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bgwilliams
04-15-2003, 01:43 PM
My donzi is running a 5.7L, EFI, 260hp Mercurser. How can I improve the top speed? Do props add significant MPH? Would a thru-hull exhaust add noticable HP and increse speed? Would performance plugs, wires, etc. help? Please fill me in if these work or let me know if I should stay put with the current set up? Thanks in advance for you input.

Thanks!

Ranman
04-15-2003, 01:59 PM
I like to throw cash at the problem. :D

You didn't say which boat you are running, but it shouldn't make too much difference.

If your engine is already operating in the recommended power band (and preferably at the higher end of that band), a prop alone will most likely not net too much oa a speed gain. This is assuming you are already running a stainless steel performance propeller. If you're on aluminum, the jump to stainless has it's benefits. The key is to figure out if your propped right, if so, you don't stand to gain much. If you're way off, a significant improvement may be possible. Props don't make you go faster, they just optimize what you already have.

Thru hulls are a good upgrade over the restrictive thru-prop set-up. A true performance exhaust is optimal, but expensive and most likely not where you want to start.

The tune up comopnents, (wires, plugs, etc.) again don't really create speed, they just help ensure the package is running correctly. you should have them, but don't expect much other than a great running engine.

If you are really looking to pick up some speed, I would think you will want to look into adding some serious HP. I would think heads, cam, intake and thru hulls would be a good start. Other engine gurus here will be able to be more specific. I would think that for 1K - 2K you would be able to get in the 300HP range and with a new prop to match the HP, you should see a significant MPH gain.

Fish boy
04-15-2003, 07:35 PM
bgwilliams,
don't have much to add to what Ranman said, but wanted to welcome you to the donzi site. I am sure you will find a wealth of information here.

You might want to try the search feature under "HP", your engine, your boat model, props,... you will be amazed at the info you will find.

Good luck and welcome.

Fish

boldts
04-15-2003, 10:42 PM
BG, Let me just add that I don't necessarily agree with the statement that a prop won't gain speed. I don't know which Donzi you have, but I own a 22 Classic. Bone stock 454MAG, Bravo1 package. When I purchased the boat last Spring, it came with a 23" Mirage prop. It was turning 4600 RPM's which is on the low end of the engine's RPM range. Boat also didn't handle very well with this prop. It had a porposing problem until you ran her wide open.

For under $300 and at the advise of a good friend, I bought a Turbo Prop (http://www.turbo-props.com) for my Donzi. The top end went from 65.7 to 68.7 MPH GPS, still turning 4600 RPM's but running only 22" of pitch. This is a bone stock prop. No labbing or other expense other than the purchase price.

Not sure how the prop would work on your application, but it was the best money spent for mine. You'd have a hard time doing any engine work for under $300. I spent more than this to have a nosecone added to the Bravo1 this year. This was done more for handling than speed, but who knows, maybe a little speed will also come with it to get closer to that magical 70 MPH mark for a 22 Classic. Good Luck and your in the right place for any Donzi performance information or help.

Rootsy
04-15-2003, 11:20 PM
YEP! pretty much what Ranman said! :D

and yes it is true that by playing with different props you can tailor to your setup and achieve possibly a bit more speed and or better handling.. unless of course you already have the best for your setup.. then well... best be thinkin about adding power... or getting the prop closer to the surface... or soemthing like that...

Formula Jr
04-16-2003, 03:19 AM
Sand the wot, wetted surface with 170 or so grit paper and don't wax the hull. This is good for two or three MPH. A Stainless prop if you get the right kind, will give you another three to four MPH. Thru hull exhaust is a major gain. An easy five Mph but you may need to re-jet or reprogram the fuel system. Shaving you head is good for another 1/2 mph gain. :D
Running light is also a factor.

I run a

bgwilliams
04-16-2003, 08:35 AM
Thanks for all of the input, I really appreciate it. I actually know my way around boats pretty well and was just looking for some confirmation and experiences of some other boaters before I statred putting time and money into the project. Let's put it this way, I know enough that shaving my head, the hull, and anything else won't help. Hey Formula Jr., can I sand your hull down first to see if it really works? By the way, I have a 22' Z22 Cuddy. It gets gets up to about 50+ mph now but I would like more. Iam trying to convince the wife that a classic is better despite less space. We will see how that goes!

Thanks for all the input.

Brian