Tech Articles / Tech Projects

Stroker LS Cam Swaps: When is Bigger Not Better?

When picking a cam for your stroker LS, is bigger always better? (Image/Richard Holdener)

They say too much of a good thing can be bad, but does this apply to cam timing, more specifically stroker cam timing? Can you over-cam your LS stroker motor?

In reality, there are a number of questions to be asked here, including what happens when you run stock or mild cam timing on a stroker? How much power is serious cam worth on a stroker? What happens when you go too far?

Luckily, all of these questions were answered in a single dyno session, as we ran no less than five different cams through a 408 LS stroker, with very interesting results.

Would you believe the right cam improved the power output by an amazing 177 horsepower?

Think about that number for a minute! What kind of upgrade is usually associated with improving the power output of a motor by 177 hp? That is power adder territory. Blowers, turbos, and nitrous can show those gains, but how can you get gains like that with a simple cam swap?

Lots of good stuff to unpack here, so let’s get going!  

Finding a Good Starting Point

In reality, improving the power output of a stroker by massive amounts has as much to do with the starting point as it does with the eventual cam timing required for the improvement. The key to big gains on any motor from a single upgrade (short of a power adder) is to equip said motor with everything else needed, then simply add the magic ingredient, in this case the required cam timing.

In the case of a stroker, you obviously have sufficient displacement to benefit from wilder-than-stock cam timing, but other components are also necessary, like cylinder head and intake flow (and design).

We all know the LS engine family, even in stock trim, responds well to cam timing for this very reason. The LS engines are all blessed with sufficient displacement, head flow, and a good intake, and in fact lack only cam timing for otherwise impressive power production. The necessity for cam timing only increases when you add displacement and even more head and intake flow to the mix. What we are saying here is that the stock cam timing becomes even more of a restriction to the stroker, so power gains improve dramatically when compared on a healthy stroker.

The real question is, what happens when you add too much cam?

Our LQ4 LS 408 Stroker Test Engine

The 408 stroker test mule started out life as a lowly LQ4 6.0L truck motor. The iron truck block was machined to accept a forged rotating assembly that included a 4.0 inch (up from the stock 3.622 inch) Scat forged steel crank, matching 6.125 inch I-beam rods and JE forged pistons.

Thanks to the combination of bore and stroke, the 6.0L now displaced close to the OG Trans Am displacement of 6.6 liters, or more accurately 408 cubic inches. The 10cc dished pistons supplied by JE combined with the 65cc chambers in the Airflow Research (AFR) heads (also available with 73cc) to produce a static compression ratio near 11.0:1. Thanks goes to the guy at L&R for the balancing of the new stroker assembly and the remainder of the machine work.

The build also included MLS head gaskets and head studs came from Fel-Pro and ARP. Keeping all that compression sealed in the chamber was a Total Seal ring package, while Sealed Power and Moroso supplied the new oil pump, pan and dedicated windage tray with remote oil filter.

Having increased displacement is all well and good, but not if you restrict the added cubes with stock heads and intake. Knowing we wanted more flow, the stroker received a set of AFR 245 LSX Mongoose heads. The 245 AFR heads offered exceptional airflow (more than we needed), though the chamber size was likely better suited for a larger 4.125 inch bore combination. Thanks to CNC porting, the AFR heads flowed nearly 360 cfm, meaning they would support over 700 hp. We liked knowing the heads would not represent a restriction for our stroker cam testing.

Topping the AFR-headed 408 was Fast LSXRT intake. The Fast intake was combined with a set of 42 pound Fast injectors, billet fuel rail and 102mm throttle body. All testing was run through a set of 1-3/4 inch QTP headers (and mufflers) with precision tuning supplied by a Holley Dominator EFI system. Each cam combo was optimized for maximum power on 91 octane fuel.                 

Establishing a Cam Test Baseline

Before subjecting the 408 to our quartet of Crane cams, we first established a baseline with a stock 5.3L LM7 cam. We doubt any LS owner would run a 408 with a stock cam, but we nonetheless wanted to demonstrate the gains offered by the cams and needed a starting point.

The mildest of the LS offerings, the 5.3L LM7 stick featured a .466/.457 lift split, a 190/191 degree duration split and 114 degree LSA. Using the Holley Dominator system, our stock-cammed 408 managed 449 hp at 5,100 rpm and 522 lb.-ft. of torque at 3,900 rpm. Obviously the mild stock cam was limiting top-end power, but the 408 still managed to exceed 500 lb.-ft. of torque from 3,500 rpm to 4,600 rpm.

Let’s Start Swapping Cams!

First up on the cam list was the 206 cam, so named from the 206 intake duration. The mild Crane cam offered .500 lift (intake and exhaust), a 206/214 degree duration split and 114 degree LSA. Run with this 206 cam, the power output of the 408 jumped to 515 hp at 5,400 rpm and 556 lb.-ft. of torque at 4,600 rpm. The fact that the 408 gained 65 hp with such a mild cam was a clear indication that the combo wanted even more cam timing. 

Knowing the 408 needed wilder cam timing, we then installed the Crane 224 cam. Compared to the 206, the 224 cam stepped up in both lift and duration. The 224 featured .590 lift (intake and exhaust), a 224/232 degree duration split and 115 degree LSA. Installation of the 224 cam increased the power output to 584 hp at 5,800 rpm 566 lb.-ft. of torque at 4,700 rpm. This represented a gain of 135 hp over the stock cam and nearly 70 hp over the smaller 206 cam.

Next up was the 240 cam with (you guessed it) 240 degrees of intake duration. The 240 cam offered .600 lift (intake and exhaust), a 240/246 degree duration split and 114 degree LSA. Once again, the cam upgrade improved the power output, this time the peaks checked in at 626 hp at 6,500 rpm and 580 lb.-ft. of torque at 5,400 rpm. This cam offered an extra 177 hp over the stock cam, 111 hp over the 206 cam and 42 hp over the 224 cam.

The final test was the 246 cam, with .624 lift, a 246/254 degree duration and 114 degree LSA, but with less-than-stellar results. The peak horsepower numbers remained at 626 hp, but peak torque dropped to 575 lb.-ft. In fact, torque production dropped through the entire rev range!

Sometimes, even on a stroker, bigger is not always better!

Graph 1: 408 Stroker-Stock LM7 vs Crane 206 & 224

The graph illustrates the power gains offered by the Crane 206 and 224 cams compared to the stock LM7 (5.3L) cam. The mild 206 cam increase the power output of the 408 stroker from 2,700 rpm all the way past 6,000 rpm, a clear indication the stroker wanted wilder cam timing. The mild Crane cam improved the peak power output by 65 hp, but the 224 cam stepped things up even more. Equipped with the 224 cam, the power output jumped to 584 hp and 566 lb-.ft., a gain of 134 hp and 44 lb.-ft. over the stock cam. Note the 224 cam only lost out to the stock cam below 3,000 rpm, but made less low-speed torque than the smaller 206 cam below 4,400 rpm. (Dyno chart – Richard Holdener)

Graph 2: 408 Stroker-Stock LM7 vs Crane 240 & 246  

Things got really interesting once we stepped up even more in cam timing on the 408 stroker. Obviously the stock LM7 cam was holding back the power output of the AFR-headed 408, and this became clear after the installation of the 240 cam from Crane Cams. Equipped with the 240 cam, the power output of the 408 increased from 449 hp and 522 lb.-ft. of torque to 626 hp and 580 lb.-ft. This represented a gain of 177 hp and 58 lb.-ft. of torque over the stock cam (which no one would use on a 408). Looking for even more, we installed the largest 246 cam, but this grind only managed the same peak hp number (626 hp), but torque dropped through the entire rev range. (Dyno chart – Richard Holdener)

***

Starting with a 6.0L iron truck block, the 408 stroker included a Scat rotating assembly. Scat supplied a 4.0 inch, 4340 forged steel crank and matching 6.125 inch rods. (Image/Richard Holdener)
The 6.0L iron block was bored to accept a set of 4.030 inch forged JE pistons. The design featured a small (10cc) dish combined with valve reliefs to provide adequate piston-to-valve clearance for the larger Crane cams. (Image/JE Pistons)
To illustrate the gains offered by each cam profile, we first established a baseline with a 5.3L truck cam. The mildest of the factory LS grinds, the LM7 truck cam offered a .466/.457 lift split, a 190/191 degree duration split (at .050), and 114 degree LSA. (Image/Richard Holdener)
The 408 stroker assembly was treated to a new standard volume oil pump from Sealed Power, along with a dedicated windage tray and pump pick up from Moroso. (Image/Richard Holdener)
The aluminum Moroso F-body pan featured AN fittings to work with a relocated oil filter. (Image/Richard Holdener)
Because any 408 requires plenty of airflow, the stroker was topped with a set of CNC-ported AFR 245 LSX Mongoose heads. (Image/Richard Holdener)
With intake port intake flow numbers exceeding 350 cfm, the CNC-ported, AFR heads were capable of supporting over 700 hp. (Image/Richard Holdener)
The AFR 245 heads were available with either 65cc or 73cc chambers, we chose the smaller 65cc chambers to maximize power production on our 408. (Image/Richard Holdener)
The AFR heads featured a dual valve spring package and stock LS rockers. (Image/Richard Holdener)
Run first with the stock (mild) LM7 cam, Fast LSXRT intake, and Holley Dominator EFI system, the 408 stroker still managed to thump out 449 hp at 5,100 rpm and 522 lb.-ft. of torque at 3,900 rpm. The extra displacement allowed the 408 to exceed 500 lb.-ft. from 3,500 rpm to 4,600 rpm. (Image/Richard Holdener)
After running the stock cam, it was time to perform a number of cam swaps. These all began with the removal of the Meziere electric water pump, damper and front cover to provide access to the LS timing gear. Prior to removal, the upper and lower gears were then lined up with the number 1 piston positioned at TDC (not shown in photo). (Image/Richard Holdener)
Removal of the front cover provided access to the timing gear and cam retaining plate. Rotating the cam pushed the lifters up into the plastic retainers to allow for removal. The long lifter retaining tools (that are no longer available) provided extra insurance against the lifters falling into the motor during the cam swap. (Image/Richard Holdener).
Cam swaps are a breeze on the engine dyno, so out came the stock cam and in went the first of 4 different cam profiles, starting with the mild 206 cam from Crane Cams. The mild 206 (truck) cam featured .500 lift (intake and exhaust), a 206/214 degree duration split and 114 degree LSA. (Image/Richard Holdener)
After the first cam swap, the power output of the 408 increased to 515 hp and 556 lb.-ft. of torque. Obviously the 408 wanted wilder cam timing. Equipped with the 224 cam, the power numbers jumped to 584 hp and 566 lb.-ft. of torque, while the 240 cam upped these numbers to 626 hp and 580 lb.-ft. of torque. Hoping for even more power, we stepped up to the 246 cam, but the peak hp remained the same at 626 hp, while torque production dropped off through most of the curve. Bigger is not always better-even on a stroker! (Image/Richard Holdener)

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2 Comments

  1. Greg Zimmerlee says:

    Like to see this comparison on 80s 350 iron block carb fed motor

  2. Jorge Zuniga says:

    This is a question for Richard Holdener. Have you tested any 5.3L lm7 blocks using an “ASA”, cam. I am interested to see how it performs on a dyno. On paper they look like great mild upgrades to a stock block with springs and lightly worked over 862 heads. I just would like to know your thoughts and hopefully a dyno graph.

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