Agnostics are indecisive and atheists simply get it wrong. There is a God. If there were no God, we wouldn’t have the Garrett GTX-R series of turbos to answer our prayers. Okay, maybe that’s a little over the top for the intro. But in all seriousness, the Garrett GTX-R turbochargers are delivering impressive performance on a number of applications. As we may have already mentioned, we selected a Garrett GTX-R turbocharger for our KA versus SR challenge. Each engine will be set up with a GTX3076R as the reference benchmark turbocharger. Considering that you are going to be seeing a lot of this turbocharger in the future, we decided to kick off our “All in the Family 2012” turbocharger profile series to get an inside look at the GTX3076R.

THE NOMENCLATURE

The model number of Garrett turbochargers helps tell you a bit about the turbo itself. In the case of the GTX3076R, the “GT” simply stands for Garrett Turbocharger. The “X” denotes the new X-series of compressor wheel technology (more on this later), the “30” represents the turbine wheel family of the turbocharger. The larger this number, the larger the turbine wheel. The “76” specifies the major diameter (exducer) of the compressor wheel in millimeters. Finally, the “R” signifies that the turbocharger incorporates Garrett’s dual ballbearing center section with oil and water cooling. So just by the name, we now know a little more about the turbo itself. While the “30” and “76” give us some sizing information, it’s the “X” and “R” that alert us to the performance technologies on hand.

RATED R

A little more than 10 years ago, the buzz in the performance turbocharger community centered on ball-bearing technology for the center section of the turbo. Garrett was one of the pioneers and we first became acquainted with the technology in the HKS turbocharger lineup produced by Garrett. Soon after, Garrett took the initiative to build a network of distributors in the US to get this technology under the hoods of performance vehicles. The advantage of this technology is evident with better transient boost response thanks to reduced shaft friction. Service life can also be superior to a conventional sleeve (journal) bearing turbocharger too. The ball-bearing technology also reduces lubrication requirements (hence a restrictor is used in the oil line). However, since there is less oil running through the center section to carry away the heat, it’s imperative to supply the center section with coolant. Failure to do so can result in having to replace your turbocharger.

About five years ago, the talk of forged, billet and CNC compressor wheels became the buzz. The “X” designates that a CNC-machined forged compressor wheel is used in place of a cast wheel. The forged nature of the “X” compressor wheel produces a stronger part with more consistent strength across each finite element. The additional strength of the wheels produced with high-tolerance CNC-machining offers the advantage of compressor wheel designs that feature superior aerodynamics and flow capabilities. Comparing a standard cast compressor wheel to a Garrett forged CNC machined “X” series, it’s easy to see how there’s more effective inducer area for a given inducer size as the blades continue closer down the shaft hub.

A comparison of the GT3076R to the GTX3076R is an interesting one to explore. While not exactly “apples to apples” (the GTX3076R’s compressor wheel is 0.4mm larger in its exducer diameter and 1.0 mm larger in its inducer diameter), it is very close. All other factors being equal, we’d expect the 1.0mm larger inducer of the GTX3076R compressor wheel to deliver an additional 3.5 percent of flow due to the increased inducer area. In fact, the difference based on the compressor chart is just over 21-percent more flow. Factoring for the larger compressor wheel diameter in the GTX3076R and you still see an 17.8 percent increase in peak flow. In this case, Garrett’s claim of 10-percent flow advantage over a traditional compressor wheel would appear very conservative. However, higher peak flow is just one advantage of the “X” factor, as compressor efficiency is also increased.