A buddy and I always talk about rpm. I'd love to hear who turns what RPM at wot. Not talking factory mercruiser stuff, but custom built hyd roller cammed engines in pleasure boats. Engines like 540's, big roots blown stuff, whipple engines, etc.

He is skeptical about anything over about 5300RPM, for longevity and parts breakage. I assume with today's good hyd roller lifters, endurance springs, and overall good parts available, 6000 shouldnt be too crazy to turn. Granted the engine is cammed to run there with good results. I dont like the idea of loading down a big blown healthy cammed engine with a big prop so that its only turning say 5100 rpm at wot and max boost. Seems to me like a invitation for heat and detonation????

So, what do you turn yours too and what setup??????

My last engine I was spinning it to 6000 rpms. Never an issue!

5800-5900 no problems

5700

5600-5900rpm depending on outside temps
Custom 575sci's - chilled - hyd roller -ECM re-map

580 cu 4.0l whipple 5800-6000rpm 8lbs boost hydr lifters..pushing 23k lbs with arnesons

cool air 6-6100,heat of august 5800. Not realy custom,500efi with stock crank.


116octHustler dyno pull 911hp 11.5 lbs,Whipple




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It depends on the engine, parts and application but anywhere from 5400-6600 rpm. All hydraulic rollers.
Eddie

Eddie has one of the best answers here as the actual parts and engine build will determine whats a good safe rpm max for any given engine build. Things like valve and valvetrain weights, stability, lifter type, spring pressures, boost levels, etc. will determine in each actual final build state what is the best max long term rpm level. A general across the board rpm range for all engine types is a mistake and would leave some engines just fine and others in trouble! Almost no higher horsepower marine engine will last as long at 6500 rpms as it will at 5500rpms and the actual hours at these rpms will help determine real average engine life. Normally most well built normally aspirated marine engines at 5500-6000 rpm limits will outlive supercharged or turbocharged marine engines running at the same rpm limits, there is no changing that difference. Also remember that generally higher rpm performance engines cost more to build than medium rpm range marine performance engines A new twist to the old addage: "Extra RPM's cost money, How fast to you want to Spin it?!" If you're building a short blast race engine then you will approach rpm limits differently than you will if you are using a recreational endurance marine performance engine, THEY ARE NOT THE SAME PERIOD!
JMO

Best Regards,
Ray @ Raylar

I was generalizing a bit in my original post, assuming we are talking about custom engines running quality forged cranks, forged aftermarket rods, quality roller lifters and springs, performance cylinder heads, and camshafts that are within reason for a marine high performance build. Of course there would be no point in spinning a stock 330 to 6000 rpm unless breaking it was the goal.

My original concern, is lets say you build a custom blower engine, 4" stroke crank, and a cam/head package that makes peak hp at say 6000rpm with a blower. Then, you install that engine in the boat, and prop for 5000rpm, near where the engine is making peak torque.

Are you better off spinning the engine at its peak hp rpm or at its peak tq rpm for longevity?? And is it true that overpropping so that spinning it at peak tq is hard on the drives and transmissions?

I was always told overpropping would do more damage than good.