Valve Spring Tension wears out a cam ?

[Toomanyhobbys]

I was told by a local speed shop that I have to be very careful about cam selection with Vortec heads that have been modified to accept over a 500 lift. This doens't make any sense to me if you are gonna run a cam at least that or close. I want to run Comp Cams Extrem energy cam 490/490

 

[Marv D]

I'm wondering if he is confused, or maybe you misunderstood what he was geting at. Every cam is designed with a specific need for seat pressure, and open pressure. You get too much spring pressure and yes, you stand a good chance of wiping a lobe away. Too little spring and you have valve float, lifter and valve bounce. It doesn't take much of that to destroy a BUNCH of things, and the cam may be the least of your worries. The cam you choose will have a spring requirement,, too many people think that's just a 'suggestion'. With modern cam ramps you better take heed to what the cam grinder lists for both seat pressure and open pressure. The days of "oh I put a set of the Z-28 springs in it" are over. The old Z-28 springs are designed for the old cams. With the new agressive XE ramps you will beat hell out of things with the improper spring.
Have I harped on this enough,, are you going to check what spring matches the cam you want?????

 

[Toomanyhobbys]

Sorry Dad, I won't let it happen again.

This is very good information. And I beleive I was the one who misunderstood, now that it has been explained to me.

 

[Toomanyhobbys]

Here is comp cams stats sheet. Can you please tell me where the spring pressure is?

http://www.compcams.com/Technical/CurrentCatalog/HTML/128-169.asp

 

[CNC BLOCKS]

We have always used the ISKY 235-D as its a 1.250 spring and we have used these on the circle track engines we have build for years with no problems and some of the hydraulic cams we use are around 500 lift and I believe its 135 @1.750 and good up to 550 liftand we always use the AC Delco lifter from GM with no issues so far and good oil is a must as we recomend the Brad Penn oil which is the old green Kendell oil (http://www.amref.com/) and is marketed as racing oil as most of the other 20/50 oils out there don't say racing oil on the bottles any more due to the lowering the zinc and phasphate which are the anti wear packages in oils.

Just my 02 cents and what works for our engine shop.

 

[dustypowers]

slop makes waste, unless running rollers then u want it to sew like a machine is how i was taught

 

[rustbucket79]

Comp doesn't spec required spring pressures, they suggest a spring choice. If you are looking at the XE274H cam, the base spring they suggest is the 981-16, which is a 1.250 single spring with dampner, roughly equivalent to a Z/28 spring. Then you thumb through the catalogue and find the spring they suggest, and look at the seat pressure listed, which is 105#. They list the open pressure of 295# at .450 lift, so you have to calculate the pressure at .490 lift using the listed spring rate of 423#/inch, giving you a net open pressure of roughly 312 pounds.
They also list an optional upgrade spring for that cam, P/N 986-16. It's a 1.430 double spring with dampner, requiring different retainers, more spring pocket machining, and in this case an additional .050" of installed height to achieve it's suggested seat pressure of 132#, and a listed open pressure of 280#.
The 981-16 spring is close to it's limit in that application and the high open pressure can cause a lobe failure during break in if everything isn't perfect. I prefer to use a double spring in this application as the higher seat pressure won't hurt anything and will control valve bounce much better, and the lower open pressure is less of an issue for lobe failure.

 

[Damon]

EXACTLY what Rust said..... I've often found that the standard recommended 1.25" spring for typical street performance flat tappet cams seems to have a very high "rate"- meaning the pressure over the nose is very high compared to the modest seat pressure. Crane has the same issue with it's 99848 springs (very similar to the Comp 981 springs). Often you'll find that the "upgraded" spring recommended for these cams has more seat pressure but LESS open pressure, due to a lower spring rate. That NEVER made sense to me. Flat tappets need quite a bit of seat pressure but not nearly what a roller needs over the nose. So why have high rate springs spec'ed for a mild flat tappet cam? I have no idea. In fact, I think I'll start a fresh thread about this. Rust- you're definitely invited.

 

[Dirt Reynolds]

In Car Craft, May '99, Joe Sherman built a 580-horse 357ci engine. He used an Isky oval track solid cam which wound well into the 7000 RPM range. The valvesprings selected were described as follows:

"Isky's recommended dual-spring assembly delivers more seat pressure but less open pressure than the norm; Isky claims this enhances spring life and reduces cam wear."

 

[pdq67]

Remember, there are two different cams we are talking about! Solid and hydraulic.

A hydraulic cam needs less seat pressure than a solid cam or you can collapse the plunger.

Solid cams since they are solid are generally ground more aggressive than a hy-cam, therefore need more seat as well as over the noise pressure.

I shoot for about 125/315 to 135/325 for a cam like a CC 282S solid and more like a 112/280 to 120/300 for the 280 Magnum. Old-fashioned STREET CAMS IS ALL!! Never over 350!!!

Rust, am I making since??

And as for the 1.25" dia., .550" lift jobber, I figure it is one of two made by Elgin!!

I can't comment about the new XE cams b/c when you get to the back of the book, they tend to fall into the smaller RACE lobe catagory, imho!!

pdq67