Who should buy the 1.21 A/R G30 Turbine Housing Kit?

Owners of larger or high-revving engines pushing a G30-825 or G30-900 toward the top of its rating, where peak flow matters more than spool. The 1.21 A/R G30 Turbine Housing Kit is the least restrictive G30 housing. For a street-focused 2.0L or a G30-660, it is the wrong size.

How much later will boost come in than with a 1.01 A/R?

Garrett does not publish a spool figure for one A/R against another, and the answer depends on displacement, cam timing and the manifold. The direction is predictable, though: a larger A/R moves boost onset higher in the rev range, so expect a 1.21 to build boost later than a 1.01 on the same engine.

Is a bigger A/R always more power?

No. A larger A/R lowers back pressure at high flow, which helps an engine already near the limit of the compressor, but if the engine cannot spool the turbine the power never arrives. Peak output is set mainly by the compressor, which Garrett rates from 350 to 900 horsepower across the G30 cores.

What V-band size does the downpipe need?

Garrett gives the G30 V-band outlet as 3.5 inch, or 90.16mm, with a 3 inch, or 76.2mm, V-band inlet. Both match the sizes Garrett uses on GTX turbochargers. Use the Garrett flange diagram to confirm the manifold and downpipe flanges before fitting.

Can it be used on a reverse rotation G30?

No. Garrett lists this part for standard-rotation G30 cores only. The reverse-rotation version with the same 1.21 A/R and V-band layout is part 740902-0099, which is the housing to pair with this one on the opposite bank of a mirrored twin-turbo engine.

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Description

Garrett G30 Turbine Housing Kit, 1.21 A/R V-Band Free Float

Garrett’s G30 Turbine Housing Kit in 1.21 A/R is the largest housing Garrett offers for the G30 frame, a free-float stainless casting with a 3 inch V-band inlet and 3.5 inch V-band outlet for standard-rotation cores. Garrett lists part 740902-0089 for the G30-660, G30-770, G30-900 and the G-Series II G30-725 and G30-825. It is a specialist part for a 3.5L engine, or a high-revving build, pushing a G30-900 or G30-825 to the top of its rating, where every bit of turbine flow counts. On a 2.0L street car or a G30-660 it is simply too big, and boost will arrive late.

Maximum Turbine Flow

At 1.21 A/R the volute imposes the least restriction of any G30 housing, so the 60mm turbine wheel can pass the most exhaust before back pressure builds. That suits engines that spend their time at high load and rpm and can tolerate later spool. Boost is held by an external wastegate, since the housing has no port of its own.

Features

1.21 A/R, the largest G30 housing size
3 in V-band inlet and 3.5 in V-band outlet
Free float, rotatable through 360 degrees on the center housing joint

Specifications

Garrett part number: 740902-0089
A/R: 1.21
Turbine inlet and outlet: 3 in (76.2mm) V-band and 3.5 in (90.16mm) V-band
Wastegate: External (free float)
Rotation: Standard
Material: Stainless steel, rated to 1050C (1922F)

Applications

Garrett lists this G30 Turbine Housing Kit for these standard-rotation super cores, rated from 350 to 900 horsepower on 2.0L to 3.5L engines:

Garrett G30-660: 880693-5001S
Garrett G30-725 G-Series II: 934117-5001S
Garrett G30-770: 880693-5002S
Garrett G30-825 G-Series II: 934117-5002S
Garrett G30-900: 880693-5003S

Notes

An external wastegate is required, because this free-float housing has no wastegate port
The G30 super core is sold separately
Standard rotation; the reverse-rotation 1.21 A/R V-band housing is part 740902-0099
For earlier boost, Garrett lists V-band G30 housings down to 0.61 A/R, part 740902-0086

Frequently Asked Questions

Who should buy the 1.21 A/R G30 Turbine Housing Kit? Owners of larger or high-revving engines pushing a G30-825 or G30-900 toward the top of its rating, where peak flow matters more than spool. The 1.21 A/R G30 Turbine Housing Kit is the least restrictive G30 housing. For a street-focused 2.0L or a G30-660, it is the wrong size.
How much later will boost come in than with a 1.01 A/R? Garrett does not publish a spool figure for one A/R against another, and the answer depends on displacement, cam timing and the manifold. The direction is predictable, though: a larger A/R moves boost onset higher in the rev range, so expect a 1.21 to build boost later than a 1.01 on the same engine.
Is a bigger A/R always more power? No. A larger A/R lowers back pressure at high flow, which helps an engine already near the limit of the compressor, but if the engine cannot spool the turbine the power never arrives. Peak output is set mainly by the compressor, which Garrett rates from 350 to 900 horsepower across the G30 cores.
What V-band size does the downpipe need? Garrett gives the G30 V-band outlet as 3.5 inch, or 90.16mm, with a 3 inch, or 76.2mm, V-band inlet. Both match the sizes Garrett uses on GTX turbochargers. Use the Garrett flange diagram to confirm the manifold and downpipe flanges before fitting.
Can it be used on a reverse rotation G30? No. Garrett lists this part for standard-rotation G30 cores only. The reverse-rotation version with the same 1.21 A/R and V-band layout is part 740902-0099, which is the housing to pair with this one on the opposite bank of a mirrored twin-turbo engine.

About Garrett

Garrett Motion has turbocharged engines since 1955, when its T15 was matched to the Caterpillar D9 crawler, and in 1962 a Garrett turbocharger went into the Oldsmobile Jetfire Turbo Rocket, the first turbocharged production car. Garrett has supplied turbocharging in Formula 1 with Scuderia Ferrari, the FIA World Rally Championship and the 24 Hours of Le Mans. It has operated as a stand-alone company since 2018, and its technology is fitted to around 150 million vehicles worldwide.

Additional Information

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BP Pricing Difference

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Garrett G30 Turbine Housing Kit, 1.21 A/R V-Band Free Float [740902-0089]

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Garrett G30 Turbine Housing Kit, 1.21 A/R V-Band Free Float

Maximum Turbine Flow

Features

Specifications

Applications

Notes

Frequently Asked Questions

About Garrett

Reviews