Thread: Give me your opinion on this engine combination....

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Originally Posted by 35chevy

One more question...The recommended valve springs for the cam install @ 1.75 and coil bind @ 1.060 which means they coil bind @ .660 lift. This cam has a .477/.480 lift and if I use 1.6 rockers it should be .509/.512. Looks to me with everything set up properly I should have .148 to spare before coil bind with the 1.6 rockers. A tech at comp cams told me a while back that won't work. Why?

I always figure it like you did, then put 'em in the bench vise and squeeze 'em down to max lift height. If you can slide a 0.010" feeler gauge in the 5 spaces between the coils for a total clearance of 0.050", you're good to go.

The Comp tech guy might have been advising you not to run the 1.6 rockers with an Extreme Energy grind. The profile is already ground right on the ragged edge of allowable geometry. Visualize the tappet edge digging into the cam lobe. With pressures reaching or exceeding 250,000 lbs per square inch at the tappet/lobe interface (with a nominal 300 lbs over the nose spring), you don't need the 1.6 rockers feeding the fire. You don't need 'em on this 350 anyway. The dyno I did above was with 1.5 rockers. You can sort of figure this for yourself by deducting the 0.050 duration from the advertised (0.006") duration. A difference of 60-70 degrees, as used back in the early days, will be very easy on everything. Latter day cams will generally be on the order of 50-60 degrees difference. Most all Crane Cams used a 56 degree difference. The Comp XE268H uses a 44 degree difference on the intake and 50 degrees on the exhaust. 44 degrees means 22 degrees on the opening ramp and 22 degrees on the closing ramp and that's in crankshaft degrees. It's only 11 degrees at the cam. You're picking up from 0.006" tappet lift to 0.050" tappet lift in only 11 cam degrees. That's why they call it Extreme Energy.