One of the things that we feel is a common mistake that people do when they are building street cars running on pump gas is to go overboard on turbo selection. We would rather have a responsive 400whp or so with lots of low-end torque than a laggy and soggy 430 hp over a narrow powerband for driving around town. It’s more fun. We should know, we spent our youth driving cars on the street with big turbos with gas that was too poor in quality to use the boost they were capable of.
We happened to have a brand new HKS GTII Turbo laying around the shop for a few years that we sorta had forgotten about. The HKS GTII is a mild upgrade over the stock turbo that was designed to have faster response, less lag and more power than the stock unit. How does this turbo have all of these diametrically opposing qualities?
One of the cool features that the HKS GTII turbo has is a true dual ball bearing center section. The bearing cartridge floats in oil to damp out potentially damaging vibrations while the ball bearings give super low friction for much faster spool, about 10-20% faster all other things being equal. The ball bearings also handle thrust loads better.
The HKS GTII turbo also has a water-cooled center section like the OEM turbo to help prevent coking and after shutdown overheating, a large cause of turbo failure.
The compressor side of the HKS GTII turbo is moderately larger than stock. The compressor wheel is a 49 Trim with a 74 mm major diameter with a 52mm inducer. This is a decent step up from the stock 68mm diameter wheel with its 48.3mm inducer. The compressor wheel lives in a largish .82 A/R housing with a large diffuser.
On the exhaust side of things, the HKS GTII turbine wheel is an 81 Trim with a 60mm inducer and a 54mm exducer, in a .74 A/R twin scroll housing. This is more than a decent upgrade from the stock turbine’s 56mm inducer and 49mm exducer. By keeping the factory twin scroll turbine housing configuration, this should be a very nice moderate turbo with a zingy response.
Strangely by looking at HKS’ Japanese website, it seems as though they had stopped making parts for many popular cars like all EVO’s and most WRX’s! However many places still have this turbo in stock so it is easily available in both new and used configurations.