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Comparing Cams on a Carbureted LS Engine

Cams for Carbs

Richard Holdener Dec 4, 2014
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For many Chevy enthusiasts, the original small-block will always be carbureted and the modern LS version fuel injected. Never mind the fact that the Gen I powerplant came equipped with mechanical fuel injection in the ’50s and ’60s and electronic fuel injection in the ’80s and ’90s. The Gen III and IV family started out life in injected form, but many enthusiasts and racing organizations have embraced carburetion, and for good reason. In all of our testing, we have yet to see injection make more power than a carburetor when tested on the same engine (that should get the internet buzzing).

The LS crowd has embraced carburetion to such an extent that there are now many suppliers offering carbureted intakes, and when combined with a simple MSD ignition controller, the LS is basically what millions of Chevy enthusiasts have always wanted: an all-aluminum, high-performance, carbureted small-block.

By now, loyal Super Chevy readers should know that LS engines respond amazingly well to camshaft upgrades. This comes as no surprise given the fact that they already possess adequate displacement, compression, and outstanding head flow, not to mention a powerful intake manifold design. In fact, the only thing missing to complete the package is cam timing, as the stock cams were never designed to maximize performance. When we combine this response to cam swaps with the popularity of carbureted LS engines, one question comes to mind. Does a carbureted LS require different cam timing than its injected counterpart? And as a follow up, if the carbureted engine responds well to revised cam timing, will the EFI combo follow suit?

Answering these simple questions required not only running two different custom cams but running both cams in injected and carbureted trim. This required either a pair of intake swaps or a pair of cam swaps. Given the simplicity on the engine dyno, we chose the latter.

Right off the bat we needed a suitable testbed. As luck would have it, we had the perfect test engine in the form of a 416ci LS3 stroker. The combo included a Lunati forged steel stroker crank, K1 rods, and JE pistons. Keeping all that compression in the chamber was a set of Total Seal rings. The short-block was topped off with a set of Chevrolet Performance CNC-ported L92 heads from Gandrud Chevrolet. To ensure adequate spring pressure and lift capability, the heads were upgraded with a set of double springs and retainers from Brian Tooley Racing.

Induction for the carbureted system included an Edelbrock Victor Jr. fed by a 950 Ultra HP Holley. EFI chores were handled by a FAST LSXR intake and 102mm throttle body, FAST 75-psi injectors and billet fuel rails. The 1 3/4-inch long-tube headers were supplied by American Racing Headers, and the combination was cooled using a Meziere electric water pump.

With the test engine ready and willing, we needed a pair of cams to test. We turned to Comp Cams for our cam and lifter needs. Truth be told, the custom Comp cams came courtesy of Brian Tooley Racing. Using the powerful cam grinds offered by Comp Cams, Brian Tooley Racing offered up a pair of custom grinds designed specifically for carbureted and EFI combinations. The EFI grind has a healthy 0.620/0.596 lift split, a 239/250 duration split, and 113-degree LSA, while the carb cam offered a seemingly wilder 0.623/0.596 lift split, a 247/258 duration split, and tighter 110-degree LSA.

Before you cry foul, know that the intake closing points on these two cams were identical and the exhaust opening points varied by just two degrees. It was the earlier opening point (by eight degrees) on the carbureted cam that really set it apart. The question now was would the seemingly wilder Comp cam make more power and if so, would there be any penalty? If there was a power difference between the cams, would the difference favor the carbureted or EFI combination? Things were getting exciting!

First up was the carbureted combination. The LS3 stroker engine was equipped with the Edelbrock Victor Jr. intake, Holley 950 Ultra HP carburetor, and MSD ignition controller. We started with the EFI cam and followed that up with the dedicated carb cam. After dialing in the EFI cam with timing and jets, we were rewarded with peak numbers of 611 hp and 543 lb-ft of torque. Swapping over to the carbureted cam upped the power ante to 628 hp and 544 lb-ft, with most of the gains coming past 5,800 rpm.

After running the carbureted intake with both cams, it was time for some injection. Off came the Edelbrock and Holley combo and on went the FAST LSXR intake and throttle body. Still equipped with the carbureted cam, the EFI combo produced 604 hp and 550 lb-ft of torque. The long-runner intake offered more torque but less peak power than the carbureted intake with the same cam. Swapping out the carb cam for the EFI grind resulted in a similar drop in power to 593 hp and 552 lb-ft of torque. What we saw here was that the wilder carbureted cam offered more power on both the carbureted and EFI combinations, though it should be mentioned that the idle quality on the tighter-LSA carb cam suffered compared to the wider EFI grind.

Comp Cams 2/18

01. Will your carbureted LS benefit from a custom cam?

Aluminum Ls3 Block 3/18

02. To ensure a stout test mule, the aluminum LS3 block was stuffed with a forged 4340 4.0-inch stroker crank from Lunati.

Forged Pistons 4/18

03. JE supplied a set of its new forged pistons for our LS stroker. The asymmetrical design reduced friction, increased power, and offered plenty of strength should we feel the need to step up to a power-adder at a later date.

Je Pistons 5/18

04. Connecting the JE pistons to the Lunati crank was a set of 6.125-inch K1 forged rods. Basically our 416-inch stroker LS3 was now sporting a bulletproof bottom end.

Efi Cam 6/18

05. To test whether the carbureted LS stroker wanted a custom cam, we contacted the LS cam experts at Brian Tooley Racing. They supplied an EFI cam that offered a 0.620/0.596 lift split, a 239/250 duration split, and 113-degree LSA.

Cabureted Cams 7/18

06. By comparison, the carbureted cam grind offered a 0.623/0.596 lift split, a 247/258 duration split, and a tighter 110-degree LSA.

Stroker Cnc Ported L92 Heads 8/18

07. The stroker was equipped with a set of CNC-ported L92 heads from Gandrud Chevrolet. Flowing nearly 350 cfm, the ported heads were capable of supporting over 700 hp in normally aspirated trim, making them more than sufficient for our cam test.

Valvespring Upgrade 9/18

08. A valvespring upgrade is paramount to any LS cam swap. Brian Tooley Racing supplied a set of its double valvesprings for our test. The stock spring supplied with our CNC-ported L92 heads from Gandrud Chevrolet lacked both adequate pressure and valve lift capability (before coil bind) for use with our performance cams.

Ls3 Edelbrock Intake 10/18

09. The carbureted combination included this LS3 Victor Jr. intake from Edelbrock.

Msd Controller 11/18

10. Both the EFI and carbureted cams were run with the Edelbrock intake and Holley 950 Ultra HP carburetor.

Carbureted Ls Combination 12/18

11. The carbureted LS combination required the use of this MSD ignition controller. The MSD controller plugged right into the factory sensors and allowed us to dial in the timing curve for testing.

Fast Throttle Body 13/18

12. We also ran both cams in EFI configuration, which included this FAST LSXR intake and matching 102mm throttle body.

Carbureted Stroker 14/18

13. The two cams were first run on the carbureted stroker using the Edelbrock intake and Holley carb. Not surprisingly, the carbureted combination favored the carbureted cam offered by Brian Tooley Racing. The carbureted cam offered not only more peak power (628 hp vs 611 hp), but more power from 5,800 rpm to 6,800 rpm.

Carb Cam 15/18

14. Out came the EFI cam and in went the carb cam. The carb cam offered increased duration and a tighter lobe separation angle, which translated directly into more power.

Efi Engine Carb Cam 16/18

15. After running both cams on the carbureted combo, we performed the same cam swap in EFI configuration. Guess what? The EFI engine liked the carb cam best too (at least for power)! The EFI engine produced 604 hp with the carb cam and only 585 hp with the EFI cam, with gains starting slightly lower at 5,300 rpm. The one downside to the carb cam was the idle quality suffered compared to the wider LSA on the EFI grind, but for power, the custom Brian Tooley Racing cam was definitely the hot ticket.

Standard Corrected Power 2 17/18

16. We suspected the wilder cam timing offered by the carbureted cam would improve power and that is just what happened. In addition to increasing peak power from 611 hp to 628 hp (torque changed by only 1 lb-ft), the tighter LSA also offered slightly more low-speed power.

Standard Corrected Power 1 18/18

17. The injected combination responded favorably to the carb cam as well. The cam swap offered an additional 11 hp (604 hp vs 593 hp), while peak torque changed by only 2 lb-ft.

Sources

Lunati
662-892-1500
www.lunatipower.com
Comp Cams
Memphis, TN 38118
800-999-0853
http://www.compcams.com
Holley Performance Products
Bowling Green, KY 42101
270-782-2900
http://www.holley.com
FAST
Memphis, TN 38118
877-334-8355
http://www.fuelairspark.com
Brian Tooley Racing
502-507-0955
www.briantooleyracing.com
Edelbrock
Torrance, CA 90503
310-781-2222
http://www.edelbrock.com

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