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Turbo Help for the Unknowing

Old 01-01-2019, 09:43 AM
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Question Turbo Help for the Unknowing

Everyone likes a short to the point post and THAT is really difficult for me but that said, I'm trying!

FMII kit installed on a stock internal NB1, tuned at 260WHP/232WTQ and threw a rod on a cold day a year ago. No surprise really, it lasted awhile.

So I threw money to the wind and obtained an NB2 and sent it to an engine builder. It was Built/Bored/Balanced and has a VVT ( in hindsight that was probably not the best choice but after porting/polishing and custom length (ground tip) +1mm valves, shim under bucket lifters and Supermiata dual springs and retainers - I'm definitely invested in staying with it ). So now it "seems" like the Garrett 2560R is a bit small for the potential. Doing any track day activities at a road course would require me to really dial back the boost in order to keep the heat generated by the turbo under control. In short I have outgrown (or feel that way) the turbo.

Now the ????

I wanna pull this turbo, insert another one that is larger without changing the current FM log manifold and downpipe (haters I get there are better flowing options). I "assumed" (see the title again) something like a GTX2871R with the 5 bolt exhaust housing/internal wastegate would be one of the few "plug and play" choices available that would give a 300ishWHP consistently at a track event without cooking the car with air intake heat while still perhaps giving a few psi's of boost at 3000RPMs?

Chime in with corrections and thoughts as well as verbal abuse - Happy New Year !
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Old 01-01-2019, 11:38 AM
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What transmission and diff? You’re playing with fire on the track at 300hp with any of the standard Miata options.

What are you doing for cooling and intercooling? Again, you’ll probably need a good plan here with hardware and ducting.

Can’t offer any help on the turbo selection.
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Old 01-01-2019, 12:36 PM
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The gtx2781 is a solid upgrade, no personal experience, but it should spool pretty well and can dish out 325-350ish hp all out.

but any more power and your 5 speed will be toast real quick on the track.

I just nuked my 5 speed on my 2nd track day at your exact power level of around 260hp. Installing a 6 speed and 3.63 torsen now.
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Old 01-01-2019, 01:04 PM
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Trying to answer on my phone, heaven only knows what spelling or errors Im going to encounter.

99 5 speef, 3.9 Torsion type II

I do realize the trasmission will not last. 2nd gear in a 6 speed will not work well for autocrossing unless I go to a 3,63 rear.
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Old 01-01-2019, 03:06 PM
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So the 2560 is probably good for 280 rwhp with FM hardware (3" exhaust, high-flow cat, good intake manifold, etc). Try to turn the boost up from there and yes, the intake charge gets hot, but that's actually just a symptom of the fact that the compressor is maxed out on flow.

A GTX2871 is a big jump -- that's a 500 rwhp turbo, and it's going to suffer significantly in spool compared to the 2560. That's not a huge concern for the track (you're rarely below the boost threshold), but if you're autocrossing enough to care about 2nd gear on a 6-speed then it's going to suck there.

There are other turbos in between that should fit. GTX 2860, 2863, and 2867. I have the 2863 on mine (with the FM2R EWG hardware) and am pretty pleased with it. Has a power limit midway between the 2560 and 2871, and spools about midway between them too.

If you run the car at 300+ rwhp on the track you will eat the 5-speed very quickly (possibly not even last a single track day) and even 6-speeds will become consumables. 3.6:1 rear gears are not that expensive (will give you roughly the same 1-5 as a 5-speed plus 4.3), and 3.3s are now somewhat available as well if you want to get an even longer 2nd.

--Ian
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Old 01-01-2019, 04:09 PM
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6 speed is stronger than 5 speed and my 6 speed lasted one (1) track day at 300+whp. My gtx2867r starts making decent boost about 4200.
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Old 01-01-2019, 10:03 PM
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Originally Posted by sixshooter View Post
6 speed is stronger than 5 speed and my 6 speed lasted one (1) track day at 300+whp. My gtx2867r starts making decent boost about 4200.
It seems to vary a lot. My first (MSM) 6-speed did a dozen or so track days at 300+ rwhp before failing. Didn't fail in the usual way either, it appears to have killed the input shaft bearing, rather than shearing teeth.

My GTX2863 makes 200 kpa at about 3600.

--Ian
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Old 01-02-2019, 01:49 AM
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So you "threw money to the wind" to build a nice motor but you're going to hamstring it with a log manifold and a GTX28R? Makes no sense to me. An EFR6258 will make the power you want and respond better than the turbo you have now. You're putting bad money after good.
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Originally Posted by codrus View Post
Basically I've come over to the camp of "If something is a reliability problem on the track, just ask Andrew and do what he says".
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Old 01-02-2019, 07:02 AM
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He's right. If I hadn't got my turbo used at a bargain as a drop in to replace my China charger I would have gone efr.
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Old 01-02-2019, 09:45 AM
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Default Agreed, The Rabbit hole is deep

At this stage I understand the throwing bad money after good statement, I actually wish i had purchased a V8 miata that i was i interested in a couple years ago, it would have been easily as cost efficient for my wants and certainly more robust.
I am was considering going E85 and reducing boost and timing for track days, not a cheap changeover either but perhaps a cheaper alternative at this point.
The price combo of Upgraded turbo+6-speed+3.63+Stage 2 clutch is difficult to stomach at the moment.
Thanks to all that gave voice, I was not aware of the other turbo options.
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