Sonix

iTrader: (1)

I'm still a little ways off from needing this info, but i'm buying it all from summit, so i'd like to be sure before I buy it....
I'm trying to decide between two cams, and the springs to match.
Heads will be 416 castings, P&P'ed with 1.94&1.5" valves.
Car will be street driven most, but may see a race track a handful of times for bragging rights. Won't be a daily driver, but a weekend fun machine.
headers, intake manifold, etc, all will be upgraded to match.

I'm deciding between the:

Comp XE268h, and lunati voodoo 268.

Specs are:

cam Lift Duration .050 duration LSA
Comp268 .477/.480 268/280 224/230 110
lunati .489/.504 267/276 227/233 110
comp274 .490/.490 274/286 230/236 110


(I threw in the 274 for comparisions sake). recommended RPM ranges are:
1600/5800
1800-6200
1800-6000

I'm leaning towards the lunati, even though it's closer to the comp274 cam....

And finally, lunati only recommends a single spring, 1.24"OD or so, comp recommends a 981 single spring (close to the same), with a 986 dual spring as a preferred choice. Which spring should I use, and would I need the spring pockets machined?

Thanks a bunch for any tips or insight!

Stekman

I am assuming the heads will be machined to allow for more valve lift.

For a 305, both I think would work. From your posted numbers, the Lunati has slightly more aggressive ramp rates than the Comp Cam (Having less advertised - conservativly, but more .050"). The Comp has the SLIGHTLY larger advertised duration, but I'm not sure how Lunati measures advertised, so take that with a grain of salt. But because Comp has a lesser .050", I would imagine it to have a lesser effective overlap than the Lunati - it would play a 'little' better with the LG4's weak compression.

What's the rest of the setup? Intake, rear end, etc. This really needs to be known before any suggestions can be made with a hint of accuracy.

As far as valve springs would go, what springs does Lunati recommend? What spring rates, what installed height. Compare them both. If the Lunati springs recommended for the Voodoo cam are closer to the 981, i would consider the 986 springs for the Voodoo, just by how aggressive it is compared to the Comp.

Sonix

iTrader: (1)

it'll be for a 350, maybe deck the block... I'll port the heads and check the CC's, then see which pistons i'll get, and if I need to mill the heads or deck the block to get a desired 9.3ish SCR.

performer RPM q-jet intake manifold.
I'm looking for a 2000-6000RPM powerband, or lower.
rear is a 10 bolt 3.23 posi, stock. it'll have a girdle and zytanium cross shaft.


lunati recommends a single spring, 1.266" od, 110lbs at seat, 1.75" installed height, 345lbs open @1.23".
Yea I was thinking the 986 springs for either would be better, as they'd allow more high RPM stability... correct?

What machining is needed for those springs and or the extra lift?
I'll be using collared studs, probably no guide plates (maybe...)....
machine down the valve guides? might as well get 'em done for positive valve stem seals then eh?

Stekman

If it's a track car more or less, I would go for a little more seat pressure (not sure off hand what the 986's are) to help prevent valve float.

Machining for more lift is basically a shop takes a special cutter and mills down the guide boss, allowing more room between it and the bottom of the retainer. And yes, then would be a good time to get it cut for aftermarket posi seals.

Cutting for a larger diameter spring is a seperate cutter, but they basically enlarge the spring pocket. If you don't want to enlarge the pockets, Isky makes a spring, the 235-D, which is a 1.26 OD, with spring rates quite similar to the 986: 130 lbs @ 1.750" and 320 lbs @ 1.200. I used these on the 416's and never had any issue with them. They're just like the 981's - an outter spring with a damper coil. Just another spring to compare with...

Sonix

iTrader: (1)

no, it'll be a pure street car essentially.

ok, so on 416's, 1.266" is the stock pocket size? (on most sbc heads?)

excellent.

ME Leigh

That Lunati sounds like a pretty nice cam. From what i've hear the Voodoo's are the most agressive ramp designs out there.

Sonix

iTrader: (1)

yea, alright, well if there are no other thoughts, i'll stick with the lunati cam, and probably the lunati recommended springs, then I won't need that extra machine work done... (save a bit of $)

hey leigh, your car running yet? that sounded like a real fun car..

ME Leigh

Yeah it runs, its freakin nuts. As soon as hits around 4000 rpm it takes off like a mother. I'm still trying to tune it some more. I need to recurve the distributor and tune the carb better.

I can't wait till it gets warm again.