turbo exhaust housing

gregT · Post by **gregT** » Wed Jul 25, 2007 7:51 pm

hi, i would like to find out if a bigger exhaust housing than the standard would throw the shafts balancing out? ive got a T28 exhaust housing on the T25 turbo. thats all that is different from the T25. thanks

WooHaa · Post by **WooHaa** » Wed Jul 25, 2007 11:01 pm

if I'm not mistaken, the flow should be better, as the t28 has a .64 housing instead.
Won't effect balancing at all, as the hole where the wheel sits, is the same diameter.

Vlade · Post by **Vlade** » Thu Jul 26, 2007 7:06 am

Only thing is with the .64 it will take slightly longer to get up to boost, that said one might require a wheel to match the housing...

Speed breeder · Post by **Speed breeder** » Sat Jul 28, 2007 1:12 pm

Please excuse my ignorance...but how do you measure the size of the exhaust housing. The reason I ask, is because I know you get different size housings for a T3/T4 turbo for example (I think .90 and .95 or something).

I would like to eliminate some lag on my car (only spools up at 3800rpm on cold days)

gregT · Post by **gregT** » Sat Jul 28, 2007 5:17 pm

i just used a vernier, dont know if it was the correct way of measuring. but i just used it tyo compare the two sizes. i measured the inside diameter

The Calibrator · Post by **The Calibrator** » Sun Jul 29, 2007 10:28 pm

Seems to be a popular misconception that the A/R is a fixed size. Its not its a ratio.
It is measured from the centre of the wheel to the centroid of the passage leading to the wheel.
You can have 2 phyiscally dissimilar exhaust housings with the same A/R.

Its normally cast into the exh housing. There are a few factors influencing turbo spoolup.
Exh wheel size
Exh housing A/R
Compressor wheel size
Exh manifold design
Wastegate design
State of tune
Boost controller

There are a lot of turbo "experts" out there and it seems most of them know just enough to turn your car into a dog. The hot stuff is a T3/T4 no matter the application or engine size and always with the biggest exh wheel and compressor to be found.
The other hotness is to take a tiny little turbo and drive it beyond its design speeds by trying to boost 2 bar from it.

Turbo's are like camshafts, be conservative and you will have a nice smooth power curve and car that is a pleasure to drive.