Dumb question about engine RPM.....

[dragracer]

So this new boat we got is the first I/O that I've ever owned. I never really worried about running the old Evinrude wide open all day long. I'm a little hesitant to do that with this 4.3L automotive based engine. At WOT it is showing close to 4800 RPM and about 47-48 mph. I've been running it at no more than about 4000rpm most of the time(40MPH). I would never dream of running a car/truck engine at that high a rpm for any extended period. Are these engines really built to take this kind of abuse, or do they just wear out a lot faster than an auto engine? Sorry for the dumb questions but I feel like I'm killing this thing running it at 4000RPM all day. It doesn't seem to object, but I'm still a little concerned.

 

[Doug Durako]

Re: Dumb question about engine RPM.....

Not sure on the newer motors, but I ran the old boat (1976 Cobalt, 260 cubic inch in line 6, 165 hp) for 12 years and 860 hours at 3800 rpm+ pulling skiiers and tubes, etc. all day long.<br /><br />Changed the oil in the motor and the drive unit every 40 hours. (about 2 times per summer)<br /><br />Never had a major problem. As far as I know, only had one new set of seals in the drive from 1976 to 2002. I did have to replace the trim hydraulic rams.<br /><br />I am hoping to get the same life out of the new boat.

 

[llerrad]

Re: Dumb question about engine RPM.....

I have 302 ford and I run the rig from 3000 to 4000 when on long trips, the engine will top out at 4900. This thing has been going for 28yrs and I live on the water so there are many hours on the beast skiing and wake-boarding. Like the guy said keep the oil changed and clean.

 

[dragracer]

Re: Dumb question about engine RPM.....

Well alrighty then! Sounds like maybe I should just run it and not worry about it. Before we took it out the first time I changed the oil in the engine and lower unit with all synthetic stuff. Used Mobil1 15w-50 in the engine. I see some posts saying to use straight 30 weight in the engine so maybe I should do that next time. I've used the M1 in a couple of cars and I REALLY like the stuff. Engine has about 65# of oil pressure cold and about 55-60 hot so I don't think it's thinning out enough to hurt anything.

 

[Boatist]

Re: Dumb question about engine RPM.....

DragRacer<br />I do not know what motor Your are running or what your max rpms are but I would not run over the max. Many older motors the max RPMs were 4200 to 4600. If that is your motor max rpm then I would get a prop with 2 more inches of pitch and lower the max rpms to 4400. You would get more speed and better fuel mileage but a slower hole shot. One other thing different than a auto engine is they recommend 30 weight straight motor oil, not 10-30 or 20-50.

 

[dragracer]

Re: Dumb question about engine RPM.....

Boatist.....It's a 4.3L....175HP rated I believe. How do you tell what the max RPM is suppose to be??

 

[Doug Durako]

Re: Dumb question about engine RPM.....

These guys can tell you, or the Clymer or Seloc manual for your model and year will have all the specs for the engine. I'd get one of those if you don't have one.<br /><br />If you fell the "need for speed" later after you get used to your boat, try dropping the whale tale---you will gain 4 or 5 mph. with the right prop.

 

[Bart Sr.]

Re: Dumb question about engine RPM.....

Sorry to go off subject>>>NICE UNIT!!!!!

 

[dragracer]

Re: Dumb question about engine RPM.....

LOL....Thanks for the compliment....we like it. <br /><br />WOW! I had no idea that the whale tail would kill that much top end. I may have to pull that stupid thing off just to see what happens. If I can gain that much MPH(with the right prop) I can always just draaagggggg a little longer when the wife is trying to pull me out of the water. Sure would be nice to get it up to about 50mph. Wouldn't feel so bad when them bass boats go flying by me at 70!!

 

[Ralph 123]

Re: Dumb question about engine RPM.....

If you really want to understand the differences between automotive and Marine engines invest a few dollars and buy "Small-Block Chevy Marine Performance" by Dennis Moore. The book lays out the differences in great detail and what it takes to turn an auto based engine into a marine engine running at 4K - 5K RMP all day

 

[dragracer]

Re: Dumb question about engine RPM.....

You mean THIS BOOK?? <br /><br />I might just buy that book! You can read the first 9 pages right there on amazon.com(if you don't mind squinting). <br /><br />Yeah I can tell right now that I definately need to buy a manual for my boat. I have seen them on ebay pretty cheap but just havn't taken the time to get one yet.

 

[Ralph 123]

Re: Dumb question about engine RPM.....

That's the one! Great book. I learned a lot from it about the basics.