Apparently I've been running a stage 2 turbine wheel in a stage 3 turbine housing. My fault for assuming rather than measuring.

I've had my new t3/t4 assembly sans turbine housing sitting on my desk, brand spanking new for over a week and finally got around to installing it in my turbine housing (still on the manifold in the car). About 1/32" from fully seating the turbine blades touch the housing. I suspect this housing was an OE mercedes housing that was originally over bored to fit a stage 3 wheel. It was originally part of an eBay rebuild - so there's no telling how bastardized it is.

My point: I want to make sure I'm correct in assuming that any standard stage 3 T3 turbine wheel should fit any stage 3 turbine housing - correct?

And: Can any machine shop overbore a turbine housing? or do I need to go to a turbo shop?

thx-rob

 

Answered my own question by removing the turbine housing and inserting the new assembly. It's SOOO close. My guess is the housing was overbored to fit the turbine wheel used in the rebuild since it's so close. Anybody know the spec for blade to housing tolerance? I'm guessing any machine shop can open this up for them if I provide both pieces. - rob

 

I do not know the actual spec, but I know that its supposed to be close, very close. Close enough that I have had to look very closely because it seemed like the wheel was touching the housing, but there was just the smallest bit of room before it hit. You probably want it as close as possible without having the wheel hit the housing.

Edit: Looks like the hole in the housing for the wheel is not even around the entire thing. Seems like there is a lip on the right side in the picture but none on the left side? That's kind of weird, is the hole perfectly round? Maybe get some calipers and check the diameter in like 6 spots and make sure it is all even.

 

There is a small gap at the leading edge of the blades. The contact doesn't happen until further in. The bore itself is evenly round- most of what you're seeing is a bias on the insertion from one side to the other. The side with the flange makes it lean.

Anybody care to use a feeler gauge on a good (preferably new) turbine and give me a number? Meanwhile I'll see what I can find on google and garrett's site.

 

call garrett... they are usually very polite about answering tech questions.

 

I took a wire wheel on the drill press to the bore and removed a lot of rusty crud. Now the turbine will spin freely if it's centered on the bearing. If I move the shaft so it rest on the bearing the blades will then touch. Photo below shows where the blades are hitting. And that just happens to be the point at which the overbore makes the transition to the original turbine housing contour. Pic below that shows what a stage 2 turbine wheel looks like in a stage 3 turbine housing bore. I wonder how much power that was costing me?

 

jeez. probably a lot, lots of room for exhaust to pass through without attempting to spin the turbine.

 

yep - was just too damn lazy to disassemble and measure things. Stuck it in, didn't rub, so I torqued it down and ran it like that.

 

works for me....

 

sounds typical for the members around here. we've all done it (except for the check book racers)

 

Probably cost a lot of spool time too!

 

Any machine shop should be able to bore it to the tolerance you want. So take it down and have a shop bore out, should be really inexpensive to do. LOL, this wouldn't have happened with a Chinese turbo. (Just Kidding!)

Mark

 

Rob, here's turbine blade clearance on a brand new GT25 hotside. I can't tell you measurements because that was a long time ago. I'd guess 30 thou from blade to housing nominal?



super big:
http://gallery.y8s.com/miata/turbo/g...geViewsIndex=1

 

the funny thing is- the turbine housing is the only part that wasn't chinese. This was the last of the eBay "down2turbo" turbos. Fortunately there's a local machine shop down the street from that does quick turn work.

that is large- I bet that's a journal bearing. I'm gonna assume that the journal bearings have a larger tolerance than bb. Also noticed that the t25 housing has a ridge/lip prior to the wheel whereas the t3 rolls right into the blade.

 

Just a question for you, if it is a stage 3 housing with a stage 2 wheel, shouldn't the housing be too big instead of too small?? I assume stage 1, 2, 3 gets bigger with each stage?

 

You're correct.

The very first photo is the stage3 wheel in the stage3 housing. That housing is a mercedes OE turbine housing- which was a stage 1-1/2 as new on a mercedes. It was then overbored to a stage3 - but apparently overbored until it fit the turbine wheel, not to a stage3 bore spec. Which is understandable if you were using a turbine wheel that had blade wear... I suppose. So now I've got a brand spanking new turbine wheel that's just a wee bit too big for a slightly undersized stage3 housing.

What you see in the bottom pic is what I was running before the turbine wheel grenaded. The blade tips (exducer) in the photo are untouched, but something tore them up at the inducer inside the trubine housing (not visible in the photo). The intent was to show what I've been running on the car forever and demonstrate the difference in size between the two.