I cut the front, cowl opening larger. That didn't seem to help much, but cutting a couple of slots in the cowl directly in front of the engine head helped. I've got a Super Tigre G-90 installed. What engine are you installing? There are a couple of versions of cowls too. Are your cowl flaps molded in the open position? If not, cutting them apart and opening them will help. I shortened my cowl by about an inch or so and I cut some slots in the cowl flaps for dummy exhaust pipes for a more scale appearance. An engine baffle helps direct airflow over the engine's cooling fins too. Top Flite manuals on the Tower Hobbies website show how a proper baffle should fit. My baffle may not be close fitting enough to the engine head and that may be why I needed to cut the slots in the front of my cowl.