I tested these on my dyno about a year ago. Motor was a 602 crate with a 650 track warrior no spacer. Base lined the motor with plates in and then took plates out and picked up a couple hp. Also picked up a hesitation when hammering the throttle. Which is why the customer put them on to begin with. Went up 3 or 4 sizes on nozzel and got rid of the hesitation and kept power the same (couple better than with the plates). So the motor seemed to require less pump shot with the plates . I can't say why it lost power for sure but they kind of hang in the venturis a little bit. Might be hurting airflow or possibly changing fuel distribution a little and the motor didn't like it. The air fuel ratio stayed the same at WOT. Only lost a couple horse on a 350 hp engine. I think their sweet spot would be for driveability issues. That being said under the right conditions on the right motor that change in fuel distribution ( if that's what it was) might pick up a couple horse.
