Project Viper GTS: Part 6 – Corsa Exhaust and Kooks Green Cats

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Overlaying the K&N Intake Baseline (green) to the Corsa Exhaust and Kooks Cats (blue) and finally the Roe Tuned pull (red), what sticks out is the massive 527.62 lb-ft of torque, which is 35 lb-ft more than when we started the day.  To put things into perspective, with the tune, the car makes more than the baseline’s peak power at 4,600rpm and carries it to 5,800rpm.  This trend of the power falling off is likely due to the restrictive intake manifold with its long and narrow runners.

Now what would be a good comparison of a great-handling, modern sports car?

Ford’s new GT350 is a game-changer on many fronts, especially its outrageous 5.2L flat-plane-crank V8 engine that spins to a stratospheric 8,250rpm and pumps out 526 hp and 429 lb-ft of torque.  While 100hp per liter from a V8 engine of this size is impressive, when you consider its 93mm stroke and 5,034 feet per minute (25.58 M/S) piston speed, this feat is actually pretty incredible.

But how does our lightly modified 20 year old car stack up to this modern, technical marvel?

The Viper’s 8.0L pushrod V10 is significantly different in character to the efficiently high-revving DOHC Ford V8.  Since horsepower is a function of torque and RPM, in order for the low revving Viper to make the same power as the high revving Mustang, it must make a lot more torque.  And it does with a 130 lb-ft advantage.  However, the area under the curve in the last 1,500rpm of our Project Viper and the GT350 are pretty similar, above 450whp.  Now there’s no real point of this comparison other than doing it because I can, and I find it interesting to compare two engines that make the same power in very different ways.

We are very happy with the power, but how does it sound?

At idle the Viper settles into an all-American chassis-rocking muscle car V8 lope due to the factory “708 Cam”, but once you dip into the throttle, that roughness immediately smooths out to a higher pitch that comes from high piston count engines like V10s and V12s.  From outside the car, the blended pitch of the Corsa Exhaust actually sounds a little more like a Gallardo short-shifting (due to the Viper’s 6,000rpm redline) than it does a pushrod V8 bigblock, smallblock, or LS motor.  Don’t get me wrong, an uncorked Gallardo or M5 have a high pitch scream and rasp of 4 times as many cams, twice the amount of valves, and a higher redline that the Viper will never sound like, but the pitch of the Corsa exhaust makes the Viper sound more like its V10 brethren than it does an American V8.

From inside the car, the increased exhaust sounds sporty but not overbearing.  It’s loud when you want it to be, and tame with a volume that’s more in line with what a Viper should be. There is virtually zero drone and long trips are easily tolerable.  This is a feat in itself having been in Vipers with other exhaust systems that have a booming drone that can drive you nuts when driving the car sanely on the street.

The Roe Racing tune greatly improved one of the biggest drawbacks of the car, the low rpm tuning.  The Viper can easily get into a bucking fit when driving at low speeds in 1^st and 2^nd gear below 1,700rpm.  Above that it’s trouble-free and happy, it just has the ability to make you look bad when idling through a parking lot. With a big block, low revving engine producing gobs of torque, you would expect to be able to pull tree stumps from idle, but you can’t because the programming is atrocious.  If you’ve followed the project in Part 2, our car has new plugs and wires and this behavior is prevalent across all Gen 2 Vipers, not just ours.  While the Viper’s supposed to be rough and brawny, I’m surprised that someone signed off and approved this behavior for production. The Roe tune greatly cleans up and smoothens out the throttle tip in and further improves the driveability of the car.

Now the POWER, or should I say TORQUE!  With our new exhaust and tune installed, the 34 lb-ft of torque increase at 4,300rpm just launches the car forward, when it doesn’t light the tires up.   Torque across the board is increased around 20 lb-ft and the increase in acceleration is substantial.  With a smoother operation at lower rpm and a huge increase in power off idle from the improved tune, our Viper not only drives much better, but sounds excellent.  We are extremely satisfied with the performance and sound improvement that these modifications have made to our car.

Stay tuned for the next installement where we cover the exhaust with HeatShield Products and significantly drop the temperature in the cabin and on the outer sills.

Sources:

Corsa Performance Exhaust

Kooks Custom Headers

Roe Racing

RareFab

Power By the Hour