ESE's works engine tuner

[F5 Dave]

. . . (where's SS90 when you need him) ...

I think he went absent when TZs bike started to make 25hp.

[F5 Dave]

. . .
But the quality of the duct and port geometry also affects the case com required.
The smaller the case vol (higher ratio) the greater the pressure rise in the case as the piston drops - this suits compromised transfer ducts with little or no inner wall shape, as it helps force the flow around thru the ducts quicker.
Good duct/port geometry allows the use of a bigger case as they dont need a large pressure ratio across the port to initiate good flow.
. . .

Ahh, hadn't thought about that. I knew that steeper pipe cones weren't suited to up the side of the liner type transfers like you might find on an RD350, or for that matter most bucket engines.

. . .
Suck too hard on crap transfers and they loose directional control - giving greater short circuiting out the Exhaust port.

I'd assumed over scavenging, but this makes more sense, or is overscavenging by shortccting so way too early to be any use.

. . .
When the transfers open there is more pressure in the cylinder than in the case.
Thus we get flow reversal at the initial transfer opening point.

Which is why esp on bikes with a mismatch of pipe & high transfers you get burning on the reeds. But it happens on TZ250s as well, which had confused me.

. . .
This also means that the transfer port that opens first - flows last, as it has the greatest flow reversal affect,down the duct.

And this is a Graham bell book error it would appear, at least in bikes with expansion chambers. This has been something that I have held the wrong (Bell) way in my head all this time.

Thanks Wayne, lots of things to think about & a few nagging mysteries cleared up, or at least not so mysterious.

[kel]

When the transfers open there is more pressure in the cylinder than in the case. Thus we get flow reversal at the initial transfer opening point. This also means that the transfer port that opens first - flows last, as it has the greatest flow reversal affect,down the duct..

Another curly one to deal with. It would seem that staggered transfer timing would have real flow advantage rather than just taming a too peaky motor.
I figure that with this reversal of flow that the boost port would open first as this would allow the flow from main and aux to potentially reach the rear of the cylinder before being directed up, like wise the aux would open next ensuring the main flows first thus limiting short circuiting out the exhaust??????
Anyone got a spare KE125 cylinder (preferably with aux exhaust ports), mine is heading for the bin!

[wobbly]

Honda first used the staggered transfer setup with the RS125/250 and was developed by Helmut Fath ( my hero) as was Exhaust stinger nozzles,for the factory teams.
With the big T port they opened the main first by around 2*, the secs and boost ports last.
Aprilia later came along with a 3 port Exhaust setup with huge aux Ex ports, they now have the mains lower to allow much bigger aux Exhaust area, with the secondarys and boost opening first.
All have the axial angles set at around 22* - 12* - 55* to clear out as much residuals from within the loop area as possible.
The big hooks on the secondarys also flips the flow over on itself under the boost, to clear this area out as well.
Greater flow reversal occurs when there is insufficient blowdown STA,and the TZ250 sacrificed blowdown for more transfer area, something we now know is a mistake - but with limited transfer port area you take your pick of what to compromise.

[F5 Dave]

Wasn't it Rotax that first used ex sub ports in earnest? Think the 256 has them doesn't it?

I've never really understood what was trying to be acheived with stinger nozzles with either venturi or simple stepped designs, presumable piston crown temp is affected but I don't see past a pressure bleedoff how it affects things.

Another odd thing about the RS port is the ex manifold part of the port step, presumably as a poormans powervalve to disrupt the out of step returning wave but still not affect it as when you want the wave, all I know is if you grind it out you lose midrange with no advantage to peak. Have never tried to emulate it.

[F5 Dave]

. . .The big hooks on the secondarys also flips the flow over on itself under the boost, to clear this area out as well.
. . . .

This is also presumably to colide the streams & kill kinetic energy so the flow out of the gaping exhaust is delayed until the boost clears the contaminated remains, or is this a misunderstanding? (I remember a 90s article by Cameron) so have always tried to emulate this to an extent. Looks right with my water from the tap up the transfers 'flow bench'

But this is at odds a bit if axial angles rather than flat roofs have proceeded further.

[wobbly]

Only Yamaha stuck with the wank flat roof scenario way after the use by date, and got their arses kicked for years in GP.
Till they finally bought a CNC controlled Jante machine from Czech, went square bore/stroke and using the 500 cylinders on the 250 easily won the champs in 2000 with Olivier Jaques.

The secondarys facing each other relatively flat will always collide, but the hooks rotate the flow under the boost as it exits the port ( easy to see with the tap water Jante trick),clearing out a big "dead" area
in front of the rear port.

All modern race engines have a nozzle restriction at the flange face, as big T ports and tripple Exhausts loose alot of velocity going into the header.
Rule of thumb is a 75% of the effective EX area at the flange.
Stepped oval duct into a round flange does work, but I have used a CNC oval to round transition in the spigot for years, as has Honda in A kit, and Aprilia factory engines, this works way better.
Here is a sim showing my new 400cc F3 engine, with and without the spigot nozzle.

The stinger nozzle effectively removes the stinger tube length from the equation - it was developed for Spencers NSR that had one stinger 150 long, the other was 450.
The nozzle is around 2 to 3mm smaller than the tube stinger .

[koba]

my new 400cc F3 engine

Hehehe, I knew it was only a matter of time!

Cool rule change huh!

I can't wait to see some good new gen F3 2-Strokes.

[F5 Dave]

. . .
Rule of thumb is a 75% of the effective EX area at the flange.
Stepped oval duct into a round flange does work, but I have used a CNC oval to round . . .

This is great, maybe not as pertinent to the single port commuter engines we are playing with, but still very interesting. Any chance of an example picture?

. . .
The stinger nozzle effectively removes the stinger tube length from the equation - it was developed for Spencers NSR that had one stinger 150 long, the other was 450.
The nozzle is around 2 to 3mm smaller than the tube stinger .

So assuming I had a 200mm 18mm ID stinger but didn't have the space for it & could replicate it with a 16mm section a couple of cm long & then just run a 209mm section to the pipe to the muffler? A 16mm stinger is 50cc size & would be certain piston crown doom to run on a 100. Is this what you are saying?

I had heard that tapered venturies apparently used on GP bikes?

[wobbly]

Here is an oval to round spigot for Robs GP100 with RGV cylinder.
36mm pipe ID, oval shape at the duct exit is 36 wide by 27 high = effective area of a 31mm round..
This nozzle effect doesnt work on single port engines - I have tried.


Re stinger nozzles - if running a 18mm nozzle on a 100cc then you could connect a 20mm stinger tube to it in basically any length and this would not affect the power at all - in fact using the nozzle with a tapered section out to the bigger tube makes more power.
Aprilia/Derby twins do this as the top pipe has a stinger 60mm long, the bottom one is closer to 220, but the effect works on any 2T.

[TZ350]

The secondarys facing each other relatively flat will always collide, but the hooks rotate the flow under the boost as it exits the port ( easy to see with the tap water Jante trick),clearing out a big "dead" area
in front of the rear port.

This is all good stuff, I would love to see a sketch of the port and proper flow pattern if possible so I know what to look for with the water test.

[wobbly]

All but impossible to show properly the scavenging pattern without one of the CNC controlled Jante screenshots but imagine looking out from inside the duct,the piston is the "floor" in front of you.
The flow attached to the septum wall blows straight past your left ear, and the flow hitting the hooks on your right side, rotates clockwise underneath this left side flow,the bottom attaching to the piston - the upper flow pushing upwards.

[bucketracer]

.......(where's SS90 when you need him) ..........

I think he went absent when TZs bike started to make 25hp.

He did say some silly things.

And now TeeZee is making 27rwhp out of his old 1978 air cooled GP125 engine.



Looks like Wobbly and Dad are hatching some sort of plan for a new water cooled 100cc engine, saw this picture on the lunch room table today.

[Ned Kelly]

And now TeeZee is making 27rwhp out of his old 1978 air cooled GP125 engine.

I think he had to have a cup of tea and a lie down.



Looks like Wobbly and Dad are hatching some sort of plan for a new water cooled 100cc engine, saw this picture on the lunch room table today.

Well not exactly sure that is what he is planning but he would be looking at my Aprilia 125. It maybe on the drawing board for development.

[kel]

Looks like Wobbly and Dad are hatching some sort of plan for a new water cooled 100cc engine, saw this picture on the lunch room table today.

NO no no, you definitely cant turn an RSA into a bucket. Apart from being against the rules Id have to personally kill you for such sacrilege. Don’t think its possible to own an RSA, certainly an RSW or RSR but RSA? pretty sure they are still lease only. Such a shame 2011 is the last year of these wonderful machines, how long will the FIM be allowed to dictate this four stroke nonsense?