We own a 1995 25' SXT Warlock cat. Needing help with a porpoising problem. We bought the boat last summer with a 310HP chevy in it.. Obviously we didn't want the motor just the boat. So, we took out the 310HP (65mph)motor and replaced it with a 540 BB Chevy W/ patriot aluminum heads. Running a 30 pitch bravo 1 prop. (bravo 1 drive).. When we are running the boat it runs,drives great until we get up to around 80mph. At around 80 we get a bad porpoising problem. We have GPS'd the boat at 88mph... BUT from the 80mph range it is a wild ride.. I'm pretty sure if we could get the porpoising problem to go away we might be able to break the 90mph mark.. Any suggestions would be greatly appreciated.. Thanks in advance!!

try borrowing a 5 blade or see if you can borrow prop that spins the oppisite direction.

You will need to put tunnal extention on the boat . Dana marine has a real nice set for around 700.00 .

Is the extention you refer to for the stern drive to lower the prop further??

Check the bottom of the boat for hook. I have heard of this before with this hull. They had the same "porpoising" problems that you are. He changed props and installed a tunnel tab. "Porpoising" stopped only after removing the hook in the boat bottom.

The boat will pack air in the tunnals on the big end. If you get to much lift you loose that air out the back of the boat wich makes the boat lower back into the water. This also will slow you down. We just made a set for my buddys DCB they worked great now I'm putting them on my Daytona. If you want to make your own make them the same width as your tunnal 12 to 14 long 1/4 inch drop .We use turnbuckles to adjust them if needed.

I owned and ran a 25sxt with 850 hp supercharged. Will look up some pics and notes. I didn't run a tab,but ran a stern power drive with a merc #3 cleaver..The boat best was 128 and ran 125 at Loto.The hulls with bravo drives seem to have more problems,, I'm thinking drive height,prop design and the engine on the trans hurts the CG. The SternPower drive set the prop back as far as a stand of box with a bravo.
The person that purchased the boat also installed a 540 NA and the boat ran in the 90s on a rope.Give us some more information..

540 is naturally aspirated with 850 demon. Bravo 30" is stock. Bravo 1 is stock. I have no trim tabs and steering is cable but I do plan to add full hydraulic. I did use 4' level in 4 different places at back of sponsons and they appear straight for that distance. I also wondered if spacing prop downward would help leverage but I know this adds drag. I'll look into extentions as the description offered by PLUMB CRAZY sounds very much like my problem. Thanks for any and all suggestions.

try a differant prop first, my friend a eliminator 25 and the thing porposed so bad at 80 it felt like the boat wanted to leave the water. i put a hydromotive 4 blade on,problem went away,my prop gut said that the boat was to light in the front when it got aired out and the bravo 1 prop had to much rake for that tunnel boat..

We have a friend that has a 31 hydromotive 4 blade and we did try that prop with the same outcome.. a tiny bit faster (less than 1mph) and still had the same porpoise problem. I think we are going to try the tunnel tabs that PLUMB CRAZY mentioned... hate to experiment with $800.00 but that really sounds like it could help the problem. Any other suggestions would be greatly appreciated and when we do the tunnel tabs we'll let you guys know the outcome.. thanks again!