Why does this solid cam need such a stout spring ?

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The Shocker

The Shocker

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I am in the process of upgrading my cam and w2 heads in my bracket car over the winter.The heads are currently at the machine shop for a valve job and to set up the valve spring heights.The cam i installed is an Iskenderian solid flat tappit and the springs they recomended call for 150 seat pressure and 330-350 open.Wanting to stay with a single i called Comp and they had a set that would work.The machinest called me and said they wouldnt fit the spring pockets ,so he had to get a double spring set up.My question is why do i need so much spring pressure with so little lift ? The specs are as follows:

.507 /.507 lift
300/300 adv .duration
.254/.254 @ 50 duration
108 lobe seperation
cam is rated for 3000-7000 rpm

My old hydraulic flat tappit had .488/.510 lift and only required 90 lbs of seat pressure and 220 open.It was rated for 2500-6500 rpm .Why are they so different ???
 
Longer duration, means that the valves need to open and shut in a smaller amount of time... a more agressive profile requires more spring.
 
my take on this is first of all your duration is pretty high making for lots of rpm capability your spring needs to be up to the task... second isky will always over kill there parts that's why they seldom fail
 
I agree with you guys on the rpm valve control thing ,but im always seeing aftermarket heads that claim they come with springs that will work up to .575 or .600 bla ,bla , lift cam and sum are a single spring .How can they make a statement like that not knowing wiether a solid or hydraulic will be used with them with 210 degrees of duration or 320 ? I guess i thought spring pressure had more to do with lift /coil bind /rpm, than duration and ramp speed ...
 
Because they are saying the spring can be OPENED to that lift with there spring... Before coil bind. they dont know what kind of cam your using, you have to plan ahead on that!
 
replicaracer43 said:
Because they are saying the spring can be OPENED to that lift with there spring... Before coil bind. they dont know what kind of cam your using, you have to plan ahead on that!
Click to expand...

My old cam was no taxi cab cam though.It was 234 /244 duration @50 and it was a hydraulic with zero lash (plus a 1/2 turn im my case).

The solid is 254 /254 @50 with a hot lash of .028/.028.

Now subtract the .028 lash from the solid and your left with .480 lift on both sides (which is .030 less on the Exhaust than my old cam ).Wouldnt the lash of the solid also reduce the duration sum to over the hydraulic ?Im not arguing here im just trying to understand how these things are determined by cam manufacturers is all .I have researched the subject sum online ,but cant find the anwers .I doesnt really matter much as im doing what Isky recomends for the springs and installed height ,but still curious what its based on ...
 
Its in the RATE of lift, your new cam is like 20 degrees more @50 than the old one, at close to the same lift, therefore, the RATE or SPEED of the ramps is higher, thus harder to controll...... needs more spring pressure to do that
 
To me that spring pressure is not that crazy. Closed on the last set of heads I did for a Solid Flat Tappet was 140 Closed and 300 Open. I use to revv that motor to 7200 Rpm all the time and it never missed a beat. Ran crisp and clean up there in that RPM.
 
replicaracer43 said:
Its in the RATE of lift, your new cam is like 20 degrees more @50 than the old one, at close to the same lift, therefore, the RATE or SPEED of the ramps is higher, thus harder to controll...... needs more spring pressure to do that
Click to expand...

Now i understand why .Just needed sumone to break it down .Basically its a matter of the valve and lifter trying to follow a more agressive lobe profile ,so they need more spring pressure to keep things following each other properly.Thanks...
 
YES that is correct! which W2 head do you have? the econo or the race? I know the rockers for the race W2 are super heavy, I have a set of those.
 
I agree with you Shocker about trying to use a single. I always looked there first too. Even though you can find numbers that look like they'd be good, the cam companies do extensive tests before making recommendations. Believe me they don't want you to use more pressure then you need......to easy to wipe a lobe and make them look bad. The spring wire size, design and the harmonics a particular lobe creates really dictates the choice.
 
254 degrees at .050 with .507 gross lift is not an aggressive ramp...as said that is a taxi cab ramp...

aluminium rockers are available for both econo and race heads..as said the old ductile iron are pretty heavy..and they come as bushed and non-bushed rockers.

solid lifter cam you need at least about 140 lbs on the seat...any loss motion will cause the valves to float without enough spring pressure.
 
70aarcuda said:
254 degrees at .050 with .507 gross lift is not an aggressive ramp...as said that is a taxi cab ramp...

aluminium rockers are available for both econo and race heads..as said the old ductile iron are pretty heavy..and they come as bushed and non-bushed rockers.

solid lifter cam you need at least about 140 lbs on the seat...any loss motion will cause the valves to float without enough spring pressure.
Click to expand...

I already have Harland Sharp shaft rollers.They are Econo Heads with the rocker stands on them.
 
OldmanRick said:
I agree with you Shocker about trying to use a single. I always looked there first too. Even though you can find numbers that look like they'd be good, the cam companies do extensive tests before making recommendations. Believe me they don't want you to use more pressure then you need......to easy to wipe a lobe and make them look bad. The spring wire size, design and the harmonics a particular lobe creates really dictates the choice.
Click to expand...

when dbls are used i always break them in with just the out'rs.
 
70aarcuda said:
solid lifter cam you need at least about 140 lbs on the seat...
Click to expand...

Not necessarily true at all with street and once in a while strip...and really depends on the cam in the first place.
If you turn high rpms all the time aka drag car...then yes, more is better and springs do wear out, but more psi than needed is just parasitic drag...

btw dont forget spring lose around 7-9 psi after run in...
 
1wild&crazyguy said:
when dbls are used i always break them in with just the out'rs.
Click to expand...

This is a subject you guys actually changed my mind on. Never really ran any monster springs, but i used to break in with milder doubles and was successful. Thanks to the stories and expertise here, i don't think i would try it now days. Ironic that the only failure i had, and i caught it early, was on a SBC with a Crower 460" / 218*@.050 hyd. with singles and that was 1,000 mi in from a no spin lifter.....lol.
 
the cam manufacturers tell you to remove the inter spring to limit their liability of lobe failure during cam break it....

proper moly lube on cam....oil system primed and ready to go...and getting the engine to fire immediately and not letting it idle are the most important things in breaking in a flat tappet cam...
 

I'm having a set of heads done for a mild roller cam. The cam calls for 105# on the closed valve and 310# on the open valve. They had just finished a set of BBC heads, 600#+ on the open valve and I forget the seat pressure. Don't forget the springs will soften somewhat with usage.
 
70aarcuda said:
the cam manufacturers tell you to remove the inter spring to limit their liability of lobe failure during cam break it....

proper moly lube on cam....oil system primed and ready to go...and getting the engine to fire immediately and not letting it idle are the most important things in breaking in a flat tappet cam...
Click to expand...
I always moly the cam lobes upon installation.I dont drop the lifters in till im ready to set the valves .Then they get lots of moly on their faces.I also put sum on the pushrod tips ,and the rocker and valve tips.Right before i put the intake on i take what ever moly is left and mix it with oil then pour it all over the cam and lifters.I allow an hour or so for the rtv to dry on the intake gaskets and then fire away before all that i have drinched can drip into the pan.Fresh oil gets a full qaurt of Resolone Zinc additive for the break-in.If i lose a lobe i lose it ,but i did what i could do .I replaced the flat cam (with only 1500 miles on it that the PO installed) in my 454 Chevy powered hauler last summer.Did the break'in like i described above and its still going strong 2500 miles and 6 months later...
 
You can use the weak springs like Loco says, or just break it in w/the single. I don't know of any single that is so aggressive that it can't successfully be used to break in the cam but you do have to make sure it fires immediately, runs for long enough, isn't turned enough that the break in paste is rubbed off, and that the lifters rotate.
 
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