Breathe Easy

Poweraid throttle-body spacer and Airaid cold-air intake give GM's 4.2-liter engine a power boost

GETTING MORE PERFORMANCE OUT OF THE GM 4.2-LITER Vortec in-line six found in the Chevy TrailBlazer, the GMC Envoy, the Buick Rainier and the Oldsmobile Bravada is not all that easy, as trailer-towing owners have discovered. Problem is, there just aren't that many upgrade parts available.

However, they are coming. And those for the four- and five-cylinder Colorado, Canyon and Hummer H3 may soon follow.

We found a couple of easy-to-install performance parts from one company that upgrades the 4.2-liter s air-intake system that show promise: the Poweraid Throttle-Body Spacer and the Airaid Cold-Air Intake system, both from Airaid Performance Filter Company.

It's amazing what a better air-filtration system and a little piece of aluminum the size of a beer-mug coaster and the thickness of your finger can do for a vehicle s performance. Of course it all depends on what the part is and the application; some engines will show smaller gains, a few may even show larger gains.

The performance increase they give the popular GM Vortec 4200 in-line six doesn't instantly make the 4.2-liter feel like a V-8, but it's close - especially in the mid-to-upper-RPM range.

The Poweraid, a 5/8-inch-thick throttle-body spacer (TBS) manufactured from aircraft-quality billet 6061-T6 aluminum, combined with the Airaid performance intake system, does add more than 20 rear-wheel HP while making a slight improvement on cruise fuel economy.

Better still, these two performance upgrades are so easy that even the most timid do-it-yourselfers can handle the installation with basic hand tools.

SPACER POWER

AS WITH ANY INTERNAL-COMBUStion engine, an air-intake upgrade that makes it easier for the engine to get a greater volume of cooler air improves power. Improving the efficiency of the air/fuel delivery also gives a performance boost. That's where these two parts come into play.

The Poweraid, for example, was developed to enhance mid-range power, torque and fuel efficiency by making the intake airflow more efficient as it passes from the throttle body to the intake manifold.

Airaid says the helical-shaped bore of the Poweraid TBS "causes a spinning action of the air charge that carries all the way into the combustion chamber, producing a super-atomized mixture which, in turn, produces noticeable gains in mid-range power and overall efficiency."

We were a bit skeptical that such a little spacer downstream of the throttle-body that already atomizes the air/fuel mixture could make any difference in the in-line six's power.

So we took our 2002 Chevy TrailBlazer to 454 Dyno in Metairie, Louisiana, to have it run on its new Mustang 1100 chassis dynamometer.

Our Chevy went on the Mustang dyno with a new air filter and spark plugs to make sure the baseline test results were as accurate as possible. A.J. Berkeley and his son, Jay, ran the base numbers at steady-state (65 MPH), and also through a ¼-mile drag-strip simulation. Then we installed the Poweraid.

This particular Poweraid TBS kit, which costs less than $100, can be installed on the Chevy TrailBlazer, GMC Envoy and Oldsmobile Bravada 4.2-liter in-line six in less than 15 minutes.

The installation requires removing the throttle body from the intake manifold, slipping the red anodized spacer in place, installing a new sealing O-ring and reinstalling the throttle body using the new bolts supplied with the kit.

While you're working on the throttle body, consider replacing the spark plugs. The Vortec 4.2-liter uses coil-on-plug technology and the coil packs sit underneath the plenum. So, while the air-intake plenum and throttle body are removed to install the Poweraid spacer, the coil-on-plug assemblies are right there; a single bolt holds each pack in place.

Changing the plugs at this time will save you at least half an hour of labor later on because you have to remove the throttle body and plenum to access the individual coil-on-plug units anyway.

POWERAID GAINS

AIRAID SAYS THE POWERAID shows the biggest performance gains in the lower RPM range. Our dyno tests showed the Poweraid TBS does a bit more: it not only added 5 HP in the cruising range (1,500-1,800 RPM), but it also gave a noticeable boost in the full-throttle, high-RPM (5,200-up) powerband of the in-line six.

As expected, our actual road test mirrored 454 Dyno's numbers; the TrailBlazer exhibited a noticeable change in throttle response at speeds above 55 MPH, and it pulled stronger when the UPM got above 4,500.

The Poweraid is one of those simple performance-upgrade parts that give the GM inline-six a power boost with minimal installation effort.

AIRAID INTAKE

ON THE OTHER END OF THE AIR-intake upgrade is the Airaid cold-air-intake performance-filter system ($299) that replaces the stock air box, delivery tube and air filter.

You wouldn't think changing an air filter and how the air gets to the throttle body would really make much difference. But our dyno runs before (stock) and after (with the Airaid) showed that it adds 14 HP when compared with the stock air-box unit.

Such an improvement isn't surprising. An engine is just a big, sophisticated air pump, so anything that improves its efficiency getting air in and/or out will improve its performance.

The stock GM airbox in the TrailBlazer, for example, is designed to pull air from around the headlight and fender area, then route it through a special molded-plastic air box with a lot of noise-reducing baffles before it enters the filter and makes its way to the throttle body.

The stock airbox and its paper filter do the job, but they're not all that efficient for helping the Vortec 4200 make its best power.

The Airaid design, on the other hand, incorporates a cold-air dam (CAD) that helps isolate hot air away from the air intake; as we all know, the cooler the air, the greater the oxygen content. More oxygen mixed with the fuel means more power.

Another element of the Airaid air-intake system is that it provides a denser airflow charge because the fresh air is entering at a much more direct route and in greater quantity.

Installation of the Airaid cold-air-intake kit is very straightforward and requires nothing more than a Phillips screwdriver and a metric socket set. It took us less than 15 minutes to remove the stock airbox and tube and to replace it with the Airaid unit.

AIR POWER

COMPUTER PRINTOUTS FROM 454 Dyno showed the Airaid added 3 to 17 HP, with the first power gains showing up around 2,000 RPM and then increasing to the maximum gain around 5,200 RPM. Then the difference gradually dropped back to about 5 HP as the engine closed in on its 6,200-RPM redline.

We did notice a slight increase in air-intake noise on the road, but only under heavy throttle. Our typical radio volume covered any engine noise otherwise.

Comparing before-and-after performance using the Mustang 1100 ¼-mile simulation, which 454 Dyno says is accurate within 0.1 second and 0.1 MPU, showed the Airaid/Poweraid combination shaved 0.2 second off the stock time (16.2 vs. 16.4 seconds) and added nearly 1 MPH (86.6 vs. 87.4 MPH) - all coming in the last 1/8 mile of the run.

That showed us the in-line six is making more power in the mid-to-upper RPM. It also shows us the 4.2-liter in-line six could use a good cat-back exhaust, but that's next on our list of upgrades to track down ...

As for now, the TrailBlazer runs quite nicely. It pulls a little stronger and is more responsive to the throttle than it was before we did the upgrade. It really feels its oats between 60-70 MPH, and it pulls stronger when the revs get above 4,500.

Those who will really notice the 4.2-liter in-line-six's improvement in torque and horsepower will be those who use their TrailBlazer to tow travel trailers during the hot summer months. That's also where the biggest power improvements will be realized while on the road.

As for that increase in fuel economy that Airaid claims the Poweraid and Airaid give the engine, we saw about 1 MPG improvement - although the exact number would take a lot more miles to determine.

Whether we get a mileage gain or not, installing the Airaid system is definitely the right step to take if you want a little more kick out of the GM 4.2-liter in-line six.

SOURCES

454 Dyno, (504) 454-3966, 454dyno.com.

Airaid Performance Filter Company, (800) 498-6951, airaid.com. Circle 227 on Reader Service Card.

Spears Auto Repair (installation), (228) 863-1878.

Copyright T L Enterprises, Inc. Oct 2005
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