Hey everyone,

I've got a 20' boat, hull dry and without engine is 900 lb, engine is a 550hp (Dyno) big block Chevy with aluminium heads...all in wet weight likely 2000 lbs with me.

SD309 with the performance intake (shoe and plate), AA impeller. Have trim.

Last year when I took the boat out, the ride plate was not installed. The boat ran very happy, but would start to be a bit unstable at very high speeds if I trimmed out. So, I added the ride plate to try and prevent that. Verified angle of 2.7 degrees, which is how it wants to be based on the machined mount.

Now it's not nearly as happy and has a tendency to porpoise at lower speeds, and has a much narrower window of "happy trim" at higher speeds. What gives? I used to be able to hit 60 with confidence, but above that got hairy. Now, 60 is hairy, and even 40 can start smacking the bow if I trim up.

Any help much appreciated!

Ok, will do. Do you think I should trim it up or down based on where it currently is? I'm inclined to think "up" since it did better without the plate. But, if I raise the rear of the ride plate...it won't be flat anymore. It will have a curve to it. Isn't that bad?

4-degrees up, relative to the keel, is a good safe starting point, for a V-hull.  Yes, the ride plate will have a slight bend near the shoe.  It should not have an "S" shaped bend (hook) near the ride plate.  If it does, your cradle might need to be machined.