312 w/ 496 HO's ?s
 

Recently became interested in a 312 with 496 HO's. One of the few I've seen with k-planes. What kind of top speed and cruising speed can I expect with this boat? I've heard that the 312s had a porposing issue at cruising speeds, is this true? Anything else I should know about the 312?

I had one with 502 mags (nearly the same HP). Ran 70 everyday, 73 under good conditions. Serious tweeking will get a little more. The extra 10HP might get you one more mph. I never had a porpoise issue but I felt the boat ran flat. I think my props needed a little work to get the bow up but I corrected that by buying a bigger boat!!!! :D

I was hoping for 73 any day and 75 - 76 under ideal conditions. I've read a few of your old threads, am I remembering right that your boat had some nicks on the props and in the bottom? Glad to hear the porposing might just be a rumor.

You are remembering correct. My motors were fresh but the bottom needed some minor work. Props were probably a little flat. A local had one just like mine that claimed he saw 75 once or twice.....I never did. (Mine did show 78 on the speedo :rolleyes: ) With 425 HP and a good running surface/props the speeds you mentioned are probable.

You wouldn't buy a boat without a sea-trail now would you???

Every 312 I have driven has run flat. I think the single step did not work the way they thought it would. The first 292 I drove pop the nose up and took off. But the 312 w/496`s would be my choice over the 502`s. I would give up the speed for the newer engines w/cwc.

Wouldn't even consider it, just trying to decide which boats are worth a plane ticket. :D

What does 'runs flat' mean?

just as it sounds flat in the water, to get more speed the boat needs to get out of the water more

Had a 312 w/ 502's. 73 mph would be tops. Slight porpoise issue at mid range, but easily corrected w/ a little tab. Mine had K-planes. Good boat for the $ on the current market.