The question on the table: Do supercharged motors respond to wilder cam timing, or does all the boost just get blown out of the exhaust valve from the dreaded overlap?

Spoiler alert, bigger cams that make more NA power also make more power under boost.

Fear not, we won’t let that stop us from showing the dyno results of cam tests run on two different test motors (a SBC and LS) equipped with Vortech superchargers.

man installing an air-to-water intercooler on dyno
Choosing the right cam for your supercharged motor can yield some big power gains (Image/Richard Holdener)

Test motor number one was sourced from the (where else?) junkyard. The L31 Vortec motor was a 350 small block named for the Vortec-style cylinder heads, the late-model small block offered a one-piece rear-main seal (less prone to leakage), the high-flow (best flowing factory heads) Vortec-style heads, and a hydraulic roller cam. Though the stock (truck) cam was plenty mild, the factory hydraulic-roller set up meant we could easily upgrade to a profile with aggressive ramp rates that provided even more power than your average flat-tappet cam.

For our supercharged test mule, we chose two different hydraulic roller cams from Comp Cams, the smaller of the two being an XR258 that offered a .480/.488 lift split, 206/212 degree duration split, and 112 degree LSA. The larger of the two cams was the XR282HR cam that offered a .510/0520 lift split, a 230/236 duration split, and a 110 degree LSA.

Let the Test Begin

The cam test could have been run with the stock Vortech iron heads, but the 350 had been previously upgraded (tested) with a set of 195cc aluminum heads. The heads were equipped with appropriate dual springs for use with the larger of the two cams. The new heads and cam were fed by a single-plane, Edelbrock Victor Jr. intake equipped with provisions for port EFI. The EFI intake was combined with a set of 36 pound, FAST fuel injectors, and Accufab 4150, 4 hole throttle body.

Run with a 6 inch crank and 3.33 inch blower pulley, the S-trim Vortech produced a peak boost pressure of 8.1 psi with the 258 cam. This resulted in peak power numbers of 451 hp and 443 lb.-ft. of torque (a gain of roughly 100 hp over the NA combo). After installation of the larger 282 cam, the peak numbers jumped to 561 hp and 501 lb.-ft. of torque, despite a drop in peak boost to 7.1 psi.

Looking back at the dyno results, we suspect an issue with the boosted small cam run, but know that a bigger cam (even with increased overlap) that makes more NA power will also result in more boosted power.

The 5.3L LS Test

Further illustrating the concept of blower combos responding to more aggressive cam timing is one of many tests run on a 5.3L LS.

The 5.3L test motor was supplied by the guys at Strictly Performance. The boost-ready motor featured a stock block, Gen. 4 rods and hard-anodized, cast pistons with the (all-important) ring gap. The 5.3L was equipped with 706 heads secured with MLS head gaskets and ARP head studs.

While stock heads would certainly work, these 706 heads had been given the once over by the guys at Katech Engines. Katech offers affordable porting options for stock heads, with additional options to further increase the flow and power potential. For our cam test, the heads were equipped with a dual spring package from Brian Tooley Racing. The heads were run with stock rockers and hardened pushrods.

Topping the heads was a factory (early) truck intake with a stock throttle body. Naturally the injectors were upgraded from stock to 80 pounders for the boosted power output. Fuel flow is a critical element when it comes to making power. The stock 25 pound injectors won’t support much more than 400 hp NA, and even less under boost.

For the first test, the supercharged 5.3L was equipped with a factory LS9 cam.

It should be noted that the cam test illustrated here is but one of many comparisons run on this test motor, as we ran this motor NA with different fuels (91 and E85), with a number of different cams (NA and boosted) and intercooled vs. non-intercooled.

For our cam test comparing the LS9 to the BTR blower cam (.613/.596 lift split, 227/244, 115 LSA), the motor was configured with an air-to-water intercooler and run on E85 fuel. Both cams were run with the same A/F and timing to minimizes power changes based on other variables. The 5.3L was equipped with a Vortech S-trim supercharger using a 3.6 inch blower pulley.

Run in this manner with the LS9 cam, the Vortech supercharged 5.3L produced 669 hp at 6,200 rpm and 573 lb.-ft. of torque at 5,900 rpm. The peak boost registered at 6,200 rpm was 8.5 psi.

After back up runs repeated the power numbers, we replaced the LS9 cam with the BTR blower cam. Run with the BTR cam, the Vortech 5.3L produced peak numbers of 716 hp at 6,300 rpm and 607 lb.-ft. of torque at 6,100 rpm. The peak boost dropped slightly to 8.1 psi with the bigger cam.

More power with less boost—it’s almost like blowers like bigger cams!

vortec cam dyno test chart, 1
Only with forced induction do you get power gains of this magnitude. This test clearly shows that adding boost even to a mild-cammed small block will yield impressive numbers. Once upgraded with aluminum heads, a mild Comp 258 cam and the Vortech supercharger, the boosted small block produced 450 hp and 443 lb.-ft. of torque. The wavy shape of the curve shows something may have been amiss on this test. After installation of the larger 282 cam, the peak power jumped to 561 hp and 501 lb.-ft. of torque. As expected, when we improve the power output, the boost dropped by almost 1 full pound on the cam swap. (Dyno Chart/Richard Holdener)
vortec cam dyno test chart, 2
We are naturally drawn to the peak power and torque gains, but every bit as important on this test was the fact that the cam swap netted a sizable gain in power through the entire rev range. Run with the factory (blower) LS9 cam, the Vortech supercharged 5.3L (from Strictly Performance) produced 669 hp and 573 lb.-ft. of torque at a peak boost of 8.5 psi. Running E85 allowed us to safely run 22 degrees of timing at the hp peak. After installation of the BTR blower cam, the peak numbers jumped to 716 hp and 607 lb.-ft. of torque, at a slightly lower 8.1 psi. When you improve the power output of the motor with optimized cam timing, boost goes down—which is a good thing. (Dyno Chart/Richard Holdener)
lifter valley in a small block chevy V8
Test motor number one was a Vortec L31 350 equipped with a factory hydraulic roller cam fresh from the junkyard. (Image/Richard Holdener)
small block chevy cylinder head on table
The factory iron Vortec heads were replaced with a set of 195cc, as-cast aftermarket aluminum heads. The as-cast 195cc intake ports were advertised to flow 244 cfm. (Image/Richard Holdener)
comp camshaft on table with cam card
To start our supercharged cam test, we first installed a Comp XR258 hydraulic roller cam that offered a .480/.488 lift split, a 206/212 degree duration split, and a 112 degree LSA. (Image/Richard Holdener)
vortech centrifugal supercharger, installed
Boost for our budget small block came from an S-trim centrifugal supercharger from Vortech. The V1 blower offered more than enough airflow for our mild small block. (Image/Richard Holdener)
accufab throttle body efi module
Rather than blow through a carburetor, we decided to go with electronic fuel injection. We replaced the 4150 carburetor with a 4-hole throttle body from Accufab. Note the Accufab throttle body featured an idle air motor, TPS sensor and a pair of vacuum/boost ports. (Image/Richard Holdener)
connectors on a fuel injector
The 36 pound Fast injectors required over 60 psi of rail pressure to feed our 560 hp motor. We also boost-referenced the fuel pressure regulator. (Image/Richard Holdener)
centrifugal supercharger installed on a small bock chevy v8
Run with the smaller Comp cam, the Vortech supercharged 350 produced 450 hp and 443 lb.-ft. of torque at 8.1 psi. (Image/Richard Holdener)
camshaft going into a small block chevy v8
After running the smaller Comp cam, we replaced it with a larger XR282HR cam that offered a .510/.520 lift split, a 230/236 degree duration split, and a 110 degree lobe separation angle. (Image/Richard Holdener)
vortech supercharger on an SBC dyno test
Run on the dyno with the S-trim supercharger and the larger cam, the boosted small block produced 561 hp and 501 lb.-ft. of torque at 7.1 psi. (Image/Richard Holdener)
LS engine hanging on chains from a hoist
Next up was a supercharged cam test run on 5.3L LS supplied by Strictly Performance. The SP 5.3L featured Katech ported heads and hard anodized pistons. (Image/Richard Holdener)
camshaft going into an LS engine
To get things started, the 5.3L was initially equipped with a factory LS9 blower cam. (Image/Richard Holdener)
factory truck Intake on an LS engine
All testing was run with the factory (early) ruck intake and stock throttle body. (Image/Richard Holdener)
fuel injector installed in an intake
In anticipation of the boosted power, we upgraded to a set of 80 pound injectors from Accel. (Image/Richard Holdener)
vortech supercharger installed on an LS engine
The Vortech S-trim blower was installed on the 5.3L using the supplied mounting bracket. (Image/Richard Holdener)
pulley on a vortech supercharger
For this test, the Vortech supercharger was equipped with a 3.6 inch blower pulley. (Image/Richard Holdener)
air to water intercooler box for a dyno room
The Vortech supercharged LS was run with E85 fuel and this air-to-water intercooler. (Image/Richard Holdener)
supercharged ls engine on a dyno test run
Run with the LS9 cam, the supercharged 5.3L produced 669 hp and 573 lb.-ft. of torque at 8.5 psi. (Image/Richard Holdener)
brian tooley racing camshaft box on table
After running the LS9 cam, we replaced it with the more powerful BTR blower cam. (Image/Richard Holdener)
LS engine during dyno test pull
Run with the BTR cam, the power output jumped to 716 hp and 607 lb.-ft. of torque. The peak boost dropped slightly to 8.1 psi. (Image/Richard Holdener)

Keywords
dyno test , LS , SBC , Vortec , Vortech supercharger
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Author: 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.