ESE's works engine tuner

[Frits Overmars]

...not only do the Transfer streams need a little time to get moving they can reverse before the port closes.
Because the engine is making good power here (peak torque 12,250 rpm) my guess is this reversal is because the cylinder is being pressurized by the rising piston and plugging pulse from the pipe.

There's more to this than meets the eye. The piston is playing a double role: it pressurizes the cylinder and at the same time depressurizes the crankcase.
But even if the piston didn't move at all, there will be flow reversal if the transfers do not close at the right moment. It's a Helmholtz thing: gas flows from one vessel to another, the pressure difference will change sign, and the flow will slow down and reverse.
This is even more striking in the inlet system. The inlet port pops open, the inlet flow will fill the crankcase and at low revs it may reverse direction while the piston is still moving upward!

[TZ350]

There's more to this than meets the eye. The piston is playing a double role:

There is nothing simple about this why can't it be easy.

I don't want much, all I want to do, is squirt just a little bit of fuel 210 times a second, how hard can it be????.

[Flettner]

Link has a new manager ( used to road race twostrokes ) so the twostroke side of their software has been fixed now! Great, just need the right people in the right places. He is interested in our injection projects.

[wobbly]

All 2Ts have some flow reversal when the transfers open, as the residual blowdown pressure is greater than the pressure in the case.
Bulk flow doesnt occur till closer to BDC if the pipe is correctly designed, and the diffuser depression holds the Ex port below atmospheric long enough
to promote a differential across the open transfers.
I discovered the flow reversal, and the idea that the port to open first/flows last when I first Beta tested the Dynamation 2T code done by Kurt Leaverton of HotRods fame.
You can see the pressure rise in the transfers, when they crack open, in the running screen of EngMod - see the sample screendump where the green transfer line jumps up at EPO.

[peewee]

I discovered the flow reversal, and the idea that the port to open first/flows last .

wasnt there some ASE papers suggesting the same thing ? thats what i heard anyways. havent seen the papers for myself however. ive opened the A ports first on engines. may of done more harm than good but i dont know. but if your statement is correct wouldnt it make more sense to open the B first ?

while im thinking of it, on a reed cage, do the petals actually open all the way and hit the metal stoppers ? engmod is saying goodnews if i can open the petals 2mm more. ive found a way to open them 1.5mm more and might try it. basically where the stoppers bolt on the cage ill just use a spacer between the stopper and petal which will lift the stopper and allow the petal to open farther. but if the petals dont even open to the stoppers in the first place, then it would be useless to bother with this idea. ya it would be easy to test if i had a dyno but i dont have one

[peewee]

i may have answered my own question. looked at the old stopper and seen significant wear about half way to the end. only very minor wear at the end. so the petals may not be getting completely forced against the full radius of the stopper but theyre definatly contacting the stopper at the half way point with a quit a bit of force it seems. so my idea should work if i lift the stopper 1.5mm it will allow the petals to open farther. and theyre .5mm boyesen fiber resin material so theyre rather flexible. what do you guys think ?

[wobbly]

Perfectly correct, Jan Thiels setup in the Aprilia engines does exactly that - open the B first.
The B is wider than the A as well, and the lower A port helps to reduce the direct short circuiting upwards into the Aux Ex ports.
This layout maximises the available transfer port STA and is great for peak power at high rpm levels.
The usual reverse stagger as seen in Honda T port engines, with the A port the highest, works better in the 3 port layout when you are looking for wider power bandwidth.
Best example would be the KZ2 kart engines, as with no power valve, and the need to be able to pull hard from around 9000 to 14000 + this layout gives better
bottom end and overev power, at the expense of outright peak.
I have dyno tested high B port KZ2 engines, and been just over 50 Hp at the sprocket, but no matter what I tried with pipe length and ignition advance I could never generate
enough power down at 9000.
So although the cylinder was very fast in outright terminal speed, it lost too much off every slower corner, fine as a qualifying engine but no good diving under someone entering
a corner - as it simply would not pull out hard enough when on the "wrong " line.

[peewee]

so whats most everyones preference around here ? open A first, B first or all at the same time ?

[F5 Dave]

I think Wob was giving you a choice to make and the reasons to make it.. Reed bends most in middle so will rub most where you show it so I don't think you've proved it isn't fully opening.

[wobbly]

Spacing the stopper away from the reed will in a way "work" but if the reed is hitting the plate too early then hardly touching at its end,
then that means the stopper radius is too tight.
You need too decrease the bend radius so that the middle of it isnt overbending the petal at full lift.

Normal and reverse transfer stagger both have their place, as I have explained.
Opening them all together was last used by Yamaha in GP racing prior to the end of the 90s when they then bought themselves a CNC anemometric flow machine.
Suddenly they changed to square bore/stroke and staggered transfers, obviously a big deal in swallowing corporate pride - following Honda and everyone else.
This sea change saw the 250 twin win 1st and 2nd ( Jaques and Nakano )in the title for the first time in an age ,with a hugely superior package at the time.
There was then and still is now, no technical advantage whatsoever to concurrent transfer openings.

[peewee]

i think your right. the petal contacts the center of the stopper and then bends upward as it continues its range of movement. thats what seems to be happening anyways from examining the wear marks on the stopper

about the port staggering, i understand what wobbly is saying. ive heard other people say opening A first can broaden the bandwidth. so i believe it to be true. ive tried it myself but had no way to test it other than seat of the pants, which is useless most of the time.

[TZ350]

Its not all about horse power.



Ran a bike up on the dyno today and the conversation got onto tyre warmers and whether they should be banned from Bucket racing to keep the costs down and the playing field level and less daunting for people wanting to get involved in the sport.

At Mt Wellington, before gridding up the bikes are left to circulate for quite a few laps so that hopefully everything is properly up to working temperature.

Typically the tyres are run under inflated here (usually 16-18 psi cold) to get heat into them and the colder the day the more under inflated they are and I guess this practice is much the same on all the smaller tracks.

Anyway the Dyno conversation got onto tyre warmers because both tyres of the current lap record holder were showing an unusual wear pattern and the owner had emailed this picture of the rear tyre to the supplier to find out why.



The Reply:- "Cold Tearing: The surface is overheating. Pressures need to be increased, try 25 rear 23 front and see what its like. Warmers will help heaps. Without them the surface gets hot but the carcass does not, overheated surface and cold carcase causes these tearing type ripples to occur."

So I did a bit of looking on the net and found one of the main points of tyre warmers is to get the carcase up to temperature and to be able to accurately set the "Hot" tyre pressure and thereby optimize the handling available from predictable tyre grip.

This looks like a much better way to optimize race long tyre grip and handling than running the tyres half flat and hope and pray you guessed at the correct cold tyre pressure for when its hot and that the under inflated carcase will flex enough to get the tyre up to working temperature and not overheat.

I think everyone agrees that hp is only part of the story and that after a certain point improvements in handling pays ever increasing dividends.

And with the pointy end of F4 getting so competitive and consequently setup and handling is becoming very important. I expect we will see more people who have already optimized the weight distribution, suspension and other handling aspects of their bikes moving on to getting the best out of their tyres too.

I don't care one way or the other myself about tyre warmers but after reading the stuff I scraped of the net I am becoming more open minded about people using tyre warmers to improve the potential and safety of their bikes.

Scraped this stuff of the net:-



Set your optimum HOT Tyre Pressures in the Pits
Tyres will increase in pressure by about 20% on the track (e.g. increase from, let's say, 30 to 36 psi) which makes a huge handling difference. CHR Tyre Warmers will get your tyres’ surface AND carcass into the proper temperature range (the same as you’ll see on the track). Without Tyre Warmers 6-8 laps would be needed to get a tyre to its proper "hot pressure".

If you pre-set your Tyre Warmers to the optimum temperature you anticipate seeing on the track, then allow your tyres to "heat-soak" for an hour and then set the Hot Pressure, when you hit the track, there will be minimal pressure change - meaning your grip and handling will remain much more consistent.

Many of the current race compound tyres are "low pressure" tyres with psi recommendations of around 22-24 psi. These tyres are much more sensitive about needing to be at their hot pressure before they work properly.

Avoid "Cold Tearing" of your tyres. Taking a tyre at ambient temperature (i.e. 20-25 degrees) and carefully pushing it hard on the track to warm it up will undoubtedly increase the very outer surface temperature of the rubber in a couple of laps. However, the rubber 2-3 mm down from the surface will not yet be warm and not be as elastic and this causes the outer rubber to grip the track surface and underlying rubber to rip or tear away from it. This shredded look or graining once developed in the tyre almost never goes away and basically ruins the tyre’s surface - thus reducing grip. By pre-heating the rubber, cold tearing is - quite simply - avoided.

Taking tyres from ambient temperature and bringing them up to race temperature on the track may take from 3-6 minutes depending on the machine, track and rider. Aside from giving up speed during these opening laps, it is truly too fast to heat the tyre in an ideal manner. For example on a 25 degree day, the rider may get the tyre surface hot in, let’s say, 4 laps which typically takes 6 minutes. This increase of 100 degrees in such a short amount of time actually "heat shocks" the tyre. Race compound tyres contain "activator" chemicals in them which are set into motion with heat. Getting your tyre hot too quickly actually spends or wastes some of the chemicals and tyres will lose grip sooner than if warmed slowly on a warmer.

Avoid the damage caused by overheating your Tyres. Tyre makers are increasingly providing the specific maximum temperature their individual tyres should be heated to (different tyres from the same maker can need different temperatures). Also, specifically, intermediate or wet tyres require lower temperatures so being able to use the maker's exact recommendation is an important benefit of a higher-spec warmer and can avoid the inadvertent overheating which can completely ruin a tyre over a relatively short period.

When tyres are heated & then cooled - i.e. “Cycled” a change occurs that can often be seen, measured and felt. On some tyres you will actually see a blue haze form over its surface as some "oils" migrate to the outside and oxidation occurs. On other tyre compounds you may observe a much drier grayish haze depending on individual tyre composition. Either way, each time a tyre is put though these hot-to-cold cycles the tyre’s grip reduces as the rubber hardens at the end of each cooling cycle and the useful life of the tyre reduces too.

[marsheng]

Kr150 Pistons.

I've done some digging around but I can't seem to find any supplier of pistons. One place has 0.25 0.5 mm etc over bores but this is a nicasil bore so I'm not sure what bike that is . I need to use either a standard piston or a B or C if they make them that way.

Cheers Wallace

[Neal]

Kr150 pistons ? 59 bore and 15mm gudgeon pin ? Look at the tyga 300 pistons

[peewee]

anybody run their engine on methanol ? looking for setup and tuning advice if i add a splash of nitro in with it

right now im using 100% methanol. pingel fuel valve, 48mm lectron with 2 powerjets, mikuni 65L/hour pump