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How Much Nitrous Can a 5.3L LS Take? We Tried to Find Out.

HOT ROD logo HOT ROD 4/11/2018 Hot Rod Network Staff

There is nothing like a big nitrous backfire to destroy a perfectly good test motor. This happened after the Internet nitrous guys insisted we subject an LS motor to the same treatment given our Big-Bang turbo combinations where we added a good set of heads, cam and intake, and a pair of turbos to a high-mileage 4.8L, then cranked up the boost to the breaking point. After seeing showoff numbers like 1,482 hp, the nitrous guys wanted in on the action.

To find the answer to the nitrous question, we secured a high-mileage 5.3L LM7 from a local LKQ Pick-A-Part, increased the ring gap on the factory (high-mileage) rings, and put it back together. All the other components remained stock, including the block, crank, rods, pistons, bearings, oil pump, pan, pick-up, and lifters.

We replaced the stock LM7 cam with a Stage 4 LS3 cam from Brian Tooley Racing. Though designed for a healthy rec-port (LS3) application, the Stage 4 cam (0.618/0.596 lift, 233/250 duration, 113+3 LSA) has proven very effective on cathedral-port, nitrous applications. The cam was teamed with a set of Fast-As-Cast, GenX 220 heads from Trick Flow Specialties. The GenX 220 heads feature one of the biggest ports we could fit on our small-bore nitrous motor. Topping the TFS heads was a Holley Hi-Ram induction system with a lid designed to accept a pair of 4150 throttle bodies (or carburetors).

Why did we bother adding the heads, cam, and intake on the 5.3L? After all, can't we just keep adding more and more nitrous to a stock motor? You can't add say, 300-hp worth of nitrous to a 300-hp motor. Reaching the 100-percent mark requires employment of the right cam profile, head flow, and tuning. Since nitrous displaces a portion of the total air used by the engine, the greater the airflow and power output of the normally aspirated motor, the more nitrous you can run. This is why we did everything we could to increase the power output of the normally aspirated 5.3L.

Increasing the output of the motor was important, but so too was our choice of nitrous systems. To supply the necessary amount of nitrous to the 5.3L, we employed not one, but a pair of Pro Plates from Nitrous Oxide Systems (NOS). Each plate offered two stages, with each stage capable of flowing 250hp worth of nitrous, meaning the plate could supply a total of 500 hp. Since our Holley Hi Ram featured provisions for dual plates, we had 1,000 hp worth of nitrous at our disposal. The motor was run with Holley's HP management system using 120-pound injectors, but each plate system was fed fuel through a low-pressure (think carbureted) fuel feed from the dyno.

After running the normally aspirated 5.3L on the dyno with Hooker 1-7/8-inch headers, Lucas oil, and a Meziere electric water pump, we were rewarded with peak numbers of 503 hp at 6,800 rpm and 408 lb-ft of torque at 5,500 rpm. We then ran and tuned each stage of nitrous individually, and were rewarded with 665 hp on the first stage and 825 hp (882 hp spike) on the second stage. Attempting to run both stages created the Big Bang, as Richard Holdener stayed in the throttle during a big lean spike. Rest assured, we will be back with a fresh (meaning high-mileage) LM7 and give the Big Bang Nitrous another go (bad Richard!!).

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