We saw this motor at the LA Boat Show and it does appear to have narrowband O2 sensors in it. That being the case, there is probably a relatively small area of the fuel curve that is monitored and controlled via closed-loop operation.
Narowband sensors are only accurate at/near stoich, unless their accurate "spot" has been moved. Stoich is ~14.7:1 A/F for most gasoline today. From air/fuel curves of other Mercury engines, I can't imagine Merc is running this engine in that range for very much of it's range. All one would have to do is to characterize the area where the sensors are in operation, then don't tune in those areas (most likely idle and around idle). The rest would be open to modification via units like our CMD Marine.
So who is going to be the first to install a wideband on a 8.2 to characterize the a/f curve?
From all the motors we've tested, the black Merc Marine motors have all been within 2% of there propshaft HP rating at the flywheel. If you use the SAE standard, they are almost below the power during sweep pools but very close to there rating. During steady state, power levels increase in most of these motors because the clearances decrease and the motor reaches higher efficiency, but its not the 30hp they say the outdrive takes. the 8.2 is rated 5hp more than the 496 mag HO, and 15 more the 502 Magnum MPI, not 30-40 more....
I see your point. And from my earlier post, i must have calculated with my head under my arm. I did not notice that untill now.
I just lifted these specs for the 8,2HO from Mercury Marines website. As you can see, they say the hp is measured at the prop.
HP/Kw @ Prop 430/321
Max RPM (WOT) 4600 - 5000
Displacement 502 CID (8.2L)
Engine Type V8
Bore & Stroke 4.47 x 4.00 in / 113.5 x 101.6 mm
Compression Ratio 8.75:1
Fuel Requirement 87 Octane (R+M)/2
Engine Control System PCM 555 with SmartCraft CAN Capability
Fuel Delivery System Gen III Cool Fuel
Fuel Injection System Sequential Multi-Point Electronic Fuel Injection
Induction System High-inertia induction system
Ignition System Distributorless Ignition w/Knock Control and Platinum Spark Plugs
Charging System 65 Amp/917 Watt Alternator
Water Drain System Single Point Air-Actuated
Exhaust System Tuned Runner Exhaust Manifolds with 316 Stainless Steel Tubular Dry Joint Elbows
Cooling System Closed Cooling, Long Life 5-Year Anti-Freeze, Brass Sea Water Pump
Accessory Drive System Serpentine Belt, Stainless Steel Spring Automatic Tensioner
Recommended Engine Oil Mercury MerCruiser Full-Synthetic Engine Oil, 20W-40, NMMC FC-W rated
Engine Guardian System Low Oil Pressure, High Coolant Temperature, High Exhaust Manifold, Temperature, Low Drive Lube, Low Sea Water Pressure, Low Voltage, Over-rev control, Knock Control
Bravo One X Ratios 1.36, 1.50, 1.65 (high altitude)
Bravo Two X Ratios 1.81, 2.00, 2.20 (high altitude)
Bravo Three X Ratios 1.81, 2.00, 2.20, 2.43 (high altitude)
Bravo One XR Ratios 1.26, 1.35, 1.50
Bravo Three XR Ratios 1.65, 2.00
Weight lbs/kg (engine only) 1080/490
Digital Throttle & Shift Optional
Warranty 2-year limited (non-SeaCore models)*
4-year limted (SeaCore models)*
*Warranty applies to Installation Quality certified boat builders
Corrosion Warranty 3-year limited (non-SeaCore models)
4-year limited (SeaCore models)
This is why I suspected that the 425 was prop too. In the manuals and old brochures I have, they also state 415 prop hp. for the 502MPI. I don't doubt yours, or Raylars measurement for a second, that is why I am getting confused. Why would merc post it as prop hp if it is crank hp. When you get to dyno a 8,2HO I would be very interested to hear what the results are. The only engine I know of, where Mercury is clearly stating crank hp. is the 1200SCI. My personal belif at this point, is that everything is crank hp, both black and blue motors.
Sorry for the long rant.
Last edited by A.O. Razor; 04-09-2011 at 06:11 AM.
It's really a marketing game more than anything else. The standard Merc engines can vary 25-30 HP. That's why you see some boats faster than others with equal power. I've dyno'd 496 HO's from 387 all the way to 430 at the prop. Regular mags 350 to 373 at the prop. The blue motors are much more consistent and ususally make more than advertised. I've also dyno'd a Volvo 8.1 (420HP) that made 385 at the prop. Of course this is with my dyno using sae standard correction factor and an electronic weather station doing the automatic calculations.
Full Throttle Marine
Thanks for info. I sort of had the same thought. Do you only dyno these engines at the prop, or do you have any examples for flywheel hp?
What this boils down to is, that you can buy a black merc that either makes the clamed hp on the flywheel or prop, depending on how lucky you are. That's comforting
When you are saying that the blue motors make a little more than rated power, I quess you are talking flywheel hp? I recall reading that the 525EFI makes around 530-540 crank hp.
The 525's make between 540-550hp with standard correction or 515-525hp SAE correction. OEM's must use SAE corrections, and if your in warmer climates such as ours, then you get better standard corrections as it calculates to 60deg F. SAE is a later standard and what most OEM's use.
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