Feature Car: Matt Welliver's Cobalt Turbo Sedan

"Oh, a Cobalt?  I think I rented one of those once.  What's the big deal?" Well, before you click on another article, let me put some numbers in front of your face:  355 horsepower and 426lb-ft torque on a stock turbocharger.  Those aren't "oh, it might be makin' this" crank output estimates - that's how much this white Cobalt SS sedan puts down at the wheels on a dyno.

In the world of sport compacts, the Chevrolet Cobalt SS is an under appreciated vehicle.  Most people take one look at the pedestrian exterior - no huge hood scoops, stripes, giant blingy wheels - and immediately think "rental car."  And it's true there are a lot of Cobalt rental cars out there.  They make good rentals; they're cheap, reliable, and plentiful.  But the SS is a whole 'nother animal.

The biggest difference is under the hood: normal Cobalts (or Slobalts, if you're particularly sarcastic) are saddled with noisy, gutless port-injected Ecotec motors.  Even the 2.4L is only around 170bhp, which these days isn't enough to be worth getting out of bed for.  The original Cobalt SS was a decent sport compact, boasting 205bhp and 200lb-ft of torque from an Eaton-supercharged, air-to-water-intercooled 2.0L Ecotec mated to a Saab transmission and stiff suspension.  But constantly escalating power outputs in competitors (as well as the fact that the Supercharged "LSJ" 2.0L didn't meet 2008 emissions requirements, and the ending of GM's contract with Eaton) meant a rework of the SS was needed for 2008.

Thus was born the LNF motor, proof that GM does listen to their enthusiasts.  This motor is a peach: an all-aluminum Ecotec fitted with direct fuel injection, a 9.2:1 compression ratio, and a twin-scroll Borg Warner K04 turbocharger breathing through a front-mounted air-to-air intercooler, produced a healthy 260bhp and 260lb-ft of torque.  These were exceedingly rapid cars - 0-60 in the mid 5's with a high 13-second quarter mile time north of 100mph was possible from the factory.  They also came with all sorts of neat performance tricks built into the ECU, such as No Lift Shift (the ECU will cut fuel and timing when the clutch is depressed with the gas wide open to allow you to slam shifts) and a Launch Control feature that stutters the motor at 4,800rpm to allow for a quick getaway.

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They weren't just fast in a straight line, either - when Car & Driver conducted their annual "Lightning Lap" track test at Virginia International Raceway in 2008, a Cobalt SS Turbo Coupe managed to lap the track faster than the significantly more expensive (and powerful, and sophisticated) Mitsubishi Lancer Evo X.  With a suspension developed on the famous Nurburgring track in Germany, as well as impressive braking hardware (those 4-piston Brembo brakes up front are standard), the SS Turbo is no joke.  And that's stock.

A stock Cobalt SS Turbo is nice, but why leave a car like that stock?  Matt Welliver knows a thing or two about tuning the SS, though: he's one of the best-known names in the NC region (as well as on CobaltSS.net) when it comes to extracting maximum power out of a supercharged, turbocharged, or turbo-converted Ecotec motor.  With such proficiency at tuning these cars, it's no surprise that Matt's daily driver is a Cobalt SS Turbo.  let's take a closer look at what makes his car so special.

CarThrottle: So what've you got?Matt Welliver: It's a 2009 Chevy Cobalt SS Turbo Sedan.  Only options are the LSD (limited slip differential) and sunroof.

CT: Why did you pick this car in particular?MW: Well, this is actually my third Cobalt, and I'm familiar with tuning them.  I had a kid recently, so my two-door SS didn't really have enough space for real life.  It was either gonna be this, an STI, or an Evo.

CT: What's special or rare about it?MW: They only made the Cobalt SS Turbo sedan for one year - 2009.  There were only 14 white turbo sedans made, making it the second rarest after Yellow - only 9 of those made!

CT: Yeah, can't say I've ever seen a white one.  What's your favorite feature or characteristic about this car?MW: It's different!  Everyone with a tuned SS has a coupe.  You don't see a lot of the sedans, you know, at every stop light.  It's really got some balls, especially tuned.  They make good track cars once you start digging into the suspension as well.

CT: For sure, I never see Turbo sedans.  What's your least favorite thing about it?MW: (sigh.)  It's a Chevy.  The interior's really cheap, and the resale value is awful.

CT: Haha!  At least you're honest!  What plans do you have in the future for the car?MW: Bigger turbo!  Right now it's fast, but these are just bolt-on modifications.  I'm going to build the motor - Darton sleeved block, Carillo rods, and a custom Garrett GT3071R turbocharger - billet wheel, 3076 internals, 3071 housing.  Oh, and methanol injection.

CT: Jeeeez. How much power is it making now, and how much do you expect from that setup?MW: Currently on the stock (B/W K04) turbocharger, it's at 355 wheel horsepower and 426 lb-ft torque at the wheels.  That's on a tune I did myself, on an HP tuner through the OBD port, at 30psi of boost on 93 octane pump gas.  The custom 3071R should be good for... I dunno, 550 at the wheels?CT: 550 at the wheels?  In a Cobalt?  That's nuts!MW: I know!  That's the point!

CT: So what would you replace this with?MW: I'd love to have an Evo 8 or Evo 9.

CT: What's your favorite place to drive it?MW: Tail of the Dragon!  I'm going back soon.  (Ed. note: hell yes.)

CT: Any shout outs you'd like to make for the build on this car?MW: Of course.  Thanks to Steve Sharpe, John Powell at Powell Race Shop, Bryan Higgins, Kevin Walsh, and Tim Avery.

CT: Thanks Matt!MW: No problem.

While riding around in the Cobalt searching for an appropriate photo location, I got a feeling of exactly how fast 355whp in a ~3,000lb car is.  The LNF is a really impressive motor, even boosted a lot on the stock turbo.  Compared to, say, an original SRT-4, the LNF has almost no turbo lag, mainly thanks to the split-fed K04 turbocharger.  Even on a hot day (it was around 100°!), it will spike to 30lbs of boost in gear and hold it, and the shove is massive. Take a look:

httpvh://www.youtube.com/watch?v=xFC3XlS2Fr8

Compared to the Chrysler 2.4L Turbo in the Neon SRT-4 (and I'm sure I'm not the only one comparing them), the SS has much better off-throttle boost response, despite having less displacement and a smaller turbo.  The high compression ratio that direct-injection allows these motors to run does well with turbocharging.  Even with the lowering springs and huge rear sway bar (and 35 series tires!) the ride isn't that bad, and the SS has no problem threading a line through corners despite the live axle in the back.  I can't imagine how unruly one of these cars would be without the LSD - it has no problem spinning both tires in 2nd gear, from a roll on dry pavement.  There is some torque steer - you can't expect there not to be, it puts 426lb-ft to the front wheels - but the thicker axles that were introduced with the turbo engine, plus the aftermarket motor mounts that put the engine closer to level with the axles certainly help.

This motor isn't really that far off of stock.  There's a custom tune, a catless downpipe (a popular modification on turbo cars, as it decreases exhaust backpressure for quicker spool-up), intake and charge pipes, a large intercooler, and a stronger clutch to deal with the extra power.  The only internal modification is the addition of SuperTech heavy duty 78mm valve springs and titanium spring retainers - which allow this LNF to spin north of 8,000 rpm.  There's not much of a reason to at this point - the K04 turbocharger starts to go out of it's efficiency range past 6,500rpm, and boost tapers off - but the valvetrain should definitely come in handy with the future build, which will make boost at higher RPM's.

Sure, the interior's not up to modern Honda Civic Si specs, but I'd happily trade the Civic's nice  interior (and independent rear suspension) for the monster motor under the hood of the SS.  Plus, with almost 30k miles (the vast majority of which were done running 20+ pounds of boost), there have been no check engine lights or mechanical issues- maybe BMW can take a page from GM Performance's book on how to make a high-pressure fuel pump work right?

The interesting thing is, this car is in the "in-between" phase right now.  It had an upgraded turbo on it previously with stock internals (the stock connecting rods on the LNF are good for around 450bhp), but that turbo was sold to fund the new build, with a sleeved block and stronger rods - and an even larger turbo.  Expect to see Matt's wicked Cobalt on the pages of CarThrottle again once this plan becomes a reality.  Because honestly, I'm seriously curious as to what a 500+whp Cobalt is like.  Aren't you?

Car: 2009 Chevrolet Cobalt SS Turbo Sedan

Engine Modifications (Internal):

• Supertech 78mm heavy duty valve springs
• Supertech titanium spring retainers

Engine Modifications (external)

• Hahn Racecraft Cold Air Intake
• Injen solid charge pipes
• ETS intercooler (huge)
• ZZP 3" catless downpipe
• Hahn Racecraft 3" cat-back exhaust system
• Dejon bypass valve spring
• Custom tune via HPTuners done by Matt Welliver.  30psi on pump gas.
• Current dyno numbers: 355whp, 426wtq

Transmission/Driveline Modifications:

• Exedy Hyper single-plate heavy duty clutch
• Exedy Flywheel

Brakes/Tires/Wheels

• Wheels: TSW Nogaro, 19x8"
• Tires: Toyo Proxes 4, 225/35/ZR19
• Brakes: stock (Brembo) with Ferodo 1000 pads

Suspension Modifications

• SSC Springs (2" lower than stock)
• Powell Race Shop 1" Street rear sway bar
• Powell Race Shop Billet Rotated Motor Mounts
• Powell Spherical Control Arm Bushings

Body Modifications

• RK Sport Vented Hood (for a Pontiac G5)
• Stubby Antenna
• Blacked-out headlight housings
• HID Projector retrofit in stock housings (FXR)
• 35% window tint
• Evo X style painted front bumper
• Black metal-flake front bowtie
• Stickers, etc.

Interior

• Gauge pod - Aeroforce Interceptor, tied into factory OBD system.
• A-pillar gauge: factory pod, gauge replaced with Autometer Lite 30psi/30inHg mechanical boost/vacuum gauge, all-black interior swap

Stereo/ICE

• Stock Pioneer Stereo
• JVC 7" in-dash touch screen head unit

Thanks to Matt Welliver for taking the time for this interview and photoshoot!  More feature cars coming soon on CarThrottle.com.  Interested in having your car featured?  Shoot me an email at james@carthrottle.com.