What causes hull porpoising?

Reid, thanks for the input, I've made some changes to get the weight back to where it belongs, and I'll get a few more lbs out of the ront of the boat this winter. I'm also going to do a tab of some kind, manual or hydraulic. Unfortunately testing will have to wait until spring. On your other topic, YES I would like the boat to run faster! I have the M318 polyhead in her. Where are some areas I can get some HP out of that motor?

Thanks

Chris,
Don't know how/when you're dividing your time btwn IN and FL, but I'm planning to stop by and see jbear around Dec 26. I've spoken to Bill Burgess several times on the phone and would love to drain him of some additional knowledge while down. But I only drink coldies once in a while. Once in the morning and quite a while at night.

Gary, While that engine is a fantastic one, you're probably already aware that few of the parts interchange with the later LA engines.
Thus performance mods get in the pocketbook pretty deep. From time to time you see alum intakes on ebay. But the next upgrade would be a camshaft and those aren't available unless you get the existing one re-ground. After market or hi-po heads, not out there. I found a really neat guy and his company in VA (check out Mopar Mecca) which specializes in Polys and other Mopars, but it comes with a price that was up there. He has Poly stroker kits that can take it to 360-380 CI and 300-400 HP. If you were planning to do a rebuild, you could make certain changes like the cam regrind, higher compression pistons, a little head work, an intake, and you wouldn't be talking all that much more than the standard rebuild and get probably to the 275 HP range, but as for simple bolt-ons, you're quite limited. I'm big on the engine because I like originality and it's a neat looking engine with those valve covers and all. (See these below currently from Ebay)I'm game to help you in any way I can.    

Boy now that cav plate is old school.Sure eliminates rudder cavitation I bet.Somebody spent a good deal of time fabbing that.I saw a guy once took a Ranger I/O ba$$boat back to the factory because of hull porpoising.When I next saw the boat I looked under it and I swear it had a wood shingle gla$$ed under each side at the transom line.And the guy loved it.
Course he had trim too.

Munday

Pretty simple to stop, just need to put the bow down. As has been mentioned, add on tabs, either fixed or adjustable will do the trick, although not the norm. Typically tournament ski boats are fine tuned by adding or decreasing the hook on the bottom. If the boat runs level now, an equal amount of hook on both sides will keep it level while putting the nose down a little. What you really want to find out is how much to add before you actually do the gla$$ work. A really easy quick way to find out how much you need is to add a small bead of silicone sealer on the bottom at the very rear edge on each side. After the silicone drys, run the boat and decide if you need more, less, or if you have it right. (Still porpoising try more, no porpoising, try less until you find just the right amount.) Believe it or not, the bead of silicone will exactly duplicate what an equal amount of hook added with gla$$ will do and is really easy to experiment with until you find the right amount. Once you have it right, measure how much hook you need and add the same amount of gla$$.
Dave