GM 140hp-181cid endurance question

[FatBack]

I've had several of these engines over the years both Mercrusier and OMC. Even had one in a 1963 Chevy Nova. They called them the Iron Duke when they first came out in autos. They are used also in forklifts to this day. Here's the question. I now have a Iron Duke in a 20ft offshore boat I picked up cheap. I have to run this engine at a sustained RPM level of 3900 to plane out. I never have had to run any of my Dukes at this performance level in the past. Will this engine hold up for a reasonable amount of time all things being equal? Oh! IT's a Mercrusier

 

[iwldntli2u]

Re: GM 140hp-181cid endurance question

I belive this engine is rate for 3900 - 4300 RPM. I have a '81 120 and the manual gives this specs. Hope this helps-

 

[DJ]

Re: GM 140hp-181cid endurance question

Fatback,<br /><br />Think of it this way.<br /><br />Run your '63' Chevy up a 10% grade in second gear at near wide open throttle-forever.<br /><br />You can sort of make your own conclusions using that information. However, surprisingly, they do last quite a long time. The "duty cycle" of an engine is designed in using different camshaft parameters and fuel/air maps.<br /><br />A well maintained engine of this type should see 1000 hours or more before becoming "tired".

 

[FatBack]

Re: GM 140hp-181cid endurance question

I know this engine is rated at 4600 RPM. Running it at 3900 for an 11/2 hrs is unnerving. I quess my real Question is, will it grenade? I don't care if it wears out. Why would a Mfg. put an engine this size in a boat this big if they didn't know you would have to run it at this RPM to get it to stay on plane. The boat doesn't say crusier on it.I don't want to run this boat at dangerous level if I'm not suppose to. 4100 gets it on top and 3900 keeps it there.

 

[sea wolf]

Re: GM 140hp-181cid endurance question

what size prop are u running? in any case, the boat is underpowered.

 

[DJ]

Re: GM 140hp-181cid endurance question

fatback,<br /><br />The reason they put a small engine in a big boat is: $$$$$. The purchase price is lowered significantly between the four and a six or eight.<br /><br />You may want to prop down as sea wolf is, I believe, eluding to. It may help you get up on plane quicker, however you will still be running as many rpm.<br /><br />If the engine is "healthy" and is oiling and cooling properly, it should not "grenade".

 

[FatBack]

Re: GM 140hp-181cid endurance question

It's a 14 by ?. Can't tell what the pitch is . I measured to get the 14. Mrecrusier part is all that's on this prop 48-78118-17. My other boat has a Mich. wheel and it's stamped right on it. But not Mercrusier - oh no. It looks like maybe a 19. Can't tell for sure. Anyway, if it takes 4100 to get it up,changing the pitch would cause more RPM in hole to lower it on the plane would't it?

 

[FatBack]

Re: GM 140hp-181cid endurance question

I forgot to say that it has a Mercarb on it and I ran the exhaust thru the hull to give it more hp. It should be around 150hp now. Sounds like a mad bumble bee now. So the 3900 RPMs is really unnerving.