ESE's works engine tuner

[TZ350]

P1050 ... EngMod2T setup talk about pipes, transfer ports and the TubMax graph

As some of you know I have been developing my 300cc NSR. Its going really well except the pipes are cracking and braking all the time. They are SS no surprise. They really do cool very quickly and obviously heat fast as well. I was wondering if lagging the pipes for the first 300mm is a good idea to keep a bit of heat in there and not let them cool so fast. Will this help with the cracking yah reckon.

Years ago on pre 95 rs hondas guys used to put beads of high temp red silacon around the chambers to take the zing out of them to stop cracking , the promblem was the rubber mounts but it did work not to bad but looked crap

I'm not sure how the SS works as I've never had a SS pipe. As with nearly everything I've owned, if the pipe was cracking the cure was to mount it so it was free to move around while still supported. You probably already on to that idea.

...anybody who has tried this, tell me about expansion chambers made of aluminum, an examples of which I saw on the French site. Since, I assume, they'd have to be made thicker than steel, does the weight savings balance the drawbacks? I assume the big drawback is heat-loss, but maybe that could be largely addressed with a ceramic coating. What alloy and thickness has worked (if any has worked)?

Don't do it. There is no weight saving, aluminium (aluminum to you) pipes won't work without an internal ceramic coating, and they will crack despite the increased thickness. Aluminium does that.

Titanium works great for pipes if you use the right grade Attachment 306191. But stainless steel is almost as good, cheaper and easier to weld.

hey wobbly let me ask something. in EngMod 2T, where it asks for the flow width of the window. if the duct exit and window are the same size and there is no kicker or radius turn at the duct exit, its rather easy to figure the flow width.

But like most cylinders, there is either a kicker or a radius turn just as it enters the cylinder. is there a easy way to get a close approximation of the flow width in this situation ?



Green arrow would be the flow width if both duct walls went parallel into the cylinder. but what if there was a radius or kicker. Would it still be as simple as the blue arrow suggests or is it more complicated than that ?

Where you have an angled exit on one wall like that I use a combination of the flow and chordal width. In reality the port flow area will be very close to the chordal width, as when the flow exits the duct its effective area will be less than a straight flow port, but more than the flow area measured vertically as you have drawn it. In between approximation is the chordal width as I have shown.

Imagine that you have a collection of coins. The diameter of the largest coin that you can shove through the window from within the cylinder bore, is the dimension you are looking for.

Well its sort of like I said, with parallel walls the coin will push into the duct and give you the exact "flow width".

With one wall angled a smaller coin will push into the port, but this gives a smaller flow width, and in this case its the chordal port width. Neels (EngMod2T) code asks for the actual "flow width" and even he says you need some judgement to approximate this where weird angles are involved.

ONLY a 1 mm change, that is enough to completely ruin any engine - 0.1mm should be an ONLY to everyone - in a KT100 0.05mm in any port size can ruin an engines power.

As Neels says you have to use some judgement to get the actual flow width correct.

Using the example he gives in the help file, if we call the bottom port an A port with a heavily sloping front wall, the flow width will be very close
to the original flow width as he drew it .



If we call the top port a B port with a hook, its effective flow width will be very close to the chordal as he dew it. The A port may in fact be much wider chordally, but because of the entry geometry the actual flow thru that port will be reduced by the cosine of the entry angles - exactly the same as the software reduces the effective area by the cosine of the axial upward angle of the duct.

Where there are two distinct entry angles, use your judgement to get what would be the real flow width.

wobbly how did you go about calculating the entrance ? the engmod help file doesnt seem to be real specific about this.

did you just use chordal width x height from case to cylinder sleeve, like the green arrow ?

or did you use something more like a flow width as the red arrows show. red arrow A + red arrow B x height of case to cylinder sleeve ?

Actually if you used a chordal width you would probly do something more like this , with the opening width split into 2 parts to give designation for the A port and B port. then simply green arrow A x height. green arrow B x height

Depends upon the cylinder design. In the case of the Yamaha you are working on the septum divider is very tapered, so the effective entry area is pretty much as you say for each port - the two green arrows times the height.

But in an Aprilia where the septum is very wide, the effective duct acts much more like the angled flow widths times the height. Then there is the extra entry coefficient added by the shape of the inner bore wall.

The length is the important factor, the entry area/exit area ratio does not make a big difference at all, except where you do not have the transfer duct volumes as part of a measured input.

I recently ran a test on this out of interest - with everything kept constant ( including the case vol ) having a 1:1 entry/exit ratio and a 1 :1.5 ratio made virtually no difference.

This ties in with my assertion that all of the mixture transferred into the cylinder is sitting in the ducts, there is no actual flow from the case into the cylinder when the transfers are open.

The duct length is very short in the MZ style thru the piston feed entry, but this is probably offset by the fact that the axial angle is so steep the effective area at the bore is tiny - thus the actual flow cc is tiny as well. But even that small duct has to be filled from somewhere, and the hole in piston,into the duct works well compared to non at all.

I worked at EMC building pipes in the early days of the Rotax 256 , and the idea of a hole in the piston, lining up with a hole in the boost port duct made a couple of Hp in the twin. We tried doing the same thing with all the transfers, spending hours grinding holes in the bores, but sadly this made less power.

Later on in the Rotax development it was worked out that the boost duct entry was badly shrouded, and once this was fixed along with a 1/2 moon cutaway in the piston skirt was introduced, power went up another couple of Hp over the hole in piston idea.

Joe's boost ports were a quick fix for crap scavenging in a piston port, and really were just a band aid - but as he was very good at ,Yamaha paid a fortune to him for the idea to be used in the twin 125 Yamaha that really was a very good little engine in its time.

Yamaha paid Joe another fortune for the dumb offset combustion chamber patent, that only got into production for 1 year in a TZ. Then they finally realised that having no squish on one side, and huge squish velocity on the other ,actually caused detonation - someone at Yamaha Corp must have felt really stupid/and or got fired.

But Dr Joe went laughing all the way to the bank - then started taking loads of cash from USA outboard people, again mostly bullshit technology, but hey I dont want to overly deride those that taught a young Kiwi plenty about the workings of a racing 2T.

You will make more power if you have a transition from the 23.7 duct outlet ( this will of course be oval ) up to the 26 pipe diameter ( round ) ie no steps at the joint face.
This is usually around 25 to 30 long and will be the slip joint spigot - this can be inserted into the pipe in front of the header as part of the header length %.

Hi Wob, this is getting into deeper water than I am used to. I worked hard playing with the ignition to get a flat TubMax (squish end gas temperature), but was I doing the right thing, is Ief's red line on this graph more appropriate? I just don't know what a good TubMax graph should look like.

You will know when TubMax is too high ( around 980*C ) as the program will scream DETONATION at you.

On a DynoJet you will need around 12.5% multiplier ( down ) to go from indicated crank Hp in EngMod to RWHp when testing your average racebike.

EngMods TubMax is a reflection of the % of fuel energy retained in the unburned end gases trapped in the squishband. The shape of this curve is affected by a myriad of elements but the biggest factor is the real ignition timing.

In a race engine the results are supremely useful for juggling the ignition timing to fix any major anomalies that can produce low bmep at one point or several in the usable powerband. Where you are running what i would call "normal" numbers for timing - say 28* at the bottom of the range and 15* at peak then some further retard to get heat in the pipe for overev capability ,the curve shape will be close to that of the torque produced, a flattened bell.

ie low 900 rising to high 900*C at peak torque then dropping away again as more of the combustion heat energy is dumped into the pipe. You have to be careful of part throttle deto at the beginning of the powerband, and then of course if the temp starts hovering at 1000* in the high power range you will get DETO lighting up on the screen.

To drop the temp it is easy enough to simply retard the timing - but more power may often be had by adjusting the stinger, or reducing the com/squish velocity. Then re-running the Turbulent model to account for the differing flame propagation speed through the chamber due to squish turbulence changing the combustion delay numbers etc.

These factors are just as important, sometimes more - than the "raw" ignition timing number at any rpm point. Each end of the bell curve can be tipped, by use of a powervalve for example,or a solenoid powerjet that is simulated by a change in A/F ratio past peak power.

A huge part of Neels efforts to recreate reality in EngMod2T’s sim results is all around the code needed to model the wave action within the pipe.

A 2T lives and dies on the correct timing and amplitude of the particle flow down the pipe, much as a 4T lives and dies on the intake tracts influence. The latest code change that now has an accurate model of the actual wall temps effects has got the results even closer, without the demon fudge
factors Neels hates with a passion.

The only caveat i would add is that there is still some leeway for idiocy to creep in, and still get a result that seems fine ie 25* diffuser angles. Go back to the old texts and you will find that very early on in the development of expansion chambers it was found that the angle that gave the best energy recovery ( amplitude Vs period ) of the depression communicated to the Ex port during the scavenging phase was 16* included.

This is now modified somewhat in that we can and do have up to 6 different cones. All interacting and changing the shape of the negative pressure ratio plot as seen at the port face when the piston is around BDC, but as is human nature we always think more must be better - even with single malts.

Just keep in mind that any energy used in the diffuser, must then reduce the energy available to be used in the reflection phase - there is only a finite ( and ever decreasing ) energy level available that starts when the piston cracks open the port.

[peewee]

hey wobbly let me ask something. in engmod where it asks for the flow width of the window. if the duct exit and window are the same size and theres no kicker or radius turn at the duct exit, its rather easy to figure the flow width. but like most cylinders, theres either a kicker or a radius turn just as it enters the cylinder. is there a easy way to get a close aproximation of the flow width in this situation ?

green arrow would be the flow width if both duct walls went paralell into the cylinder. but what if there was a radius or kicker. would it still be as simple as the blue arrow suggests or is it more complicated than that ?

[wobbly]

Where you have an angled exit on one wall like that I use a combination of the flow and chordal width.
In reality the port flow area will be very close to the chordal width, as when the flow exits the duct its effective area
will be less than a straight flow port, but more than the flow area measured vertically as you have drawn it.
In between approximation is the chordal width as i have shown.

[Frits Overmars]

green arrow would be the flow width if both duct walls went paralell into the cylinder. but what if there was a radius or kicker. would it still be as simple as the blue arrow suggests ?

Your blue arrow is faulty because your dotted red line does not exist. As the Italians say: izze reelly simple: find the smallest passage.
Imagine that you have a collection of coins. The diameter of the largest coin that you can shove through the window from within the cylinder bore, is the dimension you are looking for.

[ief]

Tnx for the files Rob, gives me something to play

Looks to easy though, hehe. (4 runs, 2 pipes, basicly from scratch, I couldn't resist and changed 1 thing on the engine, only a mm, nothing drastic,hope thats ok )

q's:

1. My baseline reading differs slightly from yours, might that be due to using a different version, I think I have the latest not publicly available.
(not to big of a difference though but still)
2. What would max acceptable tubmax reading be?
3. What hp figure would you say is needed to get 16 RWhp?
4. Is your combustion file 'good'? Seems such a strange curve to me (?)

[TZ350]

Good Work....

[seattle smitty]

As the Italians say: izze reelly simple: find the smallest passage.

Okay . . .

Imagine that you have a collection of coins. The diameter of the largest coin that you can shove through the window from within the cylinder bore, is the dimension you are looking for.

WHAT?? I'm just a dumb welder but this seems to contradict your Italians.
If you have a parallel-sided port (like those shown) that is aimed straight into the cylinder toward its center, no chordal angle, then your Italian coin will fit equally well all the way from the opening in the cylinder and on into the port. But if you start angling that same port at an ever-increasing angle to the cylinder's center-point, with your coin size unchanged, the parallel walls of the port get closer and closer together, and the port can pass less and less A/F. Leaving aside the matters of how the inlet streams effect each other and exhaust-clearing for the moment, what are you trying to measure, the size of the holes in the cylinder (why would you care about that?), or how much A/F you can pass through the ports?

I guess you mean that when you push your coin into the port from within the bore, you hold it at a right angle to the port, not to the bore centerpoint . . . right?

(I have that baffled-four-stroker expression on my face; dang!!)

[seattle smitty]

Deleted while I think more about it, LOL.

[wobbly]

Well its sort of like I said, with parallel walls the coin will push into the duct and give you the exact "flow width".
With one wall angled a smaller coin will push into the port, but this gives a smaller flow width, and in this case its the chordal port width.
Neels code asks for the actual "flow width" and even he says you need some judgement to approximate this where weird angles are involved.

You will know when TubMax is too high ( around 980*C ) as the program will scream DETONATION at you.
On a DynoJet you will need around 12.5% multiplier ( down ) to go from indicated crank Hp in EngMod to RWHp when testing your average racebike.
ONLY a 1 mm change, that is enough to completely ruin any engine - 0.1mm should be an ONLY to everyone - in a KT100 0.05mm in any port size can ruin an engines power.

[ief]

Tnx Wob, in my defence, it made 1+ hp (was an educated guess)

2nd try turned out te be a good one, rest of the day was more like pissing in the wind, just as I like it.

Anyway, last run is now going with another cbd file, attached run with my exhaust, Robs files as is except smaller exh port outlet (23.7 mm, that was the mm, 1.3 to be exact) en 1 cm shorter carb, hope I recall that right.

And the last run, didn't want to mess with Robs files to much but the cbd file looked wierd, on the other hand, what do I know, I still have no clue on all the vibes, delays and what not... anywayzzz, I enjoyed myself, hope Rob can do something with the exhaust as a start or something.

edit: the cbd run could obviously do with some more tweaking but I'm done for now.

[wobbly]

In reality you will make more power if you have a transition from the 23.7 duct outlet ( this will of course be oval )
up to the 26 pipe diameter ( round ) ie no steps at the joint face.
This is usually around 25 to 30 long and will be the slip joint spigot - this can be inserted into the pipe in front of the header as part of the header length %.

[peewee]

Well its sort of like I said, with parallel walls the coin will push into the duct and give you the exact "flow width".
With one wall angled a smaller coin will push into the port, but this gives a smaller flow width, and in this case its the chordal port width.
Neels code asks for the actual "flow width" and even he says you need some judgement to approximate this where weird angles are involved.

You will know when TubMax is too high ( around 980*C ) as the program will scream DETONATION at you.
On a DynoJet you will need around 12.5% multiplier ( down ) to go from indicated crank Hp in EngMod to RWHp when testing your average racebike.
ONLY a 1 mm change, that is enough to completely ruin any engine - 0.1mm should be an ONLY to everyone - in a KT100 0.05mm in any port size can ruin an engines power.

since nearly every cylinder uses some sort of radius turn or kicker, dont you think neels should do a update for such port arrangments ? ive seen 1 cylinder in my life that uses paralell walls and its old outdated ktm scrap

[TZ350]

Post Classic possibility for the Tiddler class.



One cylinder of a RG125T bore stroke 43x43, 44 crank hp as a twin.

[ief]

In reality you will make more power if you have a transition from the 23.7 duct outlet ( this will of course be oval )
up to the 26 pipe diameter ( round ) ie no steps at the joint face.
This is usually around 25 to 30 long and will be the slip joint spigot - this can be inserted into the pipe in front of the header as part of the header length %.

Yeah, I remeber that was mentioned before and I tried to sim it, gave worse result in engmod, same in this instance. Looking at the tubmax some more (never saw that before), what would be an ideal/ logical outcome if any? (more of a straight line or more start low and build up to high)

Re: Peewee and parralel walls, wouldn't the different scavenging configurations account for that?

[TZ350]

Hi Wob, this is getting into deeper water than I am used to. I worked hard playing with the ignition to get a flat TubMax (squish end gas temperature), but was I doing the right thing, is Ief's red line on this graph more appropriate? I just don't know what a good TubMax graph should look like.