A study on gutting the VVIS system of a naturally aspirated NSX was done by the iconic tuner, founder of Fastrax Turbo Technologies, and ex-head R&D manager of HKS USA, Jon Kuroyama. Jon just happens to be a fan of and previous NSX owner, as well as the tuner of the country’s (and arguably the world’s) fastest time attack car: the FX Motorsports Development FX750, which happens to be the NSX that I drove to a 1:37.520 at Buttonwillow 13CW last December (In-car Video).
Jon’s test bed was a 3.0L NA-1 NSX with NA-2 headers and an Fcon V-Pro ECU so timing and fuel mapping was locked and consistent between the runs. These modifications also explain why his power levels are much greater than stock, but are in line with what’s typical for the same modifications.
According to Jon, when the VVIS plates are gutted or removed, there is a significant loss of both power and torque over a 1,700rpm span, right where you need it for daily driving. He has found that gutting the VVIS plate resulted in a net loss of a couple horsepower across the board when compared to removing the VVIS plate altogether, which actually had a small gain of a few horsepower above 5,000rpm over the untouched and functional VVIS plate.
For most naturally aspirated applications, Jon recommends leaving the VVIS plates installed and functional, but since Project NSX is going to be turbocharged in the future, the VVIS plates would cause an air disturbance and gutting them will yield gains for us later down the road.
The C30A came with restrictive cast iron manifolds while the 3.2L C32B had much better flowing stainless steel headers. Most of the C32B’s power gain over the C30A is due to the improved headers, which have become a common swap for NA1 owners who don’t want to pay for aftermarket headers and who want to stay with OEM Honda parts. There has been a reported 15hp gain by using the NA2’s headers on C30 motors which almost completely makes up for the power differences between the two motor. Aftermarket headers typically don’t yield much more than single digit gains over the NA2 headers.