LT1 Rev Limit

[Cappy]

A lot of the NA mods increase volumetric efficiency at higher revs, so I was wonder what the valvetrain and bottom end limits are to engine speed. When I say limit, I mean how high can the engine be revved for multiple laps (think endurance race) with little worry.

Pushrod engines inherently have a lot of valvetrain mass, and do not handle high revs without some help. From this board, I've gotten the sense that the valve springs are the first limit reached (valve float even with stock cam), and they're cheap to replace. In what order should parts be ugraded as higher engine speeds are required?

[krispycobalt]

from what i hear it seems springs and pushrods are 1st to change

lifters, rockers, studs come after, but it seems a lot of people just do the whole valvetrain rebuild in one swoop when doing a cam swap, rebuild, etc

[SAR2K]

Proper springs can make all the difference. In addition to install height there are a few considerations. I got a lesson this week in spring/cam "harmonics". Basically when you get into the high rpm area ramp rate of the lobe will excite the springs into their natural frequency. At that point they give out and you have valve float. There is a hell of a lot to this and I'm just learning the tip of the iceberg.
As for stock springs... they just plan suck after 30,000 miles or so. It's best to go with a good set of springs from Comp, Crane, or Isky.
If you're running an aggressive lobe a rev kit can help give you some extended valvetrain life.
On the bottomend... some folks have no luck and bite the dust after a few 5,800 rpm passes. I've been able to make numerous 6,800+ runs/pulls on a stock bottomend. Alot depends on the up keep on the motor.
Steve...

[Cappy]

Wow! Isn't 5800 rpm under the manufacturer's redline? You'd think there would be a margin of safety factored in. I don't like hearing that the bottom end can't take much, because crankshafts and connecting rods cost a hell of a lot more than valve springs and pushrods.

One thing about stiffer valve springs is that they cause loss of power through friction, which also effects fuel economy. Titanium valvetrain parts would require a lower springrate, but are more expensive. I'm beginning to see how easy it could be to keep throwing money at the engine. :D

[SAR2K]

Don't freak out on the 5,800 I've mentioned, that's a worst case scenario. I've spun mine up to 7k quite a few times and MANY others break 6,500 w/o issue.
As for loss of hp from increased spring pressure... any loss due to the increased pressure is so minute that is not a factor. The gain in upper rpm stability and power gained from that EASILY offsets it.
Any yes $$$$ goes fast on an engine. :D
Steve...

[Compstall]

I have a friend in WA State that road races all summer long in SPO/ITE. He goes an entire season running well above 6,000 RPM before having the motor freshened each winter.

A couple years ago, he went the entire season like that, then he ran an 8-hour endurance race in Portland on that same motor to finish up the year. Motor still ran great at the end of the day. I watched him bounce off the rev limiter all day long.

Is that good enough for ya? ;)