Homebrew WRX Turbo Setup
 

So I'm trying to make my MSM suck less.

The usual punchlist has been completed except for E85. (Intake, Catless DP, 2.5" exhaust, Haltech, big injectors)

I'm one of those nerds who likes to think that driving around cones in a parking lot is fun, so I value a low boost threshold and good transient response The car still needs a dyno tune to dial in the timing but it makes decent power at 12 psi. Regardless, I have reached the same conclusion that all of my forefathers have.. the factory turbo on the MSM is only slightly better than a pile of steaming garbage.

So, I am looking at swapping in a good turbo. The usual suspects look like a good starting point: GT2554R, 2560R, 6258... but the 2554R won't make much more power than I have now and even the 6258 seems to struggle to make good torque below 3000-3200 RPM.

I've seen a few other threads where people have used the older TD04-13 turbos from the older WRX and it seems that it is a decent fit for the 1.8. I have a buddy with a 2019 WRX and while riding in that car we noticed that it spools almost instantly anywhere above 2400 RPM; after some digging it would appear that the inlet/outlet configuration would work in a Miata, but I have not found anyone who has tried this particular combination yet.
The new FA20-DIT uses a twin-scroll Garrett turbo that looks like a similar frame size to the G25-550 (P/N 14411aa881). I called someone at Garrett to get compressor/turbine maps but they said that those were still proprietary info for Subaru, but they agreed that it looked like it could be a good fit for the application. Also, they're relatively cheap on ebay or nasioc. The hardest part would be making a twin-scroll manifold that will fit with PS and A/C, but it is at least possible.

Does anyone else think that this might be a neat idea?

Kraken was making a manifold for the TD04 turbo but not sure that he still makes them.

Mazda MX5 Turbo Parts Archives - BLACK CAT MOTORSPORT looks like a couple in stock still in teh UK and it appears G19 has a TD04 manifold as well.

There are also mitsubishi based options available to you as an MSM owner
https://bnrsupercars.wordpress.com/mazdaspeed-miata/

Solid OEM turbo, but it's not nearly special enough to build a setup around, and you would basically need to do exactly that.
The FA20 uses TS, and dual avcs to get the low end grunt, neither of which the BP is set up for easily.

I love my TD04-13.
Got a flange for it lasercut and welded the rest up.

Super quick spool but tops out at around 4500rev
At 14psi car is stupid fast and i cant change gears quick enough to keep up with the rpms.

Have PS/AC / 3inch DP all the way and welded into the side of stock muffler. Looks stock and sounds stock.

That was my hesitation. A compact twin scroll manifold would be neat but my fab skills are not quite up to that level yet.

Did you make a divorced downpipe or do a bellmouth elbow thingy?

How quickly does it build boost at 3000 rpm or so?

TD04 on Log Mani 3” exhaust

This ^^^ shows a pull starting at 2000 RPM as well as time to boost levels starting from 3k and 4K.

DNM

Did you make a divorced downpipe or do a bellmouth elbow thingy?
NVM. Found your build thread. That looks manageable

How quickly does it build boost at 3000 rpm or so?
Pretty quick.

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Hey, I actually make a kit that is designed to let you bolt on the wrx td04/ other subaru turbos. Check out my page, and there are some pictures of it, along with some of my other work. It's a manifold/ 3" dowpipe combo, all stainless steel. I also make intercooler pipes that go with the setup aswell. I also thought they would be a good responsive well sized turbo for our Miatas.
https://www.instagram.com/503fabrication/

The welds look decent on these but that seems like an objectively terrible way to handle wastegate flow. If I'm not mistaken stock WRX's struggle with boost creep partially due to the very obstructive downpipe flange from the factory. There has to be a reason that almost every aftermarket downpipe option for WRX's either has a "bellmouth" or is a fully divorced design.

https://cimg8.ibsrv.net/gimg/www.mia...b498880caa.png

how much power are u making from ur TD04?