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Cylinder head question

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 6:32am
If you don't mind me asking, what springs are Comp recommending?
The reason for asking is that the local engine shop has been asking Comp Technical Support and they have been advising lighter springs then what is recommended on the Cam Cards.
The engine shop is doing this every time now since coming good on 3 engines that didn't survive break in. A big cost to them and they have been rebuilding engines for decades.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 7:19am
FWIW, my catalog says 926-16 springs with the 280H.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 7:57am
Compare that to a Ferrea AMC S10020 110lbs close, 300lbs open and a spring rate of 360LBS vs Comps spring rate of 415lbs.
Something seems a miss for a valve under 0.500" lift.
Personal opinion is that Comp is putting a lot more wear on valve train components then necessary for the application.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 6:01pm
So what you are saying is that all of these cam lobe failures have nothing to do with ZDPP in the oil or break in procedure, just that Comp is specifying over the top springs?

Ferrea AMC S10020 ill have 137 lbs on the seat if you install them at 1.8" (same height as comp) and 317 lbs at 0.500" lift based on that. Comp 926-16 is 109 on the seat and 317 lbs at 0.500" lift. 

Open load is effectively the same, just that Ferrea is using a higher seat load to get there, while Comp is using a higher spring rate. I'd like to see some sort of reasoning for which would be better for camshaft/lifter durability?

Stock spec is 85-93 lbs on the seat and 193-207 lbs open at 0.424" lift for reference, 261 lb/in (1968 TSM)


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 7:27pm
A little light reading:
What I'm implying is that Comp has gone the easy route of increased spring rate rather then engineer springs for the same open and close pressures with the least spring rate required to do the job.
Increasing the spring rate may keep the lifter on the lobe at highest RPM, but also increases friction, thus heat, wear and more HP to drive the spring.
I believe Comp is advertising/pushing BS instead of doing the engineering at the cost of the consumer.
If Ferrea/other manufacturers can do the same work with significantly less HP and component wear, what is Comp doing???
Work is force/distance. If the distance is the same, why does Comp want the engine to do more work for the same job??? Component wear and profit???
I admit personal bias for years now since my first of several Comp failures. Narrow lobes, poor quality, lifter wear ..., maybe just my bad luck.
Don't trust them any more and have not seen any change in the last decade that would make me install their product or trust their engineering. They are still the highest failure cam on break-in to this day from what I read.
I have not heard of an Elgin, Howards, Lunati, Erson, Crower cam fail on break in. Ford, Chev ...
Comp's - plenty - even their rollers. 



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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 8:08pm
Your reasoning is not valid in this case, assuming both springs are installed at the same height of 1.8", which I believe is somewhere around the mark for a factory head. The Ferrea spring will always have more load on the valvetrain other than at maximum lift of 0.500", using that as the basis of comparison.



You would have to make a case that the Comp spring doesn't have enough load on the seat and that is maybe leading to failures. Perhaps there is something in that. Could also be that people are not checking the actual installed height and either under or over specifying their springs.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 8:36pm
Reading through the article you posted, it also supports having more seat load to control the valve, so there may be something in that.

If you go back to the Comp 926-16 spring and install it at 1.85", the seat pressure drops from 109 lbs down to 88 lbs, that's down around where the factory spring sits. Would only take a valve grind to increase the installed height of the spring into possibly dangerous territory.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote PROSTOCKTOM Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 9:08pm
You also have to take into consideration that you'll lose 10% of the spring rate within a couple of hours of run time, so using the higher rate spring would be my choice alone for this reason. You can always shim them up to get more seat pressure if needed. So long as you have coil bind clearance your golden shimming away.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Trader Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 9:49pm
Forgetting my personal bias. 
Western, you are graphing linear springs. Within the margin of difference between the Comp and Ferrea springs the open and close pressures are very close but the spring rates are significantly different and the forces are also significantly different. These are non linear springs and the graph would not be straight lines.
If you want, try graphing using these formula:

Multiply that difference in force by 16 and convert that to HP. Valve trains can take a lot out of an engine. The perfect spring opens and closes the valve at it's extreme without loosing contact with the camshaft. Any extra force is lost energy or lost HP. A delicate balance that can produce great results if done right.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WesternRed Quote  Post ReplyReply Direct Link To This Post Posted: Jun/30/2020 at 11:51pm
Both the Comp and Ferrea springs in this example would be linear spring, you need to get into beehive springs to get something non-linear.

I would say there is a much greater risk that the Comp springs wouldn’t control the lifter on the seat unless careful consideration is made of the installed height. 

I did give some consideration to beehive springs for the heads I’m working on now, but ultimately decided that dual springs had the added safety benefit of some redundancy (dubious) and were a much cheaper option.

Could have done single with damper, but would have ended up with some crazy high spring rate that didn’t really work at both ends of the scale.




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