“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.
What happens when you run two cams that have the same overlap? Do they immediately make the same power? (Image/Richard Holdener)
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.
In its current configuration, the 5.3L was sporting a set of Trick Flow Specialties GenX 220 (Fast as Cast) aluminum cylinder heads for the LS. Impressive and effective right out of the box, the Fast as Cast heads were treated to further porting from the guys at Brian Tooley Racing. In addition to extensive porting, the TFS GenX heads were also milled 0.030 inch to help reduce the chamber size and increase static compression.
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!
There is nothing like a graph to show you the difference between two different combinations. Case in point, the difference in power between the Holley Lo-Ram intake and the factory truck intake when the modified 5.3L was equipped with the Summit Racing 8711R1 camshaft. Run with the Lo-Ram intake and Summit Racing Pro LS 8711R1 cam, the combination produced 532.9 hp all the way out at 7,500 rpm and 413 lb.-ft. of torque at 6,000 rpm. After installation of the factory truck intake, the peak numbers check in at 488.5 hp at a much lower 6,700 rpm, while peak torque jumped to 432.5 lb.-ft. at 5,400 rpm. It should be evident from the graph that the longer runners in the truck intake offered much more power up to 6,100 rpm, but the shorter runners offered more power past that point. (Dyno Chart/Richard Holdener)Because it might be argued the Summit Racing Pro LS 8711R1 cam was much better suited to the high-rpm, Lo-Ram intake, we ran that cam with both the Lo-Ram and truck intakes. Comparing the 8711R1 and the Big Nasty 5/4 race cam required that we select one intake, and for this test, we selected the factory truck intake. The reason for this choice was that, though the Big Nasty and 8711R1 shared identical overlap numbers, the two cams were designed for different effective operational speeds. Despite the overlap numbers, the Big Nasty was actually much more of a torque cam, and this showed in the results. Run with the 8711R1 cam and truck intake, the 5.3L produced peak numbers of 488.5 hp and 432.5 lb.-ft. of torque. After installation of the Big Nasty cam, the peak number checked in at 459 hp at 6,500 rpm and 438.8 lb.-ft. of torque at 4,800 rpm. Naturally peak power was down with the milder Big Nasty cam (488.5 to 459 hp), but peak torque was up (438.8 vs 432.5 lb.-ft.). The real difference in torque production was not in the peaks, but rather in the sub-3,000 rpm torque production, where the Big Nasty offered gains of over 50 lb.-ft.! (Dyno Chart/Richard Holdener)The 5.3L test mule started out life as an all-aluminum, junkyard L33 5.3L checking in with peak numbers of 365 hp and 389 lb.-ft. of torque when run on the engine dyno in (near) stock trim. (Image/Richard Holdener)No longer stock, the L33 was treated to a set of Trick Flow GenX 220 as-cast heads. (Image/Richard Holdener)Originally Fast-as-Cast, the flow rate of the Trick Flow Specialties GenX 220 heads was enhanced by the boys at Brian Tooley Racing. The TFS 220 GenX cylinder heads also received milling to up the static compression. (Image/Richard Holdener)Because of the RPM potential of the Summit Racing Pro LS 8711R1 cam, the modified TFS GenX 220 heads were also given a valve spring upgrade. The heads received a set of BTR Extreme RPM dual springs and titanium retainers. (Image/Richard Holdener)To get things started with the more high-rpm oriented Summit Racing Pro LS 8711R1 camshaft, we equipped the modified 5.3L with this Holley Lo-Ram intake. (Image/Richard Holdener)To ensure adequate fuel flow, we ran these 80-pound Accel fuel injectors. (Image/Richard Holdener)The exhaust system for the modified L33 consisted of a set of 1-7/8 inch, long-tube Hooker (swap) headers feeding simple collector extensions and Magnaflow (straight-through) mufflers (Image/Richard Holdener)Though we usually run stock valve covers on these junkyard stock bottom end motors, this one received these BTR logo valve covers with AN breather fittings and custom coil brackets that allowed removal of the valve covers without having to first remove the coils. (Image/Richard Holdener)For this test, the Lo Ram was run with a single throttle body lid designed to accept a 102mm to 105mm throttle body (Image/Richard Holdener)Tuning for each Holley intake came via a Holley HP EFI management system. (Image/Richard Holdener)For dyno testing, the L33 was stripped of all its accessories and run with a remote Meziere electric water pump. (Image/Richard Holdener)Run on the dyno with the Holley Lo Ram intake and Summit Racing 8711R1 cam (0.625/0.605″ lift split, 234/248 degree duration, and 113.5 + 3.5 degree LSA), the modified (but still stock bottom end) 5.3L produced peak numbers of 532.9 hp at 7,500 rpm and 413 lb.-ft. at 6,000 rpm. (Image/Richard Holdener)After running the high-RPM cam with a high-RPM intake, we removed the Lo-Ram and installed an intake that would be a better choice (RPM wise) for the Big Nasty cam, meaning the factory truck intake. (Image/Richard Holdener)The factory truck intake was teamed with a factory truck throttle body. It is obviously possible to make more power with a better intake (like TBSS or FAST), but we figured more guys would have a stock manifolds. (Image/Richard Holdener)To swap in the Big Nasty, off came the factory truck damper to allow access to the front cover. (Image/Richard Holdener)Removing the front cover provided access to the timing gear and cam retaining plate. (Image/Richard Holdener)Out came the Summit Racing Pro LS 8711R1 cam and in went the smaller (spec wise) Big Nasty 5/4 race cam. (Image/Richard Holdener)Run with the Big Nasty cam, the 5.3L produced peak numbers of 459 hp at 6,500 rpm and 438.8 lb.-ft. of torque at 4,800 rpm. (Image/Richard Holdener)
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.
Comments
One response to “The Big Nasty! Summit Racing 5/4 LS Cam Test”
Richard, what’s the idle vacuum like?