Dear Doctor Turbo,
I bought a GT25 back in the day when there were only 3 or so GT series turbos in existence--before Garrett renamed everything with a ball bearing a GT turbo. It's a GT2876R (.64 A/R turbine housing) per the naming convention change. Why does the turbo by garrett site list it as "not recommended for general performance applications" on the info page? I will admit it's a little large for a streetable 1.8L, but it's been great for power at low boost and isn't a bad compromise in terms of spool. Here's my dyno graph at about 9.5 psi (the RED line). (the green line is a twin turbo 1.8L miata--2x GT1548) http://y8spec.com/dyno/twins_vs_2876.gif |
Originally Posted by pbmiata
(Post 360671)
Dr. Turbo! With a name like that you can expect to get a few tech questions! I'm really looking forward to you future posts.
Welcome! I wonder- has anyone with the Doctor's background ever evaluated one of those China chargers I keep hearing about? I mean, really took one part and evaluated the tollerances, metalurgy, design of the vanes etc. and compared it to the Garrett? It would be pretty neat to have a (turbocharger) engineer's perspective. Dr. Would you be willing? |
Originally Posted by m2cupcar
(Post 360509)
Yes, welcome. To validate your identity please answer the following.
Q: According to Garrett, under what circumstance should a restrictor be used with a journal bearing turbocharger? If I knew it, then WHO KNOWS what kind of riffraff DrTurbo could be, posing as a Garrett engineer! I demand more proof...something REALLY wonky and supersekrit that only a Garrett engineer would know...something NONE of us could possibly know and verify! :giggle: |
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Heheh, how about more complete turbine maps for the GT25, 28, 30, and 32 ...
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Originally Posted by patsmx5
(Post 360583)
Thanks for the explanation. As for oil restrictors... I'm running a .070" restrictor on my GT3271. I don't have a "real" oil pressure gauge, but I'd imagine it's around 60 or so at cruise and 90ish by redline. If these numbers were correct, would a restrictor be warranted? Or even better: Would a restritor hurt anything? I've seen a lot of people run a restrictor on journal bearing turbo that had premature oil seal problems in the past that they contributed it to not using a restrictor.
I see no reason to use a restrictor with a journal bearing turbo. Unless you are seeing oil leakage into the compressor or turbine, you don't have a problem. If you are leaking as evidenced by oil in the compressor or turbine, make sure you check all the other potential sources of CHRA seal leakage before resorting to a restrictor. There are many potential causes of leakage including oil backup due to a improperly designed oil drain. Here are links to a couple tips on this from Garrett: TurboByGarrett.com - FAQ's TurboByGarrett.com - Turbo System Optimization The last thing you want is to starve your turbo bearings of oil. Dan |
Originally Posted by pbmiata
(Post 360671)
Dr. Turbo! With a name like that you can expect to get a few tech questions! I'm really looking forward to you future posts.
Welcome! I wonder- has anyone with the Doctor's background ever evaluated one of those China chargers I keep hearing about? I mean, really took one part and evaluated the tollerances, metalurgy, design of the vanes etc. and compared it to the Garrett? It would be pretty neat to have a (turbocharger) engineer's perspective. Dr. Would you be willing? Dan |
I think markp was having decent luck with the chinachargers last I heard. Welcome Dr.
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Originally Posted by y8s
(Post 360676)
Dear Doctor Turbo,
I bought a GT25 back in the day when there were only 3 or so GT series turbos in existence--before Garrett renamed everything with a ball bearing a GT turbo. It's a GT2876R (.64 A/R turbine housing) per the naming convention change. Why does the turbo by garrett site list it as "not recommended for general performance applications" on the info page? I will admit it's a little large for a streetable 1.8L, but it's been great for power at low boost and isn't a bad compromise in terms of spool. Here's my dyno graph at about 9.5 psi (the RED line). (the green line is a twin turbo 1.8L miata--2x GT1548) Not sure why the Garrett site lists that. My best guess is that it is because the sizes of compressor and turbine are not well matched. (I won't get into the details of that here.) While your power and torque numbers look good, it looks like you are not on full boost until about 4000 rpm. For a low boost setup that is not targeting big power, there are other turbos that would provide the same performance at 9.5psi with better boost response. For street use, fast, linear boost response is usually what you want. The bottom line is that the compressor wheel on that turbo is just too big. Hope that helps. Dan |
Originally Posted by BenR
(Post 361215)
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Originally Posted by JasonC SBB
(Post 361458)
Heheh, how about more complete turbine maps for the GT25, 28, 30, and 32 ...
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Originally Posted by DrTurbo
(Post 362856)
y8s,
Not sure why the Garrett site lists that. My best guess is that it is because the sizes of compressor and turbine are not well matched. (I won't get into the details of that here.) While your power and torque numbers look good, it looks like you are not on full boost until about 4000 rpm. For a low boost setup that is not targeting big power, there are other turbos that would provide the same performance at 9.5psi with better boost response. For street use, fast, linear boost response is usually what you want. The bottom line is that the compressor wheel on that turbo is just too big. Hope that helps. Dan |
Such as a GT2860 LOL...
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y8s, the smaller bb turbos like yours have a backplate that is integral to the center housing. This means the counterbore for the comp wheel is specific to that wheel's OD.
So in order for you to swap out to a smaller comp wheel, you'd have to also swap out the center housing. You're better off just starting over with a different turbo in that case, unless you can somehow find a chra + comp housing (sans turbine housing, since you can re-use the one you have). Maybe call ATP and tell them your situation. |
ATP has my original .86 turbine housing. I traded them for the .64 I have now. :)
I think I'll just stick with this for a while. |
finally some pics
7 Attachment(s)
I have gotten some request to post pics of my Miata and from my turbo Rx-7 project. Funny thing is, I looked around and I don't seem to have an pics of my Miata worth posting. I guess I'll do that this weekend. Here are some pics of the 7 to tide you over.
Looks pretty stock from the outside than the CF hood. Attachment 208425 All the good stuff is under the hood. Pretty much everything is one-of-a-kind custom fabbed except the HKS exhaust manifold. Attachment 208426 I designed and built the 1-off turbo while I was still at Garrett. It's basically a GT3276 with a twin scroll turbine housing. Attachment 208427 Attachment 208428 The intercooler was also a custom job using a 12x18x3 Garrett bar plate core. I use a draw through fan to prevent heat soak at idle and low speeds. Attachment 208429 Finally, a custom parallel flow dual oil cooler setup (one on each side) with custom ducts to the front bumper inlets. Attachment 208430 Attachment 208431 Engine management is provided by an Electromotive TEC3. Now for the interesting stuff. This is the closest I've gotten so far to a turbo Miata setup. http://i68.photobucket.com/albums/i1...7/IMG_1713.jpg Yep, that's right - I am a member of JKav's Lemons team and had a hand in building that monstrosity. Part of what inspired me to turbo my own Miata. Now the real fun begins. |
that rx7 is awesome.
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are you the homeless person doing all the welding for that build?
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Originally Posted by gospeed81
(Post 364164)
are you the homeless person doing all the welding for that build?
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I showed your car's pics to a friend (he also owns an RX-7 like yours) who's rebuilding his engine and he wants to know at what RPMs do you see boost with that T3276.
FWIW, he drags his car regularly but also uses it as a dd. Thanks |
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