Hello, just curious if anyone on the forum is running a 28' non step hull with single 502 and what top mph you are getting. I have a 98 donzi zx 28 with 502, I just bought the boat and the owner told me gps was about 65 with 4 people. I took it out this weekend and I'm only getting 55 on gps. Boat has k planes im not sure if these have a factor on this style boat I had the drive trimmed up and the tabs all the way up at wot. Any advice would be great! Thanks

The 28ZX should have a step.

Not the fastest of boats with a single 502MPI. Pretty heavy, crushes waves well. Fantastic engine compartment to work on things. I believe a 23"MiragePlus was standard prop ? Rode in one a million times but never with a GPS. Probably not much faster than low 60's...if that.

At your 55 top speed, what RPM were turning? What prop is on the boat?

Sorry the boat is the 27zx not 28, it has a bravo one prop 22p 4 blade and was running about 5,000 rpms

You were lied to.

Yeh, with a shoulder roll to boot.

Boating Magazine tested speed was 63.7 with a 502 and Mirage 23. They, too, were disappointed (seriously, they said so in the article).
I say tested because I'm guessing they weren't full of fuel with 4 bodies when they ran that number.

https://books.google.com/books?id=F3...eed&f=falseThe

P.S., I just realized the test is a stepped 27zx. Cue a more disappointing number for a straight bottom.

A couple of other problems with that boat test. Article says it has a 502 but the picture shows a 454. Article also states that the 525 EFI is rated at 500 hp. Maybe Boating magazine should stick with Chaparrals and Four Winns'.

Swap Bravo prop for Mirage, as already touched upon. 23 or you might be able to swing a 25 to an acceptable RPM and pick up a couple mile an hr. 65 is not going to happen, and never did for that matter, as already alluded to.

Too late now, but sea trail before you buy again, sadly...you can't trust some of these guys. And like the others said, try to get your hands on a Mirage 23, see how that works for you. Good luck!