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View Full Version : Biggest engine in an 18 and 22ft?



wato
03-13-2011, 09:10 AM
Hey all! Going to be buying a used Donzi this summer and am looking at 18s and 22s. I plan on selling the engine and out drive and installing a crate engine with some serious HP and a Bravo 1 X or xr depending on the size of boat and engine I purchase.

My questions to the Donzi forum are:

What is the biggest power plant you've heard of being installed with out hatch reconstruction on 18 and 22c?

What drives would you suggest respectively?

Prop options respectively?

Just Say N20
03-13-2011, 09:34 AM
18 is easy.

GEOO had over 1,000 hp in his X18 with a stock engine hatch.

http://www.donzi.net/forums/showthread.php?t=44278&highlight=Mouse

wato
03-13-2011, 10:10 AM
Thanks so much! Keep em coming!

Carl C
03-13-2011, 10:12 AM
22 is easy too. Mr. X!

gcarter
03-13-2011, 02:51 PM
I would suggest that if the boat you buy was built before about '95, plan on beefing up the stringers and inside bottom before installing any serious power.
Before that time, thses boats only saw 350-450 HP and were designed and built accordingly.
It's important to take a unified approach to these boats.
Good luck w/your quest

roadtrip se
03-13-2011, 03:48 PM
I would suggest that if the boat you buy was built before about '95, plan on beefing up the stringers and inside bottom before installing any serious power.
Before that time, thses boats only saw 350-450 HP and were designed and built accordingly.
It's important to take a unified approach to these boats.
Good luck w/your quest

I would add that this rule of thumb applies to all of these boats.

I ran 470HP in my 2001 22 Classic for about nine years on stock motor mounts. When we took it apart last year, the torque of the engine was showing on the port side stringer, both inside and out. I was constantly checking and tightening motor mounts as part of my pre-flight and I found out why, flex in the hull.

I added several layers of weave, coring, and more weave to strengthen the bilge, a custom engine cradle, and a heavy duty transom assembly to the mix. My boat had steering, but this is a must not only for safety, but to take some of the stress off of the gimbal housing and transom.

This is a lot of what Mr. X did to his Ilmor boat, because I followed some of his recipe. He took it one step further and did the coring all the way up the sides of the boat, extended the coring all the way to the nose, and glassed the connecting points to the deck. The Ilmor boat took over a year of rigging and testing by some very knowledagable people to finally get where it is today.

Donzi also added a layer of glass and coring, heavier stringers, and heavier engine mounts when they produced the few SE 500EFi factory boats that they did. The one 525EFi boat that I have seen had a layer of kevelar weave added to the options list at the request of the client's rigger.

My point, there is a lot more involved in getting these small boats ready for big power than just yanking the stock power and going with something monsterous. Then, there is the set-up and learning to drive the things. All fun stuff, but it takes time, patience, and experience
to do it right and do it safely.

Pismo
03-13-2011, 04:09 PM
Saw a Merc 600SC in a 22 once. Think it did 93mph, not sure.

gcarter
03-13-2011, 05:32 PM
Roadtrip is right.
My boat is an '88 and a former owner had installed about 500 hp W/O modifying the hull in any way.
Here's the results;
You can see the pounding the bottom took. At the point where the inner strakes end is the location of the engine mounts and delamination is visible there.

http://www.donzi.net/forums/attachment.php?attachmentid=42380&d=1232574044

Then, after grinding open the affected area of the mounts, you can see the glass had delaminated in a fairly large area.

http://www.donzi.net/forums/attachment.php?attachmentid=42489&d=1232747221

Understand my goal isn't to bolt in 800 HP, or go 100 MPH, and I didn't go as far as others have on their reinforcements. Instead, my hull is somewhere inbetween some of the more powerful factory boats and what some others have done. At the same time, because of the groundwork I have laid, it would be fairly easy to go a step or two further.

MDonziM
03-13-2011, 05:58 PM
I love the 540 I put in my 22 2yrs ago. I can't really imagine wanting any more hp (625) and I also echo what RT said. I spent about 4-5k in my bilge on new stringers, gussets, bulkhead and lots of glass. These boats were not laid up for the physics involved with big hp and speed and safety. As to keeping the factory eng hatch, I have a 3" flame arrestor and a spare 1/4" or so of clearance.

mrfixxall
03-13-2011, 06:02 PM
Saw a Merc 600SC in a 22 once. Think it did 93mph, not sure.


Mr X boat,,,,,went over 100 mph i think :)

wato
03-13-2011, 08:16 PM
Some great info here! Good thing my good buddy who agreed to my project is a marine mechanic! I am somewhat handy but require the over the shoulder once over due to in experience.

Makes sense that that reinforcements to the hull and transom are necessary. Would anyone have pictures of their projects? I have some experience with stringer reinforcement but not with transom work. Would love to see some picture if they are out there!

SO at the end of the day I'm entertaining thoughts of a 22 classic red....as much chrome as possible, a bravo one xr, with a Chev marine crate engine in the neighborhood of 600 HP with a reinforced transom and stringers.

More thoughts? or suggestions?

gcarter
03-13-2011, 09:20 PM
Here's my current project;

http://www.donzi.net/forums/showthread.php?t=50476

As I mentioned, this is a pre '93 boat, which is before AMH bought out Donzi and changed the hull structure.

If you buy a later boat, it would be more like Marshall's or Roadtrip's boat and either would be good guides...........
If they'll post their pictures!:)