Turbo Question...
 

On turbos, why does this intake side have the extra holes drilled? Wouldn't it make sense to just have a larger opening?

http://i.ebayimg.com/00/s/NDEyWDQ5Mg...TZXzK/$_12.JPG

I believe that is an "anti-surge/ported compressor housing" - supposed to combat compressor stall between shifts

I have never seen that before and I have played with lots O'turbos.

Is it a variable configuration variant?

They have a second set of moveable vanes that open and close to help spool up but them limit boost at the higher end or something like that.

That's what I thought, too.

speed holes

Pre-drilled holes to mount the muffler bearings....

I believe the power band threads thru those holes.

You'd probably find that this is a way of limiting boost. That is the turbo is matched to the engine performance required or desired not max HP.

Looking at the pic I would guess about half of the exhaust gas would go though the holes limiting the power gained.
Maybe it's been designed to use on cars with higher compression ratios? (That are not easy to lower... Newer crap disposable cars)

Serial, i expect they nailed it already. ^^^
its prolly a variable vane geometry compressor and when them vanes snap shut those holes allow the boost to bleed backwards to prevent surge shockwaves from breaking tips or denting bearings.

Or sumthing along them lines.

Google "anti surge compressor housing" or something along those lines, 'cuz that's what it is.

A Ported Shroud compressor (see Fig. 2) is a feature that is incorporated into the compressor housing. It functions to move the surge line further to the left (see Fig. 3) by allowing some airflow to exit the wheel through the port to keep surge from occurring. This provides additional useable range and allows a larger compressor to be used for higher flow requirements without risking running the compressor into a dangerous surge condition. The presence of the ported shroud usually has a minor negative impact on compressor efficiency.
http://www.turbobygarrett.com/turbob...ud-diagram.jpg
http://www.turbobygarrett.com/turbobygarrett/surge_line

It's actually pretty common from what I see. It it an anti-surge ported shroud. When the turbo spools quick and is trying to flow more air than the engine can handle (or when you lift abruptly and the blowoff valve can't flow enough) it can pile up and burp back out the compressor, causing it to stop spinning and being rather rough on the bearings. To combat this they drill the holes. When the turbo is near the surge region the pressures are such that the extra flow basically recirculates around the compressor wheel, from the volute to the intake and round and round. This lets the compressor keep spinning smoothly. When the engine sucks more air the ports suck air in.

I realize this is a forum link, but the guy copied and pasted an SAE article basically. Some good pictures there: http://www.turbobuick.com/forums/threads/turbo-compressor-maps-effect-of-ported-shrouds-and-the-tornado.381448/

Thanks for the article Flieger. Definitely some good information.

Anti-surge.

I have the antisurge option on the Garrett T04Z mated to my VR6 Turbo:

http://i458.photobucket.com/albums/q...a/IMGP2343.jpg

The GT series and others have cast slots instead of drilled holes to accomplish the same function.

"You put your weed in there"