View Full Version : popular engine choice for 18 Donzi

12-26-2014, 12:07 PM
Any thoughts?

12-26-2014, 12:19 PM

Are you really asking what IS popular or rather, what people would recommend?


12-27-2014, 10:16 AM

12-27-2014, 10:24 AM
I saw this at about $2,300 with shipping included. it is a car engine, still needs boat parts.


12-27-2014, 10:45 AM
$2500 on FB powerboat swap shop

12-27-2014, 11:41 AM
What Jim said on a budget. 350 or 383 with a Bravo and Stainless Marine exhaust if splurging.

12-28-2014, 04:46 PM

12-29-2014, 08:09 AM
Again, Thanks.

12-29-2014, 01:28 PM
IMHO, what ever you can stuff under the hood. :yes:


12-30-2014, 09:03 AM
So, what about the weight difference between a small and big block in a fairly short boat?

12-30-2014, 10:30 PM
It's about 200lbs but once you take off weight like with an aluminum intake and exhaust there really isn't much. Also I would rather have a tame big block then a wild small block but that's just me.

12-30-2014, 10:41 PM
One can, however, take comparable weight out of a smallblock just like with a big block. Osur866 can tell you all about chipping weight off a smallblock setup...

12-31-2014, 08:18 AM
If the weight of a block block does not make the boat drag its ass while getting on plane and make wave jumping no fun, then I am OK with it.

12-31-2014, 01:39 PM
If the weight of a block block does not make the boat drag its ass while getting on plane and make wave jumping no fun, then I am OK with it.

More torque makes for going up and coming out of a wave more fun. It also breaks more stuff to but I wont mention that. lol :biggrin.:

12-31-2014, 01:59 PM
Actually, I bet the new 6.0 430 HP VVT Volvo with a duo-prop would rock in an 18. 300 lb lighter than a BBC. Shame about the emissions-control crap.

joseph m. hahnl
01-02-2015, 10:45 AM
I wouldn't go with that 260 HP. You have read between the lines. First off That's a 190 HP 2 piece rear main seal block not intended for marine use. it has the potential for 260 HP with induction. Mercruiser pre Vortecs are fitted with a 300 HP service head. the Vortecs are slightly more because they have better flow. I'll bet that 260 is a flat tappet cam too. Small valve spring and no compression :8.5:1" meaning the heads are 72CC combustion chambers. They won't work with a long duration Camshaft. These are the things you need to know. So know that you know that motor is inadequate for an 18 here's what I recommend. Seeing as how you had to assemble that any ways. Find a 350, 383 roller short block or best of all 400. go. up to 10.8:1 on Static CR use a Comp cam XM270HR to bring the Dynamic CR down to run on pump gas. Use a set of good flow aluminum heads to keep detonation down . If you run Iron heads you'll need to bring the Static Compression down some. The other thing you need to watch out for is the rear main seal. that will determine whether the fly wheel you have will fit. I'm building a 350 Reverse Rotation for my cruiser. I'm using the 350 Mag I took out of the Minx. Because it's RHR I get to choose from one flat tappet cam shaft if I don't have a custom core manufactured. What I have found is low compression is the biggest hinder to making a performance application. For instance the Mag is 9.1:1 Static CR the stock Mag Cam brought the Dynamic CR down to 8.0 .the cam has virtually no duration so I have to be very conservative on duration and valve timing when designing the new custom cam. To run on an Octane rating of 89 to 91 the DCR should be 7.5 to 8.5. You get a bonus .5 for aluminum heads. Aluminum isn't for weight it's to shed heat to prevent detonation in high compression engines.

01-04-2015, 04:41 PM
I like the idea of a high rpm redline on the new Volvo. I can use a smaller prop and get a great hole shot. I ran 25", 23" and 27" on a difereent boat and engine cobo and the hole shot with the 23" was noticeably better, but allowed the engine to exceed its recommended rpm.

01-04-2015, 04:49 PM
Volvo specs a 6,000 rpm red line while Mercury Marine engine wants me to prop to a maximum of 5,200 rpm. That could be two prop sizes bigger to stay in warranty to keep the engine down to 5,200 rpm.

01-04-2015, 08:12 PM
The boat would be a rocket out of the hole with such a smaller prop sizing.

01-04-2015, 08:25 PM
If I understand the VVT claims and they are correct, I suspect there'd be torque improvements on the bottom and top ends, both. Adding further the the holeshot performance. Plus, duoprops grab like crazy.

01-20-2015, 07:48 AM
I agree.

Holy Smokes
01-27-2015, 07:41 PM
Merc 383Mag Stroker. Strong 350HP pushes my Cig 20 just fine.