Performance Boats Forum banner
1 - 7 of 7 Posts

·
Premium Member
Joined
·
1,683 Posts
Discussion Starter · #1 ·
Customer was having issues with getting his geometry correct. His OEM heads had longer valves and one of my camshafts. So the Geometry had changed. Here is his story:

Well to follow up with my last post with my valve geometry all out of wack. What happen is I had my my 781 heads sent out and machined for larger valves and with the result of my straub .600 lift cam my machinist put in .100 over longer intake valves. Which is all fine and dandy and is pretty common but what happen is it threw my rocker arm geometry all off. As you can see in my picture to achieve my 90 degree relation between my rocker and valve it resulted in my rocker tip to ride wayyy on the outside of my valve. I posted on here and after a quick response from Scott, Chris (from over at straub technologies) and many other knowledgeable guys on here I came to the conclusion of because I went with a longer valve I’d never be able to achieve a perfect 90 degree relation from rocker to valve with the rockers I had because it would ride way too close to the edge of the valve. Now I understand that most of you told me just to shorten the push rod and it “would work” and it prolly would have, but I knew it just wasn’t the correct way to do it. So I made a call to my cam builder Chris Straub and he told me exactly what was happening and exactly what I needed. Due to the “universal” rockers I had they just wouldn’t work for a none stock head. He hooked me up with a set of custom rockers he has made just for this application and I’ll tell you what! He was right on the money. Landed dead center on the valve with +-.040 sweep. I’d like to thank them guys over there at straub for helping me out and their costumer service is second to none for sure! I really suggest everyone pop a valve cover off and check this cuz if you do I guarantee them custom rockers will be falling off the shelf.
 

Attachments

·
Registered
Joined
·
3,895 Posts
I can't believe nobody has combined the two posts about rocker and push-rod geometry and write an article to clarify "how to set up a cam with correct geometry in the valve train" It is something I do every time I build an engine. Mark
 

·
steelcomp was here
Joined
·
26,529 Posts
I can't believe nobody has combined the two posts about rocker and push-rod geometry and write an article to clarify "how to set up a cam with correct geometry in the valve train" It is something I do every time I build an engine. Mark
Go right ahead. :thumb:
 

·
steelcomp was here
Joined
·
26,529 Posts
This would be a good idea, also what difference would a hydraulic vs a solid roller make.
No difference in geometry. The geometry is about the relationship between the rocker and valve. Has nothing to do with the lifter. Only thing you have to be conscious of with hyd lifter is not compressing the piston in the hyd lifter during any testing or measuring. Other than that it's all the same.
 
1 - 7 of 7 Posts
Top