GM performance enthusiasts really have had it good through the years. Most of GM's performance offerings have lived up to or exceeded their billing, and many were blessed with some amount of "performance headroom," meaning the engine was capable of producing substantially more power with only small modifications. As time marches on and the level of factory-rated horsepower from the LS engines continues to climb, this capability hasn't diminished.
Exhaust systems used to be the first place to look when searching for easy performance gains. While there's still something to be had here, the quality of the OEM systems has increased to the point it's no longer the excellent bang-for-the-buck mod it once was. Converter-back exhaust systems have also climbed steadily in price over the years, further eroding the power-to-dollar equation. It's still the mod to make if you want your Corvette to sound like it means business, but don't expect much more than 10 hp or so unless you team the system with some other modifications. A pair of full-length headers will make a substantial bump in power, but these are even more expensive and tend to be beyond the capability of less experienced do-it-yourselfers.
The upshot of all this is that enthusiasts are now looking first to the intake system in search of budget power increases. Recently, we noticed some impressive gains being posted by LS3 owners with the simple addition of a ported throttle body. Though it seemed too good to be true, we thought it at least merited further investigation.
The test subject's owner had...
The test subject's owner had previously installed a Halltech Killer Bee intake system on the car, but he hadn't performed any baseline or post-installation dyno testing.
It turns out that LS3-powered Corvettes are calibrated to run fairly rich from the factory, meaning anything you can do to increase airflow to the engine will help power production. One could argue that simply retuning the PCM to lean out the AFR would provide the same results, but numerous attempts using this methodology have not significantly increased power. This suggests to us that the engine is simply not able to draw in as much air as it needs to perform at its full capability. Our plan was to supply the LS3 its needed air by focusing primarily on the throttle body, since A) it's all the buzz, B) it's relatively cheap, and C) it's indistinguishable from a stock piece once installed.
The owner of the '08 automatic coupe shown here was looking for tangible gains with minimal visual change and none of the warranty ramifications that come with permanent modifications to the car. He had already installed a Halltech Killer Bee intake system, which alone left him underwhelmed. Though he hadn't tested it in a controlled environment, the addition of the intake system seemed to leave the car wanting a bit more to be truly unleashed. For him, the answer seemed obvious: Hand over the car to the experts at AntiVenom in Seffner, Florida. AntiVenom proprietor Greg Lovell was quick to recommend a VMax ported throttle body by Pete Incaudo and a high-performance PCM dyno tune.
The ported VMax throttle body offers a substantial increase in airflow along with an attendant power improvement. With more than 40 years of experience in the performance aftermarket and a rsum boasting associations with serious players such as AirFlow Research, Edelbrock, and CNC Cylinder Heads, it's safe to say Incaudo knows his way around the science of airflow. In fact, he has measured his porting methods and found they increase airflow from a flowbench-verified capacity of 965-967 cfm in stock form to 997-1,002 cfm after porting.
Prior to beginning this series...
Prior to beginning this series of tests, the Killer Bee was removed and replaced with the stock air intake. The baseline dyno results were 363.80 rwhp/354.22 rwtq. Next, the Killer Bee was reinstalled, producing 378.57 rwhp/363.72 rwtq. The car was subsequently tuned to a best result of 379.79 rwhp/369.24 rwtq.
Here's a side-by-side comparison...
Here's a side-by-side comparison of a stock throttle body (left) and a VMax modified unit. As you can see, they're completely indistinguishable from the outside.
The inlet bore of the throttle...
The inlet bore of the throttle body is where the real difference is made. The stock piece exhibits a rough surface finish from the casting process.