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Ask Away! with Jeff Smith: The Great 5.3L Truck LS Swap Debate

With all this talk about truck LS engines, I hear a lot of talk about swapping a 5.3L truck LS engine into a car. Why would you want to go from a 350-cubic-inch small block Chevy to a smaller 5.3L engine that is only 326 cubic inches? To me that doesn’t make any sense. I know the 5.3L LS truck engines are cheaper than the 6.0L but I don’t see the sense in spending a lot of money to put a smaller LS engine in my car. As I see it, either step up and build a big LS engine, or stick with the 350 small-block.

J.D.

You have a valid point, but let’s look at some numbers. In a straight ahead comparison of a 350-cubic-inch small block Chevy versus a stock 5.3L truck engine, it’s really not a fair fight.

Let’s start with a stock 350 crate engine like the 290-horse 350 crate engine available from Chevrolet Performance. The engine we’re referencing is the semi-complete engine that’s rated at 290 horsepower at 5,250 rpm and 326 ft.-lbs. of torque at 3,750. This engine has 8:1 compression (not great), stock iron heads, and a decent 222/222 degrees at 0.050 flat tappet hydraulic camshaft. Those are decent power numbers for a near-stock small block Chevy.

Now let’s look at horsepower numbers for the stock 5.3L truck engine coded as the LC9. Yes, the 5.3L new engine is more than twice the money, but we’re going to use this engine as an example of what you can expect from a good used 5.3L engine. This 5.3L motor is 326 cubic inches with far better 9.5:1 compression, aluminum heads, and a hydraulic roller cam spec’d at a very conservative 196/201 degrees at 0.050-inch tappet lift. This engine is rated at 320 horsepower (30 horsepower more than the SBC) and more torque (335 ft.-lbs. versus the small-block’s 326 ft.-lbs.) despite the fact that the small-block is 24 cubic inches larger than the LS engine. Displacement usually makes more torque.

ASK-07-01

This is a well-used iron 5.3L motor I am building with stock heads, stock 9.5:1 compression and a mild Comp hydraulic roller cam. The cam specs at 223/231 degrees at 0.050 duration and 0.610/0.617-inch lift on the intake and exhaust with a 112 degree lobe separation angle. This engine should make at least 425 horsepower at 6,500.

So right away, the smaller 5.3L motor—all else being equal—will beat the small block in a drag race because it makes more torque and more horsepower. But wait, the 5.3L has aluminum heads, so its’ going to be 40 pounds lighter than the iron-headed small block, so it will have an even a greater advantage.

Now, to make things really fair, let’s bump the cam in the 5.3L motor up to something similar to the small block’s 222 at 0.050. We have some power numbers on a 5.3L motor with a 224/232 degrees of duration at 0.050-inch cam that our pal Richard Holdener just tested at Westech.

With the stock LS truck intake manifold and headers, this little engine made 414 horsepower at 6,800 rpm, which is much higher in the rpm curve so it requires better valve springs (which Holdener’s engine had). Granted too, the engine had forged pistons, but the compression was similar to stock so the advantage would be minimal in terms of horsepower. Still, even rating this conservatively at only 400 horsepower at 6,500, that’s 110 horsepower better than the small block 350 engine. The reason for this is because of the LS engine’s superior cylinder head flow.

A good counterpoint is that it will cost conservatively around $1,500 to $2,000 to swap a carbureted LS engine into an early Chevy. This means the 5.3L engine is going to be more expensive to swap in. But you are gaining lots of power even though the engine is displacement-challenged.

I will agree with you that a 6.0L is a better idea if all-out power is your goal. But if part of the appeal of the LS engine is the fact that it’s different, it’s more efficient, and it makes great power, then the decision to swap in the LS engine is easy. The good news is that there are no wrong answers to your question. If you like the small block and you are comfortable with its limitations, then by all means have at it. But if the LS is attractive, it is certainly an engine with much greater potential.

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  1. Pingback: Ask Away! with Jeff Smith: The Great 5.3L Truck Swap Debate Revisited! - OnAllCylinders

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