ESE's works engine tuner

[F5 Dave]

. . . Balsa is the light wood material used in modeling planes, isn't it?

Yeah & they used to strengthen it with a product called Dope. I have a bottle somewhere, I don't know what is in it, but I wouldn't get your hopes up.

Yes I wonder how close you need to get to avoid the Tfr/Aux as opposed to just blocking off the pin area to Tfr.

[Yow Ling]

could you try these, a bit too Rangi maybe?


bit of superglue then boosh all done

[F5 Dave]

no no, I don't see any problem at all

[dinamik2t]

To avoid editing my old post, after Dave commented:

It should be more like the time-area.
One could make a small radius domed plug, which would still connect TFR-AUX when the top of the dome is before or after the horizontal wall divider.
Any dome radius would connect the two, at some point, for some time-area. So, the question is 'how long before a certain area does bleed pressure ?'.



(...)

[bucketracer]

TeeZee's plug post was all about end caps for a short pin.

The piston pin was to short for the new piston's cir-clip spacing. Previously when the pin was able to shuttle back and forth it elongated the cir-clip grove, widening it to the point where a cir-clip very nearly came out.

This time Chambers made up some close fitting shouldered aluminum plugs to stop the pin slopping about. It appears that the repeated hammering by the pin was enough to drive one of the plugs far enough over the cir-clip for the end of the plug to be nibbled by the transfer port.

TeeZee and Chambers were running it up on the dyno and it wasn't until they stopped the motor that the plug fell out far enough to jam in the transfer and lock the motor up so that they couldn't turn it over again to re start. When the motor was stripped it was very hard to get the cylinder off and later the remains of the plug was found lying in the inlet port.

Both the old piston and cylinder survived without any damage and Chambers now has it all back together and running like a charm.

[dmcca]

Was up late last night pulling my GasGas dirtbike down. To complicate matters, I can't help myself & while it was down being freshened up (& looing for an errant noise) I have to correct the squish clearance which is at 1.9mm.

Does the noise sound like piston slap or a rattle?... check the left side PV cylinder, the one behond the torque chamber cover, sometimes they need to be shimmed otherwise they move side to side and rattle.
Im currently working on an '11 model GasGas EC250 and Im amazed at how bad the workmanship is on that thing... so many problems its ridiculous... i should post up the portmap for a laugh, left aux EX port opens 1mm before right, main Ex is 2mm wider on one side than the other and shaped like a sideways egg, rather than an oval, port edges are razor sharp, cylinder is extremely badly pitted from poor casting with deep holes everywhere, intake tract is a joke... im really shocked at how bad it is. The last 2010 model i worked on was nothing like this, but there are too many issues for it to be a one off lemon that made it through the production line.

[dmcca]

But you are right about the turbulent flow: the port floors should under no circumstances lie beneath BDC....

Frits, As a general principle i understand that its best not to have the port floors below BDC but in reality how much difference would a small step at bdc have given that the port is only fully open at BDC momentarily and for almost the entire port duration the flow has to negotiate the piston edge as it partly covers the port?

[F5 Dave]

Thanks DMCA, yes I am aware of the freeplay of the PV actuator- but only last week. Mine had none. Although I forgot to melt the plastic out of the nylock nut & sheared the M4 thread so it had to meet mr welder to get it off.

Mine doesn't look that bad on first inspection, its an 07, but I haven't gone crazy, its a 300 dirtbike & has so much creamy power that's its perfect for a dirt muppet like me. Piston worn pretty bad & an A in a B bore which is a little worn. had 0.12mm clearance, that can't have helped. New Woosner arrived for $210NZ so pretty happy with that.

Still a bit concerned with the rattle that popped up & lost power every so often. Can't find a reason. No signs of deto if it was the ign timing going potsy. Maybe the governor's balls were momentarily displaced (ooeer!) Was running fine at other times & pulled effortless wheelies even on rain mode. Hmm, might check all those CDI switches & connections.

On the topic though my '00 GasGas trials bike had the most shocking intake I've seen. The inlet manifold 'missed' the reedblock offset by a good 8mm!! I ground the side it hit flat wall & put in a acetal block in the overhang side.

[TZ350]

I am getting a pipe kitset from Wobbly and a piston of ebay to rebore the 3 ex port cylinder but it wont make any more power, or power spread than the current single ex port and RS pipe setup unless I can increase the inlet port time area.



I use Blairs rotary valve design program to basically rough out the dimensions needed then I enter the data into EngMod2T to see what the likely results are.

I am looking for 11 bar at 12,250 rpm



But may have to settle for 10.5 bar because of the phyisical limitations on how big I can make the new rotary valve and inlet.



Even so it sure is going to be bigger than the original GP125 hole.



The larger rotary valve compaired to the original.

[Gigglebutton]

[QUOTE=TZ350;1130249983]I am getting a pipe kitset from Wobbly and a piston of ebay to rebore the 3 ex port cylinder but it wont make any more power, or power spread than the current single ex port and RS pipe setup unless I can increase the inlet port time area.


Let me know when you get the pipe. I'll weild it up for you.

[TZ350]

TZ had some pics way back with rlffler files bent to suit i guess the idea was from tuning for speed.I will post when i find them

Found them...... more pics on the original post.

Tomas and Alexi heat and bend some rifler files to the shape they want.

Tomas said that if fine file marks are made across the direction of air flow then small air vortices develop and these act like ball bearings and the air mass slides easily over them.

It used to be all the rage to polish the ports but with a mirror polish in the port, the air boundry layer that clings to the port wall is quite thick and moves like treacle.

But a surface finish that promotes micro vortices that act like small ball bearings reduces the boundry layer too next to nothing and the air mass's resistance to flowing along the port is greatly reduced.

Tomas says a smooth polished surface that has been sand blasted is best and a fine file or sandpaper finish that cuts across the air flow is also very good but file or sand paper marks that go in the direction of air flow don't help much.

As a point of information, this is why golf balls are dimpled, rather than smooth - less drag, so they go further.

A quick check of my old fluids text (Massey, Mechanics of Fluids 6th Ed.) says the (thin) turbulent boundary layer promoted by the rough surface delays separation of the flow, reducing the drag caused by the gross separation (turbulence) of the flow across the surface.
Cheers,
FM

While we're on it (not easy for transfers mind); Small rotary carbide bits seem to work ok but are very good at leaving ripples, large flame type ones are much better but need a grunty Bosh(sp) or air powered with decent compressor to drive. Decent Stone bits take out irregularities leaving a flat surface with a honed appearance, mighty fine.

The good thing about stone and resin bits is that they can be re-shaped by running them up in a hand drill and working them against the side of a spining stone wheel in a bench grinder.

Some other posts on the same page have a few interesting ideas on port surface finish for best flow.......

[TZ350]

Let me know when you get the pipe. I'll weild it up for you.

Great, thanks, will do.

I am building a complete new motor for the tripple exhaust port cylinder and Wobbly pipe, and I have a few new ideas about how to arrange the air cooling system so the head runs much cooler, and a better carb and bigger inlet port that I want to try out too.

The aim is to extend the current 30+hp and 4k power spread to 5k, who knows if it can be done but we will give it a go.

[dinamik2t]

Interesting potential. Good luck with the new engine - even though luck shouldn't have anything to do!

The 4 bolts behind the R.valve what do they support? Any chance of rewelding and opening new holes in a trapezium pattern? It would give some extra area for the port, if needed.

[TZ350]

The 4 bolts behind the R.valve what do they support? Any chance of rewelding and opening new holes in a trapezium pattern? It would give some extra area for the port, if needed.

The original inside plates diameter was to small for a bigger rotary valve so I fitted a bigger inner plate.



The original counter sunk screws are used to fasten the bigger inside plate to the crank case, the outside ring of holes go right through to the crank case too and are for holding the outer cover on.



Unfortunatly the inlet is not centered on the crankcase but a little forward of the centerline and the inlet tract is on an angle with the front part of the inlet tract angling towards the center of the crank case.



The divider in the middle of the inlet port has a small kicker on it to help re direct the center part of the inlet stream.



The rotary valve inlet as modelled in EngMod2T, pretty easy to see that the ideal model is much harder to realise in real life.



EngMod2T model of the Big Blue EI 24-36 flat slide carb. The inlet tract tapers outward from the 24mm high velocity area just behind the slide to the 40.8mm diameter of the rotary valve port.

The angle that the walls taper out is important, too steep and the flow separates off the wall creating turbulence and reducing the overall mass flow through the inlet tract. From looking at venturi loss data I think 14 deg divergence is about the max for higher induction air velocitys and it can be steeper as the inlet tract area increases and the air velocity reduces.

The design aim is a big inlet port, short inlet tract and a divergent angle joining the two thats not so steep that it promotes flow separation.

Reducing the divergent angle by moving the inlet port closer to the carb wont do you any good because the inlet spends a lot of time only half open so you want the bigest inlet port practical.

Basic trigonometry shows that its just not possible to have an inlet port the size of a high hp side carb Aprilia, with a Bucket 24mm carb and an inlet tract short enough to work well at 13,000rpm without flow separation from the steeply diverging walls.

In the end it may be the maximum divergent angle possible of the inlet tract more than the maximum flow possible through a 24mm carb that limits the ultimate power obtainable from my 125.

[TZ350]

From:- http://www.engineeringtoolbox.com/or...uri-d_590.html



The fluid slows down in the cone with smaller angle where most of the kinetic energy is converted back to pressure energy.

A gradual expansion of flow downstream of a nozzle eliminates flow separation, allowing recovery of most of the original pressure head. In the case where the main flow separates from the wall, a large percentage of the fluid energy is lost in the eddies caused by the separation.

A whole lot more on venturies http://www.flowsystemsinc.com/spe001.htm



Looks a lot like my modified carbs where they have a flow straigtner at the front, then the 24mm venturi followed by a divergent pressure recovery area that forms the inlet tract.



So it looks like, how steep you can make this angle without encountering flow separation is one of the major things that will determine how much power can be wrung out of a rotary valve 125cc 2-stroke limited to a 24mm carb.

It doesn’t necessarily have to be motorcycle related, if you have a few smarts pretty much anybody can find Goggle clues that help in tuning racing 2-strokes and getting the best out of any sort of performance engine.