Hollow stem valves

[Rob Wright]

Originally Posted by Ed Wright

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

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.

[Jim Hanig]

Originally Posted by Rob Wright

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.

How much did you have on the seat?

[Chris Hill]

Originally Posted by Rob Wright

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.

Would you mind posting graphs of the data if available?

Chris Hill
Old valvetrain engineer

[Rob Wright]

Originally Posted by Chris Hill

Would you mind posting graphs of the data if available?

Chris Hill
Old valvetrain engineer

I will when I get back to base next week

[Rob Wright]

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.

[CFMCNC]

Good info.Bill C.

[Ed Wright]

Originally Posted by Rob Wright

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.

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?

[Greg Hill]

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.

[James L Miller]

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.

[SSGT Mustang]

Originally Posted by James L Miller

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.

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.