“Overlap is the most important element of cam timing.”
“No! Duration…or lift…or LSA is the most important element in cam timing.”
The reality is, none of these are the ONLY element to consider when choosing a performance camshaft for your application.
If power is your major concern, the very best method is to look at actual back-to-back dyno results versus other cams you might be considering—as this tells you not about possible outcomes, but actual outcomes.
Dyno results on power production are all well and good—but power production is only one of many reasons why enthusiasts choose a camshaft. The other (many) elements can include price, sound (the chop), and even compatibility with a stock torque converter. Often times these elements are the deciding factor, despite what the dyno says. After all, how many people would pick a cam that makes five to ten more horsepower, when it costs twice as much as the cam that makes slightly less?
Reasons for cam choices are as varied as individuals, but today we focus on overlap and why it (despite the keyboard warriors) does not determine the effective rpm range of a camshaft.
Our L33 LS Motor for This Camshaft Test
Before testing or discussing the two Summit Racing Pro LS cams, we needed a suitable test motor. Sitting on the stand, just begging to be put back in the game, was our trusty stock bottom end 5.3L.
Originally plucked (big score!) from a local wrecking yard, the all-aluminum L33 5.3L LS engine featured the very desirable aluminum block, matching aluminum 799/243 (the most desirable factory cathedral port) heads and early (not ideal…but still good) truck intake. Though it was possible to run the cam test on the stock motor, our L33 had already been subjected to endless testing (like, hundreds of dyno pulls) and a whole slew of upgrades.
Because of the RPM potential of the combination, the heads also received a valve spring upgrade in the form of the BTR Extreme RPM dual spring package. The head flow would come in handy when running the Summit Racing Pro LS 8711R1 cam and short-runner intake.
The First Test Camshaft
To kick off the cam test, we first equipped the 5.3L with a Summit Racing Pro LS 8711R1 camshaft that offered a 0.625/0.605″ lift split, a 234/248 degree duration split and 113.5 + 3.5 degree LSA.
The interesting aspect of this cam comparison is that the Big Nasty 5/4 cam shared the same overlap, despite having wildly different cam specs (0.550″ lift, 218/230 degree duration split, and 105 +3 degree LSA). The folks at Summit Racing wanted to provide a cam with all the chop, but with much more low-speed torque, essentially offering a torque cam that sounded all-the-world like a nasty race cam!
Because the Pro LS 8711R1 cam specs were optimized for higher engine speeds, we first equipped with 5.3L test motor with a short-runner intake, also designed to optimize power production at higher engine speeds. When combined with the 1-7/8-inch headers, 105mm throttle body, and Holley HP engine management system, the Summit Racing-cammed 5.3L spun right up to 7,500 rpm, run after run.
Equipped with the Summit Racing Pro LS 8711R1 cam, the TFS-headed 5.3L produced 532.9 hp at 7,500 rpm and 413 lb.-ft. of torque at 6,000 rpm. I guess the combination of wilder cam timing, short-runner intake and ample head flow allowed the SBE 5.3L to really shine on the big end.
The “Big Nasty” Cam Comparison Test
After running the Summit Racing Pro LS 8711R1 cam with the Holley Lo-Ram, we made a decision to first perform an intake swap. Despite sharing the same 14 degrees of overlap, the Summit Racing Big Nasty 5/4 race cam was actually much more efficient at lower engine speeds.
The Big Nasty would be a better match to a long-runner intake than the super shorty Holley Lo-Ram, but because we wanted a direct back-to-back test, we first ran the 8711R1 cam again with a factory truck intake. Run with the truck intake and 8711R1 cam, the 5.3L combo produced 488.5 hp at 6,700 rpm (800 rpm lower than with the Lo-Ram) and 432.5 lb.-ft. of torque at 5,400 rpm (600 rpm lower).
After running the 8711R1 with the truck intake, we tore into the 5.3L and swapped in the Big Nasty!
Equipped with the Big Nasty cam, the modified L33 produced 459 hp at 6,500 rpm and 438.8 hp at 4,800 rpm. Naturally, the milder Big Nasty produced less power than the bigger 8711R1 cam, but it did offer more peak torque (by six lb.-ft.). The minor gain in peak torque did not show the real strength of the Big Nasty specs, which came down below 3,000 rpm.
Compared at 2,800 rpm, the Big Nasty offered an additional 51 lb.-ft. of torque, and out-powered the bigger cam up to 5,400 rpm.
Remember, these two cams had the same overlap, yet offered wildly different power curves!
Richard Holdener is a technical editor with over 25 years of hands-on experience in the automotive industry. He's authored several books on performance engine building and written numerous articles for publications like Hot Rod, Car Craft, Super Chevy, Power & Performance, GM High Tech, and many others.