Add 100 HP to Gen III Small-Blocks

Installing a cam in a Gen... 

   

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Installing a cam in a Gen III engine is made easier because you don't have to pull the intake manifold. Dyno Bob made his own two-piece timing cover to make these swaps easier.

So with the addition of a set of headers and an admittedly lumpy cam, we've managed to add an even 100 hp to our Little Bro 5.3L motor. This doesn't come without a price, however. We've pushed the torque peak from 4,000 rpm to 4,800 and lost a bunch of torque below 3,000. But baby, when the tach hits 4,000, this motor will feel much more like a healthy 350 instead of a little 325! At 413 hp, this equates to 1.27 hp per cubic inch (hp/ci), all with stock heads.

But the story's not over. Next month, we'll lay on the LPE CNC-ported heads, and a Comp Cams LSX intake to really pump up the LS1's little brother. As a teaser, think about how much pump gas power equals 1.4 hp/ci.

What's A 5.3?
Everybody knows what an LS1 5.7L motor is and how much power it makes. But fewer seem to know the details around its 5.3 little brother. Basically, GM just made the bore smaller (3.780) and kept the stroke the same (3.622). All other parts interchange, just like the Gen I small-blocks. The 5.3L is used most often in 11/42-ton pickups and vans and has come in horsepower ratings from 265 to 300 hp while torque ranges from 320 to 330 lb-ft depending on its application.

The 5.3 heads are very similar to those used on the LS1, but the chambers are smaller to keep the compression up and the intake valves are 1.89-inch instead of the larger 2.00 for LS1s. Exhaust valves are the same as the LS1 at 1.550 inch.

The easiest way to think of this engine is as a small-bore 327. The bore is 0.220 inch smaller than the original 327, making up the difference with its longer 3.622-inch stroke that is the same as the 5.7 LS1 along with the same rod length. Even the stock heads exhibit exceptional flow and there's probably some power to be had by minor pocket work as opposed to the full-on CNC porting. All this makes for an excellent mid-displacement street engine.

We used the stock truck intake... 

   

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We used the stock truck intake (right) for all the tests in this story. On the left is an LS6 intake used in the Corvette that is worth some power, but only in the upper rpm range. The stock truck intake may not look as pretty, but it worked very well on our Lil' Bro 5.3 making 413 hp!

Test Results
Test 1:
This was our baseline test of a totally stock 5.3L all-aluminum SSR truck engine, complete with the stock exhaust manifolds running through a typical performance dual exhaust system.

Test 2:
The only change was to add a set of 131/44-inch dyno headers to the engine with the same exhaust downstream. This change was worth about 10 lb-ft of torque and 10 hp over the cast-iron manifolds.