rpm @WOT

[jka]

Back with a Q on the '94 190 Horizon with an OMC 5.0 EFI.<br />At WOT the engine is producing 3000-3200 rpm...I get about 48 mph with the 21 inch prop. That's the highest rpm I can achieve.<br /><br />One line of thinking is....that low of rpm with 48mph is good: engine isn't working hard to get speed. However, I've seen posts in here where peeps with the same boat get 4600rpm.<br /><br />Should I be concerned ? What should rpm be? Owner's manual isn't much help.<br />tyvm

 

[Rickles]

Re: rpm @WOT

I'd check the accuracy of your tach.Seems kinda low for the speed you're getting.Use a good shop tach to verify the rpm.

 

[achris]

Re: rpm @WOT

Tyvm,<br /><br />Don't be concern, be VERY concerned!<br /><br />This engine is being overloaded beyond belief! You run a very real risk of burning valves and piston crowns. The load is reflected through out the rev range, not just at WOT. <br /><br />Get that prop off and put a smaller one on, fast! <br /><br />I'm not a OMCspert but that 4600 sounds about right.<br /><br />Chris...........<br /><br />Edit: and what Rickles said.....

 

[sculbert]

Re: rpm @WOT

Achris is right. The advantage you will also see is you can keep the top speed and get better bottom end and will plane out much quicker. Plus save your engine. Your engine is working its butt off right now. I would suggest you try a 17 and a 19. See if you can barrow a couple used ones first and find out whick works best for you. Make sure you extra people with you carry an average payload that you will normally be running with when you try it. You want to be able get to your max RPM under these conditions.

 

[jka]

Re: rpm @WOT

Gents, <br />thanks for the feedback. I'm still a bit confused. if the engine is running at slower rpm, and still producing good mph...what's the concern? I would think it's LESS stress on the engine. Merc, The boat gets on plane in about two seconds..its very quick.<br />thanks<br />john

 

[Bondo]

Re: rpm @WOT

Lugging the motor is MORE Stressful..............

 

[cuzner]

Re: rpm @WOT

With a 21p prop on that engine,with a 19 ft bowrider you should be 4000 to 4500 rpm.at wot.Check to make sure your tach is working,and heed the advice of the experts,the prop you have on should come close to the top end of rpm at wot for the engine.<br /><br /><br /> Jim

 

[WillyBWright]

Re: rpm @WOT

I agree with the tach thing. Thing that confuses me is that if it were set for a 6 cylinder the rpms should read 50% high, set on 4-cylinder and it should read double. Sounds like you're reading about 75% of actual. I'm not sure what could cause that except for a bad tach. Everything else sounds fine. I'd certainly expect that motor to push that boat about that fast with that prop. Only thing wrong with the equation is the tach reading.

 

[jka]

Re: rpm @WOT

thanks a lot fellas. I appreciate your help! I'm going to give the 4winns dealer a call tomorrow regarding the tach. This boat sounds and runs just too good to be anything but the tach. I'll post the results. i checked in the OMC manual and it says full throttle operating range 4200-4600.<br /><br />john

 

[jka]

Re: rpm @WOT

well, the verdict is in. Got the boat back from the mechanic. When the new dashboard console was put in two years ago the 4winns mechanic did not set it up for 8 cylinder. Apparently, the is a switch to set for the tach...4,6 or 8 cylinder.<br /><br />Today, the mechanic looked and it was set to 6. Thus the faulty rpm reading. He said running the boat had no impact on the engine and did not harm it and would have done no harm as the posters above noted.<br />He also said...getting 48 mph with a 21 inch prop and excellent hole shot is perfect for this boat and he would not change the prop.<br />I'll test in two days and report back.

 

[jka]

Re: rpm @WOT

I tested the boat today. it ran perfect...42-4600 WOT.

 

[jka]

Re: rpm @WOT

ps,<br />guys,<br />thanks for all your help. its nice to know people are willing to help