Hey folks - just recently got signed up here on the site. I purchased a '94 31' thunder from one of my customers a few months back and thought I'd start getting involved online. I actually own a boat repair shop in Stockton, CA so i'm fairly versed in the boat industry, albeit I'm not versed when it comes to the performance stuff, we do more mostly gas engine repair, service and diesel work.

Couple questions i've got:

I know that trying to improve top-end speed is normally a complicated endeavour, but I wanted to find out how "improveable" the 31' thunder is? Are there any folks out there that have done mods and seen improvements? If so, what kind of gains are you seeing? I'm concerned that the hull being older technology, not being stepped and such that making any gains will be negligible.

The boat currently has 502MPI's. I figure it can't be too difficult to make 600hp with that discplacement, just need to buy the right top-end parts...
Assuming that I wouldn't be pissing in the wind trying to push the hull to go faster, what has to be done to the 502MPI to make 600hp?

Looking forward to meeting you fellow scarab owners - also hoping to find owners out here in northern california....

Thanks -

Eric Koster
J&H Marine

Welcome, Eric. There's a thread right now in General Discussion about 600 HP from 502's. The folks on here will have a million ideas, probably revolve around HP and props for most amount of reasonable gain until you hit the point of diminishing returns.
Good luck - Jeff

Well said Jeff.
Welcome aboard Eric. There's a lot of different ways to go about it, from bolt on and old school builds for HP to reducing the amount of drag the hull and drives create. Blue printing the hull can improve top end by 10%. Post some pics of your boat in the "Club Scarab" thread. There's other members from your area in there also.

Wayne

Thanks for the input guys. One thing about the boat is that the previous owner had bottom paint put on. It's going to be a pain, but this winter I plan on getting it all off and having my glass guy re-paint the bottom. The boat also has OLD mirage's. My rep from Boatswains Locker in Costa Mesa (who is a record holder that used to race offshore v-hull)is coming up this week and he's bringing a pair of bravo 1's to try out, so hopefully there will be some improvement there....

Any typical things to do to the Scarab hull for blueprinting purposes?

Hey Eric, they use long sanding planes to true up the running surface of the hull. Below are two pages from a magazine article. Starting from the THE HULL paragraph they cover the benefits of blueprinting. I'm sure your rep will be familiar with the process.

Wayne

What kind of speeds are you looking at achieving? Also what kind of speeds are you seeing with stock MPI's?

Well - as of right now, I am a little disappointed. Boat runs about 63 tops (gps). Thats with bottom paint and the old mirages (23p, 1.50 gear ratio)though. I don't really know whats reasonable to attain without spending MUCHO bucks. I'd like to be in the 75-80 range....

My KV is run'n NA 600's. Loaded for the weekend it will hang just under the 80 mark gps all day long. Have seen 83 one time in the right conditions.

TRS's? What's the length/weight of your KV? What does KV stand for? I'm guessing you are carb'd?

I have hp500's running no bottom paint, 26p, 1.5 at 80 gps. My motors aren't stock (but mostly). But that gives you an idea. I think that 63 mph for your boat sounds a little slow. But that could be a result of your bottom paint. So figure to be where you are wanting to be for speed you'll need to be 600 hp a side at the flywheel.