Feedback from more than 1 source shows 25+ HP gains with the hood closed. 30+ HP has been reported to us with "hood open" pulls. The additional gains with the hood open helped influence the decision to develop the Big Gulp to get additional air to the intake.
Keep in mind on the dyno it is very difficult to simulate the air flow. Therefore, some of the additional gains seen with the hood open on the dyno may be realized with the hood closed under actual driving conditions.
