressure tap near the swaged end.

1967brutus

7300 on the 18 x 6W, basically at lean limit is a bit low, which suggests the air intake is slightly restrictive... Standard carb would allow something like 7600~7700, a bit depending on state of break in if appliccable.
Mine does about 7400 in the "ground-rich condition" that is needed for flight.

You might want to get a pair of .91 FS mufflers... The WILL provide good presssure.

FWIW: back then I brazed one pressure tap in a standard header, for Dave. I did place the tap under an angle, and it seems to work for him,

1967brutus

It's a tiny engine.
The rings are (according to the instructions) matched to their cylinder bores, and if anything one is supposed to make sure that the rings stay with the liner they were in at delivery.
But in intself, the rings slipped very easy around the pistons, and appear to be loosely fitting in the slot, sticking out quite a bit. There is a relatively huge amount of ring tension against the liner, and despite the conical ringcompressor, the pistons were fairly hard to get installed in the liner, and the rings caused quite a bit of drag, despite using lots of oil at assembly.

This thing runs, and I am sure it does make a LITTLE bit of effective power as is (mind you, it is designed to run 25~30% Nitro, but I am just using gas). But the intake manifold is a disaster WRT design and flow capability. I think I can make HUGE improvements there, if I manage to re-do that.

As it is now, the cylinders 1-4 are connected to one carb, and 5-8 to the other.
The nasty thing is that cylinders 1, 2 and 3 are drawin mixture within 270 degrees of each other, then there is a pause, and cyl 4 is drawing in mixture without any interference of other cylinders. This has to happen through extremely narrow bores in the intake distributor. So narrow, that the "central bore" that connects the 4 branches to each head, is allready restrictive for ONE cylinder, let alone 3 or 4. THis whole situation causes a very uneven mixture strenght to each cylinder. The thing needs to be very rich in order to have the leanest cylinder rich enough to fire. It GUZZLES gas (even gas, yes...) and the exhaust stinks to high heaven.

Due to the firing order (which is also induction order of course) I will need to group cyl 1, 4, 6 and 7 to one carb in order to have one induction stroke evenly spread every 180 degrees of crank rotation. That will provide much more even mixture strenght.

That is going to take quite a bit of effort because of the physical shape of the manifolds...

John_M_

The twin 6 v12 is using a single rotary type walbro clone carb mounted atop of a large induction plenum manifold.... there is so much ring drag from all 12 cylinders it refuses to accelerate... ign timing is off as well, very laggy throttle response, hard to tell due to the internal resistance.

Those rings are too stiff, and over tensioned... same with the v12... its a conversation piece for the most part... I'm sure it can be improved upon... Their V4 was probably their best performing engine.

Have fun, something to tinker with

1967brutus

I think that is a bit a matter of "no other way to do it". If the rings would be less tensioned, they would also be a lot narrower in their relaxed diameter and would become near impossible to slip over the piston top land into the groove,
Drag is reducing noticably, but it is not only the rings, there are also two very stiff oil seals on the crankshaft.

Whatever the case, I have the feeling the rings are bedding in and starting to seal quite a bit better.
Initially the thing would idle no lower than about 2500 RPM and it needed about half throttle opening. Right now, it idles reliably at 1800 RPM with about 1 mm carb opening, and mechanically it is capableof running below 1500 (if every cylinder gets the proper mixture that is).

Although the cylinders appear to beak in uneven, several cylinders are starting to get considerable ring seal allready: If I put a spanner to the flywheelnut and turn it over "swift", Iclearly feel each separate cylinder going through compression.
New intake runners are my first bet...

But I do agree, it is a conversation piece... It MIGHT be able to power something like a crawler, IF running glow and LOTS of Nitro, but in its stock form it is a horrible and poorly designed piece of junk. Pretty nice made, nice looking design, not in every aspect a piece of crap, but in the aspects where it counts, most definitely.

But it is indeed a LOVELY thing to tinker with, I'm having lots of fun to say the least, and I do have a fair bit of optimism that I will be able to get this thing running, AND performing, at least "somewhat"...

John_M_

Are the rings cast iron?

Here are the two twin 6 v12's, you already know which one I like the best, and its claimed to be version 1

V1
https://ibb.co/GxcdpX5

V2
https://ibb.co/G0kPbSH

Glowgeek

Yeeeeeup, the Rcexl CDI I got from ZYHobbies is defective. Put a CH CDI on the 200Ti and it runs perfect. Nice increase in fuel economy over GI too. Now I can move on.

Interestingly, it spools up a Xoar 18x8 lightning fast from idle, similar to YS 4S engines, but only reaches 7350 peak rpm. Advancing the timing from 33° to 34° offered no increase in peak rpm but no detonation even when overly leaned either.

Typically when I see super fast transitions like this I also see over revving, reaching max peak rpm rating for the engine, and prop for a little more static load. Not so with the 200Ti.

PRODUCT SPECIFICATIONS

Type:4-strokeDisplacement:2.00 cu in (33.00 cc)Bore:1.10 in (28.20mm)Stroke:1.03 in (26.40mm)Cylinders:Inline twin, chrome platedEngine (Only) Weight:51.5 ozCrankshaft Threads:M8x1.25mmBenchmark Prop:17 x 8 APC @ 8,900Prop Range:16x8 - 18x10RPM Range:2,000 to 9,200Fuel:10%-30% syntheticMounting Dimensions:160 x 110 x 142mmMuffler Type:PipeCylinder Type:16.5cc x 2 / AACCarb Type:Barrel, 2-needle valveCrank Type:Ball bearing