Real Engine Horse Power

Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
edited April 2016 in Rinker Express Cruisers Forum

Many of you guys know this - but the number of questions we have been asked recently by guys about to purchase boats with what some of us would term too little H.P. for the set-up - may not.

An engine rated at 300 H.P. has that rated at a set of fixed conditions regarding generalized fuel, air temperature, air humidity and load, but - in the REAL world these may be far different than those used for rating purposes AND then the other REAL world factors come into play -  loading of gear and liquids - referred to as the "wet" weight performance, hull condition and then the real  -  fuel quality, ambient temperature and ambient humidity - as well as, in some cases, performance robbing high altitude situations.

All internal combustion engines run best with a cool dense charge of air. Spring and Fall will, in most cases give you your best performance, fuel and torque stats.

All of the above features will reduce an engine's rated performance. More than one, in combination can significantly alter H.P. and torgue curves.

There are however other parameters that greatly influence an engine's performance. Build final H.P. and break-in process and propeller selection and quality. Propeller selection and quality is easier to fix but not everyone knows that most major "mass" engine builders state that their H.P. ratings are +/- 5% of their published HP ratings. This allows for difference in build tolerances and parts as well as assembly quality. That would be 30 HP on a set of twin 350 Mags!....what did you get?

Break-in is another way to end-up with a great engine or one that has significantly less HP/Torgue. While some minor break-in does happen with some engines at the factory, the first 20 hours are very important and the first 5 are critical. Most engine manufacturers advise a full warm-up then getting the engine quickly onto plane and keeping it there for the first 20 hours varying the engine across the RPM band from comfortable cruising, about 3300 rpm +/- to 4400 RPM and neither lugging or idling the engine too much or WOT runs. - for bigger twin cruiser combinations. For smaller single engine bow riders that may mean 2200 RPM to 4000 RPM

I told the Eastern Canadian Mercruiser rep who had my 2014 twin 502s hooked-up on his computer to do a final check-up a story. It went like this: ..... My friend owned a marina. He sold a set of 300 HP outboards to a guy. I was in the store when the guy brought his rig back in and said the engines were crap. They were beautiful engines. At first impression I thought he was an idiot. My friend remained polite, he said the engines were warrantied as long as the guy had followed break-in procedures. They guy swore he had. The tech put a code reader on it. He called my friend over. They were both looking at the screen with their mouths open. The guy had taken right off the dock the first 50 times or more with brand new engines with no wram up- and had wound them out to redline right from the start. My friend showed the guy who "looked busted". He got very defensive and real angry and said he'd sue my friend for blah, blah, blah. My friend said something to his tech. The guy came back with about 50 pages stapled together. My friend said give this to your lawyer - see you in court.  Since he lived next door to me I asked him over the fence a while later, "Did you ever hear from that guy" He said "No, the stats don't lie." I asked what the bill would be to repair the engines. he said about 20K

The Mercruiser rep hooked-up to my engines laughed and said Oh, Yeah Mr. T....want to know if you have been a good boy?...LOL He showed me EVERY piece of data on my engines' use from the minute it was first started. He said, "What would you like to know?" Because my Vessel View could give me any performance data, super accurate at any time I asked for a few days of the usage reporting. He sent about 5 pages of how I had used the boat to a printer, warm-ups, RPM bands, dates - EVERYTHING!. he said, "Mr. T you get a gold star!".

SO - when someone says I think I can "get by" with a smaller engine in a boat I say FORGET it. By the time you add up all of the conditions your boat will face and that it might also have less rated HP and be used in hot humid weather give the poor engine a break and go for more HP.

That 100 HP more is probably what your hull needs anyway to perform as it was intended to. As AL asked (rhetorically I assume) in a post yesterday.....  "Have you ever heard a guy complain that he had an extra 100HP?".....No I haven't but I have heard too many guys to count say "I should have gone for the higher HP engine."

For those of you looking to purchase at this time of year "go for the HP", IMO, - you will be FAR happier. We're boaters, not lawn bowlers. We're competitive guys - we don't like our neighbours' lawn mowers to be faster...own it guys!  :-)


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