Safe rpm at WOT with a stock Evinrude 75hp

[tunnelvision07]

What's the most rpm's I should run with a stock 75hp Evinrude so I don't blow it up? The only mods are drilled lower unit and hustler exhaust. It's on a 12' tunnel hull

[Mark75H]

Don't go beyond stock rpm, power goes down as rpm increases if you have not done a bunch of other mods.

If you want to go fast and faster, prop a std powerhead for std rpm

[tunnelvision07]

Thanks for the help. I appreciate it!

[zul8tr]

Don't go beyond stock rpm, power goes down as rpm increases if you have not done a bunch of other mods.

If you want to go fast and faster, prop a std powerhead for std rpm

Sam

I know he prefaced his inquiry with "so I don't blow it up" but if that wasn't the issue......

What about stock Mercury Mark 25 and 28, 2 cyl powerheads that are rated at 5500 there abouts and being used on quiki units without internal edits and consistently run at 7000 with no problems?

Another example is the Merc 200 series fish engine that was used in the first edition 25ss that runs at 7000 with the same internal bearings etc. as the base Merc 200.

Then there are the old 44ci Merc blocks that I have seen with no mods put on a quicki and run at 7000 with no issues.

Are the Mercs designed better than the Rudes to be able to run at the higher rpms?

Can't he just run extra oil and go at the higher rpms and be aware of the risks?

[Mark75H]

Thanks. My first post does ignore the "blowing it up question" in favor of going faster (which is not posted, but inferred)

The second line in my post refers directly to going faster with the triple.

The for power, 2 cylinder motors are not fighting inherent exhaust tuning found in the triples.


That I know of, there are no problems with running either of these motors into the 7,000+ range.

[Yellowjacket]

Then there are the old 44ci Merc blocks that I have seen with no mods put on a quicki and run at 7000 with no issues.

Are the Mercs designed better than the Rudes to be able to run at the higher rpms?

Can't he just run extra oil and go at the higher rpms and be aware of the risks?

Of course old Merc's are better than Rudes... so what's your point???.

I'm told by reliable folks, that you absolutely can run a stock 44 merc to 7,000, but it won't last very long doing that. The reason being that you will burn the big end rod bearings out of it in pretty short order. The real limit is 6,000 rpm without eventually causing the rods and crank to be damaged. A few zings up there won't harm it, but if you stay above 6k for a few minutes at a time you're going to ruin it.

If you open up the big end clearancs, you can spin the wee wee out of it, and that's all you need to do... And no, putting extra oil in a 44 merc won't get you there either. If it was that easy everybody would just lube it up and go......

I'm about to tear into my Merc 500 for just this reason.

[Mark75H]

No problem that I have seen with running the 44's at 7,000+


In fact, they usually run 8,400. I have not seen a bearing failure

[MN1]

Didn't the factory Mod 50s run 9,000 rpms or higher?
Mark N

[zul8tr]

Of course old Merc's are better than Rudes... so what's your point???.

I'm told by reliable folks, that you absolutely can run a stock 44 merc to 7,000, ........

Yellowjacket
No point just asking a question.

[Powerabout]

old engine bad design pistons or are we talking all new spec kit?
That would be 1000rpm difference at least