Paxton’s New NOVI-2500 Supercharger and Carburetor PowerHat Review

Evolution – it’s the way of the world; constantly refining, rebuilding, and inventing. Without evolution, where would we be? I know I wouldn’t be able to type this article on my first computer, a Apple II E, and I would still have to load my single-color video games through the floppy drive. Even a company that has produced a proven product can make it better with technology, and that is exactly what Paxton did with the introduction of the new NOVI-2500 supercharger. But even to push the envelope a bit further, they have developed an all-new carburetor bonnet called the PowerHat.

Blow thru carburetors have only recently become popular within the last six to seven years. Enthusiasts were scared to try blowing boost through a carburetor due to the unexplored tuning perspective, though it didn’t take long for popular carburetor tuners to figure out how to make it work. In the end, a properly built blow thru carburetor can be damn close to its EFI companion in terms of consistency and reliability.

Evolving the NOVI-2000 – Paxton’s NOVI-2500

The differences in the 2500 vs the 2000 is the redesigned and larger compressor wheel

The Paxton NOVI-2000 and the Vortech YSI have a lot of history in high performance street cars and racing applications. The YSI is commonly referred to the “Renegade blower” as it has been the popular supercharger of choice in the NMRA EFI Renegade class. Corvette, Viper, and other high horsepower street applications use the NOVI-2000 when trying to make 1000 crank horsepower through a serpentine belt-driven blower. Also the YSI is extremely efficient, presenting a 78-percent peak efficiency in a decently sized island, while the NOVI-2000 came in at 71-percent. Where the NOVI-2000 fell short is that they are only good to about 1000 horsepower to the crank, or around 850 to the rear wheels.

Even when comparing the NOVI-2500 (black) to the YSI (red), you can see the YSI does have a slightly better peak efficiency, but the 2500 has a much broader compressor map and is more efficient in larger areas. Click the image above for a larger version.

The hindering portion of these superchargers isn’t the design of the compressor housing or gear case, but rather the compressor wheel design. A lot has been discovered, in terms of airflow technology, when it comes to designing a more efficient compressor wheel, and that is exactly what Paxton did to push the performance envelope and introduce the new Paxton NOVI-2500.

As we said before, the NOVI-2500 uses the same basic supercharger package, though with a redesigned and larger compressor wheel configuration. “The NOVI-2000 has been a highly successful piece over the years and we knew that by using our current suite of tool and technology, we could improve on its performance, “ said Engineering Manager Mike Reagan. “The impeller wheel and shroud contour was created using CAD and specialized compressor design software. From there we tested and tweaked the NOVI-2500. The NOVI-2000 did not originally have access to these modern compressor design and testing tools.”

Not only does the 2500 support about 300 horsepower more than the 2000, it also has a much broader compressor map. This means that not only will it be capable of running more boost (30 PSI) it will work better on a wide variety of engine applications. “We spent about six months developing the new compressor stage,” continued Reagan. “The impeller is a bit taller and the inducer is incrementally larger as well (3.534 on the NOVI-2000 and 3.75 on the 2500).” The best part about the NOVI-2500 is that if you are looking to upgrade your 2000, it is a direct upgrade without further bracket modifications.

Compressor mapping is based off a wide variety of calculations, including gas type, cylinder head efficiency, cubic inches, projected air intake temperatures, and RPM. The easier-to-figure-out calculation is the pressure ratio, which is typically the amount of boost you want to run, plus 14.7 (atmospheric) divided by 14.7 (again, atmospheric). Though it doesn’t take a mathematician to look at the graph above and see that the 2500 will support more airflow at higher boost levels, while being more efficient.

NOVI-2500 Specifications:

• Internal gear step-up ratio: 3.50:1
• Inlet hose diameter: 4.00”
• Outlet hose diameter: 3.00”
• Impeller inducer dia: 3.75”
• Efficiency peak: 76%
• Impeller speed max: 60,000 RPM
• Max. pressure: 30 PSIG
• Max. flow: 2000 CFM
• Max. horsepower: 1300

The magic comes from the redesigned NOVI-2500 compressor wheel. The impeller wheel and shroud contour was created using CAD and specialized compressor design software. The impeller wheel is 3.534-inches on the NOVI-2000 and 3.75-inches on the 2500

Carburetor enclosures, bonnets, and now the PowerHat

While many blow thru carburetors use very similar technology, the way to properly introduce that boost into the carburetor has been a long argued topic. Vortech originally designed (and still offers) a case that completely encloses the carburetor, pressurizing everything evenly. Some said that the design was complicated and only a simple bonnet is needed.

Depending on who you talk to, the simple bonnet design can be a less-than-desired design. Sure, it does the job on forcing the air under full boost situations through the carburetor, but is the distribution across the primaries and secondaries equal under low boost, or road driving conditions? “We have seen that moving the position of the bonnet within five degrees on any given direction can vary 15-20 horsepower and half the motor running lean with half the motor running rich,” said Bob Endress of Vortech/Paxton.

The PowerHat is a new carburetor hat design that helps feed air from all directions across the top of the carburetor

The evolution of the basic bonnet sprouted an air diverter; designed specifically to do that – feed air more evenly over the primaries and secondaries. The design flaw to the diverter bonnet is that the diverter itself is fixed inside the bonnet, and unless that diverter is aligned dead-nuts straight over the primaries and secondaries, you might as well kiss that air distribution feature goodbye.

Vortech/Paxton set out to create a new carburetor hat that would provide even pressure across the carburetor and when clocked in any direction, yield the same results. They have the expensive tools and simulators that allows them to construct a hat that will perform precisely in any application.

The Technology Behind the PowerHat

At first sight the PowerHat looks like a giant, polished air cleaner that is sealed off, minus a single three-inch inlet (though they also have dual inlets available). Flip the PowerHat on its belly and now it looks like a giant compressor housing. Remove the two pieces of cast aluminum from each other and inside is an air diverter that resembles an air filter, just without the cotton. It resembles that for good reason; because that’s basically what it is. To properly encompass the carburetor with even airflow, a bit of restriction is needed to fill the hat completely. Without that restriction, the air would rush over the carburetor at whatever direction the hat was pointing, some being sucked in and some just bouncing around aimlessly inside the hat.

The PowerHat comes with features designed to bring the boosted air around the carburetor for proper distribution

But now with the air swirling around the hat like a washing machining on a spin cycle, how do you get the air flowing inward to the carburetor? That is exactly what that little fin on the back of the bonnet does. “Even playing with the distance that divider sat from the diverter played a big roll in the air distribution,” Endress explained.

Vortech/Paxton says that in addition to providing better drive-ability and more horsepower, it is done with less jetting in the carburetor. “We were up about 60 horsepower and down about 10 jet numbers when testing against a conventional 90-degree bonnet,” said Endress.

Jan Moeller Upgrades from the NOVI-2000 to NOVI-2500

660 horsepower and 588 lb/ft before and 766 horsepower and 631 lb/ft after - a gain of 103 horsepower and 43 lb/ft. Click the image for a larger version of the dyno graph.

Jan Moeller of Xtreme Motorsports in Arizona has a unique first generation Ford Lightning truck. It features a 410ci Windsor with AFR 205 heads, TFS-R intake, and a FAST XFI. The best ET they had ran to date with their Lightning was a respectable 8.83 @ 135 mph. The problem they started running into on the NOVI-2000 is that it was starting to fall off on the top end while they were trying to run 22-23 psi of boost. To help combat that problem, the Xtreme Motorsports team sprayed a 100 shot of nitrous. However, they were able to get their hands on a new NOVI-2500 for an upgrade.

The power increases are stellar to say the least “We simply strapped the NOVI-2500 on in place of the 2000 with the same pulley combination, running the same race gas,” Moeller said. “We were surprised how much power it picked up and how much more stable it was at higher RPM.” You are reading the above dyno graph correctly – 106 horsepower and 43 lb/ft of torque to the rear wheels from this direct bolt-on upgrade. While the power delivery looks identical between both superchargers, it is obvious on the top end that the 2500 doesn’t taper off and holds strong.

Testing? Of Course We Are Testing!

The powerplant we are putting in our ’65 Mustang “Biting the Bullitt” will feature both the new PowerHat and NOVI-2500 supercharger. The engine is a Dart block and CNC headed 427 cubic inch small block Ford. It features Ross 9:1 forged pistons, and Eagle’s crank and rods. It will be driven on 91 octane pump gas with the additional octane being fed from a Snow Performance water/methanol kit to a AED blow through carburetor. The Crower hydraulic roller valvetrain caps off the street aspect of the motor as we won’t need to be pulling the valve covers off constantly to adjust our last.

While we won’t pushing the upper limits of the supercharger in testing, we will see how little boost we need to produce to crack our 1000 horsepower goal. Additionally, the Mustang will see a heavy amount of street driving and we will keep you up to date on how it performs on the street as well as the track. Will we pick up more power while being more stable on our air fuel ratios? Will the NOVI-2500 deliver all the power we need? Stay tuned as we get our 427ci monster on the dyno at QMP Racing coming up very soon!

Our carbureted blow-thru 427ci small block Ford will be testing both the NOVI-2500 supercharger and PowerHat with goals of 1000 HP on moderate boost

Article Sources

About the author

Mark Gearhart

In 1995 Mark started photographing drag races at his once local track, Bradenton Motorsports Park. He became hooked and shot virtually every series at the track until 2007 until he moved to California and began working as a writer for Power Automedia. He was the founding editor for its first online magazines, and transitioned into the role of editorial director role in 2014. Retiring from the company in 2016, Mark continues to expand his career as a car builder, automotive enthusiast, and freelance journalist to provide featured content and technical expertise.
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