Project Viper GTS: Part 4 – Baseline Dyno and K&N Intake Test

Smooth Tube TopThese ROE Racing Polished Aluminum Smooth Tubes are slightly different in design than the original GT2/ACR smooth tubes, which are straight silicone tubes of the same diameter as the airbox outlet and throttle body.  The ROE tubes are much larger in diameter (3”) than the throttle body’s OD and are aluminum in construction which will not distort and crush down from heavy vacuum like a straight poly/silicone tube could.  Notice the size of the taper on the bottom black silicone segment as the 3” aluminum tube meets the smaller factory throttle body.

To commemorate their 1998 FIA GT Championship and the 1998 24 Hours of Lemans GT2 victory, Chrysler built 100 street-legal “GT2 Championship Edition” Vipers in 1998.  All of the cars were white with blue stripes, had a GTS-R inspired wing, front dive planes, a racing harness and a factory rated 10bhp increase (460hp) due to K&N air filters and “smooth intake tubes” that replaced the corrugated rubber tubes that connect the airbox to the throttle bodies.  In 1999 the Viper ACR was introduced and also had the same “smooth tubes” and air filters with a 460hp rating.

We already saw a close to a 15whp peak gain from K&N air filters alone, which is greater than the factory rated 10hp bump for the GT2 and ACR cars, so how much more would these smooth tubes actually improve?  There is a lot of hearsay on Viper forums for how much power smooth tubes actually make, so we were looking forward to the results of this proper back to back comparison of the smooth tubes compared to the stock corrugated tubes.

Smooth tube insideThe factory tubing is much smaller in diameter and turbulent from the large corrugations.  To meet the smaller OD of the factory airbox, the ROE tubes have a ¼” thick insert that takes up the difference, which you can easily see from this view.  As air exits the airbox, there is an immediate step to 3” before smoothly tapering down to the factory 62->60mm throttle body.  You can see this taper in the far end of the smooth tube.
Stock Intake TubesThe stock corrugated tubes look a bit bland and were replaced by smooth tubes on the Viper GT2 and ACR models.
ROE Racing smooth tubesThe ROE smooth tubes bring a little ‘bling’ into our engine bay as well as double the hose clamps.  You can see the significance of the tapering of the rear silicone connector as it enters the throttle body which would likely accelerate the air into the intake manifold.
Viper on dyno spinningNow with our ROE Smooth Tubes installed within 20-30 minutes of our previous dyno runs and under the same heat and humidity, we were ready to see what the horsepower gains were going to be.

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