john.tempest

Hey guys, as the title states, I am taking a set of the CNC ported GMPP heads and putting in the comp 26918. My question is how big of a cam can I safely run with these springs? I know they advertise .625 but is this realistic? Anybody done this combination before. I would like to put a cam with at least .6 intake and exhaust, but I need some feed back.

It is going to be a stroked 408 ls with -8 CC Wiseco pistons, LS3 intake, and a ported TB.

Thanks!

ahritchie

iTrader: (1)

Why not spec a cam that is designed to meet your performance/driveability goals and specific application details (what are they???) instead of just trying to slap in the biggest possible cam that the springs can handle? Just a thought...

TyCZ28

With the big heavy intake valve in those heads i wouldnt even run over .600 with those springs. your looking at running an EXTREMELY mil 220's duration .580's lift cam which is TINY for a 408

john.tempest

Not trying to slap in the biggest cam possible. I have specs for a cam that I believe will meet my needs. I am just wondering how big of lift those springs can handle and whether I had to go to a set of double springs for the LS3 heads, which it looks like I do.

My cam, like I said will have at least .6 lift, for the 408, but I just wasn't sure what springs I needed.

redtan

iTrader: (5)

Think you're a little confused. The LS3s have very lightweight valves due to them being hollow stem.

Plus what does duration have to do with how heavy the valve is? You can certainly run more than 220 duration even with a heavy stainless valve.

TyCZ28

Compared to a lighter ls1 or ls6 valve i personally wouldnt not want to run anything over .600 with that spring. most lobes getting into the 230's comes with more than .600 lift which is playing with fire on those springs. personally id run bigger springs than over cam a set of springs and have it break.

john.tempest

Well there seems to be a bit of a debate here. I don't mind upgrading to the double springs, I just have the beehive style springs sitting and would like to use them if I can to save some money, but again, I don't want to break a spring or cause excessive wear anywhere. Anybody else wanna chime in?

96capricemgr

iTrader: (1)

Valve weight and rpm are every bit as critical as lift, all three matter a whole hell of a lot.

redtan

iTrader: (5)

There is more to lobes than just duration. A very aggressive lobe at .570 lift will be a helluva lot harsher on the valvetrain than a smooth endurance lobe at .630 lift. So again, lobe design is going to be much more critical in whether or not it will work with these springs rather than looking at lift itself.

And with custom grinds and lobes you can have 254 duration and still be under .600 lift.