2 Strokes Down Under

Hi all. This might cause a furore or maybe it wont.

What is the current best theory of the lower edge of the transfer port divider shape?

If that wasn't clear enough, I have an IT 400 and have just had it bored for the next sized piston. When I look at it now, the base gasket flange has the divider between the transfer ports square and machined as a part of the cylinder base.

On other bikes, I have seen them sharpened to a point, and I have seen them curved gently. My guess is that as it is now, flow up the ports would be more turbulent and at a lower velocity than edged or curved.

Anyone have a good reference to this stuff for the layman?

Fred there is no "theory" if you see a knife edge on a transfer divider whom ever did that has no fucking idea what they are doing , need a kick up the arse and tools condiscated.
You can leave it square or put a radius on the edge makes no real difference, wider the better.

yes, an aeroplane wing is an aerrofoil shape which is the most aerodynamically efficient shape for air traveling in a single direction for a given cross sectional area.

so pretty much always rounded on the leading edge (while at subsonic speeds), its more efficient (less turbulence).

But much more important than knife vs rounded edge is that the transfer ducts are pointing in the right direction, which is why on some motors the bridge is a chunky V shape so that the wall of one duct is not in the same directional plane as the transfer next to it.

I beleive the IT490 cylinder is like this...

if you were to knife edge this, you would ruin the direction of the flow in the transfer ports.

I just had a look at a photo of stock IT490 transfers and theyre not half bad for an old aircooled pile of steaming shit

no seriously, there not bad

cheers,. Mine is an IT 400 D. 1977. make any difference Jeram?

No effing clue haha

Post up a photo of what you've got

Jeram wrote:yes, an aeroplane wing is an aerrofoil shape which is the most aerodynamically efficient shape for air traveling in a single direction for a given cross sectional area.

The main function of the wing is lift. The main function of the port is speed of flow. Both are a Black Art compromise with competing needs.

Jeram wrote: so pretty much always rounded on the leading edge (while at subsonic speeds), its more efficient (less turbulence).

My limited knowledge of aerodynamics tells me the way you leave the air is more important than the leading edge.

Improvement might be made with the leading edge but the shape, the surface and direction of the port are more important. And there can be a mix and match comprise played with these perimeters as well.

OzzyElsie wrote: The main function of the wing is lift. The main function of the port is speed of flow. Both are a Black Art compromise with competing needs.


My limited knowledge of aerodynamics tells me the way you leave the air is more important than the leading edge.

Improvement might be made with the leading edge but the shape, the surface and direction of the port are more important. And there can be a mix and match comprise played with these perimeters as well.

Rounded leading edges on wings are a common design feature on sub sonic aircraft there is no super sonic gas speeds in a engine.
There is no black art in transfer design, 'flow' does not equal HP. Ports that 'flow' well will not make as much HP as ducts that are aimed correctly. There is only one design to have and it depends if you can fit it into the cylinder.

OzzyElsie wrote:

Jeram wrote:yes, an aeroplane wing is an aerrofoil shape which is the most aerodynamically efficient shape for air traveling in a single direction for a given cross sectional area.

The main function of the wing is lift. The main function of the port is speed of flow. Both are a Black Art compromise with competing needs.

Jeram wrote: so pretty much always rounded on the leading edge (while at subsonic speeds), its more efficient (less turbulence).

My limited knowledge of aerodynamics tells me the way you leave the air is more important than the leading edge.

Improvement might be made with the leading edge but the shape, the surface and direction of the port are more important. And there can be a mix and match comprise played with these perimeters as well.

I'm not sure what your point is.
there is no trailing edge in this case, or more specifically we have zero control over it (its a square edge at the cylinder wall), so the leading edge is the dominant variable.

Stuffing around with the transfer port divider will make FA difference.
My DG pipe was a worthwhile improvement to my IT400D.
As was Boyessen reeds on NSR250 reed blocks and UFO carby slide stuffer.

Correct me if Im wrong, but as I understand it this bike is a 'tight arse build', for lack of a better term .
So I dont think hes out to buy pipes and reeds. Just simple/free improvements.
But I agree, if he wanted to spend $'s to get a substancial improvement thats where you'd start, with the pipe and reeds etc


So when you remove the bolt on improvements, your left with the option of doing lots of small improvements which individually give sweet FA gains, but combined give a noticeable little power boost.

Not really, the question was more along the lines of "I've noticed a difference here in the leading edge shape, across multiple different bikes, does it make a difference?"

Seems there was a simple answer by many of you and that answer is no, it doesent make a difference.

And yes, it is a bit of a tight arse build, but really I just want to ride the bloody thing and make sure it is reliable.

Thanks everyone for all of your input.

Ahh ok, go ride it then