Max RPM

What determines the max RPM for an engine?  Why does the standard 5.8 with a carb redline at 4,400, but the GT-40 redlines at 4,800?

The engine in my '99 Air Tique 176 revs to 4,750 at WOT (45 MPH by GPS).  I have run it up there a grand total of one time, just to see what it would do.  

If I swap the heads and cam and add an intake, like I am planning to do this winter, can I safely run 4,800 RPMs without fear of hurting anything?  I'm currently running a 422.  I wonder what prop I'll need with the extra power.

We don't run it super fast.  It'll hit almost 4,800 at WOT now with the original parts.  I'm just wondering why PCM says that the max RPM is 4,400 for the current setup, but specs basically the same engine to have a max of 4,800 when in GT-40 configuration.  My current engine can hit the max for the GT-40.  Why is the GT-40 "allowed" by PCM to hit that RPM, but the non-GT-40 should stay under the 4,400 redline?  Are the GT-40 heads built to withstand the extra 400 RPM and the regular heads are not?  Maybe the springs are different or something?

Here's Andrew trying out the 176.  He's happy to get to use it himself next summer!

KENO is spot on (he usually is)  The rotating / moving parts in the 5.8 SBF engine are reasonably similar, whether carbureted or EFI.  Since the non-GT40 heads and carburetor fuel delivery system won't breath like a true GT40 engine, your peak HP and torque will be at the lower RPMs that PCM recommends -- so there really is no reason to wind the engine up.  Obviously the higher the RPMs, the faster the engine will wear out, so there really should be a compelling reason to run at higher RPMs.  One could argue that your prop should be the deciding factor in WOT engine RPMs.

JQ

JQ

Jeff,

I think your 14 year old will agree! 

I guess I'll toss in a few comments.  First, I wouldn't worry a bit running WOT at 4,750 for a rip that lasts 20 seconds.  I think those of us that drop the hammer and run WOT when water conditions allow really only do so for 10 or 20 seconds, maybe a minute once in a while.  I do run 4,000 or a bit more for longer periods of time, granted it's a GT-40.

I like what you are proposing, you'll have GT-40 level HP when done, and should get close to 50 I would think.

I'm not sure I agree with a few comments above that say that manufacturer's max rpm number is decided because of when the engine runs out of the power band.  I think they determine the number based on rotating parts surviving for some period of time, not sure what they consider reasonable, could be 1 minute, could be 10 minutes, no idea.  But I do think that engine breathing ability, oiling system, type of moving parts determine their max rpm ratings.