How is an OMC Cobra marine 2.3 rated at 128HP?

Daniel Black · Feb 17, 2019

I found some old paperwork from my Grandpa's 1988 Bayliner Capri that lists HP as 128. Why are my '86,'87 Ranger 2.3s rated at 90HP? From my understanding the block, head and internals are all the same, just different gasket materials. I know the OMC uses a Rochester 2bbl and a point distributer and probably has a special marine cam but I still can't figure a 30HP difference. Are HP ratings different for marine engines? Is the Ranger rating with all optional accessories on the motor (A/C, Power Steering)? A 28HP gain would be a noticeable difference in a Ranger. What's the deal?

Dirtman · Feb 17, 2019

Marine engines have no emissions equipment or power robbing accessories. they are also almost always tuned different since they run at high rpms and have little need for low rpm torque. That and there is really no telling how they came to those hp numbers. The truck may be at the wheels, the boat at the crank or any number of random scenarios.

Denisefwd93 · Feb 17, 2019

Dirtman said:
Marine engines have no emissions equipment or power robbing accessories. they are also almost always tuned different since they run at high rpms and have little need for low rpm torque. That and there is really no telling how they came to those hp numbers. The truck may be at the wheels, the boat at the crank or any number of random scenarios.

Also you don't have the losses of wheels drive shaft dragging brakes transmissions, EGR, power steering,

Daniel Black · Feb 17, 2019

My understanding is that car/truck ratings are at the flywheel, not on a chassis dyno. My Ford manual shows '86 Ranger 2.3 90HP. It doesn't say 4x2-4x4, auto/manual, with or w/o a/c or power steering. Thats what led me to believe they're rated at the flywheel without front accessories. Trucks have emissions stuff that a boat doesn't but it can't equal that kind of power.

Dirtman · Feb 17, 2019

There's no standardized test procedure for hp figures. Especially 30 years ago. Hell on an engine like that it wouldn't be unreasonable for the HP numbers to be completely mathematically calculated during the engineering phase and never tested on a dyno.

But still if you put both engines bare on a dyno I'll almost guarantee the truck engine will have a lower rpm torque curve but make less overall hp and the marine engine make no torque but more overall hp at a much higher rpm. Thats just in the way the engines are setup.

That doesn't mean the marine engine is better, in fact if you tried to run it in your truck it probably wouldnt even move without massive gears.

tomw · Feb 18, 2019

When rating hp for retail sale, the makers are restricted to what they can do, the 'dressing' of the engine with accessories, coolant pump, fan, exhaust, etc. Previously, they rated hp with a bare engine and headers... nothing like what was in the showroom. The government got into the picture with the FTC making noises, so they became a lot more conservative in their ratings.
It may be that the boating industry had not been under the FTC spotlight then, so they could make up whatever numbers they liked, based in a reality that may not exist.
tom

bobbywalter · Feb 18, 2019

the cam and lifter scenario in the boat is not the same which you know...

but cr was different iirc with piston and cc on head. the way you can curve the distributor and valve events along with the exhaust flow is totally different...boat gas was typically 89-91 octane and free of ethanol.

combined with the right cam... 128 may be low. or pretty close.

kimcrwbr1 · Feb 18, 2019

A boat engine is under a constant load you have go and stop. There is no vacume advance. In general the tolerances are alot tighter and the advance curve is retarded to keep from detonation. Its like pulling a trailer up a mountain pass full time. There are more variables that affect performance hull design, weight is the hull clean and trimmed properly, engine health. Then you use WOT rpm to determine the prop pitch. My volvo penta 2.3 is also rated at 120hp with a 1 barrel carb and points ignition.

shadetreebronco · Feb 20, 2019

I know outboard engines are horsepower rated at the prop instead of the flywheel starting in the mid 80's.

Daniel Black · Feb 22, 2019

All interesting. I was just wondering if any OMC parts would translate to more power for a 2.3 Ranger.

Dirtman · Feb 22, 2019

It would probably translate to a truck that would run like crap until about 3,000 rpms.

ExploreNW · Mar 16, 2019

Dirtman said:
Marine engines have no emissions equipment or power robbing accessories. they are also almost always tuned different since they run at high rpms and have little need for low rpm torque.

You're right about no EGR but they have the same power robbing accessories that a car would have. Boats have water pumps, alternators, power steering, and many cabin cruisers have A/C as well. The Mercruiser 260 (Chevy 350) in my Sea Ray has 2 water pumps, one for the salt water heat exchanger and one for glycol coolant. It has a fwd-rev gear box. It has a regular RV torque cam, same specs you'd find in a Winnebago. Boat engines make more power because they have a smaller rocker arm ratio and much higher valve lift, reducing vacuum/increasing CFM. More air + more fuel = more power, there's no secret... Marine and automotive heads/blocks/crank/rods are exactly the same, but boats often have slightly lower compression or dished pistons so the bottom end will stay together longer at high output. If you want marine level power out of your 2.3 but you want to keep the low-down grunt, change your rocker arms, use the marine intake & carb and you'll get there :derisive:

AFAIK a stock Ranger motor only has 0.238" lobes and a 1.64 ratio, giving 0.39" lift. There are plenty of CFM to be found at 0.500" or even 0.450" lift. Grind out some '98 rocker arms at the 1.86 ratio and your valve lift goes up to 0.443, there's your power!

How is an OMC Cobra marine 2.3 rated at 128HP?

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