ESE's works engine tuner

[wobbly]

The bulge, just outside the bore in the T port exhaust of an RS125/250 Honda type cylinder, hugely increases the flow rate during blowdown.
This increase in effective flow is dramatic enough, when compared to a straight sided exit, that it must be taken account of when modelling the port in EngMod2T.

[F5 Dave]

above answer is obviously refering to Kobas post.

I was going to say he didn't draw in the bridge in the picture which changes things somewhat.

[Farmaken]

Would the bulge have a similar effect on a single Ex port ??

[F5 Dave]

its not trying to avoid any obstruction.

[TZ350]

Page 240 bits and bobs, every other 10th page have collections too.

When using a simple powerjet nozzle the tip position matters in that no flow will occur until the slide is well past the exit hole, and there is sufficient airflow
to drag fuel up the feed tube above the bowl level.
With the aftermarket add ons and the ones as used by Lectron you can shorten the dump tube so that the flow will only occur at high slide openings,as well as high air flow.
These also have a built in "lag "control in that it takes time for the fuel to rise up the tube and dump out the exit into the air stream.
With a solenoid controlled setup all this is pretty much irrelevant as the flow can only occur when the solenoid is not powered up, and this
is TPS as well as rpm dependant inside the ECU program..
The carbs as used on the MX bikes has the dump tube very low in the bore as they added and subtracted fuel at low slide positions in those bikes.
For a race engine I bend the tube up to around 1/2 bore, as this is where the exit is on the Kehin SPJ carb for RS125/RS250 Honda.
And the general setting is the solenoid is powered up ie no flow below 4000 and 60% TPS and is powered up again at around 12400 to lean off the mixture and increase revon.
This causes a problem with Ignitions that are used with only a capacitor, as at startup the solenoid is powered up, dragging all the voltage out of the ECU, so I convert the ECU output
to a 3 step truth table, and have the setting such that below 1500rpm the solenoid isnt powered.

If Wiseco is your thing ....

New Zealand supplier in Auckland of Wiseco rings, sleeves and piston kits.

http://www.sportspro.co.nz/products/...eco_rings.aspx

A priceless tip. Never perform a modification you haven't done before on a part you still intend to use.

"If it ain't electric it can't be good" hmm? Sure, you can do all kind of tricks with drills, grinders, milling cutters etc. But there is nothing wrong with a file.

Two golden rules when modifying cylinders, pistons, etc:

One: stop before you reach the inscribed lines.

Two: wherever possible, do the finishing touches with a hand file.

It will save you a lot of errors. And if you are looking for a more 'technical' reason: grinding and milling will in general remove material perpendicular to the direction of flow; you risk producing a surface with a lot of pot holes. Filing removes material in the direction of flow; it will automatically offer a smooth surface to the flow.

Filing is a slow process compared to the various 'electrical' operations. But that is an advantage, not a disadvantage. The goal is not to finish a part in a hurry; the goal is to avoid having to redo it.

Scavenging

My reaction would be that the RSA "model " that took years to develop and had a mile of devil in the details, will work best in any bore - as long as the stroke ratio is maintained.

Thus both the radial and axials could be copied as all you are doing is scaling equally in both directions.

The radial angles set the directions to minimise short circuiting, and the axials maximise the scavenging purity - both together form the loop shape and duration.
Anything other than a square bore/stroke and you have instantly compromised the angle area capability, and all the R & D done by Aprilia is null and void.

Most two-stroke people define radial scavenging directions by quoting the distances where the ports would intersect the center line (the leading distance and trailing distance in the drawing below left). Gordon Blair used that notation in his publications, and 95% of us followed suit.

But there is a better, more universally applicable way.
I will explain with an example, not of scavenging directions, but of port timing: I might say that a transfer port height of 13 mm is perfect for a racing engine. That may be true for a 125 cc engine, but it would be nonsense for a 50 cc.

But if I say that a transfer port timing of 130° is perfect for a racing engine, then that is valid for any engine, regardless of its cubic capacity. Absolute distance values (millimeters, inches etc.) are not suited for universal guidelines. Degrees are, as are percentages of bore or stroke. rpm values are not; mean piston velocities are.

I express transfer duct directions in degrees. Each duct has a leading flank and a trailing flank. Each flank intersects the bore at a point which I can define with a positional angle. And each flank hits the fore-aft center line of the bore with an included angle which I call the directional angle. The drawing below left may clarify what I mean. And the drawing on the right is an example of an existing cylinder (it may be small, 6.5 cc, but it has been unbeatable for over 10 years).



Now you can express the radial characteristics of the transfer ports with positional and directional angles, regardless of bore and stroke.
And you can express the ports' axial characteristics with axial angles, but that only holds for engines with identical bore/stroke-ratios, as Wobbly explained.
Your approach of using a height h1 in the cylinder where the transfer port's roof would hit the opposite cylinder wall, is very good, but you need to express h1 as a percentage of the stroke. Then you will have a truly universal value. Then you will also see that short-stroke engines require smaller axial angles.

… now would be a good time to write something about the radial angles of the A-transfers.

Surely a duct with a radial angle of over 20° offers a smaller cross-section to the flow than a duct that enters the cylinder perpendicularly?
Yes it does. But there are two good reasons to angle it upward anyway.

First, perpendicular mixture streams coming from the A-ports would collide and slow one another right down. The upward angles provide for less velocity losses and less
pressure losses, so despite their smaller cross-section, upward ports may flow as much, if not more, than perpendicular ports.



(Now you may well ask why the B-ports do not get the same treatment; that is because the central scavenging column, resulting from all incoming scavenging streams together, must not have too much radial velocity, or the loop scavenging will result in a loop-loss into the exhaust).

Second, there is a thing called scavenging balance (I invented the word for my personal use, so this may well be the first time you ever saw it).
If you looked closely at the scavenging picture of the MB-cylinder I posted earlier today, you may have noticed that the 'radial scavenging directional resultant'
had a value of 101,045°.

90° would have meant 'straight up'; more than 90° indicates that the central scavenging column is leaning towards the exhaust side of the cylinder.
But we don't want that; it is bad for the scavenging of the rear part of the cylinder, and it is risky because it may provoke scavenging losses straight into the exhaust.



But how can we prevent a scavenging column from toppling over to the exhaust side like the leaning tower of Pisa? Not by pushing against its basis, but by pushing higher up. Hence the radial angle of the A-ports. The pictures will tell the story. (If only the Pisa architect had known a bit more about two-stroke tuning....)

the sine of this 'axial scavenging directional resultant' is an indication of the scavenging column's axial velocity. If the column moves too fast in relation to the mean piston velocity, there will be severe scavenging losses; if it doesn't move fast enough, the cylinder will not be completely scavenged.

[wobbly]

Well in saying that T ports use the bulge because of the bridge interfering with flow is the obvious answer, and I agree.
But these are bloody 2 strokes we are talking about and very little seems to work in the way you might think at first glance.
I would put the question, and it may be one hell of a discovery if it works.
Take a maxed out single Ex port like the one on TeeZees 31 Hp 125 engine - that is blowdown limited by design - though the small carb may mask the effect somewhat I would say.
Grind the bulges on the top 1/2 of the port, outside the cylinder wall, above the transfers to see if this increases blowdown flow.
Pretty easy to test with a suck thru the Ex port, before and after, on a flow bench, and a piston sitting at the transfer open point.
Then to the dyno - it will do one of five things.
Flow more and make more power,flow more and make less power,flow less and make more power, flow less and make less power - or finally - do nothing, all of which will make sense only after the tests.
Shit, I really hope it makes more power,as I love thinking outside the box - and to make a discovery that works , most dont sadly.

[SS90]

above answer is obviously refering to Kobas post.

I was going to say he didn't draw in the bridge in the picture which changes things somewhat.

By about 4% in regards to flow (more or less)

[F5 Dave]

. . .
Then to the dyno - it will do one of five things.
. . . . . - or finally - do nothing which will make any sense.
. . . . .

Fixed that for ya. This is how I first read it & made me laugh & laugh as it often mirrors a trip to the dyno with more questions raised than answered, except on those rare beautiful occasions when progress is made & things work the way they were supposed to.

[TZ350]

Take a maxed out single Ex port like the one on TeeZees 31 Hp 125 engine - that is blowdown limited by design - Grind the bulges on the top 1/2 of the port, outside the cylinder wall, above the transfers to see if this increases blowdown flow.

Now that is something to look at.

The Suzuki GP's exhaust port angles to one side, interestingly a std Suzuki GP 125 cylinder has a small bulge on the tight side.



The rotary engine guys talk about radusing the edges of the exhaust port for a significant flow improvement, so something else to look into.

[Frits Overmars]

Would the bulge have a similar effect on a single Ex port ??

That depends on the port width. A single port will not be as wide as the total width of a bridged port, so the effect will be less pronounced, but the principle remains the same: each particle of exhaust gas wants to leave the building ASAP and the shortest path is radially outward. Therefore the radial lines from the center of the cylinder bore to the edges of the exhaust port describe the initial shape of the exhaust duct's side flanks.
But the duct volume should be no larger than absolutely necessary, so continuing those radial lines would be counter-productive. As the exhaust duct floor drops, these side flanks can be curved towards each other, keeping the flow cross-area of the duct constant. The picture shows the underside of the duct.

[Farmaken]

So, my cylinder ( TF 125 Suzuki ) is similar to TZ`s in that the Ex duct turns left as it exits the cylinder and there should be some benefit to be had from opening the duct (not the port ) above the transfers on the long side as Wobbly suggested ???

Ex port is 71% bore Dia
56.5 mm Bore
50 mm Stroke

??????????????

[dinamik2t]

In MOTA, there used to be a small calculator, measuring exactly the "bridged port radial attitude angle".
Eg for an RS with 32mm arc port width (each) and 3mm bridge, it gives about 37*:


Say TZ's was a bridged port with 0 brigde, it's arc width should be around 48mm - 24mm each. It will be 24.5*.

Well in saying that T ports use the bulge because of the bridge interfering with flow is the obvious answer, and I agree.
But these are bloody 2 strokes we are talking about and very little seems to work in the way you might think at first glance.
I would put the question, and it may be one hell of a discovery if it works.
Take a maxed out single Ex port like the one on TeeZees 31 Hp 125 engine - that is blowdown limited by design - though the small carb may mask the effect somewhat I would say.
Grind the bulges on the top 1/2 of the port, outside the cylinder wall, above the transfers to see if this increases blowdown flow.
Pretty easy to test with a suck thru the Ex port, before and after, on a flow bench, and a piston sitting at the transfer open point.

We might be able to 'semi-test' the effect in EngMod like this: In ExPort, choose Bridged mode and use a zero value in everything describing the bridged port shape. Then sim once with zero side wall angle and once with, say, 20 side wall angle.

I didn't have enough time to run full tests now, but in peak power of a random 56 bore, 0* side wall was at 30.48KW while 20* side angle was 30.46KW. Delivery, efficiency and temps, all the same too.

[teriks]

--snip-- A single port will not be as wide as the total width of a bridged port --snip--

Except for my 92% single port, that already have such bulged shape. -Sometimes a ringless piston is a good thing

We might be able to 'semi-test' the effect in EngMod like this: In ExPort, choose Bridged mode and use a zero value in everything describing the bridged port shape. Then sim once with zero side wall angle and once with, say, 20 side wall angle.

I don't think you will get anything really useful out of any 1D simulator in this case.
You'd need some, at least in my un-epxirienced opinion, very complex 3D CFD calculations coupled to the 1D simulator to get anything that might be reasonable.
-Yes, I'm humbled in that field as well after doing some fluent stuff at work. It's not only EngMod that can have such effect...

[bucketracer]

So, my cylinder ( TF 125 Suzuki ) is similar to TZ`s in that the Ex duct turns left as it exits the cylinder and there should be some benefit to be had from opening the duct (not the port ) above the transfers on the long side as Wobbly suggested ???

We have some std TF cylinders here at work, later when I get a chance I will dig one out and see how the shape of the exhaust tract compaires to a std GP cylinder.

[TZ350]

Hi Everyone

3 consecutive weekends racing is completed with me currently sitting in 9th position in the 600 Supersport Championship.



Timaru's Levels Raceway hosted round 2 last weekend 14th and 15th. It rained constantly on the Friday practise day but the weekend was hot and sunny.
Unfortunately the track was very slick however due to a lot of oil being dumped on the first few turns which definitley hindered everyones lap times. After qualifing in 13th position of 20 I certainly wasnt looking forward to the start, trying to make up positions and avoid the oil was a risky combination! It went ok although I dropped a couple of places while avoiding a crashed rider and ended up in 11th place in the 1st race.
Race 2 was going a heap better, I was managing to keep up with some faster riders until my race came to a grinding holt due to a miscalculation with the fuel which saw me run out 3 laps from the end.

It was a weekend of mixed emotions: I was gutted to DNF but happy at the same time that I had been running a better pace and most of all had been thinking of my friend Cam Jones who was seriously injured Sunday morning. He is still in Intensive Care. Please keep him in your prayers and keep an eye out on Trademe for items being auctioned with the proceeds going to a fund for Cam.

The 3rd round was held in Invercargill this past weekend. I couldn't wait to ride one of my favorite tracks ever on the CBR600! Qualifying left me in grid position 9 - far better than the previous two rounds which gave me a boost of confidence. I ended the 1st race in 9th with a seriously torn tire. It was good experience for me to ride with the rear moving around so much and feel how the bike behaves with deteriorated rubber.
Race Two and Invercargill weather did its thing in time for me to go around the outside of a few people at turn 1 putting me in 4th position. I held on to 4th for a few of laps until I began to struggle to see with my visor fogging. It was my fault for not sticking the pinlock antifog strip in properly but I was still happy to finish in my highest placing this year of 7th.

Huge thanks;
to my team - Jamie, Scott, Georgie, Shannon, Travers and especially mum and dad - for all their hard work and making it a fantastic few weeks. I cant thank Jamie enough for getting me out there this year.
to Pete Finlay, the Castrol Honda boys and Blue Wing Honda for all the help and support I could ask for.
to my sponsors and supporters - Baywatch Motor Lodge, please stay here when you are in Timaru, Uncle Geoff and Aunty Gay, Race Pace Trainers, Deep Web - Web Design, Blue Wing Honda, HJC helmets, Sidi boots, NGK spark plugs, Tridon Toledo Tools, Carcolors, Bearing Wholesale, Metzeler tyres and Total Oil.
And finally to all the other riders for the great racing and making our sport awesome to be part of.

My next championship race will be the 4th round at Hampton Downs on March 17/18th. We will also use the Pacific Club race meeting at Taupo in February as a shake down for nationals there late March.



Until then, Avalon.