The first enhancement we made to Tabula Rossa, our '99 hardtop, was,naturally, to dump the mild-mannered, as well as plain-ugly, stockcat-back exhaust for something with the machismo befitting a Torch RedCorvette.
The B&B Tri-Flo Bullet exhaust system we installed isdefinitely that, with a deep, barely muffled sound that has receivedmany compliments so far--including a surprising one from a Harley rider!The downside, however, is that what's loud outside the car is also loudinside the cockpit, and that can wear you down on a long road trip.
While flipping through a Mid America Motorworks catalog recently, westumbled upon a listing for KoolMat C5 insulation kits, which aredesigned to reduce the drivetrain heat and road noise that radiatethrough the floor and into the cabin. KoolMat is a high-temp compositematerial made of densified silicone that is cured into a fiberglass matand permanently bonded to a silicone rubber mat. KoolMat performs wellin extreme conditions, from 500 degrees Fahrenheit to 40 below, and isused in many racing applications, including in NASCAR and the NHRA, tohelp protect drivers from heat fatigue. While we were definitelyinterested in reducing the amount of exhaust heat radiating through thetorque tube tunnel, what really got our attention was the accompanyingsound reduction--up to 23 decibels.
We contacted MAM and ordered thepre-cut, 13-piece, rear KoolMat kit (PN 612-618) along with the 9-piecefront kit (PN 612-619), and arranged to have it installed during arecent visit to the Denver area by our friends at Dreamworks PerformanceEngineering. Using our handheld decibel meter, we measured the soundreadings under a variety of conditions, then installed the kits one at atime so we could measure what impact was made by each step. At the timewe performed our installation, the KoolMat C5 Bulkhead kit--forinsulating the vertical panel behind the seats--was not yet availablethrough Mid America, so we contacted KoolMat directly, and added thethird part to our evaluation.
The KoolMat kit required a fair amount ofextra trimming to get it to fit to our satisfaction--particularly in therear as the kit is based on a C5 coupe--so we had to work around theminor differences in adapting it to our fixed roof. But the precut kitis significantly easier than trying to cut it yourself from a roll ofKoolMat material, and the results were well worth the effort. We noticedthat the KoolMat did a good job of controlling radiant heat (especiallywith keeping our thighs from burning against the torque tube tunnel),although that was not what we were measuring for--but it was only whenwe had installed the entire three-part system and completely sealed offthe cockpit that we realized the significant improvement in volume wewere seeking.
*This Story First Published in April 2005 Issue of Vette Magazine
AVERAGE INTERIOR SOUND LEVELS w/ KoolMat Installed
At Idle: 68db (-24db)
3,500 rpm, in Neutral: 73db (-13db)
30 mph, in Second gear: 68db (-28db)
75 mph, in Sixth gear: 92db (-11db)
85 mph, in Sixth gear: 96db (-12db)
*Numbers in parenthesis indicate decibel drop from having the Bullet Exhaust installed without KoolMat insulation