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FR-S/BRZ Forced Induction Comparison - 86 Showdown

Turbo vs. Rotrex vs. Roots. Which forced induction rules the FR-S/BRZ community?

Aaron Bonk
Apr 12, 2017
Photographer: Luke Munnell

Our inaugural 86 Showdown presented by Continental Tire wasn't just about which Scion FR-S or Subaru BRZ was the fastest around Southern California's Streets of Willow road course. It was a real-world comparison test between just about every method of forced induction available for the chassis (and one lone naturally aspirated soul). And the story is a familiar one: We reached out to drivers willing to punish their street cars on the track and then met up with them at our stomping grounds of choice in Rosamond, California, this time equipping all nine drivers with Continental's newest rubber and successor to its ExtremeContact DW —the ExtremeContact Sport,

86 showdown meng tea frs Photo 2/13   |   Meng Tea's Jackson Racing-supercharged FR-S with TRD/Victory Function - one of eight boosted cars at our 86 Showdown!

Everything from naturally aspirated to forced-fed cars were allowed, but Robert Stangarone driving the RS-R-liveried FR-S was the only one to bring out something without boost, and also with an automatic gearbox. Focusing on hardcore suspension upgrades and essential aero improvements, Stangarone was able to muster a 1:28.779, good for fourth place. The rest of the gang came bearing some sort of forced induction to power their way through the 14-turn road course.

86 showdown robert stangarone frs Photo 3/13   |   86 Showdown Robert Stangarone Frs

You've understood that the Subaru-built FA20 engine needed help ever since the first time your Toyobaru lost to an engine-swapped '80s Civic. You also knew that boost was the answer; you just weren't sure which way of going about generating all of that positive pressure was best. Have a look at who secured the event's top spots, though, and the sort of forced induction you ought to go with might've gotten just a little bit clearer.

THE TURBO

Think small-engine forced induction and the turbo is the most obvious choice. Here, there are no belts or pulleys robbing that 2.0L engine of the little power that it's already got. It's the first form of forced induction you're likely to consider and, for smaller-track road racing, it might not always be the best.

How it works: Turbocharging starts with a specialized exhaust manifold that feeds used-up exhaust gases from your engine into the turbo's turbine housing. Next, that housing's turbine wheel starts spinning and, because they're connected by a common shaft, the compressor wheel on the other end starts doing the same thing. Spin fast enough and positive pressure starts building up within that compressor housing, which'll ultimately make its way toward your engine again.

86 showdown turbo turbine and compressor wheels Photo 4/13   |   Every turbo is made up of turbine and compressor wheels joined by a common shaft. Used-up exhaust gases enter its turbine side and spin the assembly while the compressor side packs all of that incoming air together and sends it into the engine's intake stream.

Why you like it: Nothing can match the power potential and versatility of a proper turbo system, and Brett Humanic, who landed the number-six spot with his Modern Automotive Performance-turbocharged FR-S knows this. Unlike superchargers, which are driven off of the engine's crank pulley at a fixed ratio, turbo boost can be manipulated with the push of a button. "What attracted me to a turbo system as opposed to a supercharger was the upgradability and performance numbers by price," Humanic says. "I paid $26 per whp as opposed to most supercharger systems that near $75 per whp—and even then, it's a much smaller gain."

86 showdown brett humanic frs Photo 5/13   |   Brett Humanic's Rocket Bunny FR-S leading the group of turbocharged cars.

Arturo Rodriguez—who landed ninth place due to engine gremlins—doesn't disagree, but warns of the sort of turbo troubles he'd experienced. "We overlooked some critical vacuum routing, [which] caused the car to think that it was hitting peak boost [when it wasn't]," he says. "It also affected top speed given that my blow-off valve was just letting go of all of the air." And yet he wouldn't change a thing (other than that vacuum hose). "You just cannot beat the shove that turbos give you when you exit that corner," he says.

Why you don't: It takes a big set of wheels to make big power. The trouble with turbocharging, though, is that it takes a whole lot longer for those big wheels to start spinning fast enough to do what you'd like them to do. Go drag racing or even road racing on a track with long enough straights and, all of a sudden, this becomes a whole lot less important, though.

"People tend to think all turbo kits are going to lag or creep up on you and be less controllable but that's simply not the case," Humanic argues. "I'm running a Precision 4831 turbo and at only 10 psi on e85 I'm making 330 whp and 270 lb-ft of torque," he says, but goes on to admit that that turbo does generate some extra heat in the engine bay when compared to a supercharger, but isn't anything that a vented hood won't fix.

86 showdown heat shielding wrap Photo 6/13   |   Nothing will make more power than a proper turbo, but they aren't perfect. Turbos generate heat, don't always provide instant power, and can be harder on engine internals when compared to supercharging.
86 showdown liquid to air intercooler system Photo 7/13   |   No turbo system is complete without some form of intercooling. Here, the intake stream is interrupted by a liquid-to-air heat exchanger that pumps coolant through its core as the incoming airstream passes around it.

The numbers: Get yourself the same sort of MAP kit that Humanic's got and you've just made a solid 300 whp on 91-octane pump gas and there's still room to turn up the boost. According to MAP, its kits can be customized for as much as 700 hp.

Price tag: There's no bigger discrepancy in what you can spend than with a turbo kit. Piece one together with your favorite Chinese parts for less than a couple grand or invest in that MAP kit that starts at $3,999 and will probably last you a whole lot longer.

THE ROTREX SUPERCHARGER

The two fastest times of 86 Showdown happened at the hands of a couple of Rotrex-supercharged Scions. That ought to tell you something.

86 showdown gary yeung frs Photo 8/13   |   Sitting at the top of the leaderboard 2.37-seconds ahead of second was Gary Yeung and his Rotrex-superhcarged FR-S. Gary was easily pushing the most power out of the group having the only FA20 with built internals, hence able to boost much more than the field. It doesn't hurt to have things like JRZ suspension either!

How it works: Rotrex superchargers work like nothing you're used to. They're small, they're efficient, and they don't make a whole lot of noise. They look like the centrifugal superchargers you're used to, only inside you'll find a traction-drive system that makes boost by creating friction between a whole bunch of rolling bits. This means they can spin a whole lot faster than what the crankshaft says they can—about 20 times faster, in fact, which means more boost and more power.

86 showdown rotrex supercharger system Photo 9/13   |   Rotrex superchargers are a cross between your typical centrifugal supercharger that's limited by engine speed and turbochargers that can spin infinitely faster. Specialized planetary gears inside allow all of this to happen.

Why you like it: Spend your money on one of Jackson Racing's Rotrex kits and you've just gotten yourself something that'll let you win at the track and pass a smog test the next day. It's also the most thoroughly tested Rotrex-based kit for the FA20 that you can buy. Jeff Nucum, who nabbed second in the Showdown with his C30-based kit sums it up: "Jackson Racing provided a CARB-approved kit, and since this was my track car and daily driver, it was important [for me] to have that. Also, knowing that Oscar Jackson Jr. runs the kit on his personal car and has track tested it gave me confidence."

Passing smog tests is all fine and good, but what you really care about is the sort of powerband that the Rotrex provides, which is exactly what sold Meng Tea (eighth place) on the Jackson Racing system. "[It] gives the car more than enough power without sacrificing any handling characteristics," he says. "[And has a] very controlled powerband with no surprises." In other words, the Rotrex's linear power delivery and immediate response make it just about the perfect power adder for smaller tracks like Streets of Willow.

And it's that same linear power delivery that'll keep those connecting rods of yours from poking holes out of your block. Significant power spikes can be hard on things like rods and their bearings, which makes 300 hp out of a Rotrex a bit more forgiving than the same sort of power out of a turbo. Speaking of keeping those rods inside of that block of yours, centrifugal superchargers like the Rotrex also make intercooling easy, and can be plumbed in the same way you'd do for a turbo.

For fifth place Phil Chien, it's how quiet the C38-based kit of his is what matters to him. "[It's] a powerful centrifugal supercharger that's capable of significant power yet with fairly quiet operation," he says, "allowing me to be able to pay attention to more important aspects of the car while pushing it to its limits."

Why you don't: If you're satisfied with the 270 hp that Rotrex can give you, then you can stop reading now. If you want more power, though, then supercharging might not be for you. Unlike turbos that can allow for easy boost adjustments and far more configurations, your choices in Rotrex units are limited, and once you've got the right one, won't yield any more boost than what you've started with.

As is often the case with just about any form of forced induction, more power means more heat. Nucum experienced higher-than-normal oil temps throughout the day (255° F) despite the 25-row oil cooler, Motul oil, vented hood, and redesigned under-body panels he's got. It should be noted, however, that coolant temps remained normal and that these sort of oil temps only occur for Nucum when pushing the car on the track.

86 showdown jackson racing oiling system Photo 10/13   |   Rotrex kits like those from Jackson Racing include their own self-contained oiling systems, which means you won't be tapping into the engine block or oil pan and which means installation just got a whole lot easier.

The numbers: If you're eying a Jackson Racing kit, plan on a 50-percent power increase with either of its FA20-based systems, or about 270 hp.

Price tag: Jackson Racing's C30-based Rotrex kit, for example, starts at $3,995. Order yours pre-tuned or with the larger C38 supercharger and spend as much as $5,095.

Disclaimer
More horsepower by way of a big hunk of aturbo is good and all, but the sort of tight and technical track that Streets of Willow is proves that horsepower isn't always everything. We didn't even get into the sort of suspension upgrades that had to be made to ach of the competitor' cars, like adjustable coilovers that allow for corner-balancing, anti-sway bars that correct oversteer, and chassis braces that reduce unwanted flex. Spend all your money underneath the hood and you may win the Internet with impressive dyno numbers, but you won't fare all that well on the track.

THE ROOTS-STYLE BLOWER

Manifold-type blowers like Edelbrock's will never be the most powerful, but peak power doesn't always win this kind of race, and, in this case, stuck Jonathan Polidano just a half-second on the wrong side of second place.

86 showdown jonathan polidano frs Photo 11/13   |   Jonathan Polidano was the only FR-S running a Roots-style blower. According to him, he makes 323hp on e85 and 265hp when on 91 pump gas.

How it works: Roots-type superchargers like Edelbrock's Eaton 1320 TVS unit attach directly to the cylinder head by means of a custom manifold and use a series of rotating and intermeshing lobes driven directly off of the engine's crankshaft to compress incoming air.

Why you like it: Roots-style blowers are bulky and old but none of that matters. Edelbrock's kit was good enough to land Polidano ahead of three turbo cars and a couple of Rotrexes. Most of the time, a supercharger will provide better low-end response when compared to any turbo, which can be ideal for the street or tighter, smaller tracks. Power's almost immediate, too. Here, you won't be waiting around for enough exhaust gases to be generated to spin some turbine wheel.

86 showdown edelbrock e force supercharger Photo 12/13   |   Edelbrock's E-Force supercharger is based off of a traditional Roots-style design that spins at a 1:1 ratio with the crankshaft, but none of that really matters when you consider its instant response and its 242 whp.

Like the Rotrex, Edelbrock's blower also features the same sort of straight-line power curve that behaves more like a naturally aspirated engine and less like something making boost. And since that linear power curve means it's free of any of those cylinder-annihilating torque spikes, that FA20 of yours might last a little bit longer. Unlike a lot of Roots-style systems, Edelbrock's comes intercooled by way of a liquid-to-air setup that drops inlet temps and reduces detonation—a feature you've pretty much got to have if you're planning on a track day.

Why you don't: Here, low-speed torque will make you happy but not forever. Positive-displacement blowers can only spin as fast as that crankshaft will let it, they can't always be intercooled, and they can make a whole lot of noise. Problem is, because of their proximity to the cylinder head, air-to-air intercooling is impossible in most applications and not necessarily all that efficient in others.

86 showdown e85 fuel conversion system Photo 13/13   |   Although superchargers are limited by however fast the crankshaft can spin, that doesn't mean more power can't be found. Additional bolt-ons and modifications like tuners that allow e85 fuel to be used can result in significant power gains without any change in boost.

The parasitic losses associated with supercharging can be a bummer, too. Since superchargers are driven off of that crankshaft, rotational energy that could otherwise be used to produce more power is needed to drive itself. Of course, the net result is always more power, but it's no free lunch. A supercharger will also never produce as much power as a turbocharger, but its simplicity and ability to pass emissions tests because of how it interacts with the catalytic converter goes unmatched.

86 SHOWDOWN LEADERBOARD
1.1:24.854Gary Yeung(Rotrex supercharged)
2.1:27.226Jeff Nucum(Rotrex supercharged)
3.1:27.731Jonathan Polidano(Roots supercharged)
4.1:28.779Robert Stangarone(naturally aspirated)
5.1:28.972Phil Chien(Rotrex supercharged)
6.1:29.482Brett Humanic(turbocharged)
7.1:29.681Nathan Walton(turbocharged)
8.1:30.779Meng Tea(Rotrex supercharged)
9.1:33.856Artu Rodriguez(turbocharged)

Sources

Jackson Racing
Yorba Linda, CA 92887
714-921-4500
http://www.jacksonracing.com
Modern Automotive Performance
http://www.maperformance.com
Edelbrock
Torrance, CA 90503
310-781-2222
www.edelbrock.com
By Aaron Bonk
356 Articles

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