Maximum safe RPM?

I've always wondered this and never received a concrete answer. I've heard people say as low as 3500 and as high as 5500. I usually keep it at around 4000-4500. What do you guys think?

We have a 400hp 383 hammerhead in our Malibu.

What is the max RPM you would suggest to run it at?

What does the owners manual say? My PCM 343 manual says I should try to pitch a prop for max rpm of 5200 at WOT.

4000-4500 rpm when you do what? Cruising on the lake?

Originally Posted by 16igordon

I've always wondered this and never received a concrete answer. I've heard people say as low as 3500 and as high as 5500. I usually keep it at around 4000-4500. What do you guys think?

We have a 400hp 383 hammerhead in our Malibu.

What is the max RPM you would suggest to run it at?

I've never worried about over-revving the family boat with the stock prop. Wide open. 5000-5500 rpm should be no problem on these fairly custom and robust SBCs...

Yes when cruising around the lake. Would never get that high surfing or boarding.

Totally fine. I see people run over 5k all the way back to the dock all the time. As long as you aren't near the redline I wouldn't think it would hurt anything at all.

I would feel totally comfortable up to 5000 rpm with a hammerhead which is just a bored 350

I've never been above 4k. But I only board with an occasional surf set and I've never had my boat above 30mph. No need to. Weighted out at 23mph I am usually at 3400 on my 350.

I don't think propping the boat to achieve a certain rpm applies in the real world to wake boats. My boat could prob run 7000 rpm if the computer would let it. i propped down from 17.5 stock to 12 right now.

We've blown up 3 of those hammerheads they blew at 4500+

Run in all day at 10% below the redline. Run it to the redline for 15 minutes if you want to. Just remember that you are putting distance on the engine when you rev it high so everything is more stressed and your fluids and tuning need to be at their best.
The most load on the engine is at full throttle at peak torque. Peak torque RPM is also where you get the best fuel use. Redline RPM puts the most stress on the connecting rod bolts and wrist pins but there should really be no issue with those on any small block Chevy at the RPM that boats normally run.

If Indmar Hammerheads blow up below their redline regularly in a boat, then Indmar does not build good engines. I think they probably do, but switch to Mercuriser or Ilmor if you are concerned.

Originally Posted by antoddio

I don't think propping the boat to achieve a certain rpm applies in the real world to wake boats. My boat could prob run 7000 rpm if the computer would let it. i propped down from 17.5 stock to 12 right now.

Sure it could. You'd have floating valves or broken valve springs, etc, but I'm sure you would be fine.

Well yea. It could only do it for a few seconds haha. But at WOT it would try to get up there if the computer didn't stop it.

no rev limiters?

and a 383 is a stroked 350, not simply bored over. Its a mild stroker so those RPMs shouldn't be an issue

My PCM manual says sustained RPMs should stay at or below 4000rpm. Hammerhead internals are similar.

See Chapter #4 http://www.indmar.com/Libraries/Manu...al_1.sflb.ashx

Since the internals of the engines are all the same, there is no one best engine manufacturer, as there is only one! The accessories and PCM tuning are the only differences, and some of those are the same as well. Sustained high RPM and load will shorten engine life, it is simple physics. As you approach the upper limit the wear increases exponentially, so depending on your red-line or what is suggested in your owner's manual, operation less than 20% of red-line will go a long way giving you many years of trouble free use of your GM Marine engine, adapted by the various engine suppliers.

I forgot that Ford has added an engine to the marine industry, but the GM engines are everywhere.

Speaking of the gm engines. Anyone know if the 5.7's are the older flat tappet or are they roller lifters