Actual Horsepower

[dduburk]

I have heard that after 1991 it was determined that the actual horsepower that is stamped on the motor is not the actual horsepower. The actual horsepower is 10-15% less through combustion and the transmission and that the horsepower is now measured from the propeller drive. We have purchased an old 1973 Lund with an stearn drive Mercrusier 165HP. I am trying to verify what the ACTUAL HP is for this motor. How can I verify this and is there any printed documentation regarding this?

 

[QC]

Re: Actual Horsepower

Welcome to Iboats!<br /><br />Based on your comments, and my understanding, the "motor" makes 165 bhp. With todays' ratings which are, as you have stated at the propshaft, my guess is it would be about a 135. It is typically around a 30 bhp difference. I get this from all of the old 260 Mercs out there, they were all of a sudden 230s when they changed the rating system. I'm sure others will chime in with more accurate info.

 

[DJ]

Re: Actual Horsepower

lainey,<br /><br />QC is correct. The older engine/drives were rated at the crankshaft, like your set up.<br /><br />Your propeller HP is about 15% less than crank HP.<br /><br />That's still a GREAT engine/drive package.<br /><br />Here's a tip. Those engines DO NOT like to run anything over 4300 RPM. Prop it with a large blade area prop that will net you about 4100-4300 RPM with a light to moderate load. Those engines didn't mind "lugging" a bit. They were not designed to be high revvers.

 

[QC]

Re: Actual Horsepower

DJ,<br /><br />Quick question as I have always wondered about this. Wouldn't an Alpha "suck" the same amount of bhp out a 2.5 4 banger as it does out of a 5.7? I understand parisitic losses pretty well, I don't however, understand why this would be a percentage thing as opposed to a fixed load that the engine must overcome. I am sure different gear ratios will have an affect. Maybe that's the whole difference?

 

[dduburk]

Re: Actual Horsepower

DJ,<br />Is there any documentation on this other than just word of mouth? I need to "prove" this in order to put my old boat on a lake that has a max HP limit of 160 HP. (My boat is 165HP) I wanted to present it to the board of directors...to show my boat is actually running approximately 15% less than the 165 in hopes they will allow us to boat there. We bought a lot...then the boat...then read the regulations!! Now we are stuck with a boat that more than likely we won't be able to use on the lake at that location! Should have read the regulations first!!! Nothing like hidesight! Thanks for the replys! Lainey

 

[Limited-Time]

Re: Actual Horsepower

lainey,<br /> Before ya go through the trouble of trying to document the prop shaft HP, you may want to inquire as to what your board of directors deems as gospel when it comes to HP ratings. If it's advertised HP the argument may be lost before it starts. Changing the point of reference does not change the actual HP of the engine, it only verifies the loss of power through the transmission. Anyway,good luck in your quest.

 

[QC]

Re: Actual Horsepower

Lainey,<br /><br />I disagree with LT only because there was a definite point in time when manufacturers of I/Os began using propshaft vs. flywheel power. I have been searching the net and getting frustrated, but I have read articles in the past about this. I would write Mercruiser, shoot I'd call them until I found someone that can produce a document. I would also write a letter to TrailerBoats mag and see if they publish an answer. That would be a good piece of evidence for your board too. These guys should be able top react to reason. My guess is that any 150 Outboard puts out more horsepower than your 165 and any of those would be legal on your lake according to what you have written. They would also be a LOT faster . . . which is what I am guessing they are trying to limit ultimately.<br /><br />Good luck!!!

 

[waterone1@aol.com]

Re: Actual Horsepower

Does the board of directors examine and "grant permision" to every boat on the lake ? If not, I would put the boat in the water and run it responsibly and enjoy it. We are not talking about a gross violation here (5hp). You already own the lot and the boat, if they "catch you", what will they do, tell you to remove the boat, maybe give you a fine ??

 

[Limited-Time]

Re: Actual Horsepower

Quietcat,<br /> You may have a point there, only in as much as the HP rating at the prop shaft will be higher, (due to the gear reduction) not lower than the actual crank shaft output as stated in my previous post. So the actual “Engine HP” will be less than the advertised 165. If in fact it was originally measured at the prop shaft. The auto industry went through the same thing in the mid 70's rear wheel vs crank shaft HP ratings. BTW I like the way waterone 1 thinks.

 

[dduburk]

Re: Actual Horsepower

Waterone 1, Actually I already asked what the consequences would be if we went ahead and used the boat...the answer...if we get caught we would be banned from the lake for LIFE even if we would ultimately acquire a smaller sized boat & motor. We would be able to keep the lot...but no lake priviledges!!!

 

[craze1cars]

Re: Actual Horsepower

Is this a 4 banger? If yes, possible easy and cheap solution to this problem....remove the "165" decal and buy yourself a nice 3.0 decal or something similar that doesn't identify the HP. Or just leave it blank. Most of the newer Mercruisers do not decal the motors with their HP ratings, so it would fit right in...and most people associate the venerable 3.0 with a 135 or 145 hp rating, so it should pass muster quite easily.

 

[QC]

Re: Actual Horsepower

LT,<br /><br />You're still druggin' dude . . . . The crank or flywheel bhp will always be HIGHER than the propshaft bhp. Does not matter what the gear ratio is. Trust me. The difference is solely in the fact that the gearbox (any gearbox) eats bhp. Especially bad with Outdrives as power must be redirected twice at 90 degrees each. So, when they were rated at the flywheel, they usually put out 15 - 30 bhp more than they do now when rated at the propshaft.<br /><br />Check me out on the gear ratio thing, remember bhp = torque x RPM divided by 5252. If the gear ratio changes then both the RPM and torque change and the bhp remains . . . equal. There can be a slight change due to the mechanical differnces between the two ratios, but basically they would put out the same bhp at the propshaft.<br /><br />Check out Mercruisers ratings for their inboards (rated at the flywheel) and the corresponding I/O ratings (propshaft). I cannot guarantee that Merc uses the same timing, fuel map etc. on both engines, but you will see a very consistent difference in the rating numbers.

 

[waterone1@aol.com]

Re: Actual Horsepower

Sorry to hear that you already drew attention to yourself by asking what would happen. Just an idea, but what if you approached them and asked if you could put a restrictor screw or plate to stop the throttle from going to wide open, maybe limit it to 3/4 ??

 

[JasonB]

Re: Actual Horsepower

craze, given that particular year, I believe his engine is a Chevy inline 6cyl. I believe the engine you are thinking of would be the 3.7l 4cyl that I think came out later?<br /><br />Have you spoken with them to see if they will make a reasonable allowance for 5hp?<br /><br />Try this link: http://continuouswave.com/whaler/reference/ICOMIA28-83.html <br /><br />It is supposedly teh standards document defining HP ratings. My guess is that teh doc number 28-83 may mean it was adopted in 1983. Didn't read all the way through, but maybe there is something in there you can use.