Bass and Walleye Boats would buy an old used performance boat, say a Bullet, with a tired engine and modify it in stages and publish the cost and the increases in MPH after each stage of modification. They ended up with a boat that was 20 miles per hour faster (from 68 to 88 MPH) But consider the costs before proceeding, in terms of cost per mile increase, reliability, and resale value if you ever intend to sell the boat and motor. Also you should be able to do the work yourself and have professional help nearby.
BWB modified a 1985 Bullet 19-footer with a 1992 Johnson GT200 outboard and the results as follows:
Bass and Walleye Boat Project Budget Basser Part I:
http://www.bwbmag.com/output.cfm?ID=1290691 Bass and Walleye Boat project Budget Basser Part II:
http://www.bwbmag.com/output.cfm?ID=1290745 Bass and Walleye Boat project Budget Basser Part III:
http://www.bwbmag.com/output.cfm?ID=1238419Bass and Walleye Boast project Budget Basser Part IV:
http://www.bwbmag.com/output.cfm?ID=1252549 Bass and Walleye Boat project Budget Basser Part V:
http://www.bwbmag.com/output.cfm?ID=1282501Bass and Walleye Boat project Budget Basser Part VI:
http://www.bwbmag.com/output.cfm?ID=1388953"As purchased, the Bullet/Johnson combo attained a top speed of 68.1 mph at 5120 rpm. With the bottom repairs, blueprinting, solid mounts and modified gearcase, we hit a best speed of 77.2 mph at 5850 rpm."
"The Boyesen reeds also helped us break the elusive 80 mph mark, as we hit a best of 80.3 at 6050 rpm"
"With the EFI system installed and tuned, we hit a best of 85.2 mph at 6450 rpm."
"It?s important to note that, so far, we?ve performed all the labor in this exercise. To have someone else do it (with hourly charges ranging from $50 to $90) would add at least another $3000 or more to the tab, and we?d be over our $15K budget. This story has been aimed at those who can do much of this work themselves with only minimal help from professionals."