Hollow stem valves
 

Any performance gains by using hollow stem valves?? Pros and cons??

Re: Hollow stem valves
 

Jaf, I bought a set manley solid valves for my LS3. The hollow stem were 6-8 weeks out and $250 more for a savings of only 9 grams a valve. that might seem little but x 16 valves and that adds up. So the new valves, heads,cam, lifters,rockers along with the factory hollow stem valves all went on a spintron to see where i stand and valve control was good to 9400 RPM. on both solid and hollow stem. point is I don't think it matters. I was worried having heavy valves but the spintron proved me wrong. I did find out that my valve springs were too heavy on the seat. I hope this helps...Luke SS 311

Re: Hollow stem valves
 

I have not had good luck with Manley valves of late. I have lost 2 engines recently due to exhaust valves dropping the head off. What are you using for exhaust valves? 350 super stock engine. Anyone else having this issue?

Re: Hollow stem valves
 

Mike, this engine is a 396 LS3 COPO Super Stock engine. I use the extreme duty XH-432 exhaust valves from manley. A friend lost 2 engines ( 396 big block stocker ) using another top brand valve. is it the luck of the draw? who knows. fingers crossed...Luke SS 311

Re: Hollow stem valves
 

It matters a lot if you have a cam with "iffy" lift curves. You can easily lose 1,000 RPM of peak limiting speed by changing to solid stem from hollow in some combinations.

For heads popping off valves, I'll bet a hundred they had severe bounce at closing. That's generally what will make things break. Good thing some people test this stuff. ;)

Re: Hollow stem valves
 

you mean too much seat pressure or not enough???

Re: Hollow stem valves
 

I wonder who recommended the spintron test...well worth it.. no guessing or mismatch parts...Thanks Rob!! Luke SS 311

Re: Hollow stem valves
 

What did you see on the Spintron that indicated too much seat pressure?

Re: Hollow stem valves
 

It generally just didn't look as smooth with more deflection near the nose and a little bit of drumming at the closing point. 150 lb less spring Force cleaned it all up and made it look beautiful.

High spring force is definitely not your friend all of the time.

Re: Hollow stem valves
 

How much did you have on the seat?

Re: Hollow stem valves
 

Would you mind posting graphs of the data if available?

Chris Hill
Old valvetrain engineer

Re: Hollow stem valves
 

I will when I get back to base next week

Re: Hollow stem valves
 

Wow! I don't have to lose 150 lbs on the seat for my valves to start hitting the pistons. How much did you originally have on the seat?

Re: Hollow stem valves
 

A smart guy told me one time that the lighter you make it on the valve side and the stronger you make it on the push rod side the better off you are. That being said the lighter the valve the less pressure you need.

Re: Hollow stem valves
 

I was watching a video with Billy Godbold and Scooter Brothers and they said they built a system for a restrictor plate NASCAR engine that had 70 pound spring pressure on the seat and something like 140 pounds over the nose. I'd like to know the rest of the details on that build.

Re: Hollow stem valves
 

Ed. that was my thinking originally throw the biggest valve springs but once again the spintron proved me wrong. Went from 850# to 700# ...Luke SS 311

Re: Hollow stem valves
 

Ed
One thing everyone forgets is the results on exhaust side can be questionable because in the real world the exhaust valve is trying to open against cylinder pressure on the spintron there is no cylinder pressure!

Re: Hollow stem valves
 

Correct. But that force goes away the moment you lift at the stripe and the engine is still at high rpm for a few seconds....

Re: Hollow stem valves
 

The NASCAR guys use 6mm and 7mm hollow stem titanium valves, high rocker ratios, and perfect valve train geometry, which helps them run lower spring rates. Though I'm not sure that they are as low as 70 lbs on the seat.

Nevertheless, those low spring pressures and rocker ratios don't seem to work for drag racing.

Re: Hollow stem valves
 

Somebody asked me to post some data, so here is a graph that contains a comparison of high and low pressure springs - 1238X (blue) is the lower of the two.

You can plainly see the higher pressure spring arrangement is not as stable as the lower pressure spring.......Key in on the nose deflections and bounce at closing. The latter is a mode that tends to break parts. In this case the higher pressure spring is bouncing .010" where the lower spring is about .002"-.003"

Also, a trace with a light-weight hollow stem valve (green) is included in the graph. In this case the lighter valve wasn't different enough to matter, but nobody should ever assume this is always the case. I've seen the same valve comparison with a different cam knock over 1,000 RPM of peak limiting speed out of a system when the heavier valve was installed.

Re: Hollow stem valves
 

Good info.Bill C.

Re: Hollow stem valves
 

My intake valves are the close ones. I run both as close as I have learned I can get away with. I run my intakes at .040". Have gotten by with .036". Lose 100 on the seat, they hit.