The vast majority of gearheads fall into two categories when it comes to choosing a camshaft: those who go too big, low-end torque and driveability be damned; and those who go too small, ensuring good street-going manners while leaving the performance potential of their powerplants unfulfilled.
The cold, hard truth is that guys who get it just right, picking a 'stick realistically matched to their engine combo and intended use, are in the minority. And that's unfortunate. We're not saying it's easy to pick the right cam, but if you're brutally honest about your goals and intentions--and willing to accept the counsel of experts--there's no reason not to have an engine that delivers exactly the powerband you're looking for.
By all accounts, Pete Cervantes created a stout little 383 stroker for his '69 Nova, seen in our June '07 "Horsepower Rules" compendium of 10 proven street/strip machines. A larger 'stick was discussed with the engine builder at the time of engine assembly, but the decision was made to go a conservative route to ensure good street-going manners. A Comp Cams XE268H hydraulic flat-tappet cam (PN 12-242-2) was slid into place, sporting 224/230 degrees duration at 0.050, 0.477/0.480 inch lift (punched up to 0.510/0.512 inch with 1.6:1 rocker arms), and a 110-degree LSA. The Nova threw down respectably with 353 hp at 5,800 rpm and 375 lb-ft of torque at 3,900. It's had a good, torquey powerband and responded well to the squeeze--on a 125 shot, the '69 ripped off an 11.84 at 117 mph, which is nothing to turn your nose up at.
On the other hand, Cervantes couldn't help but wonder what could have been had he gone with a more aggressive cam of the roller variety. We decided to take up the challenge and got on the horn to one of our favorite cam experts, Comp's Billy Godbold. We did what you should do when picking a cam: We sent Godbold the engine and vehicle specs and Cervantes spelled out exactly what he was looking for: a broad, flat, street-friendly powerband that revved a bit higher than before--and would also enhance the nitrous experience. "In other words," Godbold said, "he wants it all." Well, who doesn't?
Godbold considered our specs and performance goals and came back with a curveball: one of Comp's new Xtreme Fuel Injection cams, a 280XFI HR13. This 'stick runs 230/236 degrees at 0.050, along with 0.576/0.570 inch lift, and has a 113-degree LSA. Our response, of course, was, "You know the thing has a carb on it, right?" We briefly debated the issue but got past the hangup once Godbold explained the method to his madness. We really wanted three things: more power, a wide powerband, and good performance on nitrous. "The lobes we use in the XFI cams are the best design we have, period," Godbold declared. "All the engine cares about is the cfm the head is flowing, so the sooner we can get into higher lift the better the head looks." So not only did we increase lift, but we were also able to get into that lift at a quicker velocity--thanks to both the nature of a roller cam in general and the XFI lobes in particular. In this way, we took maximum advantage of the good-flowing ported and polished heads. The combination of the other two goals led us to the other critical factor: "No doubt that 113 LSA is producing a very flat torque curve and it works good with nitrous," Godbold continued. "We'd have gone with a tighter LSA without the nitrous."
Saying the 113 LSA works well with nitrous--and that the whole cam worked wonders on our combo--would be a massive understatement. The nitrous runs improved, as you might expect, as we came up with 38 more ponies and another 33 lb-ft on the squeeze. We can also tell you the numbers on the motor: 42 extra horsepower at almost identical rpm levels, all the while still picking up 13 lb-ft of torque. But look at the graphs, at how somewhere near 4,250 rpm the curves diverge, the newer cam continuing north as the older 'stick falls off. And to hear Cervantes tell it, you can feel it where it counts: "When you're on the street, you just give it the gas, and the power is already there," he told us. The power is all the way across the rpm range--and that's a good thing, indeed. But it gets even better, since this wake-up 'stick sliced 0.5 second off this Nova's e.t. and added another 4 mph to its trap speed. We won't say this cam is for everyone--it's not, of course--but the whole exercise vividly demonstrates why it pays to spell out your exact goals and seek expert camshaft help to achieve them.
Mission accomplished. Time to go shopping for a rollcage.
The Real WorldWe can tell you it's harder to swap a cam in a car than on the engine dyno, but you already know that, and a picture's worth a thousand words, right? In that vein, we bring you this telling shot of '69 Nova owner Pete Cervantes pushing down on his front bumper--and puttin' some weight behind it, we might add--so that Westech's Ernie Mena could just slip the old cam past and out of the engine bay. It definitely takes more time and effort to swap cams on an engine that's in a car, but that rear-wheel payoff is certainly sweet--as are the lessons learned by taking a real-world street/strip car and subjecting it to before and after testing. We hope you agree, and we want to thank Mena, Steve Brul, and the rest of the Westech crew for making this project possible.
What we Did
Swap the hydraulic flat-tappet cam in a 383 stroker for a much more aggressive hydraulic roller cam
This newly free-revving small-block makes more power everywhere.
383 STROKER SPECS
Our replacement cam of choice was an XFI 280 HR13, which Comp's Billy Godbold calls "the best lobe profile we've done." As for the stick it replaced, the venerable XE 268H, Godbold says, "It's about as good as flat-tappets get. We replaced our best flat-tappet cam with our best roller cam." What's so good about the new 'stick? Among other things, the intake and exhaust lobes are tailor-made for their tasks. Crudely speaking, an intake lobe gets the valve open, lets as much charge in as possible, and shuts. "Typically, the exhaust has a smaller closing ramp," Godbold tells us. "There's still flow when it's closing, so we try to smooth it. It's helping to pull in the next intake charge, so we don't want to slam that signal off." The cam is also optimized to work with 1.6:1 rockers and beehive valvesprings. "They work at a high frequency," our guru continues, "and save a tremendous amount of weight." It works for us.
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.
Beehive springs have been around for a while now, but the visual difference between them and traditional springs is still striking. Whichever spring you use in a cam swap, it's critical that you follow the manufacturer's recommendations for spring type and setup. Our springs, for instance, specify an installed height of 1.800 inches at 130 pounds--you must check these figures and make sure the springs are 0.060 inch away from the listed coil bind height (1.100 inches in our case) when subjected to your cam's maximum lift.
At this point, we still had a good chunk of this engine's top end left to reassemble, but with a fresh set of Fel-Pro 1205 intake gaskets laid on and the intake waiting, we stopped to look at our valvetrain handiwork: Magnum retrofit hydraulic roller lifters, pushrods, Pro Magnum rocker arms, and rpm-friendly beehive valvesprings. Of course, our new high-zoot camshaft is out of sight CHP
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