Internal vs. External Balance in Relation to Redline

[Vipersix]

I figure as long as I've got everything torn down for a block replacement I'd look into the costs vs. benefits of going to an internal balance. Pretty much the only reason I would do this is to up the ante in the RPM market. This is one area in which I am hesitant to venture because I really don't know too much concerning a higher RPM.

Would moving to an internal balance even help me out significantly if I were to increase my redline to say, 7250 or so? What factors would I need to look out for?

If anyone has successfully increased the redline substantially I'd appreciate any advice you can give.

 

[seijirou]

Internal balance will certainly help. I wouldn't call an external balance a balance as much as a patch over a problem. High rpm engines aren't hard to build, just very expensive, and you have to consider a new set of issues.

Lightweight internals to take some load off the crank, and help get that internal balance. Titanium rods that won't stretch as much under tension. Titanium valves, good rocker arms, and a good set of triple wound springs. You can't just run any old cam in a high rpm motor either, because the valve spring pressures needed to stop valve float can also wipe out the lobes on a cam.
You need to consider rod length with how high you're going to twist it up. It is actually possible to have a piston move faster than the flame front of combustion if you don't select the right connecting rod.
Naturally your spark needs to be flexible and healthy, and finally don't forget your accessories. When your engine is doing 10k rpms your alternator is easily doing 13k, it may not be balanced for that and you certainly don't want shrapnell flying through your engine bay at those speeds from an exploded alternator.

That's just a touch on some of the things to concider.
But boy does a 302 doing 11k rpms sound MEAN!

 

[Vipersix]

So bumping it up just 1k isn't all that big of a deal then? If I went with an internal balance, a good set of springs and grind my cam to match said RPM values I should be good?

11-13k is cool but impractical for my needs. I would imagine just a hair over 7k just fine.

 

[seijirou]

Don't even worry about internal or external balance for anything under 8k rpms.
You won't have to worry about the camshaft or rod length either. A hair over 7500 isn't all that high. You will need to upgrade your valvesprings and you may want to consider hardened pushrods. Otherwise, aslong as the balance is good, whatever the balance may be, you'll be fine.

Mind you, I'm only talking about the components of the engine physically working at these engine speeds without failure. Having a combination that will breathe and make power at whatever rpm you desire is another matter