Okay guys, I need help. I had some scorpions installed in my 1988 Sonic 30SS and top speed is a mere 62 MPH on full fuel and water tanks in fresh water. WHAT THE H...????

Anyone with any ideas? Oh yeah, I also had the X dimension raised one inch as per Sonic recommendation.

Swapped my old Ballistics with Bravo I props, I few more revs with the Ballistics and the best speed of 62 MPH.

Similar weight boats in Powerboat mag with scorpions are doing 77 MPH!! I expected at least 71 without a stepped hull.

Obviously, a compression test of the motors is in order first.

Bummed out.

sorry to hear man that sucks!!!

are you spinngin eth props fast enough? what RPMs are your engines at?

Yea CBR, give us some more info. RPM's, Props, timing. Do both engines run the same? How well does it come on plane? Were the engines new, rebuilt or used?
Nothin worse than spending a bunch of money on something and being disappointed with the out come.

Revs were right at 5,000 and the Scorpions max out at 5200 so that is not the problem. Props were recommended by Sonic also, so that is not the prob. either.

Anyone running 350 HP scorpions in a 7,000 pound boat? The prop slip formula says 71 MPH, and the mag tests are over 75 MPH in similar boats.

I don't get it!

Do you have a speedo or GPS ?

CBR, what prop slip numbers are you seeing, what size prop. I'm running a pair of small blocks in my Nova II. The boat weighs in at about 6000 with full fuel. My engines are putting out around 425 HP. The problem I'm having is getting the props hooked up. I'm running an X dimension 2 inches higher than stock and I'm seeing prop slips upwards of 25% and a top speed of 59 GPS. Looking at the geometry of the bottom I have 2 blade tips out of the water by about 3 inches when I'm on plane. This year I'm putting on smaller diameter props and higher pitch. I've got 22"p Hydromotives now, and the boat doesn't really like them too much. I have problems getting out of the hole and I've had some blow out and my revs are way too high. So high that my secondaries dont come on until 5000.

Sorry to hear about the problem! This may sound funny but do the engines sound like they are running 5000 rpm? Is it possible the tachs are not accurate and you not getting WOT? Try a pair of 3 blades. I have a set of 23 Mirages you can try. Are you able to get enough trim? These boats need to be out of the water to get moving. Maybe lowering the X has something to do with it. If all else fails you might try 1" spacers in the drives.

I know it sucks but stay calm we'll figure it out.

JR ,
Have you tried some surface piercing props worked on an Alpha SS I had... or some drive spacers.

CBR,
What motors were in there before? Were they bigblocks?

If so, why was the x-dimension raised...less weight back there would mean that the boat would already be sitting higher than previous. Just a thought...

Let me be the first to ask. Without trying to offend, why not Big Blocks?