TUNING NOTES
Many guys--our subject '69 Nova's owner included--don't retard their total timing when running relatively small shots of nitrous. We don't condone it, but we know it happens, and our before testing was done "as is." After our cam swap, our runs on the motor were made at 40 degrees, a figure that Westech's Mena retarded to 36 degrees when we hit the juice. At car owner Pete Cervantes' request, we made one last motor-only pull with the timing left at 36 degrees...and equaled our best numbers of the day. Iron heads can sometimes be relatively insensitive to timing changes, and this seems to be one of those cases. We note it here in the interest of full disclosure, but guys, if you're gonna squeeze, retard that timing!
Though we've said it before, it bears repeating--when switching from a flat-tappet to a roller cam, you must use a thrust button to limit cam endplay. We picked up this slick setup with our other Comp goodies, which included a new Magnum timing set. The cover incorporates a welded thrust-plate tab for use with the included needle-bearing-type cam button. We set our endplay at 0.015 inch, right in the middle of the 0.010-0.020 inch Westech recommends.
Of course--and we cite the Comp catalog here--the proper length pushrod is the one that creates proper valvetrain geometry. Note the marks left by one of our rocker-arm roller tips when activated by the proper length pushrod--the marks in the Dykem show that the roller has moved across the valve tip but remained roughly in the center during its travel. This is the type of pattern you want to see.
We showed you proper valvetrain geometry above on an installed valve, but before we got too carried away, we double-checked our piston-to-valve clearance before final installation. We pretty much knew we could get away with our chosen lift figures based on the bigger cam specs that had been contemplated at this engine's inception, but it pays to double-check before piston meets valve--right? Even with the bigger 'stick, we had 0.175-inch clearance on the exhaust side and an amazing 0.295 inch on the intake.
Pushrod length must also be accounted for when switching cams--Mena used a tried-and-true adjustable checking tool to determine that we needed 7.300-inch pushrods, which are 0.100 inch longer than what you'd find in a factory hydraulic roller cam setup.