You just have to try things. Try what Bertram recommends. Try my points if you want.

Getting passed on a long straight can be for many reasons: gearing, two speed timing, tire diameter, speed in and out of corner, racing line, clutch, tuning

Ask the old guys or fast guys at your track to drive your car and give you feedback.

There are guys who will pass you regardless of what engine they are using. They have a special something many of us are searching for when we buy engines or upgrade equipment. Usually they can be super aggressive but smooth in every corner like Alex Hagberg. I wish I could buy that.

Good luck. Enjoy.