By feeding your blower with a TB that is 7.6mm larger than stock, parasitic loss is reduced, HP is increased, throttle response is dramatic. The stock TB is 67.4mm and the stock blower opening is 70.5mm. The LS4 TB is 75mm.
Modification (Porting) to the blower inlet is required or the larger throttle plate will contact the blower and not allow full opening, If you are not planning on porting the inlet of your blower, you will need this throttle body adapter/spacer plate. Since the inlet of this throttle body is larger than stock, you will also need a larger LS4 silicone coupler.
To see full gains, you would want to port the entire inlet of the supercharger.
The increase in throttle response is very dramatic, we only recommend adding this product after you have a full stage 3 kit, header/downpipe, dual pass endplate, and cams/valve springs.
**PCM calibration required. In HPT under engine idle airflow the ETC area scaler is normally 2950 (this works out to throttle plate area in millimeters less the rod area).
67.4 dia, pi*r2 = 3568 less throttle rod area (620) = 2948
75 dia, pi*r2 = 4418 less throttle rod area (730) = 3688
You'll need to change the 2950 to 3688. Many users have reported better results going even higher. We have tested numbers ranging from 3775 to 5500 without issue.