spilman

joejohn, I used Throttle Up; they let you try the props and if they are not damaged, you just pay to ship em & try another set. They are test props and perform as such; not perfect edges. But you can get near your optimum rpm's & speed and then have them lab a new set and make the purchase. OR, I sent them a set of Hydromotive 4 blade 26"p and labbed and reduced diameter; tested and made notes, sent then back for free "fine-tuning". Julie and Matt were knowledgable, helpful and always answered the phone; rare these days. They did the work promptly and their Labbing is very precise, the props looked fantastic and performed as they said; hit the numbers. Of course I want more speed, but w/twin 350mag/MPI's running stock with 400 hrs, (except for Stainless Marine Exhaust) I can't complain. The only issue, & it's not huge, is they are a bit pricey. But you really do get what you pay for; & they will tune them up for free if your not happy. Good luck; I had a 22ZX 454magB1, it was a rocket.
BTW, my 28 AT with the same motors goes 71 best conditions so the 28 Donzi is a tad bit faster

spilman

jj, also if you add sc's the rule of thumb is every 20hp yields 1mph(in the 70-90mph range); each inch of pitch will give/take 200 rpm's. Whipple is not making the sc for the 350mag/MPI anymore, plus it was 2k more than the Procharger.....I am still considering the Prochargers.

philtj

[QUOTE=LKSD;2274212]28 is a great boat. Sc's would be the hot ticket in there. We have done our fair share of them. I am also doing a whipple in my new Donzi.. They are wave crushers. If you get one & want to upgrade it whether you want Sc's or just more power without em give me a shout.. However exhast alone wont make much difference. You will need to do a lot more to get the speed without using an sc.. Jamie / Lakeside

.[/QUO

philtj

I have a 1999 zx 28 with twin 350 mags. I can only get the boat to run 61-62mph. I bought the boat out of long Island and the previous owner had it bottom painted. I had the bottom removed from the sides and transome. I plan on having the rest removed this winter. I have spoke to a few other people who say the bottom paint should take off 2-3mph not 8-9. The boat has 22 pitch mercury four blade props and @ 61.5mph gps the engines are turning 4850-4900rpms. I love the boat but would like to run 70 mph. Any ideas?

LAKESIDE RESTORATIONS

Stupid question, but did you try trimming the drives & raising the tabs? Or did you have a big crew on board or possibly some other hinderance??

69-72 is about where most of them run with twin 350 mags if I remember correctly.. Some once in a while do run a bit slower, however I would think you should be seeing at least about 65..

One other thought is that your speedo if not a gps may be off or partially blocked.. Did you use a hand held gps for the spped or was the indash unit updated already to gps, I believe the older zx's didnt come standard with the gps speedo.. Jamie

philtj

Yes i trimmed the drives until they blow out and then stabed them back down with the trim tabs all the way up. Most of the time i have 3-4 people on the boat but that does not seem to matter becuase i did a couple of wot runs with just myself and full fuel and the mph were almost the same. I am using a hand held gps the speedo actully reads a little faster than the gps is saying.
I had my props reworked over the winter and the shop said they were way off. I havent driven the boat since then but i think the four blade verse three blade may be slowing it down but the guy at the prop shop disagreed with me saying the four blades should run just as fast or maybe 1 mph slower.

Shanghied Again

You other problem is you are running the wrong props, even though the 28ZX is a step bottom boat see if you know someone that has 23 pitch mirage 3 blade props. all the 28ZXs I have sold did not run 4 blade Bravos, 4 blade is great for wholeshot and mid range put are not great for top end. you should be at 5000-5200 with mags. the 1999 was a 70mph boat.

LAKESIDE RESTORATIONS

Good point Frank.. You beat me to it on the prop blade count..

philtj, Most zx's with twins run 3 blade props & singles usually were 4 blades as a rule..

For what it's worth you may also want to try picking up a set of props from Julie @ throttle up.. She can also tune a set to your hull.. Jamie

philtj

Thanks for the read back guys. I pick up a set of 23 pitch mirage plus which accourding to the information i have should be the ones it left the factory with. I should have the boat on the lake next weekend. I will let you know how it goes.

32storm

I had the opportunity to run a 28 with twin stock MPI 350's. Low 70's at best. I wasn't impressed with the ride. Engine compartment had descent room, but the cockpit was cramped with bolsters. Cabin was pretty bare bones, and seemed like a lot of dead space between instrument panel & passenger dash and where cabin actually began.