Looking to get more lift from my cam and save having to teardown the whole bottom of motor with cam swap and just make up with adding more boost. I will be upgrading to a roller rocker and doing the springs at the same time.
I think the LT1 stock valve springs have an 85 pound closed seat pressure. Currently seeing 7.5 pounds of boost and will be upgrading brackets and intercooler in the hopes of seeing north of 12 pounds.
Comp cams beehive 26918 springs have a closed pressure of 130 pounds.
with a 2 inch valve the surface area of the valve is 3 square inches, so 12 pounds of boost would take away 36 pounds and leave 130-36 = 94 pounds closed seat pressure. Seems like it would be enough. At 15 pounds boost would still have 85 pounds.
OR I can go with an older school 977 dual spring that starts at 155 pounds closed seat.
I will have stock valves so I prefer to keep the spring to what is needed and keep with the lighter beehive retainers and am leaning toward the beehive path. Seems like 85 pounds would be enough and would not put any additional stress on the valves, timing gears, etc.
Stock lifters tend to start collapsing at ~125 psi closed seat psi. Some of the newer lifters (LS7 or the older LS6) will handle considerably more closed seat psi.
A number of years ago I had Lingenfelter machine up an 86 TPI motor, port the heads, and I used their hydraullic flat tappet cam for the TPI.
They put a dual valve spring on there at the time, I don't know the specs, but there is a good chance it was the 977 spring referred to above. I did not have any problems with it.
If you look at their hydraullic roller cams spec sheets, they recommend the dual springs with the 155 pound seat pressure and there are no notes to upgrade from the factory lifters.
Have you had issues with collapsing lifeters in the past?
I am leaning toward the beehives as I dont want any more spring pressure than is necessary.
Flat tappets are different than hydraulic roller tappets.
I have shimmed the factory roller tappets to see just under 135 psi, but can you be really absolutely sure that they are not collapsing slightly at high RPM. The newer lifters (LS6 or LS7) are actually designed for higher closed seat pressures.
Flat tappets are different than hydraulic roller tappets.
I have shimmed the factory roller tappets to see just under 135 psi, but can you be really absolutely sure that they are not collapsing slightly at high RPM. The newer lifters (LS6 or LS7) are actually designed for higher closed seat pressures.
Do you think the issues show up at high RPM or low RPM?
At high RPM, supercharger boost will subtract from the closed seat pressure, so from my calculations above at 12 lbs boost, a 130 pound spring will be reduced by 36 pounds closed.
Thanks for your input, I will keep looking into this. Comp cams did not mention any lifter concerns with the beehive springs, but I did not ask them specifically, which I will do.
Do you think the issues show up at high RPM or low RPM?
At high RPM, supercharger boost will subtract from the closed seat pressure, so from my calculations above at 12 lbs boost, a 130 pound spring will be reduced by 36 pounds closed.
Thanks for your input, I will keep looking into this. Comp cams did not mention any lifter concerns with the beehive springs, but I did not ask them specifically, which I will do.
Calloway was 130 on the seat and 310 open if that helps and around 12 psi boost..
Calloway was 130 on the seat and 310 open if that helps and around 12 psi boost..
The issue comes into play when you are trying to shim the springs to get the proper open seat psi to keep the lifters from leaving the cam cam face (valve float) in the upper RPM range.
Many people will shim to get the desired psi in the open position and inadvertantly exceed the closed seat psi in the process. I have run ~385 in the open seat psi without issue, but always tried to stay in the 125-135 psi range on closed seat psi with factory Gen I/II HR lifters.
I will say that I have exceeded those numbers by a large margin once I moved to the LS6 lifters (and the LS7 lifters will allow a bit further).
Aaron
You can do as much or more damage by not having enough seat pressure as the valve can bounce on closing with an agressive cam. Been there done that once. Pounds the seats to death. The nice thing about a solid lifter cam is you check the lash from time to time and pick up on things going bad early on. If you start losing lash from pounding the seats you lose spring pressure with it and it fails faster. Even worse driving easy does not stop it though does slow it down.. If I had a cam with fast ramps and 550 lift i would be thinking in the 150 to `160 on the seat and 385 open.
Corvette Store
Best valve springs and seat pressure for boost
