z8cw

Most other's I have seen are reversed or come in all sort of shapes.



12A Yaw port optimized for flow on the bench

z8cw

Or stage 2 exhaust from a tuner in Japan

z8cw

[quote name='Old Splatterhand' date='Feb 21 2005, 08:58 AM']

since noone really dares to think out loudly, i'll try...

let me swing my magic stick and write something that contains 100% pure fantasie and 0% hard data or anything real-world related.



my guess is, that a round opening-line helps to distribute the exhaust more evenly over the exhaust-phase, thus getting a more harmonic exhaust cycle with less reflections.







Thanks for the thoughts. Yeah I wish we all had the time and money and just test slightly different shapes by tearing down the motor once a week just slightly altering the ports.



A sound theory needs to come first but obviousely it can't replace real world experience and testing.



CW



One more pic..the scoot xport seems straight line too

rotarygod

Read Paul Yaw's page on flowtesting to understand how he got to that shape. He explains which shapes work better for the top and bottom.



http://www.yawpower.com/Flow%20Testing.html

z8cw

That's where I got the pic from.



Still that doesn't cover the dynamics of the flow with the apex seal passing over the port.

RETed

Sorry for the slow responses, but I just started a new job...



You would think smooth, consistent exhaust flow would be more desirable.

Check out any information on collected versus divided turbo turbine housings and performance.

Divided turbines and turbo exhaust manifolds perform better when the exhaust pulses are totally separated.

This used to be one of the big secrets a few years back, but enough info has "leaked" out that's it's pretty common knowledge.

As a rule of thumb, you can run one or even two "steps" bigger on the turbine A/R when you go from a collected to a divided set-up.

The unmolested exhaust pulses from each rotor "hit" the turbine harder which aids in spool-up.

The 13B is unique where the exhaust gas energy is so high over a piston motor.

This is why rotary turbine A/R's are so large versus a comparable piston engine turbine A/R.





-Ted

l8t apex

so wide it looks like there is little apex seal support. I did that on my 1st porting job and they cracked .

z8cw

Ted,

You are absolutely right. The divided manifold and turbine housing has been proven to work better. The only contrary experience is from owners with a T51r kai kit. The manifold is vband and the turbine housing is undivided and people love this turbo. It seems to spool up fairly fast for its size. You could possibly explain it that with this set-up the shape from exhaust port to turbine blade doesn't change. The pipes stay round all the way through. As for our typical application we go from round exhaust port exit to the square flanges and back to the round turbine housing. Maybe the consistent shape makes up for the larger diameter in the turbine.



I think you might all agree that the secret to spool up is velocity. Higher velocity will push the turbine harder and will help battle pulse reversion. Two small runners all the way to the turbine will prevent the exhaust flow from slowing down. When you change diameters in a collector or undivided turbine housings you give the gases room to expand and slow down. This isn't just the theory but has been proven by other members. The tricky part is to find the right diameters runners for spool up vs heat vs top end power. In general I think the runners are mostly to large. Most aftermarket manifolds just match up to the exhaust port openings and give little concern to the optimal diameter for one's application.



CW

93BlackFD

OEM exhaust ports

C. Ludwig

Here's a set I did with Racing Beat templates. Looks pretty much identical.