It could well be argued that the current LS1 is the best iteration of the small-block ever to grace the engine bay of your favorite GM performance machine. A pretty bold statement to be sure, especially given the number of performance small-blocks produced over the last 50 years or so, but the LS1 has a lot going for it. Even if we skip over the all-aluminum construction (a fact that greatly improves performance by improving the all-important power-to-weight ratio), the LS1 motor has serious performance potential. We know for a fact that the stock short-block can be taken well beyond 525hp in normally-aspirated trim with nothing more elaborate that an intake, cam and a set of ported stock heads. Try doing that with a single-cam 4.6L Ford mod motor and see how far you get. Heck, doing it with the 4-valve Cobra motor would be a real accomplishment, but the LS1 manages big power (and torque) without resorting to overhead cams and the associated complications.
The fact that these motors respond so well to modifications is music to the ears of GM enthusiasts. Naturally there is a wide variety of performance hardware available for the LS1. Included in that array is the trio of cams run through our test motor, all in the name of maximum power. Sure, a single cam swap in an LS1 would be welcome information, but rather than offer the readers of PHR a simple back-to-back cam swap, we went the extra mile and ran a total of three new performance grinds from the Comp Cams catalog. Running three cams instead of just one might allow our readers to best choose their weapon. Not all LS1 owners are out for maximum peak power, especially if that big power number comes at the expense of low-speed torque and (more importantly) driveability. While we all like to sit around and bench race peak power numbers, the reality is that we would be much happier with additional low and mid-range power. Bumping the power curve from 2,500 rpm to 4,500 rpm on a street car would be much more useful since the motor spends much more of its time there. Compare the number of times you rev the motor to redline to those short torquey bursts off the line. Mid-range power gains can be enjoyed every time you touch the throttle.
While low-speed and mid-range power gains are of prime importance to a street car, there are those looking to do nothing more than maximize full-throttle acceleration. This group of enthusiasts lives and dies by ETs and trap speeds. If it doesn't make the car run quicker in the quarter mile, they are not interested. For these LS1 owners, power production is most critical from 4,000 rpm to 6,000 rpm (or higher depending on whether you have control of the ECU parameters). Maximizing power in this rpm range often requires a sacrifice in low-speed power production. Sure, drivability may be a bit softer, but the trade off is well worth bettering your ET by three to five tenths. Not surprisingly, there is a middle ground between these two extremes. Lucky for the middle-grounders, there are a wide variety of cam profiles available to tailor the power curve to their liking. Let's take a look at the results of our three-way cam comparison and you enthusiasts can choose for yourselves.
Before letting our fingers do the walking through the Comp Cams catalog, we needed a suitable test motor. As luck would have it, Westech Performance had just what the doctor ordered in the form of a GM Performance Parts LS1 crate motor. The LS1 crate motor was originally scheduled for use in an F-body and was fresh off the assembly line. The motor came complete minus a mass air meter and starter. The street rod assembly included a dedicated wiring harness and ECU designed to allow installation of the LS1 into any pre-1976 street rod or street machine equipped with a 4L60E electronic overdrive transmission. The dedicated wiring harness was well labeled allowing easy hook up on the Westech Super Flow engine dyno. Naturally the transmission functions were not employed on the dyno. Since the F-body LS1 came with a returnless fuel system, we fabricated our own fuel rails, lines and regulator using a pair of aluminum rails originally designed for (of all things) a 5.0L Mustang. The rails were used in conjunction with a Barry Grant adjustable fuel pressure regulator set at the recommended pressure of 58 psi.
The LS1 test motor was run previously with the stock exhaust manifolds, but we had since switched over to a set of 1 3/4-inch Hooker long-tube headers. We also took the liberty of installing a cone filter over the ProM mass air meter and hooking up the Meziere electric water pump. The motor was run sans any accessories and through a pair of 3-inch Flowmaster dyno mufflers. The final modification was to install an AccuFab 75mm billet aluminum throttle body. The polished aluminum throttle body not only out-flowed the stock throttle body by 100 cfm, but the polished exterior would be right at home on even the cleanest show car (street rod guys take note). Equipped with the stock cam and run with the stock street rod ECU supplied by GMPP, the LS1 immediately fired to life and posted some pretty impressive power numbers. Originally rated at 320hp (full accessories and exhaust), our LS1 produced 407 hp at 5,500 rpm and 409 lbs.-ft. at 5,000 rpm. The motor produced more than 350 lbs.-ft. of torque from 3,000 rpm to 6,000 rpm and over 375 lbs.-ft. from 3,000 rpm to 5,600 rpm.
We noticed that the stock power curve had a sharp dip starting at 5500 rpm. Not being able to control the timing or fuel curves (we were limited to fuel pressure adjustments), nothing we tried could remove the dip in power. The power curve repeated time and time again, each time with the drop in power at 5,500 rpm. We don't think this is indicative of the factory curve (we've never experienced this on the chassis dyno), but we had no way of eliminating the power drop. With no more options, we began yanking parts in anticipation of our first cam swap. As it turned out, swapping cams in the LS1 turned out to be much easier than a conventional small-block. It was not necessary to move the intake, valley cover, heads or even the lifters. We simply pulled the damper, front cover and then rotated the stock cam. This pushed the hydraulic roller lifters up out of the way, where (to our surprise) they remained in place. This allowed us to pull the stock cam and install our 0first performance grind. Easy cam swaps--another big plus for the LS1!
To properly illustrate the effect of cam timing, we decided on a trio of different cams from the Comp Cams catalog. With 11 different grinds for the LS1, we had plenty to choose from. Rather than take the smallest available, the largest available and then choose a middle ground, we put a bit more thought into our choices. Ideally, we wanted a trio that would bolt in without causing piston-to-valve interference. With cams available sporting over .600 lift and with 240 degrees of duration, we suspected that the largest of the Xtreme XE-R cams were probably off limits, so we looked elsewhere. Eventually we decided on an Xtreme RPM XR265HR and a pair of Xtreme RPM High Lift cams. The High Lift cams included an XR275HR and a slightly larger XR281HR grind. The smallest of the three (XR265HR) sported a 212/218 duration split at .050, a .522/.529 lift split and a 114-degree lobe separation angle. Note that the dual-pattern cam favored the exhaust, a feature shared by all three cams. The middle of the three, the XR275HR offered slightly more lift with a .566/.568 split as well as more duration. The XR275HR cam featured a 222/224 duration split and the lobe separation angle was slightly tighter at 112 degrees. The big boy (XR281HR) upped the duration figures to a 228/230 split at .050, added a tad more lift (.571/.573) while sharing the 112-degree lobe separation of the smaller XR275HR cam.
In anticipation of the elevated rpm range offered by the cams, we took the liberty of replacing the stock beehive valve springs with the upgraded springs offered by Comp Cams. Their part #26918-16 springs increased the seat and open pressure to ensure adequate control and allow for the extra lift offered by the larger Xtreme Energy cams without fear of coil bind. Installing the XR265HR cam resulted in a significant increase in power. The peak power numbers jumped from 407hp and 409 lbs.-ft. of torque achieved by the stock to 439hp and 426 lbs.-ft. of torque. Oddly enough, the torque peak occurred 200 rpm lower than the stock cam, while the peak horsepower number occurred at the same 5,500 rpm. Installation of the XR265HR cam improved the power output from 3,000 rpm all the way to our ECU-induced redline of 6,200 rpm. This XR265HR cam offered both a sizable increase in top-end power with a healthy chunk of low and mid-range torque. Basically, the cam upgrade elevated the entire power curve, certainly a desirable outcome.
After about an hour, we had the second cam in place and ready to go. Like the smaller XR265HR cam, the XR275HR cam increased the power from 3,000 rpm all the way to 6,200 rpm. The larger XR275HR cam lost out in peak torque compared to the smaller XR265HR cam (422 lbs.-ft. to 426 lbs. ft.), but managed to push the peak horsepower number up to 450hp. Note from the supplied power curves that the power production was pretty flat, reaching 450hp at 5,800 rpm and carrying that number out to 6,100 rpm. We suspect that the XR275HR cam would have run well out past 6,100 rpm, but our ECU-imposed rev limiter did not allow us to put that theory to the test. Given the sizable jump in duration (at .050) between the stock and XR275HR cams, we were somewhat surprised by the big torque gains that occurred between 3,000 rpm and 3,900 rpm. It is this torque increase that will put a smile on your face every time you get behind the wheel.
The last cam to be tested was the XR281HR. After reviewing the results of the dyno testing, we are glad we chose to include this cam. This is a good example of what happens when you over-cam a motor. Actually, the XR281HR (like the previous two) offered a hefty chunk of torque from 3,000 rpm to 4,000 rpm. The gains compared to the stock cam were smaller thereafter but things really started to happen once the motor revved past 5,000 rpm. By 6,000 rpm, the XR281HR was just getting started, but the ECU pulled the plug at 6,200 rpm. Given free rein, we suspect the XR281HR cam would make peak power out near 6,500 rpm and likely not fall off dramatically to 6,800 rpm. Of course you can only take full advantage of the impressive top-end power if you have the ability to remove the rev limiter and tailor the fuel and timing curves. It is important to remember that all of the testing was done with stock heads and (more importantly) a stock LS1 intake. This XR281HR cam would really benefit from an intake and ported heads to compliment its high-rpm nature. Given the stock rev limiter, this larger cam would not be the ideal choice for most street motors.
Graph 1:Stock (F-Body) LS1 vs XtremeRPM XR265HRWe don't find it to surprising that the new Xtreme RPM cam profile increased the peak power output of the LS1 test motor, but we were very impressed by the big torque gains that occurred throughout the rev range. Note that the installation of the XR265HR cam increase the power output from 3,000 rpm all the way to 6,100 rpm. While you'd certainly notice the jump in peak power from 407hp at 5,500 rpm to 439hp at 6,000 rpm, it is the added 20-25 lbs.-ft. of torque from 3,000 rpm to 4,500 rpm that will sit you back in your seat.
Graph 2:Stock (F-Body) LS1 vs Xtreme RPM High Lift XR275HRStepping up to the larger XR275HR cam brought even more peak power. The LS1 now produced 450hp at 6,000 rpm, but the added power upstairs brought a small penalty in peak torque. The XR275HR cam produced 422 lbs.-ft. at 5,000 rpm. This compares to 426 lbs.-ft. at 4,800 rpm for the smaller XR265HR cam. It is at this point that we started wishing for our LS1 Edit software program to allow us to control the fuel and timing curves along with increasing the rev limit. This cam had more to offer past 6,000 rpm, but the ECU in our street rod assembly called it quits at 6,200 rpm.
Graph 3: Stock (F-Body) LS1 vs Xtreme RPM High Lift XR281HRThe increased duration offered by the XR281HR cam hurt power production compared to the smaller cams, but the larger cam still managed to post better low-speed torque numbers than the stock cam. It is out past 5000 rpm that the XR281HR cam started to get with the program. Without proper control of the rev limit, fuel and timing curves, this cam would not be the ideal choice. The XR281HR managed to post the highest peak power numbers with 455hp at 6,200 rpm, but the peak torque number was down by 1 lbs.-ft. compared to the smaller XR275HR cam. With good heads, an intake and full control of the fuel and timing, this XR281HR cam would make serious power.