a tuning question

[izzy]

My buddies make small plugs for trout.the lures are about 1/2 inch to 1 1/2 inches long. pieces of clear medicine vials are used for faceplates.

We have learned way to stop them from twirling and such,by shaving the faceplate,but have not figured out what makes the bodies swim fast or slow(we want fast) some of the lures you can just hold in the current and they swim... and others bearly swim even when they are being retrieved.

thanks for any help