Turbo Tech With Palm Beach Dyno – Decoding Turbo Model Numbers

When it comes to turbocharger model names and numbers, each manufacturer seems to have their own idea on what naming convention to use. How does a Garrett GT55 stack up to a Precision 6766? What do those numbers even mean? If you’re confused, don’t worry, you aren’t alone. To help clarify things, Ken Bjonnes of Palm Beach Dyno put together a video to help clarify things.

“I can’t explain why they have all chosen to express the sizes and features of their turbos differently, but I’m going to try and explain what the differences are,” Bjonnes says. “The first step is to know what it is we are measuring and comparing with the turbos.”

While there are probably a dozen or more key specs than can be measured and compared, Bjonnes seems to favor Precision Turbo’s naming convention for it’s straightforward and logical convention. “Starting with Precision Turbo, their models are named after the [compressor] inducer size and [turbine] exducer size,” explains Bjonnes.

“So a Precision ‘6466’ will have a 64mm compressor inducer diameter, and a 66mm turbine exducer diameter. Those happen to also be the dimensions that most sanctioning bodies will use when writing rules, and those are the numbers which I use the most to give me an Idea of what kind of power the turbo will make.”

When discussing turbo sizing, it’s really important to understand what is being measured. Note that on the turbine side, the inducer and exducer sizes are reversed from the compressor side. Some companies will use “outside diameter” instead of “exducer” (on the compressor side) or “inducer” (on the turbine side).

The next brand of turbocharger that Bjonnes discusses is BorgWarner. “BorgWarner uses a four digit number as well,” he says. In his example, he’s using a Borg Warner EFR 7670 turbocharger, which sounds like it would be significantly larger than a Precision 6466, but it isn’t.

“That ‘76’ number is their compressor wheel’s outside diameter, and ‘70’ is the outside diameter of the turbine wheel,” Bjonnes explains. “They are using the two larger measurements of the wheels, while Precision uses the two smaller ones.” If we were to convert that into apples-to-apples measurements to compare it to Precision’s turbochargers, the EFR 7670 turbo would be a “5761”, as the inducer and exducer sizes of the wheels are 57mm and 61mm, respectively.

Bjonnes then moves to the smaller company – Xona Rotor, who really starts to switch things up with their naming convention. “I’m running a ‘105-68’ and your first thought is, ‘Whoa, that sounds huge!’ when in reality, that’s just a new naming convention,” chuckles Bjonnes. “The ‘68’ is the same second measurement as Precision uses – the turbine exducer diameter. The first number, however, isn’t based on any physical dimension of the turbo, but its output rating in pounds of air per minute.” If we were to convert the Xona turbocharger to the Precision convention, it would come in as a “7268.”

Switching gears to one of the major brands when it comes to turbocharging, Garrett’s naming convention is different still. “Using the turbo that was on Jimmy Kakaletris’ car [a seven-sec Coyote], the part number is GTX3582R,” Bjonnnes relates. “The ‘GTX’ is obviously the line the turbocharger comes from. The ‘35’ is not any measurement on the turbocharger.”

“That number actually references the frame-size of the turbocharger [ed note: much like the old T2/T3/T4/T6 exhaust flange naming convention, and how the exhaust flange size became a general descriptor of the turbo’s overall size], while the ‘82’ is the exducer size of the compressor wheel.” Converting the GTX3582R into Precision nomenclature, would be a ‘6662.”

Most companies provide pretty in-depth turbocharger specs on the website, so that you can really dig in and compare apples to apples between not only models from the same company, but those across the industry.

Now, moving to a smaller turbo company, Comp Turbo, there is yet another naming convention. Bjonnes uses their CTR3793 as an example. “I have no idea what that ‘37’ means. The only thing I can think is that it’s trying to mimic the Garret frame sizing convention, and that’s a big part of what I’m trying to get across. I don’t know why companies all name their turbos so differently,” Bjonnes says.

“The ‘93’ in the Comp Turbo size is the exducer size of the compressor wheel.” If we convert the CTR3793 into Precision’s numbering system it would be a “6467,” which we actually found as a suffix to the model number in one spot on Comp Turbo’s website.

Bjonnes’ point is, that while the naming and numbering conventions may vary across the manufacturers, with a little digging, you can put them into a quick perspective with one another, but is quick to warn, “There is more than just the sizing of the turbo to consider. You really need to dig a little deeper than just part numbers and wheel sizes to understand what it is that you’re getting.” To that end, Bjonnes includes a bonus discussion on reading compressor maps at 13:47 in the video, if you’re so inclined.

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About the author

Greg Acosta

Greg has spent over a decade in automotive publishing as Senior Editor of Race Pages magazine. In his free time, he is a firearms instructor and volunteer in the police armory.
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