1997 Mazda MX-5 Miata: TiAL Sport Turbine Housing And Wastegate
April 22, 2013
If you've ever been around aftermarket turbos, you can probably already appreciate the TiAL Sport stainless v-band GT28 turbine housing, shown here on Project Miata's engine, sans Garrett GT2863R turbo. No bolted flanges! The v-band inlet and discharge are seriously convenient, and they eliminate the possibility of threaded fasteners relaxing, galling or seizing in the manifold.
What you can't see is that the housing is investment cast from Nitronic 50, a high-grade, heat-tolerant austenitic stainless steel. Its properties at elevated temperatures are superior to traditional turbine housing materials, so the geeks at TiAL Sport were able to reduce weight by roughly one-third without a loss in structural performance.
The TiAL Sport turbine housing is non-wastegated, making it compact and allowing the freedom to size and locate the external gate where it makes the most sense. In our case we're using the company's MV-S wastegate, the smallest one in their lineup. Since we're running a decently healthy 0.86 a/r housing and a decent chunk of boost, our wastegate flow requirements are reasonable. While it's really tiny, probably the smallest wastegate out there, the MV-S still manages to package a pretty substantial valve diameter inside.
Note the "divorced" wastegate dump tube arrangement. By reintroducing the wastegated flow far downstream of the turbine wheel, there's less backpressure (it acts like a larger exhaust), and there's no impingement on the flow exiting said wheel. This improves the turbine's performance.
What the what? Yes, the TiAL Sport MV-S has ports for water (coolant) cooling. The use of water cooling is optional, really only necessary if you've blanketed the wastegate in heat shielding and there's no airflow to the unit and you're running ungodly turbine inlet temperatures.
We won't need to run coolant to the gate (plugs are supplied), but it's pretty neat that all MV-S gates are thusly equipped if need be. Along those lines, the bolts supplied with all of TiAL Sport's v-band turbine housings are made from Inconel, a high-nickel superalloy.
The craftsmanship of TiAL Sport's stuff is amazing, too. It's almost like jewelry. Made in Michigan, too. Woot.
This boss was added to the bottom of the turbine housing by a local fabricator. It's where a mount will tie the housing to the block to reduce vibration of the whole manifold-turbo-downpipe system. Vibration is an issue on un-balance shafted four-cylinders in general, but for some reason Mazda's BP is particularly thrashy and has been known to wreak havoc on turbo manifolds, downpipes and other ancillary engine items.
Oh, and the TiAL Sport turbine housings are like Legos. Their GT28, GT30 or GT35 housings of every a/r size share the same inlet and outlet footprint, so you're not "locked into" just one housing. Going bigger (or smaller) is easy peasy.
By the way, the owner of the shop that made the manifold and downpipe unfortunately didn't want to be named here, onaccounta they're already swamped with work and don't want more. I'll respect his wishes. Anyway, the odd round plate you see above is where the original wastegate feed was located. It wasn't ideal so I had it capped and reworked to the location on the right side of the collector.
Elsewhere, this turbo system plays nicely with the power steering pump, air conditioning compressor and requires no modifications to the chassis to install. It's a pretty well made setup. The manifold is made from schedule 10 304 stainless steel elbows, with a proper collector and a relatively low internal volume so as not to damp out exhaust pulses before they can reach the turbine. Sixteen-gauge 304 stainless makes up the wastegate dump tube and full 3-inch downpipe, which both have flex sections to take up thermal expansion.
So, yeah, things are moving along in Project Miata-land.
Jason Kavanagh, Engineering Editor