ESE's works engine tuner

[TZ350]

seen this today also........Much sturdier than i remember

Thanks for the Ariel crank pic.

[TZ350]

Starting from the beginning I have been trying to find the posts that talk about pipes and collate and edit them. There is heaps of it and pages 620 630 640 and 650 have un edited collections of raw material.

p352

The exhaust open point has very little to do with creating power due to "pressure" on the piston for "longer" with lower timings.
The gas pressures soon after TDC ,that creates the real power, is up over 80 bar, the pressure at Ex open is a couple of bar at best.
Moving from 200* to say 190* creates jack shit extra exertion of pressure on the piston to create torque, that then creates HP.
But the real issue is that down at 190* duration we get a huge amount of superposition of the gas pulse exiting the exhaust, on top of the residual pressure at the port.
This adding of a new pulse on top of an existing residual pressure means the wave front running down into the header has a huge relative amplitude, and this creates a huge depression at the port around BDC.
This also means we have port/pipe resonance over a much wider range and at a much high higher level than can be achieved at 200* duration.
In a conventional design we are forced into a corner by needing to create as much BlowDown STA as we can, and raising the timing is the only available route.
This pushes us away from the ideal port/pipe interaction timings, but is a compromise we are forced to accept to create the + 200psi bmep's needed, to be competitive.
Just another small detail that many overlook, or are unaware of.

p411

The header length should be in the 31 to 33% range.

p412

If I were to explain pipe design I would need to write a book,but in general things are pretty straight forward in relation to the % values.

End of header is always 31 to 33% and end of diffuser is always 62 to 68%.

To see the effect of a silly long header, you can watch the pressure ratio at the Ex port, and thus the effect this has on the depression in the cylinder.

We are looking for the lowest and widest negative ratio we can get around bdc when the transfers are fully open.

A long header delays the beginning of the depression too late in the cycle, when in the power band.

In a race 2T we are always fighting power range Vs peak power.

Shorter diffusers create steeper angles, thus greater wave amplitude, but this narrows the effective band width.

So - in general the best compromise is around 66%.

P413

The % I quoted for header means that portion of the length from piston to rear cone end.
Its from the piston to the beginning of the diffuser, what happens in between isnt relevant.
Unless of course you use a small Ex duct and a bigger header, that makes more power.
And of course same for the diffuser end, that is simply 66% of the length from the piston to the end of the rear cone.

For a race engine there are no minuses to a long rod.
Using 110 in the 50 stroke means you are on the money with the Aprilia RSA - that went OK for a 2T.
Increased weight and increased small end load don’t mean shit unless you are reving the 50 stroke to 16,000 - then all light weight parts are needed.

Picture says more than a 1000 words
(got them from kreidler.nl forum )

p420

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.

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.

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 centre 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.

P427

Nothing too much off the mark - except the old bullshit tale about the pipe pulling the reeds open.
How it goes is that the diffuser sucks like hell on the cylinder around BDC - this pulls gas out the transfers, they pull on the case, and this opens the reeds, allowing more mixture in.
Crap.

Here is a sim trace of a RGV100 at 13,000 making 40 odd crank Hp.
BDC is exactly between TPO and TPC, the reed lift down the bottom isnt showing the reeds much open till TPC - well after BDC, so the pipe action isnt affecting the reed lift at all, apart from
a delayed reaction due to petal stiffness and column inertia in the intake.

Re smaller case volume, I have measured one of those engines and its case com is exactly 1.3 on one side and 1.29 on the other with around 540cc from memory..
This is alot smaller than an Aprilia at 640cc.
But its case vol is relatively large in comparison to 2T technology at the time.
In a 125 project I have just finished, with a case reed, 1.3 gave the best result.
Going down to around 1.24 of the RSA spec lost around 2Hp with the reeds, no matter what I did with intake length and petal stiffness, pipe geometry or carb size.

Re the squish shape and chamber geometry.Yamaha always had odd ideas about what was correct, or best, and never really led the way at all until unleaded became mandatory.
Then the YZR was fast once Kennys boys got them on Asklands dyno.
And they kicked everyone's arses , even in 250 when they fitted the spool valved cylinders off the 500

… the pipe sucks like hell at BDC,the sim pressure ratio trace shows that dramatically when the diffuser shape is correctly designed.
Pipe depression causes a big pressure ratio across the transfer duct/cylinder boundary, and it is this effect that causes the bulk flow around BDC. But what I was alluding to, was that to then go on to say that the pipe opens the reeds, around BDC, just isnt true.

Re the carb venturi - having the smallest point within the carb up at the slide will reduce the divergent angle up to the RV area. If bad turbulence created a flow loss capability, the bench would show this immediately, on the dyno it could be several things causing less power to be produced.

Yamahas spool valve would seem to be the best system for a single or 3 port setup.
It is always close to the piston, no matter what leading edge height it has, and can also control the secondarys at the same time. Aprilias multi section blade is a good patch up of a flawed design, but it doesnt control the secondarys - maybe not such a big issue in a full noise application.

For the T port, Hondas dropping gate works very well.Its design in the RS250 cylinder is much better than the ones Husaberg showed in that the pivot point is alot further
away from the piston.Thus the arc away from the piston is alot slower.
Suzukis twin multi section tubular valves are complex but clever as well, and like Hondas gate they conform well to the port roof when open.

P428

In order to take full benefit of a large crankcase volume you need free-flowing transfer ducts. That means: large cross sections, short gas column lengths and large time.areas. Of course I don't know which dimensions you entered into the sim, but am I wrong in thinking they may have been more restrictive than the Aprilia values?

Skinny exhaust pipes, high crankcase compression and narrow transfers with timings over 140° were common in the sixties. These factors were interdependent: the skinny pipes hardly produced any decent exhaust suction, so you needed the pumping action of the small crankcase volume. And because of the narrow transfer windows you needed long timings to get anywhere near workable time.areas.

The energy of a moving gas or mixture column depends on its mass and its velocity. In ducts with large cross sections the flow velocity does not rise too high because the crankcase pressure can drop fairly rapidly. In short, narrow ducts the velocity will rise alright, but the mass in the ducts will be small. And in long, narrow ducts the long plug of gas will resist acceleration and will only slowly come up to speed. Because long columns are such slow starters, the kinetic energy at the latter stage of transfer will only make up for what went missing at the initial stage.

P438

When unleaded became mandatory in 98 most teams had a hell of a time keeping deto under control, having to run very rich and retarded.
The cylinders with the straighter pipes always gave allot more grief, until a lowly dyno operator at Yamaha discovered that
when he stuck a large pressure probe into the header, the deto went away.
They managed to keep this secret for a couple of years but when teams like WCM got hold of the bikes, and left pipes lying about as you see in the pics, word soon got around.
The "things " intruding into the header take varying forms, but all do the same thing - the usually bottom "bent "pipes don’t have the same issue, so don’t need the so called deto buttons.
I have a couple somewhere from a Red Bull bike - I will pic them and post here .

Blowing a pipe,except for the initial header shape, looses power big time,as the angle changes are blurred.
HRC has the trick method of pressing the pipe in two halves, and welding the seams, as a press tool can imprint distinct "corners" where for example the mid joins the rear cone.
Years ago when working with Jim at JL I tried blowing the pipe into a split mould around the mid section, but even this lost around 2-3 Hp per pipe on Hines dyno at Zip,when testing his Superkart title engines.

A larger muffler ID exposes the wave fronts to more packing material area, thus reducing noise - a step back down from the perf core to a smaller exit tube will increase the wave amplitude and make MORE noise.
Stinger/muffler lengths/diameters are very hard to analyse, only way is to cut and try, but with small dia mufflers - generally shorter is better for power, but not noise.

One trick with earlyer TZ carbs was to remove the air corrector jet altogether, made them rev on way better with a slightly bigger main.

Re the muffler situation. - the small engines like a 125 have a completely different sonic signature to a 250 - you must use a DbA meter at a set distance every time.
I spent forever working weekends for the NZ Kart Federation with a Db meter hung above the track trying to find a way to quieten down the 250s.
On the meter the sound level was always less when using a bigger muffler core - to the ear it was alot "louder".
In the end we went to the ICC type muffler, with the front modified to accept the 32mm OD stinger.
This was a long 100mm tube with a 50mm core, and a 40mm outlet, thus a huge amount of absorption area, plus a resonant volume that cut high and low frequency noise considerably.
We got to the stage where the inlet was then louder than the exhaust - then we started work on carb inlet chambers and venturi nozzles etc.
The whole thing is super complex,and as usual what works to help noise - usually kills power big time - but the big diameter muffler stuck on the end of a 125 or 250 made no difference to power at all,when compared to the best small muffler, but no
way would this be practical on a bike..
A smaller muffler was always super critical on length and diameter, every change made a difference.

The most effective silencer I once made for a 125 cc kart had a length of 400 mm, an outer diameter of 80 mm and a core diameter of 35 mm.
Smaller core diameters did nothing for engine power and were worse in silencing. An end cap with a smaller exit diameter made more noise, just like Wobbly says.

I think its a good time to remind everyone that the whole reason we heard about the possibility that 30 Hp was feasible from a 100 bucket was due to the software I was using at the time.

Now, we plug TeeZees 125 Aircooled engine into the latest version of EngMod2T and voila we get a result.Gaining the experience to run the software effectively is time consuming - but nothing like the time it would take to learn the hard way, what not to do.

[Frits Overmars]

I wasn't sure because the engine could be run in either direction.

Clue 1: turn the rear wheel and observe the clutch cage.
Clue 2: look at the curvature of the fan disc vanes.
Clue 3: look at the shape of the kickstart dogs in the center of the fan wheel.
Clue 4: push the starter button.

[TZ350]

Clue 1: turn the rear wheel and observe the clutch cage. Clue 4: push the starter button.

I tried, but how come the picture on my computer screen didn't move..... ?????

[Sketchy_Racer]

anticlockwise. front pulley is fitted to end of the crankshaft itself so rotates at engine speed. at high ratio the rear pulley is doing engine speed times CVT ratio so it can be spinning pretty quickly.

Are you sure? After the clutch near the wheel is a gear set which i believe is only two gears so would reverse the direction, meaning if the motor ran anticlockwise looking at the photo the bike would go backwards also looking at the centrifugal fan the impeller shape would suggest that the motor runs clockwise. I am however, likely to be wrong.

[F5 Dave]

. . . and its the first time I have seen an RS chassis flapping the front wheel about as he changed direction coming down the hill,. . .

Oh yeah they totally do that if you crank up the rear & add some bumps as there isn't much travel. Taupo on the old track interconnect we used GP before last had the RS flapping like a beitch till I learnt to avoid those bump on the right of the track (once was enough). I'd previously seen the steering damper on DDips bike(s) & thought, you've got to be joking. . . . but I wasn't laughing after that, - he's a smart guy & Mt Wgtn is a goat track so it makes sense.

Last weekend I almost launched myself at Kaitoke with an ill timed application of gas in a low gear while changing directions put the front wheel down pointing the wrong direction. Decided not to do that again.

[FastFred]

Clue 1: turn the rear wheel and observe the clutch cage.
Clue 2: look at the curvature of the fan disc vanes.
Clue 3: look at the shape of the kickstart dogs in the center of the fan wheel.
Clue 4: push the starter button.

Can't see any kickstart dogs but the centrifugal fan looks like its curved for clockwise rotation, well its actually hard to tell as you can have forward or reverse curved blades.

[husaberg]

Timing marks works for me.........................

[ief]

How do you figure that? Or do clocks act differently on that side of the globe?

[Frits Overmars]

How do you figure that? Or do clocks act differently on that side of the globe?

Yes, they run upside down. But so do the locals, so everything falls into place.

Can't see any kickstart dogs but the centrifugal fan looks like its curved for clockwise rotation.

I tend to agree on the fan vanes. And here's a little help re the dogs:

[speedpro]

Are you sure? After the clutch near the wheel is a gear set which i believe is only two gears so would reverse the direction, meaning if the motor ran anticlockwise looking at the photo the bike would go backwards also looking at the centrifugal fan the impeller shape would suggest that the motor runs clockwise. I am however, likely to be wrong.

The rear gear set has 3 shafts - input with the clutch, intermediate, and final which has the wheel mounted on it.

You can get intermediate shafts with different gears on and matching gears which can be pressed onto the input shaft to alter the final reduction ratio. They're listed on the link I posted for stupid cheap prices.

[TZ350]

... here's a little help re the dogs:

Thanks, FastFred is blind as a bat and I didn't recognize the dogs and even now I can't see them clearly enough in the picture to make out which way they engage.

CVT's have not been that common here so I have not actually seen a CVT in real life only pictures like this.

You will be able to have lots of fun with us as the team and I flounder our way through this CVT thing .... its all good

[Frits Overmars]

Thanks, FastFred is blind as a bat and I didn't recognize the dogs and even now I can't see them clearly enough in the picture to make out which way they engage.

My initial reaction (clue 1 - clue 4) was because I thought you were asking something about the engine in the picture. I did'n grasp that you were asking about the picture itself without having that engine at hand. And yes, the dogs in the picture are too small to recognize anything. I only pointed out where to look for them.

You will be able to have lots of fun with us as the team and I flounder our way through this CVT thing .... its all good

It pleases me especially that you guys are picking up on it.

[TZ350]

The rear gear set has 3 shafts ...

Thanks, like Sketchy I was unsure if it was 2 or 3.



I can see that 3 keeps the motor turning in the conventional direction, the same direction as the wheels, being anticlockwise in this picture.

Do you know the overall input/output ratio of the reduction box?

I would like to run the variator clockwise on the right hand side of the bike.

My guess is that the variator front pully could be run backwards but the shoes and slots in the rear clutch pully mean it can only be run anti clockwise. Maybe the shoe assembly can be turned around and with straight slots the thing could be run clockwise too.

[Frits Overmars]

My guess is that the variator front pully could be run backwards but the shoes and slots in the rear clutch pully mean it can only be run anti clockwise. Maybe the shoe assembly can be turned around and with straight slots the thing could be run clockwise too.

That ought to work. One thing to observe though: if the reduction gears aren't straight-cut, reversing the rotation may cause an unwelcome axial load on the bearings.