Speed Secrets: It’s Time for a Carbureted 5.3-Liter Cam Swap

In this episode of Speed Secrets, Richard Holdener explores a LS cam swap, but it’s no ordinary swap. Check out how a carbureted 5.3-liter engine responds to a cam swap.

To test the gains of a camshaft upgrade on a carbureted LS engine, Richard Holdener with Speed Secrets teamed up with Comp Cams.

Even though the LS engine was never factory equipped with a carbureted induction system, there are a few reasons to swap it over from the EFI system. At a wrecking yard, it is often cheaper to purchase a used long block rather than a complete engine, and at that point it is less expensive and less complicated to go carbureted than to hook up a factory or aftermarket EFI system. But while the new carbureted induction system might get the junkyard long block up and running, it is still left with the factory camshaft, and a camshaft upgrade is worth a lot of power on an LS.

Starting with a used 5.3L LS long block from a local wrecking yard, Richard added a dual plane intake, 4 barrel carburetor and long tube headers. Then, he upgraded the factory valve springs with Comp 26918 valve springs in anticipation of the future cam swap. On the dyno, the carbureted 5.3L LS made a respectable 337 HP and 378 Lb-Ft of torque with the stock LM7 camshaft.While the stock power output was not bad, why leave any power on the table? Especially in an LS, where cam swaps can make such a big difference.

Removing the front cover, timing chain, and factory camshaft, the team then installed a Comp XR273HR with .530/.534 lift and 220/224 duration with a 112 LSA and reassembled the 5.3L LS engine. On the dyno the junkyard carbureted 5.3L LS made 415 HP and 397 Lb-Ft of torque with the camshaft upgrade. Even though the XR273HR is a mild cam, it improved the power output of the 5.3L dramatically with gains of 78 HP and 20 Lb-ft of torque. In conclusion, even on a carbureted LS, the right cam makes a big difference.