operating range question 83gt150

[motodave]

I have a new to me 83 gt150, J150STLCTE on a 83 ranger 372v. I noticed the factory stamped operating range on my motor is 4500-5500 rpm. My question is, does this mean operating it below 4500 is considered 'lugging' the motor? I understand that of course running the boat for instance where its not planning out is hard on the gearbox, as theres only 1 gear, but is 3500 - 4000 on plane extended running a no-no? So far my motor runs wide open, trimmed out, 5000rpm max at 60.8 mph gps. I will be pulling a tube around a little this summer, but mostly fishing running from spot to spot. Should I look into a prop change? BTW I am not after more speed, 60 in an antique vessel is plenty for me. Thanks for any input guys!

 

[emdsapmgr]

Current thinking is that the proper propeller should permit the engine to run in the upper end of the normal operating range, or 5500. Prop it to run at that rpm. If you run it at 5000 max, you are lugging it. Each prop change (from a 19 to a 21 for instance) will make about 300 rpm's difference when it's close to the normal range. Your engine is the XP/GT version and will still make reliable hp up past 5700, so slightly over 5500 is not a problem. Your power pack will limit your rpm's to no more than 5800, about where the engine runs out of breathing capability anyway.

 

[V153]

Yeah I'd shoot for at least 5500 or so wide open. I believe some of those XPs/GTs were rev limited to 6100? If you can find a # on the pack it'll tell you.

Nothing wrong with extended cruising at 3500-4500. Not gonna hurt anything.

 

[motodave]

Thanks for your replies emdsap and V153, I'm guessing it got changed by PO. There's a shop fairly close and he's very familiar with these motors, I'll see what he has available and try a different one when funds allow. I'm guessing that it's like putting a smaller sprocket on the rear of a motorcycle = higher top end but less low end grunt? Thanks for the help guys, I would have just let it go like it is if I wouldn't have asked

 

[Joe Reeves]

83 gt150, J150STLCTE on a 83 ranger 372v. My question is, does this mean operating it below 4500 is considered 'lugging' the motor?

No.... Lugging and the eventual result of coking up (Waxy carbon looking buildup in the cylinders) is due to running with a engine problem that results in a low rpm with the throttle butterflies set for a much higher rpm such as.... throttle set wide open and the engine running at say 3/4 throttle.

If your engine/propeller setup is as it should be and the top rpm can be obtained normally (not exceeded)... you can runs that engine at any rpm you so desire without encountering problems.

 

[V153]

I'm guessing that it's like putting a smaller sprocket on the rear of a motorcycle = higher top end but less low end grunt?

Basically yes. But then throw in pitch and rake and number of blades, etc.

There are a plethora of props available. What kinda boat is it on? Motor height?

 

[motodave]

Thanks Joe! V153 it's on a 83 ranger 372v, I'm still a noob and don't know how to measure motor height but would like to know, is it how far the leg hangs below the bottom of the hull? Measured to centerline of prop? If so it's about 6 inches

 

[Joe Reeves]

Thanks Joe! V153 it's on a 83 ranger 372v, I'm still a noob and don't know how to measure motor height but would like to know, is it how far the leg hangs below the bottom of the hull? Measured to centerline of prop? If so it's about 6 inches

Not sure what you're asking..........

If determining whether the engine is short shaft, long shaft, or extra long shaft, the measurement is taken from the portion of the engine that would normally rest on the transom down to the cavitation plate that exists just above the propeller. Where 15"=short.... 20"=long.... 25"=x-long.

If asking where the engine should be sitting on the boat height wise... the cavitaion plate just above the propeller is the crucial item. Normally it is located about 3/4" below the keel (bottom of the boat) at the transom. However... many boats function better with the cavitation plate slightly higher than the keel without cavitating... a case of trial and error. Personally I use the 3/4" measurement first as a starting point UNLESS you hear different from someone who has the same rig you have.

 

[emdsapmgr]

Joe gave a nice explanation in post #5. He's correct. Once you get the engine so it runs the proper max rpm's- it's "optimized" to run at any throttle position that you want - throughout the rpm range. That way you get max performance and max fuel economy. If the engine only runs 4500 at max throttle, that's lugging.

 

[steelespike]

Once you have a prop operating at wot within the rpm range your free to operate at what ever throttle position suits your needs.
You wouldn't normally operate at speeds just below planing speed for extended time as it is probably the least economical speed.

 

[motodave]

Thanks again for the info guys, its great to be able to bounce questions off very experienced people and you have saved me some trial and error once again!