Remember 1997? In January of that year, and for only the fifth time in its glorious history, a new generation of Corvette was introduced. The C5 was an example of that exceedingly rare occurrence of being an "all-new" product that was, indeed, essentially all new. The C5 was also an incredibly impressive sports and grand touring car in its debutante form.
It hardly seems possible that over five-and-a half-years have passed since the first C5 coupes went public. There are three body styles and two distinct models in the line-up, and the C5s just seem to keep on getting better and better. And as the factory models have proliferated and improved, so have the offerings of both performance enhancements and dress-up items from the Corvette aftermarket. By personal observation, we'd have to say that custom exhaust systems rank number one in popularity, followed by custom air inlet setups, on the performance side, and chrome-plated OEM wheels are, without a doubt, the hot item for C5 appearance upgrades.
Custom exhausts come down primarily to a matter of which system's appearance and sound is most appealing. Chromed factory wheels? It's a matter of perceived and actual quality and what company you prefer dealing with. On the other hand, there is a definite and wide-ranging selection of custom C5 air inlet systems. Early next year, we'll have exhaust and induction system buyers' guides. Meanwhile, we take advantage of opportunities to check out-and test-custom parts whenever such an occasion presents itself. We had just such an opportunity recently, to follow along with the installation, with before and after dyno tests, of RM Racing's Twin Flow air inlet system on a semi-stock (a custom cat-back exhaust system had previously been installed) '00 C5 coupe.
Stock...quiet, filters the...
Stock...quiet, filters the air quite well, reasonable cost to produce, and easy to install on the assembly line. Nuff said?
The stock C5 (at least for LS1-powered cars) uses a single, flat panel-style filter element that's housed in a large plastic box in the nose of the car, in front of the radiator. It's an excellent location for picking up cool, outside air through the openings in the front bumper cover. This terrific position is somewhat wasted by virtue of the factory airbox breathing through one rather small opening. And no matter what else you may do to the engine, if you can't get an adequate supply of air into it, power production will suffer.
The RM Twin Flow system utilizes dual conical oiled gauze (K&N) air filters that feed air direction into a pair of 3.5-inch inlet tubes, located in the nose. The pair of inlet tubes are "Y'd" and then feed incoming air to the mass airflow sensor and onward into the engine.
Installing the Twin Flow is a no-brainer: loosen the clamp holding the Mass Airflow Sensor-to-throttle body duct to the throttle body, the vent hose and wire harness hooked to the duct, and the two straps that retain the stock airbox, then remove the airbox, complete with the MAS and ductwork. Disconnect the MAS and ducting from the stock airbox and clamp them to the Twin Flow inlet. The Twin Flow has its own mounting bracket that holds it in the stock location, and the balance of the install is simply putting things back where they'd been to begin with. The entire procedure took less than an hour, and everything fit where it belonged.
Here's RM Racing's Twin Flow...
Here's RM Racing's Twin Flow unit, clamped to the factory MAS and ductwork, and ready to be re-installed.
Then it was time to see if the expenditures of time and treasure (around $355) paid off. We'd baselined the Corvette on Technodyne's Dynojet 248C before swapping the air inlets, garnering a surprising 316.5 hp and 326.2 lb-ft of torque at the tires-the highest figures we've seen to date on an essentially stock (remember, custom cat-backs), LS1-powered C5. With the RM Racing air inlet in place, we recorded 326.7 hp, a gain of 10.2 ponies, and 332.5 lb-ft of torque, up 6.3. Not bad!
Not bad at all-a custom part that fits well, looks good, and delivers the goods as in more power.
 Ready to go, after we do some...  Ready to go, after we do some tests. |  The proof of any modification...  The proof of any modification is what-if anything-is gained, and the best way to verify most performance gains is on a chassis dyno, with before and after tests. |  The airbox, mass airflow sensor,...  The airbox, mass airflow sensor, and all ducting up to the throttle body, are removed as a unit. Here's how it looks minus the factory pieces. |