By Richard Holdener
By now, it should be common knowledge that the LS engine families (Gen 3 and 4) respond VERY well to cam swaps. We have covered this phenomenon time and time again and always with the same results.
This started back when Chevy first introduced the original cathedral-port, 5.7L LS1 and continued with the 4.8L, 5.3L and 6.0L truck motors. The factory cathedral-port combinations responded so well to cam swaps that enthusiasts were worried when Chevy replaced them with the LS3 and L92, rec-port heads. Their fears were soon put to rest, as despite the tremendous increase in airflow offered by the new rec-port heads, the LS3 family was just as receptive as the previous generation, cathedral-port applications. The reason both types of LS motors are so receptive to cam changes is they possess everything else required to make power, including an effective combination of displacement, compression and (most importantly) head flow. The only area lacking to produce amazing power is more aggressive cam timing.
Since both the cathedral-port and rec-port heads respond so well, the question now is which one responds better? To find out, we set up a comparison between a cathedral-port, 5.3L and a rectangular-port LS3.
Before getting to the dyno test, there are few things to consider about the 5.3L, including the fact that compared to the LS3, the 5.3L offered reduced displacement, meaning it required relatively milder cam timing. The 5.3L also offered lower compression, smaller valve sizes, and less overall head flow. The stock 5.3L heads (706 castings) flowed considerably less than the LS3 heads, by 80-90 cfm. Other differences included intake manifolds, with the LS3 being possibly the best factory LS intake ever made. By contrast, the stock (early) truck intake used on the 5.3L was likely No. 3 on the list, behind the LS3 and late-model truck (sharing the number three spot with the LS6 intake).
We mention all of these things as they make a difference in how receptive the combination might be to a cam swap. Increased displacement, head, and intake flow will help the cam swap make power, while the reverse will minimize the power gains.
The one other factor to consider when looking at the results is the factory cam timing of each combination. The LS3 benefits from increased displacement (and bore size), an impressive intake, and massive cylinder head flow. On paper, it looks like the LS3 will be hard to beat, but the factory LS3 cam is also much wilder than the stock LM7 cam.
This means the 5.3L will start at a much lower power output, even with less displacement, head, and intake flow. The mildest of the factory offerings for the small-displacement truck motor (shared with the 4.8L), the LM7 5.3L cam, featured a .466/.457 lift split, a 190/191-degree duration split, and 116-degree lsa. By contrast, the LS3 offered more of everything, with a .551/.525 lift split, a 204/211-degree duration split, and 117-degree lsa. With an extra 14 degrees of intake and 20 degrees of exhaust duration, the LS3 was already well on its way to being a performance cam (especially for a little 5.3L-see graph 3). In theory, the more aggressive cam timing would make it harder to extract gains from the LS3, but that is why we were here, so let’s get to those dyno results!
First up on the dyno was the 5.3L. The 5.3L test mule was a high-mileage unit equipped for dyno use with Hooker long-tube headers, a Meziere electric water pump, and FAST management system. Run on the dyno in this configuration with the stock cam, the 5.3L produced 353 hp at 5,200 rpm and 384 lb-ft of torque at 4,300 rpm. Given its use in truck applications, the 5.3L was obviously tuned for torque.
Though there was available piston-to-valve clearance for wilder cam timing, we chose a COMP 273Lr cam for the 5.3L. The 273Lr cam featured a .610/.617 lift split, a 223/231-degree duration split, and 112-degree lsa. Going beyond this intake duration pushes peak power up past the 6,500 rpm range and starts to hurt torque production. After installation of the COMP cam and valve spring upgrade (required for the higher lift), the 5.3L produced 442 hp at 6,200 rpm and 412 lb-ft of torque at 5,000 rpm. There was a slight drop in torque below 2,900 rpm, but how often do you run at WOT at 2,900 rpm anyway? Measured peak to peak, the cam-only upgrade improved the power output of the 5.3L by 89 hp, with even greater gains occurring out past the power peak.
Next up was the GM LS3 crate motor from Gandrud Chevrolet. As previously mentioned, the LS3 offered more displacement, head, and intake flow, but also featured a much more powerful factory cam profile. The increased displacement allowed us to choose wilder cam timing for the 6.2L. For the cam-only test, we selected a Stage IV from Brian Tooley Racing. The Stage IV was about as big a cam as you could fit with the available piston-to-valve clearance using the factory combination. The Stage IV featured a .619/.595 lift split, a 233/250-degree duration split, and 113+5-degree lsa. Obviously, this cam was considerably wilder than the LSr cam run in the 5.3L, but so too was the factory LS3 cam wilder — by 14 (in) and 20(ex) degrees — than the factory LM7 cam.
Run in stock trim with headers, Meziere and FAST ECU, the stock-cammed LS3 produced 496 hp at 5,900 rpm and 491 lb-ft of torque at 4,700 rpm. After installation of the BTR cam, the power numbers increased to 570 hp at 6,500 rpm and 515 lb-ft of torque at 5,000 rpm. This represented (peak-to-peak) gains of 74 horsepower and, again, much higher past the power peak.
Okay, so the cathedral-port combo offered greater cam-only power gains, but the real winner here is anyone who owns an LS motor. Whether you have an LS1, LS3, or even LS7-based combination, any LS motor will respond well to a cam swap.