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.