I just received my new stock S5 modified turbo and the first thing I noticed visually is the turbine wheel gap between the housing and wheel (HOT SIDE) My first thought that this was wrong. Pulled my spare stock S5 turbo and S4 and my BIG Turbonetics TO4B turbo and noticed that there is barely a gap between the turbine wheel and hot side manifold.

My concern is that this gap will cause a turbine tip leakage of exhaust gases and make this turbo not efficient. This S5 turbo has a full new CHRA with new bigger cold and hot wheel and the hot side may have been modified to fit this CHRA.

Any thoughts.

At first I thought a picture would be good but then you would be staring at a turbo. They all look the same to me. The gap is approx .610mm if not more. Visually I thought it was 1mm.

I hope its ok cause I have over $1200 in this thing.

Ian

 

I have to say based on my extensive experiences with permutations of stock hybrid turbos on my TII since 2001-

Try the turbo and see how it performs.

Turbo rotaries seem very indifferent to exhaust side inefficiencies. Also, the less efficient the exhaust side (idea of clipping for instance) the less chance of boost creep as the wastegate won't have to flow as much.

True story-

One time when I sent my BNR Stage 4 center section in for a rebuild I ran my stock Hitachi turbo CHRA in the BNR Stage 4 exhaust housing.

Stock exhaust wheel is 2.51" major diameter, 2.15" minor hanging out in the roomy exhaust housing bored out for the P trims 2.91" major/ 2.54" minor diameter.

Like 1/4" gap all around.

It spooled fine to my amazement. You can probably still find the post here on the forum.

Is the extra clearance you are worried about at the major diameter of the turbine wheel or the minor diameter? It will make even less difference if its at the major diameter from my experience. I played around with opening up the turbine housing scroll slots and again, barely any difference in spool.

What I did that did finally impact spool (low rpm, peak boost rpm was the same) in a bad way (but solved my boost creep problem) was to port the stock manifold to less of a velocity stack and port the turbo exhaust housing runners big up to the wastegate runners.

Don't do that unless you have to.

 

Thanks BlueTII. I gather its not a big deal then. Will see when I install it. I am expecting it to be alot better in boost response then my Turbonetics 60-1 turbo.

 

I found out that porting the turbine housing to direct more flow into the WG opening reduces spool, no so much boost threshold but more like the instant boost response on tip-in