I searched, but didn't get an answer.

When we talk about the stock turbo size, the last number means turbine nozzle area.

For example, TD05HR-16G6-10.5T has 10.5 cm^2 nozzle area.

But when people talk about MHI turbine housing size, for example, 7 cm^2 or 8 cm^2 housing, it means:

"8cm^2 is referring to exhaust discharge area in the turbine housing. More specifically, it is the smallest cross-sectional area of the scroll, turbine housing. Very similar to Garrett turbo's A/R. The smaller number means faster spool-up but more back pressure at higher rpm. Bigger number means longer spool up but less back pressure, thus more top end power."

quoted from:

https://www.evolutionm.net/forums/ev...fications.html

Then what is the stock EVO turbine housing size?

My friend's 04 STi has TD05H-20G with 8 cm^2 turbine housing, and I would like to know how this turbine housing compares to our EVO TD05HR housing in size.

 

You had the information, unless you are asking the wrong question..
The turbine housing for 2003-2004 Evos is 9.8cm^2.
The turbine housing for 2005-2006 Evos is 10.5cm^2.

 

Thanks for the reply.

So the nozzle area = the smallest cross-sectional area of the scroll ?

 

I am not so sure that this is absolutely right. But, I've already had a few too many Hefe-Weissbiers for my own good

 

Also the MHI 20g's with a 7cm and 8 cm turbine housings are not divided, it's a single inlet.

 

So basically those numbers indicate the same thing, but EVO's twin scroll design decreases the effective (or net) cross-sectional area although it is 10.5 vs 8 ?

Hm...STi has 2.5L engine, and it is still not clear why they use smaller turbine housing than us. Maybe that is why their dyno graphs usually have more flat power band than EVO's at high rpm?