LS engine swaps are all the range, and while there is certainly a case to be made for the power potential of a solid LS-based small-block, the need for complicated electronic fuel injection scares many enthusiasts away. Many companies now offer carbureted intakes for LS applications and thanks to the ignition controller offered by MSD Performance, LS performance is now much more attainable for traditional enthusiasts.
Working with the factory cam, crank sensors and coil packs, the MSD controllers provide the necessary ignition portion of the carbureted performance equation. With fuel coming from the carburetor and intake and spark coming from the controller, hooking up a carbureted LS motor couldn't be easier. With carbs and LS engines being peanut butter-and-chocolate good, what about forced induction? Can the carbureted counterparts enjoy the same boosted benefits as EFI motors? In short, how do you add boost to a carbureted LS?
Being real-world enthusiasts, not only did we want to add boost to an LS motor, but we wanted to do it on the cheap. Anything is possible with an unlimited budget but what about boost for the average guy? With this in mind, we started not with a high-dollar crate motor, but with a junkyard 5.3L LM7. Just as we did with our Modern Mouse series, we purchased a high-mileage, iron-block 5.3L from a local supplier, upgraded it with the intake, carburetor and ignition controller for normally aspirated use, then added the necessary components for turbocharging.
When we say upgraded, we mean only those things that were absolutely necessary, including a turbo kit, intercooler and CSU carburetor, but no changes were made to the long-block itself. Normally we would at least swap out the factory head gaskets and studs for Fel Pro and ARP units, but for this adventure we stuck with the stock stuff. Running a modest boost level, the stock components were deemed more than adequate. The lone upgrade made to the motor was a cam swap, which we tested in normally aspirated and turbo trim to illustrate the gains offered to each.
We purchased the iron block 5.3L for $300. That the motor came without the trans, harness or other components usually involved in a swap did not bother us since it was destined for the dyno use and carbureted dyno use at that. After an oil change to 5W-30 synthetic, the LM7 was equipped with an electric water pump, 1 3/4-inch long-tube headers and the Edelbrock Victor Jr. intake. The intake was installed with a set of Fel Pro intake gaskets, to which we added a Holley 750 HP carburetor, and the MSD ignition controller. An Aeromotive fuel system was on hand to ensure adequate fuel delivery in both normally aspirated and boost conditions.
Having never run this 5.3 before, we were excited when it fired up on the first crank of the starter and settled into a nice idle with plenty of oil pressure. The 750 HP carburetor was equipped with an external jetting system from Percy's, making changes in air/fuel a simple turn of the screw. Dialing in the timing curve was even easier with the MSD, and very soon we were rewarded with peak numbers of 335 hp and 366 lb-ft of torque. In truth, the single-plane Victor Jr. was not the ideal choice for this otherwise stock 5.3L, but we chose it over the more effective dual-plane design for use with the turbo. We were concerned about fuel distribution (and signal) after we added boost.
Though cam swaps on the LS are the easiest in the industry, there is a reason why others wouldn't go to all the trouble to properly test cams on a turbo motor. The cam swap is easy enough, but testing the cam in both normally aspirated and turbo trim required either swapping cams or turbo systems twice. We opted to perform the cam swap once and install and remove the turbo system, allowing us to run both the stock and mild Crane cams in NA and turbo configurations.