300 HP OMC V8

[ROGER V]

I am looking to repower my 30' offshore v-hull. I currently have a pair of 25 " 3.0L 225HP EFI Mercs on the back. I know a great deal about what Mercury has to offer, very little about other manufacturers and nearly nothing about the 4.0L V8 300HP OMC motors. I am interested in the motor because of the large displacement. <br />A few questions:<br />What are the major problems with the motors?<br />What years were they manufactured?<br />What years are the best?<br />Is counter rotation available?<br />If so, does the crank spin opposite or is it in the LU?<br />With low water pick ups added can the LU withstand a surface piercing set up?<br />What LU's are available?<br />Are any fuel injected?<br />Are they oil injected?<br />Does anyone have torque and power curves they can share? (I'm looking for the curves for the Mercs also).<br />What do they weigh?<br />Are parts available?<br />What do the alternators put out?<br />How solid are the isolation mounts?<br />Are aftermarket upgrade parts available?<br />These engines were never very popular (my observation) why?<br />What are the fuel requirements?<br />What is the fuel consumption at WOT?<br />Is there different models (commercial, High performance)?<br />Thanks, Roger

 

[bouner]

Re: 300 HP OMC V8

Anything else that you want to know???

 

[Dhadley]

Re: 300 HP OMC V8

It sounds as if you want to race these. Thats fine but they are definately a breed of their own. If you set them up like a V6 you will not be pleased with the results. The motors were produced from 1985. In 1988 they went to the 4.0 liter version. They were sold in the US thru the mid 90's but were still sold overseas after that, <br /><br />Recreational motors -- The alternators are 35 amp, the first counter rotators did indeed run the powerhead backwards. These were Second Effort (OMC factory race center) units. After Second Effort closed the factory reversed the rotation in the gearcase. The mounts are very good as produced. Someone is bound to tell you to use solid mounts. They are OK in the lower but when used in the upper, you stand a good chance of breaking the port stern bracket. The gearcase is plenty long to start with. Additional length from a nose cone / low water pick up will add tremoundous side loads and will also add drag and slow you down. In an Offshore configuration witha nose cone you will break things you never dreamed of. Trust me. The pistons, rods, bearings, seal rings etc are the same a the V4 and V6 loopers. The cranks and blocks may be a bit hard to come by. They are carb'd. <br /><br />Race motors -- There was a Formula 1 version that had a different gearcase (obviously) and was fuel injected. Basically a totally different motor.<br /><br />Hope that helps. Good luck!

 

[rodbolt]

Re: 300 HP OMC V8

hello<br /> wow no mention of the fuel thriftyness of this motor .<br /> a dealer friend of mine has one with the exaust snout cutout. runs well idles all day but if you run much harder than 4000 it does like fuel.<br /> I think the big reason for lack of popularity is lack of hulls to put them on. as more and more offshore boats are designed for 30 inch motors and 600 plus horsepower I think the new merc,suszuki bomb and yammi 250'300 motors are going to sell better.<br /> good luck and keep posting

 

[mattttt25]

Re: 300 HP OMC V8

heard a lot of good things about the new 300hp z300 yamaha. good review in last month's boating magazine.