Looking for some help with porpousing

[Slowboy]

I put a new 400 sbc with a 6-71 blower into the boat late last year. With no tuning, and only 4 pounds of boost the boat ran 80-81 reguarly on my indash gps speedo.
The boat is a 1980 18 foot Mako, the bottom in the center is flat (delta pad boat). This hull was designed for low horsepower applications and probably designed to go 50-60. I understand that.
I did some work to it this spring and now it porpouses unless you have the diverter set so there is no rooster tail, set level.
I replaced the stringers in the boat, actually had the top half of the boat off the lower half, built some bulkheads in the front, basically stiffened everything up and tried to make it strong.
I set the pump back so the leading edge of the intake is about 1/2 inch in front of the transom. Pump is set back pretty far. I think it was about 4 inches farther back than last fall. I set the engine back about three inches farther than it was before. Main reason I set the pump back was for loading water, and easier impeller changing. Engine set back for clearance from back seat to blower belt.
I put an agressive shoe on it from american turbine (the old shoe was only allowing 12 psi of intake pressure at full speed, obviously cavitating) The pump has a ride plate (set all the way up, this seems to work the best), a 6 degree wedge aiming up, and a droop snoot.
This did not porpous this bad last fall, I would think that the pump set back would have helped out, it sure did help load the pump. Did setting the engine back push back enough weight to help promote porposing?
Any ideas would be helpful.
I have an intercooler sitting here, as well as some blower pulleys for more boost. I also have an aa impeller. I plan on putting methanol injection on this if needed. Three digits are the goal. I think the boat has 85-87 in it right now.
Thanks, Ryan

[Cas]

By moving the engine back, it changed the center of gravity of the boat so yes, it has a lot to do with the porpoising issue.
To start, I'd be trying different set-ups with the wedging and ride plate. Try it without a wedge, 4º up, 2º down, etc. As far as the ride plate, the most common starting point seems to be about 2º up in relation to the bottom of the boat.
At this point, a lot of what you have is forcing the transom into the water, forcing it down and the bow up. With the weight of the bow, it's wanting to come down.
You have a pump that set at 4º down, add the droop which probably has 8º up and now you have a net 4º up. Add the 6º up wedge and you now have a total of 10º up. That's good for a big rooster but probably not helping the boat much.
On my boat, it likes the ride plate set at 2º up with a 2º down wedge, 0 porpoising but my pump isn't set back as far as yours.
does it porpoise as bad with a passenger?

[Slowboy]

We are going to take it out this afternoon. I will have a passanger with me today which should even out the boat, and have eyes on the speedo. With the diverter all the way up, the rooster tail is only about 10-12 feet high.
I tried turning down the ride plate last time I was out. I moved it down about 3/8 of an inch. It porpoused so bad that the bow would dig into the water and it would almost throw you out of the boat. I was thinking about removing the ride plate to see if it gets better.
At least I can trim it out, last year it would porpous slightly, but no amout of diverter trim would make it go away. I was always under the impression that max performance is with a roost about 3-4 feet high. I will have an update later this afternoon.

[bp]

so how did it run?
most droops are between 7 and 9 degrees of up angle; the difference in angle between the flange and the steering pin centerline. by adding 6 degrees "up", you're between 13-15 degrees up (the pump intake is normally set to give you 4 degrees down, so total angle compared to keel might be somewhere between 9-11 before you ever get to the diverter. by dropping the diverter all the way down, you're nozzle angle compared to keel is quite a bit less than 10 degrees (don't know exactly, you'd have to check that with an angle finder).
but, since you say the boat doesn't porpoise with the diverter all the way down, i'd look closely at the nozzle angle with the diverter in that position (with the 6 degree still installed), then adjust with wedges until that angle measurement is close to the same, with the diverter a few degrees below the mid point in it's travel. that way, the diverter can actually be used to trim the boat. don't worry about the height of your rooster - it will be wherever it is.

[moneysucker]

One thing too is when trying to eliminate problems, you have to work in small increments. Going from all the way up on the ride plate to all the way down will cause other issues to arrise. Like BP said, You need to see where the settings are when the boat is handling well and then make changes from there in small increments. You need to get an angle finder on both the intake, keel, nozzle, and ride plate so there acn be some deductive reasoning here on our end.
Who did the set back and how was the angle set on the intake?
Good luck.

[Slowboy]

I put my baffels back in before we went out. Usually lose at least a couple of miles per hour with them in. Went out to the lake with a friend in the passenger seat. Boat pourposes around 30-40 miles per hour, but once opened up is smoothes right out. Full speed there was no pourposing at all, ran straight and smooth. Seems to ride alot flatter (bow down more) than it did last year. Also ran alot slower than last year, could be the baffels. Only had 76 out of it.
I set the pump back, and Im sure it is not done correctly. I am sure there is not 14 degrees of up angle (6 wedge, 8 droop). The boat does not throw much of a rooster tail, with the diverter all the way up probably about 10 feet. I will put an angle finder on everything later today.
I tried adjusting the ride plate down, about 1/4-3/8 of an inch for starters, mainly to see if there was a big difference, and there was. It hopped around so bad the bow would hit the water and it would almost throw you out. Seems to be the best the higher I go with it.
I did notice that when hitting the throttle from idle, that I had to pedal the throttle, or the engine would hit the rev limiter. I took the bowl off, and removed the impeller, major wear ring problems. Got to fix that first. There is quite a list of things to do on this boat.
Thanks for the help.
Ryan

[bp]

you -should- take angle measurements of all this stuff, plate included. a digital protractor provides a greater accuracy than an angle finder, but an angle finder can be used too.
locate a flat surface on the keel, next to the shoe, to be used as the base reference point. all subsequent angles (plate, shoe, droop, bowl, nozzle, whaterver) should be based on using the reference point as "0". you really can't be -sure- of anything until you accurately measure it.

[Pops@Aggressor]

Thanks, RyanYour problem is the motor location. set it back to original by Drive shaft and you should be OK. If big HP. Talk to the GURUs.
28 to 30 forward. Then when you can add a bottom -do away with that Delta Pad-Thats the Manufacture's Cheap & Quick way to set a pump. No good for Jets. Add a keel when you do and you will see some numbers. dave

[Slowboy]

One thing we did figure out (with some help) was that my ride plate did not have stiffeners (braces) on it. It is just made of 1/4 aluminum like most of them are, and flexes pretty easily by hand. I am sure this is creating a hook. I am going to move the engine forward some, and do some modifaciations to the rear seat to get the engine as far forward with keeping the back seat. This is a lake boat, gotta have room for friends and coolers.
I plan to paint the boat next winter, and will spend some time on the bottom to help performance.
Thanks, Ryan

[Jet Hydro]

This boat is one that I did a while back and it has a Delta Pad bottom. It`s a 18` Baja with a SBC.
http://www.hotboatpics.com/pics/data/500/15497P1030528.JPG
Fix your ride plate and move the motor forward a little and your problems will be gone. Now on another note, Take care at those speeds with a Delta bottom as you may get wet ;)

[bp]

steve, why bolt the cradle to the outside droop flange?? i had thought about that, but too hard to test with different wedges.
here's what i did with the tanker...
http://i215.photobucket.com/albums/cc266/havabp/Pump003.jpg
here's what it looks like all together. i want to try it with 6 degrees down wedge, then i might go back to 4...
http://i215.photobucket.com/albums/cc266/havabp/PumpMay2008002.jpg

[Jet Hydro]

That set-up was just on there for testing till the new Aggressor bowl got here.
Then we went with the Aggressor cradle under the bowl.
We wanted to see what the difference was between the bowls ;)
The owner kept the Aggressor bowl on the boat when we were done testing :D