Project Spec-V: Part 26: Installing the Bigger Turbo
10/29/2007
To meet our power goals we called upon Garrett Turbochargers for something bigger. The good folk at Garrett supplied us with a larger GT30R turbocharger. The GT30R is a mid frame size turbo with a low friction for less lag ball bearing center section. It is capable of producing power levels in the mid 400 range. The GT30R is blessed with super efficient compressor and turbine wheels that are a good match for our motor. We used a GT3017 Turbo which has a 56 trim 71 mm compressor wheel in a .50 a/r TO4S compressor housing mated to a 76 trim 60mm turbine with a .82 a/r turbine housing.
This turbo can produce considerably more power than the GT28RS Disco Potato that we were intending to run at this point. The GT30R will have about 1000 rpm more turbo lag which we think is a fair trade off, our long stroke QR25DE will have plenty of low end torque anyway.
For simplicity, we wanted to retain an internal wastegate, the trouble is until recently there were no mid frame internal wastegate exhaust housings on the market for the new GT series turbos. ATP came to our rescue with their new internal wastegate GT series exhaust housing. The ATP housing has a large flapper valve that can flow as well as some external gates. The housing has a built in diffuser which flairs to a full 3 for superior exhaust flow. The housing also divorces the wategate flow from the turbine discharge, another trick that helps boost turbine efficiency.
To help make our downpipe fabrication easier, ATP supplied the special divorced flange that mates to their turbine housing. This flange is grooved to accept a 3 turbine discharge and a 2 wastegate discharge tube.
Since the available space to fit the turbo was quite limited, we had to use some specialized bends from Burns Stainless and The Chassis shop to fabricate our downpipe which is a work of art 3 with a merged collector for a 2 wastegate discharge.
The compressor on our GT30R dwarfs the GT28RS.
The Turbine discharge is a lot larger for a lot more flow as well. Note the divorced flow path for the external wastegate.
Burns Stainless supplied us with thin wall 90 degree and straight 321 stainless tubing. With a 3 radius the burns 90 is extremely tight. With exotic 321s superior properties, you can get away with real thin tubing for less weight. 321 is expensive, more difficult to fabricate and harder to weld but it is a superior material. 
We also used these stainless steel doughnuts from The Chassis Shop. Doughnuts are made by welding two stampings together to create a tighter longer radius bend that can be made than a mandrel bend. These things can help you package many sorts of things in tight places.
Mike Smith, Jim Wolf Technologies master fabricator starts by test fitting our new turbo to our old manifold.
Once he has an idea of where the new turbo can fit, he gets a rough idea of where the larger T3 size flange has to fit.
Mike saws off our old T25 flange in a bandsaw.
He then surface grinds the flange area flat.
Mike welds the new flange to our manifold using a TIG welder. Tig stands for Tungsten Inert Gas. The welders electrode is made of tungsten a super hard metal and the welders torch has a nozzle that dispenses inert argon gas to shield the weld area from air, prevent the molten metal from absorbing oxygen with weakens the weld.
After a quick fit check, the flange is ported to the manifolds runners for better flow.
Now its time to make the downpipe. Considering how tight it is around the turbo, this is a very difficult task. We used a section of 3 doughnut to make the first part of the downpipe.
Mike welds the flange to the doughnut.
321 Stainless tubing is hard to cut as its is a very tough metal.
The tubes are test fitted. Since we used a very thin 321 tube, the mitering must be very precise and the fits exact as we have to use a very fine electrode and filler rod.
The surface grinder is used to help fit the tubes exactly.
A very tight fit
When fitting a part it is first tack welded to temporarily hold the parts together while the fit is being checked.
The small tack welds can easily be broken and rewelded if the fit is off.
Once the fit is perfect, Mike welded the parts together. With thinwall stainless it is important to backpurge the part when seam welding. Backpurging is filing the tube up with argon gas to prevent oxygen from getting to the back side of the weld. This can make the weld up to 30% stronger. Here you can see the argon hose taped to one of our tubes during welding.
Mike seam welds our part
The completed weld.
Mike then marks where the hole in the downpipe for the wastegate discharge must go with a sharpie marker. Up to 40% of the engines entire flow can pass though the wastegate so a nice merged union is best for flow.
The wastegate discharge pipe, downpipe and flange before welding. Stainless is very hard to miter because its tough and gummy. Mike spent several hours mitering the wastegate tube as it is a very complex 5 axis fit.
A very nice fit before welding!
First the hole for the wastegate tube must be made in the downpipe. A drill is used for the corners.
Then a cut off wheel to cut between the corners
The rough cut hole, now we are ready to weld.
The parts are welded together
Our welded downpipe!
The hole in the downpipe is ported smooth to the final shape.
The turbine flange is surface ground to remove any warping that may have occurred during welding.
Next the locations for our O2 sensor and wideband a/f meter sensor will be installed are marked
The holes are made with a step drill
Then the flanges are welded on
After welding the threads are cleaned up with a tap just in case of warpage
Our downpipe is bead blasted to give it an even look
Our super sano finished downpipe
Installed in the car it allows a full unhindered 3 path for exhaust to flow
Now our GT30R is read to have the rest of the pipework installedNext we will reassemble our cars intake system and Clark Steppler from JWT will work on retuning our ECU.