Donze Z 21
 

I have a 1988 Donzi Z with a 454 & 23 pitch mirage prop.
I barely get 55 mph out of it and it porpoises (even with trim tabs)
Does anyone have any experience with installing a bigger motor (496 or 502)? I am willing to do this for more MPH, but I am worried about the porpoising.

Re: Donze Z 21
 

I had the same boat with a big block, How long have you had it? It takes some time to find the right tab and drive set up but it would ride nice for me. The best I saw was about 60 mph with a 454/330 with a cam and other small changes.

Re: Donze Z 21
 

I have a'97 18 Classic...the dolphin like porposing is just the way donzi's ride unless your going fast. Good luck with it.

Re: Donze Z 21
 

This is my 4th summer with the boat, I find to make it ride level I have to trim it so the bow is too low and it plows.
To get any speed out of it, I have to raise the tabs, trim out the drive and I get the porposing + low 50's in speed.

What prop were you running?

Re: Donze Z 21
 

I have had them too & many other Donzi's, both my own & clients & ones for sale.. The classics do porpose usually between 30 & 45 mph if you dont have them trimed, propped & tabbed right. They are sensitive & respond quickly. If you prop, trim & tab them properly they should ride & handle like a Ferrari... A lot of seat time is sometimes required to get to this point, but when you do WOW look out!! You'll be flyin' in almost anything... :) Jamie / Lakeside