WOT in 165 OMC

[D_Smith4321]

Hi there, I am a very newbie to boating and have my first question. I bought an old Reinell 190 with a GM straight 6 250ci engine. The prop is a little beat up and was looking to replace it. I can't seem to find the optimum RPM's in my Clymer's manual. The prop on it right now is a 13 inch x 16 degree pitch. The rpm at wot right now is 2750. Anyone know what the optimum rpm's are for this engine and also suggestions on what type of prop would be suitable. Boat will be used for pulling tubes and skiers.

Thanks,

Darren

 

[Haut Medoc]

Re: WOT in 165 OMC

Welcome to iboats......
I am not familiaar with OMC gearing ....
That said, you should be getting 4200 rpm @ WOT on that engine....
I would reccomend a full tune up, & a compresssion test.....
There are some here who have your exact engine, so stick around for some more feedback.....
I think you should be getting 4200 out of that prop size........
You most likely have some performance issues......​

 

[ziggy]

Re: WOT in 165 OMC

my 75 L6 mercruiser wot is 3900-4300rpm.

i don't know if that holds true for an omc or not as i don't have a book to refer too , just a comparisson of my mercruiser. point is i could be wrong. but 2750 seems a little low. are ya sure yer tach is working correctly.....might check it agaist a shop tach....specially since ya got a 16 pitch ontoit. i'd think ya should spin that 16 too fast. i'm achieveing 4300 with a 19 pitch alulminim.....

someone will stop by and let ya know the facts for omc i'm sure......

 

[D_Smith4321]

Re: WOT in 165 OMC

Thanks for the replies. Tune up and compression test are on the to do list. Repairing trim and tilt at the moment.

 

[ParallaxBill]

Re: WOT in 165 OMC

I'm practically in the same boat as ziggy, so to speak. My boat is an 18' 1972 Glassmaster Tarpon tri-hull and with a sweet running GM 250 L6 I get a WOT 4,300 rpm @42mph with a new condition 14.5"x19 pitch Michigan Wheel aluminum prop. My hull is clean and the boat is not waterlogged. Those figures are "now" with 3 adults on board, fishing gear and 12+ gallons of fuel.

BTW, I was getting nearly the same performance with a 13.75"x21 pitch Mercruiser SS prop. I need to test it again before being sure of the numbers however.

Hope this helps, but seek a good tune up, compression test etc. as others will suggest.

 

[ParallaxBill]

Re: WOT in 165 OMC

Another btw Darren. When I first got my boat on the water last summer I thought I was only getting 3,500 rpms out of my boat but it sure seemed faster. I found out the previous owner had inserted the tach lightbulb too deep and it was blocking the movement of the tach motion from behind.

Ya never know what can hang you up.

 

[Silvertip]

Re: WOT in 165 OMC

2750 rpm is not a "little" low, its about 1500 rpm low. I agree that the tach needs to be verified. The throttle linkage needs to be checked to make sure the throttle plate is fully open. A full tune up is certainly in order.

 

[NW Redneck]

Re: WOT in 165 OMC

Good advice here so far. Make sure motor is tuned up and operating correctly, then verify your wot RPM's with you existing prop. A DMM that reads RPM with a clamp on one plug wire is the easiest way if you have access to one. My OMC owners manual shows max RPM for 165hp/250ci is 3800-4200rpm, Idle speed 500-600RPM, point gap .019", dwell 31-34*, timing 6* before TDC.

 

[D_Smith4321]

Re: WOT in 165 OMC

You are absoulutly correct NW Redneck. The advice on this website is great. I am doing a lot of reading. Hopefully I can get all the parts I need tomorrow. What is a DMM? The previous owner (original) converted the ignition to electronic so I am going to assume no dwell or points to set correct?

Thanks again,

Darren

 

[NW Redneck]

Re: WOT in 165 OMC

DMM- Digital Multi Meter. The one I used is a Blue Point I borrowed from a co-worker. No points with EI. Sorry, don't have anything on those. I'm still "kicking it old school.....uh....Dog" with points. LOL

 

[ParallaxBill]

Re: WOT in 165 OMC

If your ignition has been converted to an electronic replacement module (like a Pertonics unit) that actually replaces the points/condenser then it will likely be okay, but check your basic engine timing. 6' BTDC. My motor has a Pertronix conversion and they say it will be working or not at all.

Also include in your tune up a new distributor cap, rotor button, plugs AND wires. Wires gone bad don't usually look bad but can severely impair performance. Change it all if you are not fully convinced yours is almost new. It's fairly cheap insurance.