riding past redline

I started taking my 550 to the track. It's been pure adrenaline Zen. My bike is making lots of power on the high end, to the point where I'm finding myself regularly pushing beyond the 10K redline, up to 11-11.5K.. I wondering how bad it is to go past redline in general, and if it's not so bad, can I go even higher? It's still pulling super strong at 11K rpm.

Do what you like, but here are two observations –

Contrary to what you may think your bike isn’t making decent power past redline – just noise. Take a look at the chart below and notice what happens after the engine reaches 8,500 rpm. At that point power begins dropping. By the time you reach redline it’s making less power than it does at 7,500 rpm. If you were to extend the line on the chart you would find the engine makes less power at 11,000 rpm than it does at 5,000 rpm. Guys who race successfully have learned to keep the revs at or near the top of the power band, and that is not above redline. If you doubt the chart spend a few dollars and put your bike on a dyno. It will verify the info in the chart.

Over revving the engine will kill it. A guy on KZ650INFO stated that he often revved his KZ650 up to 11,000 rpm. I mentioned that this was destructive, but naturally he did not believe me. After a few weeks he reported that his engine was dead because the pistons and valves had struck each other. He suspected the rods had stretched to the point where the contact was made or that the valves simply were not closing quickly enough due to the stock valve springs. He never verified the cause and never got the engine running again.

Ed

To get a engine to make power over its stock redline requires A LOT of work. The biggest problems with over revving is usually the weight of the stator breaking the crank, then valve float, then pistons hitting valves.
Take off the charging system, some MAJOR port work, cams and carbs, better valve springs and you can safety run it up the rpm range until the piston speed gets to high.
I dont remember exactly but the 4000 fps range for piston speed sticks in my memory for most engines.

You are in for catastrophe if you dont watch it,

If you really are still making power up at 11k your shell bearing crank is good for many more revs over the factory redline.
Some modern sports bikes rev to over 19k rpms.
Valve float and bounce is your main limiting factor and this is what is likely to kill your motor first
Stronger valve springs and lighter retainers will help push that further up the rpm's.
Also feed the motor with the best oil you can afford and make sure the pump is at it's best .
You need to get the bike on a dyno to see what is really happening.

What size are the sprockets?

ps: I wouldn't assume anything. check the diagrams & count the teeth.

That's half the reason I went with APE springs even though I only fitted a small 750 cam .342/335 (365 lift someday maybe). I only push mine to 500 maybe 700 now that the cams make power up a little higher. It defently makes a diff when going from 4th to 5th (keeps it in the power range a little better when slamming 5th) but don't push it quite as hard in the lower three. A few on here have and are running your bike at the track so I'm sure they will chime in with some good advice.

Thanks all. The sprockets are stock as far as I know. I'm running Castrol synthetic and change oil every 2-3K miles. Only major mods are a Kerker race exhaust (1.5" competition baffle), Factory Pro Stage 1 jet kit and K&N filter. Here's the dyno. Looks like hp is peaking around 10-11K rpm with torque just starting to fall off.



My understanding is that the main risk is valve float and that if that gets bad enough that pistons meet valves then the engine is toast. But before then, as the valves just start to float, there should be a loss of power. So I'm guessing that I'd get a "warning" of loss of power before catastrophe...or maybe that's just wishful thinking.

I shift at or just after redline. Even then if I miss a shift, I'll listen for noises. Kibblewhite springs and Andrews 1X cams. I'd be more nervous if I had hotter cams.
Steve

Yep! power will flatten as the valves start to float but sensing that point on the run is another matter.
Probably wise to fit a rev limiter at 10.5 / 11k so that you aren't going past peak power and risking damage for no reason then revise the situation if you go for more mods and a fresh dyno chart shows an increase above that.
With more mods you may get more power overall but no more revs which would then enable you to pull higher gearing and still be faster without the danger of over revving.

I remember a little side story in Motorcyclist magazine back in the day about one of the editors taking a KZ550 to the races. As I recall he installed a pipe and maybe pods (can't remember) and went to the track. His story detailed how eager the bike was, pulling deeply into the redline. The KZ hadn't been out too long at that point and he described the giddy experience of pulling much bigger bikes on some of the straights.

Fast forward to modern times and I saw a GPz550 in the paper where the seller volunteered that it had a rod knock. Some research showed that such carnage was not overly unusual on 550's that had been raced. I'm sure there are guys here that know more than me about such matters but it does suggest some care should be exercised when burying the tach into the red zone.

I don't know much about the 550 motors but the 650/750 motors have a real good bottom end it's the
valve springs and cam chain adjuster that will kill one at high rpm's.

I set my shift box between 9500 rpm and 9800 rpm and the rev limiter is set at 10,025
but have been on the limiter at 12,500 rpm's.

The 550, much like the 650/750's are stout little motors. But all that aside, if you are racing... really racing, your motorcycle is simply an expendable tool you use to get you around the track as fast as possible.

In that pursuit you will break things.

That's racing.