niceguy

I am curious why everyone only turns their motors to around 5500? I realize continuous use at 6k or above would use up valves springs pretty quickly, but other than that why not spin them higher on occassion? Wouldnt blower motors make a little more power? Or would the extra power and rpm not do any good without re-propping for the extra power and rpm, then make it a turd unless you spun it up all the time?

I was just thinking the other day, why not cam it and spin it to say 6k or so? I would think it would still run good at 5500 or lower, but then wringing it out would net that extra mph or three. LOL

Chris Sunkin

The faster you go, the more stress it puts on your rotating assembly. You're not going to get 6K rpm+ out of a 540 with a Scat or Eagle crank for more than a short while. You go to a $3000 crank and $2000 rods and put them into a block with thick webs and billet caps and providing it's all assembled and oiled properly, you're correct- spinning it faster makes more power.

GPM

I turn it up from time to time, no major problems with the motor, yet. I run the Crower crank and rods.

jdnca1

I know several boaters turning Eagle crank/rods 6500-7000 on a regular basis...In the drag racing world some guys use Eagle up to 2000HP before they step up to the next level.... I also know several boaters who turn stock HP500 bottom ends to 6500 with few issues...of course eventually the crank will break on the stockers..

Most of the "longevity" issues on the aftermarket stuff comes down to the quality of the machine work....

jdnca1

You can...and should provided your valve train is up to the task of making power to 6k and above...If the VT is not stable it will eventually self destruct and/or quit making power

Chris Sunkin

If we're talking 8-second drag runs or the occasional run-up to that RPM, OK. If we're talking about running at these levels for sustained periods (as in running offshore- long distances) you'd better have good stuff in those motors.

Young Performance

Not to mention, Bravo drives are not very fond of that kind of rpm. Merc doesn't have an engine that spins that many rpm, so they never designed the Bravo to do it.
Eddie

articfriends

iTrader: (1)

I turn my blown 540 6200 occassionally,hp peaks at 5900 or so and is turned 6000 often. The real answer to your question is when typical bbc is built strong enough to turn past 6000 and cammed big enough to actually hp peak that high or higher the tq peak is also shifted up, with a typical 1200 rpm spread between peak tq and peak hp a 6500 rpm motor ends up making peak tq at 5300,sometimes even higher. Now to get it to run fast you can't pull alot of prop and it kills your cruising speed,driveability,docking and low speed handling,Smitty

niceguy

This is exactly what I was looking for. All of you guys answers are awesome.

KAAMA

iTrader: (1)

I used to always hear back in the 1980's/90's that anything above 5500rpm in a marine engine was bad for the engine for all kinds of reasons. Somebody correct if I am wrong and I am sure there may be some exceptions to the rule, but 5500-6000rpm isn't "chit" for a well machined/built big block destined for marine use---you're just gettin' it warmed up at that point.

If you're a weekend warrior like me, I usually run my 565cid engines at cruising speeds of 3500rpm 98% of the time anyway, but are still capable of 5600rpm or so.----held it there once a few years ago for about 4 minutes.