What are your thoughts on thin stem valves on a street/strip car? I have no problem on a racer but for some reason I'm worried about repetitive strain on a car that gets a good share of street duty.

Anyone have experience with this?

 

Depends alot on camshaft profile and vavle spring pressure. If you're using a flat tappet with a chevy lifter (.842 dia) the cam manufacturers are limited on ramp speed on the lobe. But a roller can take a much steepier ramp. This on the closing side of the lobe closes the valve quickly and has a tendency to break valves.
You can use a 7mm intake and a 8mm exhaust in a circle track engine with a flat tappet and 180# closed and #480 open without alot of problems but if it's got a roller they won't last real long and need to be replaced often. In roller circle track engines I use a 5/16 and 3/8 valve and dont have problems with aggressive lobes and 280# seat and 740# open as long as you useing good valves.
On a street engine you can't get the real aggressive lobe because most of them aren't small enuff to use in a street engine anyway. I'd say if you use a good valve you shouldn't have any problems.
The thing that breaks valves is valve bounce and they all do it. It's when the valve closes it will bounce off the seat. If this much more than .025 it is a matter of time before something breaks. This can be controled by vavle train weight, springs, pushrod dia and wall thickness, and valve seat angle. Alot of the cup guy's are playing with 50 to 60 degree seats this acts as a collet effect and causes the valve to stick in the seat and not bounce. They had some problem with them sticking hard enuff when it tried to open the valve it would flat cams. (they have to use flat tappets) This was with the higher seat angles. It does produce added power as the valve doesn't bounce and lose some the intake charge and eliminate some reversion problems.

 

Interesting.