Quote:
Originally Posted by Dougal
It's due to the different exhaust wheel size.
The exhaust scroll creates a vortex, the exhaust wheel interrupts that vortex to create torque on the shaft.
In a free vortex the further you go in, the higher the gas velocity. So bigger wheels interrupt the vortex further out where the gas velocity is lower, that's why you need a smaller A/R ratio with a bigger wheel.
My engine originally came with an IHI turbo which is equivalent to a T3 with a 0.42 A/R exhaust housing.
I'm now using a T25 with a 0.49 A/R housing and they spool up at almost exactly the same point.
Multiply the A/R by the wheel radius and you get what I call the effective flow area. It's a handy number for comparing the spool up point of different turbos.
Remember A/R is usually in inches, so you need to know the wheel radius in inches. A T3 usually has a 60mm (2.36") exhaust wheel.
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With all the variables in turbo construction, does your "effective flow area" calculation give you your best fit recommendation of the Garrett GT2560R? Or do you favor a turbo that's close but has a ball bearing?
Would you please demonstrate the calculation on the turbos you recommend? I'd like to see the results and meaning you glean from the results.
Also, Marting will probably not be buying a new turbo. My guess is that these arn't available used??
Rick