What Surface Scratcher above said.

Also of extreme importance - has the boat had its core replaced? Hydrostreams are notorious for having rotten balsa cores, and a rotten core plus water-soaked float boxes add hundreds of pounds of weight. ANY new owner of a Stream should make sure the core is bone-dry and properly sealed with resin/epoxy. If there's no proof that the core has been re-done, then it needs to be replaced.

See if this helps....First the porpoising...These pad hulls are all about balance and by putting a much heavier motor on the Viper you've changed the balance point. You can compensate for this by adding ballast up front. Sand bags are popular because they can be tested all over the boat. If you have any engine setback that you can get rid of, that should help. It's a bad idea to move the fuel tank forward because at different fuel levels, the boat will handle differently. Moving the battery is more trouble and expense than the benefits that would give you, IMHO.

As far as the chine walk, it should be much more controllable once the boat is better balanced. Solid mounts, tight steering, good pad surface, and proper engine height....y'all will be able to use a lot more of that Merc's power. :up:


Finally, be careful, there's potential for trouble with that much hp! :vking:

I am writing this for a friend that has acquired a Viper this past year. Any suggestions would be welcome!
We have taken the Viper out for its first ride since purchase. This winter he has installed a Mercury with the following specs.
1991 2.5 V6
20" DSH, with solid mounts, a Sport-Master lower unit and 300hp rated Hydraulic steering.
14x28 big ear chopper is what is currently installed, but do own a 14x28p Cleaver "Buckshot" to try next.

No matter where we adjust the trim and engine height with the jack plate we have extreme romping (Porpoising)! And extreme Chine walking attempts! He is looking for any suggestions that might help.