ESE's works engine tuner

[TZ350]

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If not "Genius" then incredibly clever and very interesting two stroke project. Impressive work.

[TZ350]

[SwePatrick]

Alex, you should take contact with Mahle and make their blend of nicasil ingredients official, That´s a hard task for you

Going the easy way with a steel liner is like the opposite of your new t-shirts

[F5 Dave]

Needs a cylinder leak test rig. We've covered them about 300 pages ago. Lock the crank with piston above top of ex. That should tell what the seal is really like.

[Frits Overmars]

Needs a cylinder leak test rig. We've covered them about 300 pages ago. Lock the crank with piston above top of ex. That should tell what the seal is really like.

Something like this Dave?

You could lock the crank in any position if you so desire, but it might be instructive to 'scan' the cylinder by holding the piston in a number of positions with a long ring spanner on the crankshaft nut. That way you can establish the point of maximum wear.
I also used this method to check whether the piston ring was stuck in its groove, and if so, on what side of the piston, without even opening the engine.
If the ring is stuck, lifting the piston away from the bore because of the inclined con rod angle will also lift the ring off the bore, aggravating the leakage.

[jfn2]

Hi all
My questions are concerning the 'T' shaped, vertical bridged, exhaust port used in some engines, one being the Yamaha YZ125. I believe it was Woobly said with this type of ex port to reduce the area at 1.5 x the bore in the exhaust duct, to only 95% of port area at the bore. My first question is does this still hold? My second is how far down the duct should you blend the 'T' shape into the main stream?
Most of the cylinders I've seen, they've ended it less than half way down the duct. I understand the exhaust wall is fairly thin in some cylinders so another question is can you curve this blending process to try to extend it down the duct? Thank you for any replies. Jeff

[wobbly]

The T port engines respond exactly the same as 3 port , both have large blowdown capability , and need all the help available to keep the velocity up as the piston is lowering from EPO.
In most cases the smallest area should be at the duct exit , the face where the manifold fits on.
A couple of engines I have done have a female spigot as part of the cylinder , in this case I have made a new spigot that presses into that female step , and then forms a new male slip fit for the header to attach to.
The exit area should be 75% of the EFFECTIVE area of the port at the bore - that is the chordal area X the cosine of the duct roof down angle.
In a full noise T port duct the exit should be oval - with the width at the same size as the header diameter.
This means you end up with an ellipse of 42 wide by 31 high if its like an A kit Honda performance capability.
Then the spigot has a transition from this oval shape out to the round header.
The spigot should have its floor colinear with the duct exit angle , and all of the transition angle is done in the roof - this means lifting the header exit centerline some 3mm above
the center of the cylinder duct exit shape.
No steps anywhere - some have reported that steps help mid range power off corners , but if the spigot is lifted then that setup has the same mid power as the steps , but way more top end.

[andreas]

I, thinking there should be a duct exit/min area factor of the blow down area, as opposed to the effective ex area. Is there such a formula?
And why is it the chord area and not the curved?

[wobbly]

You are right - as Frits has pointed out a couple of times , the duct exit area should be tied to the Blowdown STA .
This would be technically correct , but the 75% area guide idea was derived from a huge number of race engine projects finalised in EngMod.
The exit area is tied in fact to the gas speed Mach number , as it turned out virtually all the engines I have done made best power with the duct exit Mach at 0.8 , and this was virtually always seen
with a 75% area ratio or very close to it.

The chordal area is that actually presented to the gas flow , the curved ( arc ) width has no influence whatsoever on the gas flow Mach number or the Cd thru a duct.
You can have say a 40mm Exhaust chordal width port on a 54mm bore or a 70mm bore. The effective duct area will be identical in both cases , but the 70mm bore will have less arc length across that chordal 40mm.
Thus arc widths are of no use at all in port calculations , to establish angle area or STA.

[andreas]

You are right - as Frits has pointed out a couple of times , the duct exit area should be tied to the Blowdown STA .
This would be technically correct , but the 75% area guide idea was derived from a huge number of race engine projects finalised in EngMod.
The exit area is tied in fact to the gas speed Mach number , as it turned out virtually all the engines I have done made best power with the duct exit Mach at 0.8 , and this was virtually always seen
with a 75% area ratio or very close to it.

The chordal area is that actually presented to the gas flow , the curved ( arc ) width has no influence whatsoever on the gas flow Mach number or the Cd thru a duct.
You can have say a 40mm Exhaust chordal width port on a 54mm bore or a 70mm bore. The effective duct area will be identical in both cases , but the 70mm bore will have less arc length across that chordal 40mm.
Thus arc widths are of no use at all in port calculations , to establish angle area or STA.

Thanks Wobbly, The port window as is curved is not fed only from one angle, it would see gas flow from the partial circle between the cord and cylinder wall above also?

[F5 Dave]

Pressure will be equal inside the cylinder, and high pressure at that. It can only squeeze out one port.

[Vannik]

Thanks Wobbly, The port window as is curved is not fed only from one angle, it would see gas flow from the partial circle between the cord and cylinder wall above also?

Yes, the calculation for the flow area in a T-port takes into account the side wall angles.

[andreas]

Vannik, makes good sense.

[Jhonn]

hi all,

I am following this site already for a couple of years but never posted someting. First of all I am dutch and love to work on 2 strokes, I do lots of hands on testing on the dyno, I work mostly on KTM 85-125 engines as I raced one myself. I receltly started using EngMod and just moddeld the SX85 engine, however I get reliable output but I am not 100% sure if all my inputs are OK as the engine does not realy react to adjustents that I tested in real life. So are there people out here that might can help out with some Engmod quistions or want to check my DAT2 file as the software looks realy good but I need to get more expierence with it.

here you can see one of my latest project, I made 125cc KTM cilinder with an RSA-Wobbly duct I also changed the internal radius of the transfer ports and many more.

[lodgernz]

Thus arc widths are of no use at all in port calculations , to establish angle area or STA.

Although the arc width is useful inasmuch as the chordal width can be easily calculated from it, when using a graph paper cylinder to get the port dimensions.