Is high RPM bad for 4.3 engine over time?

Searayguy185

Member
Jul 17, 2017
87
Wisconsin
Boat Info
2004 Sea Ray 185 Sport 4.3 V6,

2008 Toyota Highlander Sport
Engines
Mercruiser 4.3 V6, Alpha 1 Generation 2
Wondering what people's opinion is on running a 4.3 engine anywhere from 3000-4000 RPM for a extended amount of time. I understand it will do it, but my question is will it drastically reduce engine life? Thanks
 
That's it's "normal cruising" RPM. Other than in a laboratory, zero effect.
 
So I have industrial customers the run generators for 5,000 hours at a stretch without major maintenance. These all run at the same RPM all day every day. It is all about the maintenance.
 
Engines are happy when they run consistently under designed loads. For my boat that is 3600. I have no problem running extended periods at that rpm point. Constant starts and stop put more stress. Most important get your engines up to full temperature before you hit the gas.
 
The 4.3 is a fairly compact assembly, as in short crank and rods. So it can handle some RPM. Id expect its WOT to be about the mid 5k's. 3K-4K is a comfortable range for the engine.


Wot 4400-4800 for that motor I had a 27AJ with twin 4.3 alpha 1’s 3600 rpm cruise at about 24kt 80% load on that is 3840
 
Agree with others. No problems running a 4.3 in that rpm range. It is basically a 5.0 minus two cylinders. The only known issue with it is oil leaks around the timing cover - most of them will develope a leak there at some point. Mine has 650hrs on the clock with no major problems - I am not hard on it, but I run it.
 
Agree with others. No problems running a 4.3 in that rpm range. It is basically a 5.0 minus two cylinders. The only known issue with it is oil leaks around the timing cover - most of them will develope a leak there at some point. Mine has 650hrs on the clock with no major problems - I am not hard on it, but I run it.

A minor correction, a 4.3 is a 350 (5.7) minus 2 cylinders.
 
My experience has found trying to keep an engine in the 60-70% range of it's rated horsepower will give you the most life out of it. This is results found with continuous duty applications. Not sure where that applies with a 4.3 but would guess narrowing that range to 3200-3600 would be better for extended periods. IMO, combustion pressures were the biggest contributor to premature failures both above and below their sweet spot.
 
95DA1B69-A6E1-40A9-89EE-F7BC7942E5F1.png
My experience has found trying to keep an engine in the 60-70% range of it's rated horsepower will give you the most life out of it. This is results found with continuous duty applications. Not sure where that applies with a 4.3 but would guess narrowing that range to 3200-3600 would be better for extended periods. IMO, combustion pressures were the biggest contributor to premature failures both above and below their sweet spot.

If I followed 60 to 70% of maximum horsepower rating I did the calculations (I happen to have Dyno sheets for my motors showing what horsepower is made at what rpm )I would be running my boat somewhere in the 27 or 2800 RPM range at that point my boat would be pushing too much water and not over the hump putting tremendous pressure on the engine if you follow a general rule of 80% wide-open throttle I think for Boat application that becomes a better philosophy once a boat has planned out the amount of stress on the engine drops ,that I believe is the sweet spot we should be trying to achieve Anything more than that or less than that increases wear and decreases fuel efficiency since my boat was officially surveyed by boat test.com I had a guideline to follow as far as what rpm to run the boat. having my motors re-built and re-propped I was able to lower my rpm’s by 200/300 at my cruising speed and generally cruise at 3200 making about 20kt I can plane down to 2600 RPM with a lot of tab but it puts a tremendous amount of pressure on the engines.
 
View attachment 64993

If I followed 60 to 70% of maximum horsepower rating I did the calculations (I happen to have Dyno sheets for my motors showing what horsepower is made at what rpm )I would be running my boat somewhere in the 27 or 2800 RPM range at that point my boat would be pushing too much water and not over the hump putting tremendous pressure on the engine if you follow a general rule of 80% wide-open throttle I think for Boat application that becomes a better philosophy once a boat has planned out the amount of stress on the engine drops ,that I believe is the sweet spot we should be trying to achieve Anything more than that or less than that increases wear and decreases fuel efficiency since my boat was officially surveyed by boat test.com I had a guideline to follow as far as what rpm to run the boat. having my motors re-built and re-propped I was able to lower my rpm’s by 200/300 at my cruising speed and generally cruise at 3200 making about 20kt I can plane down to 2600 RPM with a lot of tab but it puts a tremendous amount of pressure on the engines.
In your opinion....
I shared mine. It comes from over 30 years in the business.
 
In your opinion....
I shared mine. It comes from over 30 years in the business.

Well no ,not in my opinion ....it’s a fact based on your statement what I calculated at least for my boat at 60 to 70% max hp that was the point I was making How do you suggest anybody calculate 60 to 70% of their max horsepower? How does one come up with what rpm equals what hp ? Considering the original posters engine is equipped with 190 hp 60% of 190 is 114 hp not sure where that’s going to fall on the RPM curve but I’m guessing it’s under 3000 RPM which will cause premature wear so to help the op I was quoting facts about what “is” followed by most boaters 80 of max RPM and you can run that all day long without abnormal wear .sweet spot for op boat is 3500 per boattest.com
https://www.boattest.com/oem/32/boats/573/0/on/640x360
 
The topic is asking for opinions on high rpm and engine longevity as I read it.
Did you read my initial post? Pretty sure it states in continuous applications. Dyno readouts are meaningless in comparison to a prop pushing a boat. A jet drive on the other hand might have a closer reflection as it is basically building pressure in front of a nozzle. A closer principle to a dyno.
Your opinion is to run it at 80% which is really not far 70%, but then you say you cruise at 3200. Do you really believe you are putting 80% to your prop at 3200 because that's what the dyno said? If your hull is as efficient as you make it sound, I am guessing you are sitting somewhere around 1/2 to 2/3 throttle at 3200-3400. I would take a guess that it is closer to the 60-70% I was referring to.
Unless you have the proper equipment to monitor engine load, fuel flow or throttle position would probably give you the best reference I suppose. There is nothing magic about the 60-70% I suggested. It is what I have found in my experience. With those engines, load % is easily monitored from their ecm's.
Low loads cause low combustion pressures and operating temps. High loads cause high combustion pressures and operating temps. I would not recommend either for longevity. Find somewhere in the middle that your hull likes and it doesn't kick you in the pocket book.
 

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