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)

 

+1. Great question!

 

LOL, funny trick question! However, you shoulda picked a harder one. Even a turboknewb dumbass like me knew how to answer that question.

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!

 

What is your favorite color!

 

Heheh, how about more complete turbine maps for the GT25, 28, 30, and 32 ...

 

Pat,

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

 

That type of competitor benchmarking is routinely performed by companies like Garrett although probably not for smaller companies turbos. Now days, a lot of these small companies are buying Garrett/Mitsu/IHI/etc turbos, disassembling them, and reverse engineering to steal their aero designs. Then, performance just comes down to how well they can measure and reproduce the originals. This usually doesn't turn out well. If they are doing their own aero designs, they surely don't have the design and testing resources to compete with the Garrett designs. Then there is the question of reliability. The materials and manufacturing processes are likely not as well controlled as for an OE type manufacturer. The ultimate test is performance and reliability in the field. If you are considering going with an off-brand turbo, I would definitely recommend doing some research first. As far as me doing any benchmarking - I must decline. While it would be interesting, it would take an enormous time commitment not to mention the money to buy the candidate turbo. I already have a day job and don't have any spare cash. Keep the questions coming though and I will answer what I can.

Dan

 

I think markp was having decent luck with the chinachargers last I heard. Welcome Dr.

 

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

 

Blue, no yellow. Ahhhhhhhhh!

 

I said FORMER Garrett turbo engineer. Sorry, I don't have access to that stuff anymore. I'll pass along your request to my friends at Garrett though.

 

darn. either I run more boost or find a smaller wheel. is there such a thing as a bolt-on wheel and housing for that turbo?

 

Such as a GT2860 LOL...

 

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.

 

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.



All the good stuff is under the hood. Pretty much everything is one-of-a-kind custom fabbed except the HKS exhaust manifold.



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.




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.



Finally, a custom parallel flow dual oil cooler setup (one on each side) with custom ducts to the front bumper inlets.




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.



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.

 

are you the homeless person doing all the welding for that build?

 

I wish. No welding skills yet. We have another guy on the team with those. I do have access to the welder though and have been thinking about taking a class.

 

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