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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 04-18-2008, 06:04 PM   #1
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Default T3 hell

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
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Old 04-20-2008, 01:08 PM   #2
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Default here's what I'm talking about

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

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Old 04-20-2008, 01:14 PM   #3
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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.
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Old 04-20-2008, 01:33 PM   #4
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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.
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Old 04-20-2008, 02:51 PM   #5
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call garrett... they are usually very polite about answering tech questions.
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Old 04-20-2008, 03:33 PM   #6
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Default gettin' better

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?

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Old 04-20-2008, 03:35 PM   #7
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jeez. probably a lot, lots of room for exhaust to pass through without attempting to spin the turbine.
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Old 04-20-2008, 03:40 PM   #8
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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.
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Old 04-20-2008, 03:42 PM   #9
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works for me....
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Old 04-20-2008, 04:02 PM   #10
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Quote:
Originally Posted by m2cupcar View Post
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.
sounds typical for the members around here. we've all done it (except for the check book racers)
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Old 04-20-2008, 04:34 PM   #11
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Probably cost a lot of spool time too!
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Old 04-20-2008, 04:41 PM   #12
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Quote:
Originally Posted by m2cupcar View Post
Apparently I've been running a stage 2 turbine wheel in a stage 3 turbine housing. My fault for assuming rather than measuring.

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

thx-rob
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
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Old 04-20-2008, 05:27 PM   #13
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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
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Old 04-20-2008, 05:27 PM   #14
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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.

Last edited by m2cupcar; 04-21-2008 at 09:57 AM.
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Old 04-21-2008, 05:26 AM   #15
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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?
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Old 04-21-2008, 09:56 AM   #16
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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.
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