New motors suck!!
 

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?

Turbo, you kinda read my mind. I have thought about spacers but not surface props. I'm going to do some testing with props first and go from there. But that a good thought. Who makes surface piercing props that would work? These are not the original drives to the boat. The originals best I can tell were just Alpha 1's.

jr, you have a worse problem than I do. Good luck!

That is a kind offer, Ken. But, when the labbed Bravos are on, that should pick up some speed. I hope your motors are first on the mechanics repair list!

The key question I have is how much faster are your boats on salt water rather than fresh at the same RPMs? That should get me a couple of miles I would think.

It was very good to know that an older Sonic 31SS with 475 HP motors is doing 74 MPH. Hence, with my 350 HP motors it seems I am at the right speed after all. Obviously a 1988 Sonic weighs much more than the 7,000 lbs for a new one. Anyone know how much?

Why did I pick small blocks? See my www.hyperfishing.com site and see all the aluminum stuff festooning the engine hatch and swim platform.

I guess supercharging is in the cards for next year, with IMCO shorty drives.

Thanks folks.

You might also try the land and sea drive extensions ... saw a test once were if the drives were raised they worked even better... three inches of prop is alot and might still need semi piercing cleavers ..... the combo might kick though

you need to run a scan tool on the motors and see if you have WOT alot of times you may not be running 100% and what the computer says the rpms are.

Good ideas turbo and 38.

It seems the most logical explaination is simply that I have an older and heavier constructed boat, hence it weighs much more than the new ones.

sound about right to me. The boat is older and weighs much more. There is not the high amounts of torque you are looking for.
I dont think 62 is all that bad. Seems like there are many suggestions of ways to keep squeeking mph out of her