Valve Springs

[JimNolan]

Guys,
   I've got a question. I had a Comp Cam Kit that came with #426 valve springs. The collapsed height would give me 317 lbs spring pressure and they are already installed on the heads I'm going to use. I decided to go with a different Comp Cam with the same lift but that cam says to use a #940 valve spring that would deliver 213 lbs collapsed pressure. Both these valves have about the same installed height and both coil bind heights are far from causing a problem. Lift is less than .500" on either cam.
  Is there any reason for me not to use the 33% heavier spring with the cam that says it should have a 33% lighter spring. Jim  Thanks

[jayb]

In my opinion there is no reason not to use your existing springs.  I think they will work fine - Jay

[JimNolan]

Thank you Jay. Appreciate that. Jim

[jimeast]

Is the spring a single or a double?  I'm curious what the cutoff in spring pressure is to dictate break in with the inner spring removed, or if the spring is a single, doing break in with a wimpier spring?

Note: I'm assuming a flat tappet, your cam maybe a roller.

[JimNolan]

jimeast,
   It's a spring with a flat type inner spring that I think they call a dampner. From the measurements it shows that the installed pressure with the new spring is within 15 lbs/in and when the spring is collapsed at my lobe lift it's only 70 lbs/in difference to the plus side. I don't understand how an XE265 (smaller cam) would have heavier springs than a 268H cam. It's not like the 268H cam is made from aluminum and can't use a heavier spring. Jim

[rockhouse66]

I am guessing that XE has a much more aggressive ramp.  I think it is one of those assymetric grinds and you can actually see the difference in lobe shape on the opening/closing ramps with the opening ramp being pretty steep.  Comp probably doesn't want to leave the valve behind when the cam goes over the top of the lobe.

[jayb]

Is the spring a single or a double?  I'm curious what the cutoff in spring pressure is to dictate break in with the inner spring removed, or if the spring is a single, doing break in with a wimpier spring?

Note: I'm assuming a flat tappet, your cam maybe a roller.

Just as a rule of thumb, I think if you are running more than about 175 pounds on the seat or 350 pounds open, you should swap out the springs to lighter weight ones for break-in.  There are lots of different opinions on that, but those are the numbers I go by.

[machoneman]

I agree with the idea of using the lighter springs for break-in as with today's lifter/heat treat/oil issues it's way too easy to flatten a flat tappet cam lobe (or three!). 'Course, with a roller or hydro roller this issue becomes moot.

[JimNolan]

The 268H Cam with a perfect 1.900" Installed Ht. and a 940 spring calls for  93 lb/ft. with valve closed and 213 lb/ft with valve fully open. There is .200" left over before coil bind of 1.400".
The XE265 Cam with a perfect 1.800" Installed Ht. and a 926 spring calls for 109 lb/ft with valve closed and 317 lb/ft with valve fully open. There is .170" left over before coil bind of 1.140".

What I have with 1.850" Installed Ht. and a 926 spring is 88 lb/ft with valve closed and 317 lb/ft with valve fully open. There is .210" left over before coil bind of 1.140".

I can change springs if need be. I can't get hold of Comp Cams, they don't respond. So, give me a yes / no answer guys. Thanks, You guys probably have more experience than the guy that won't answer me at comp cams anyway. Jim