Safe spring pressure for BB cam break-in

Discussion in 'High Performance Modifications' started by Greg Mc, Mar 29, 2021.

  1. Greg Mc

    Greg Mc Veteran Member

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    It is common knowledge that in order for a Hydraulic FT cam to survive during break-in you have to lower the spring pressure...especially for a BB. Does anybody have target #s for safe spring pressures to reduce the chance of losing a cam. I have a set of used springs that I am wanting to use but I don't want to go to low and bounce the valve and create another issue.

    Cam specs: Lunati Voodoo 268/276 duration and .542/.554 lift. The break-in spring I want to use is a old (well used) double with the inner spring removed. With the inner spring removed and installed at 1.88 spring height it reads 100# on the seat, at a lift of .550 the spring reads 235#. If I remove the damper the spring goes down to 90# on the seat and it takes 25# off at .550 lift.....so new rate over the nose is 210#.

    The recommended Lunati valve springs for this cam have a spring rate of 348 and would be 118# at 1.88 and at .550 lift the pressure would read about 310#. The engine is assembled with the single springs but I left the dampers installed. So do I pull the springs back out, remove the dampers so I can get the lowest possible pressure over the nose of the cam? BTW, the heads are peanut port 236 with stock valves.
     
  2. carhead22000

    carhead22000 oldblue

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    i broke in that same cam on my bbc...with the springs the way they were...worked out fine.i used hotrod oil.lots of joe gibbs on assembly.your gonna love that cam.....works amazing in a street car.
     
  3. carhead22000

    carhead22000 oldblue

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    let me know how it works with those heads..i have a set...also have a 496 bottom end....so was thinking of using my trickflow heads on 496.putting peanuts on the 454...thanks
     
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  4. 1980RS

    1980RS Veteran Member

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    Old used single outer spring is what I use for a cam break in, nothing more. Change them out after the engine cools off, reset the lash and of to racing with the new cam.
     
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  5. Rustbucket350

    Rustbucket350 Veteran Member

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    I'm not an expert but I'm pretty sure you're overthinking this. That's a very mild cam for a big block. I'd use factory springs, dump some comp cams break in oil in it, run it for 10-15 minutes, and go burn tires. What do I know though? I'm just a guy on the internet.

    Seriously. The factory springs are about as soft a rate you can get. If your new cam has a problem with them you have a cam problem not a spring problem. I always say I rev factory small block springs to 7500. And I do without valve float. No magic. How much worse could big block springs be? My guess is they're probably better.
     
  6. Greg Mc

    Greg Mc Veteran Member

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    Hydraulic cam break in with a BB......not sure you can overthink this one. I called Lunati and they said i would be fine with just pulling the inner springs and leaving the damper, 235 lbs at lift is soft enough to not cause an issue. Will run some break in oil, may also add some additive and let it roll.
     
  7. 1980RS

    1980RS Veteran Member

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    My weak ass break in springs are #85 seat and 175 open, but since I do not rev the engine past 2500 there is nothing to worry about, cams look great after the break in period. Don't forget to add an extra quart or two of oil during that 20 minute period to splash the crap out of the cam.
     
  8. MagicRatt

    MagicRatt Veteran Member

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    Also, make sure your lifters rotate freely inside the bore. A lifter that don't rotate will surely wipe a cam lobe no matter the spring rate. Ask me how I know.............

    Rich
     
  9. Greg Mc

    Greg Mc Veteran Member

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    Didn't really think about adding extra oil but may try that. I did make sure the lifters rotated before I installed the intake but with these big blocks I know there is no guarantee. If it wipes a lobe, I'll swap to hydraulic roller. I am running a blocked bypass so hopefully if there is any issue the filter will catch everything. I have a wire mesh screen that sits on top of the filter but haven't decided if I am going to run it during break in or not.
     
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  10. 1980RS

    1980RS Veteran Member

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    I also set the carb to run at 1500 rpm or higher before I tear the engine down and make sure the fuel bowls are full when first fire up. I do take the distributor when the plug is on No.1 then I will turn it until I see the spark fire on my ST-125 plug tester, give it another 1/4 inch and get ready to fire it up. Make sure you prime the oil system before dropping in the distributor also as you need to get it running right away and up to speed quickly. Like I said, it's been almost 30 years since I have lost a flat tappet cam doing it this way.
     

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