Help with A/Ratio calculation

[orsum]

I have a K26 #6 turbine housing and I would like to calculate the AREA to RADIUS RATIO of the housing.

At point of intersection

Inlet. Area A (16mm*16mm)*3.142

= 804.353

Length R = 51mm

A/R = AREA RATIO

= 15.77 - 1

I see quotes on the internet saying a reasonable figure for the K26 #6 is 0.64 - 1

Where am I going wrong?

orsum

[Error404]

A/R is the area to radius ratio, you seem to be calculating something else.

It is the cross-sectional area of the outlet divided by the radius from the centre of the turbine centre axis to the centre of the outlet.

[orsum]

Error404,

This is what I am doing.

The cross-sectional area of the "INLET" divided by the radius from the centre of the turbine centre axis to the centre of the "INLET".

Which is the reverse of your recommendation.

I have checked again and this is the same thing I read each time Area of inlet/R

Were did you get your info?

orsum

[orsum]

I found were I was going wrong with my calc it was in mm as soon as I convereted to inch hey presto my turbin Area to Radius Ratio came out to 0.62

Regards

orsum

Link to info

http://takemebeyondthehorizon.wordpress.com/2009/08/17/how-to-go-fast-faster-the-math-behind-turbocharging-part-6-turbine-selection/

You should obviously match your exducer bore to the Turbo Airflow Rate (cfm) that you’ve calculated before. You should lean towards a larger diameter in case you’d like to increase your power a bit, but this graph isn’t definitive. You should contact the turbo manufacturer, or anyone with enough experience to find the best fitting turbine for your goals.

The second quantity is the Area/Radius Ratio. This is a bit more important than the Exducer Bore, as this is the general sizing of the turbine. The Area/Radius Ratio will determine the specifics of your turbo. This is the ratio between the Area (in2) of the turbine outlet (or inlet) and the Radius (in) from the center of that cross-sectioned area to the center of the turbine. Here is a picture to simplify it a bit



”Fig. 3-11.” Chart. Maximum Boost, Designing, Testing and Installing Turbocharger
Systems. By Corky Bell. Cambridge, MA: Bentley Publishers, 1997. 32.
Print.

This is the basic picture of the turbine, and it shows that throughout the whole turbine, the Area/Radius Ratio is always constant; from the turbine inlet all the way to the turbine outlet. The Area determines the velocity at which the exhaust gases exit the turbine scroll and power the blades. The exhaust gases are what are rotating the turbine scroll, which is connected to the compressor side and in turn rotates the compressor wheel (which compress our intake air). The Radius determines the amount of power that the exhaust gases will have. The larger the radius, the more torque the compressor wheel will have to compress the air.

Basic knowledge states that a larger Area/Radius Ratio will give you more power, while a smaller ratio will give you better(meaning quicker) response. Here is another graph:



”Fig. 3-14.” Chart. Maximum Boost, Designing, Testing and Installing Turbocharger
Systems. By Corky Bell. Cambridge, MA: Bentley Publishers, 1997. 34.
Print.

The problem is that there is no “perfect” or “right” Area/Radius ratio. If you want more power, by all means go for a higher(bigger) ratio, but the engine/turbo response might be too laggy for you. Choose a smaller Area/Radius Ratio, and your car might feel too jumpy, since the turbo will spool up too quickly. A small Area/Radius Ratio can also lead to not enough torque spinning your turbine scroll, which means your compressor also won’t work to its maximum efficiency.