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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.


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.


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. Karl Ecker says:

    Hey Jeff, I may be a bit old school here because I am old, but have built hundreds of motors in my life, I am having a little trouble with the math here. I am looking at the comparison and lets say we do this crate engine to crate engine, Summits LS5.3L is $3050, the 5.7L can be had for $1709 leaving me $1341, will call intake and carb costs a wash because they are fairly close. now factor in the cost of fitting the LS into the swap, because it’s new mounts, hoses, belts, pulleys, exhaust fitment and a host of other things that ALWAYS!! pop up in non direct swap I bet a conservative number is close to $500 in extras, so lets say I only end up $1850 difference. All us old guys out there know there is no replacement for displacement and that is were the first $900 of the $1850 will go, is a eagle10.5:1 383 stroker kit, a $300 trip to the machine shop to bore and clearance it and $50 gasket set, so I’ve got $600 left for the top end, comp cams magnum top end kit 230/480 (Summit CCA -K12-213-1) is $336 and a set of Summit full fulcrum roller rockers is $226. so now I have $38 left and GEN1 high compression 383 stroker with a much better than stock top end. ZERO!! fitment issues and I will bet the remaining $38 🙂 it will leave the stock LS long block crying at the dyno. 😉

    • Thes upgrades are less work than the swap too.. Clear winner here.

    • Or you could get one at a junkyard for $600 since there are thousands out there.

      • Mark Diamond says:

        Where are all these so called cheap junk yard 5.3 LS motors? The cheapest I have ever seen one is in craigslist going for $1000 and better.

        • Have you actually tried to find one at a junk yard or salvage yard? Got my 5.3 for 600$ with harness and ecu from a salvage yard that pulled it for me.

      • I bought my iron block 5.3 for $400. There is currently an aluminum block 5.3 in the same yard for that price. You just have to find the right yards in your area.

      • The way to do it is buy a wrecked Tahoe, Yukon or Suburban with under 150k or so miles since these are 500k mile motors you’ll have plenty of miles left on it. I paid $600 for a 2002 Tahoe that was “T” Boned. That way I had harness, ECM and everything you’ll need for the most part. I put a Muncie M21 4spd behind it which was very easy to do. Drill a few holes out and install a speed censor on the the gear box and still use the stock analog speedo. I put it in a 1970 C10 short bed pickup and didn’t even have to swap the oil pan. The best thing about doing it this way is I sold the tranny with 4wd transfer case, rear end along with several other items then scraped the rest. Ended up with no cost investment. Upgraded the motor before installing with new cam, lifters and heavier valve springs. Along with my stock 12 bolt 3:73 rear end this truck hauls ass and is as dependable as a new car. There are a few hurdles to cross such as a higher flow fuel pump and engine mount perches but all in all it’s a fairly simple swap.

    • Or you can go to a junk yard and get lc9 5.3 with around 150k miles…for 500-800$….stick a a small lowly ol lsa hot cam into it and a pair of headers with the stock truck intake and a tune and that 5.3 will bend that gen 1 383ci over a bench absolutly ass rape it!!!! And total build cost and swap cost combined would be considerably less then 2500$ ….if you think a gen 1 small block has anything on an ls in terms of power production then build yourself a 434 stroker with sb2 heads and show up at your nearest ls-fest and tell them you want some! !!….I bet 1000$ you leave their butt hurt!

  2. Here are some more numbers for you if you’re into that numbers game. N/A 6.2L (376 ci) LS with a 212/218 .525/.529 cam and long tubes running on 91 octane at 11:1 compression made 421 hp to the tire and gets 25+ mpg highway. Put 10k miles on it per year, and all the maintenance it requires is regular oil changes.

  3. Jeff I like the article but you left something out. Actually most people leave this very important detail out. The torque curve! Comparing peak numbers the engines seem similar but the greatest advantage of ls engines is its almost flat torque curve. Most stock ls engines including the 5.3l your comparing have something like 80% of peak torque available from 2000rpm all the way to redline. As much as I love the gen 1/2 sbc they just can’t compete with that.

  4. Ok so there should be a build off here to see which is better price for price so if someone spends 10000 on a 5.3l L’s and another was to spend the same on a 350 I wonder which one will make more power for the buck

    • Gotta remember fuel mileage and reliability advantages. Personally i like both. Im gonna build a gen 1 for my s10 but i seriously wish id put a 6.0 or 6.2 in my 96 half ton when the motor went. They are both awesome motors and LS engine are becoming relatively easier and are starting to (finally) get cheaper to swap.

  5. Mark Diamond says:

    I wanna build a twin turbo 5.3L to put in my 56 olds 88 project.

  6. I recently purchased a 2005 5.3 engine I don’t know much about motors bit it came with the 6.0 heads, 6.0 cam, and 6.0 intake and all accessories with under 30000 miles i pretty much stole it for what I paid my question is this, what kind of horse power could I expect from that motor

    • The only 6.0 part that is going to be better than what the 5.3 has already is the cam. The intake is the same and if I recall correctly the heads aren’t going to flow any better but will lower compression. Super Chevy did a test of a bunch of stock cams in a 5.3 if you Google it.

      • Hot Rod apparently, not super chevy.

      • It depends on the year 6.0L heads being used. If it’s the newer “square” port heads like the LS3 designs, coupled with the matching intake manifold and TB, it can be a sizeable increase in flow for the older engines with the cathedral port heads. I believe they started with the square (or more accurately rectangular) intake port heads. One would need a tune to truly utilize the advantages of these modifications though.

        I’m pretty sure they started putting the “square port” heads on the HD 6.0L’s when they switched to the GMT900 body style, 2008+ but it might not have started until 2010, so don’t quote me on that lol.

        I didn’t think the 6.0L heads would fit on the 5.3L due to bore size, but I do know the 6.2L heads are far too big. So maybe the 6.0L is the absolute biggest displacement heads you can fit.

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

  8. can you advise me on swapping out a 5.3 for a 6.0 in a 2003 gmc full size truck

    • A swap from a 5.3 to a 6.0. Is as simple as it gets. Swap the engines, they’re identical externally, and swap the ecm from the 6.0 in place of the 5.3. done.

  9. On 5.3 cathedrel heads, what power increase can be expected from a port/polish job with proper tuning

  10. I have a 99 5.3 I swapped into my 88 had everything wires and vats where flashed when we flashed the vats it started right up but idled high killed it and started right up again I’ve tryed everything still nothing it’s getting fuel good pressure and it’s getting spark but won’t start when I sprayed starting fluid in the throttle it started then dies can someone help me

  11. Let’s put aluminum heads on the 350 and make it 9.5 to 1 with the same amount of cam and fuel and let’s see what the power yield from a 5.7 and 5.3 that have basically the same components. Then you can say which is better but with both engines having different components it is not angels comparasion.

    • sure you could do that but would add $2000 on to the build to get the same numbers of a turn key for $2000. so dollar for dollar the 5.3 is the biggest bang for the buck. I got a 383 that was going into a toyota truck but think with the weight savings and reliability changed that plan to a 5.3 sold the wife with fuel injection lol. But well find a hot rod to put the 383 in maybe a c10

  12. Kevin hartley says:

    What must the diff ratio be on a K20 4×4 with 15 inch tyres and a 350 cu inch chevvy motor.
    It is presently 4.1

  13. LS is the only way to go no matter what the project in our current world.
    Lets face it, unless you like to play with octane additives, hardened seats and the whole non leaded fuel issues you get at todays gas pumps go LS !
    The article failed to mention the number one reason to make the jump: LS engines are considered to be GMs only true Ethanol based engine, this alone is critical for no hassle daily driving.

  14. Rene Doyharcabal says:

    I have a ’38 Chevy 2 door rod with a 350 small block coupled to 700R4 tranny. I get around 13mpg in town. I’m curious as to what I could expect with an LH6 high output 5.3 liter aluminum block. Any ideas?

    • Clay Seachris says:

      Always depends upon rear gear ratio, in my ’56 Chevy 4-door with stock rear-end. I get 30mpg on the highway with an average speed of 70mph at 1700 rpm. Stock 2001 Suburban 5.3L iron block with 4L60E trans, headers and dyno tune. Still plenty of low-end torque to smoke the tires if need be. My best friend has a ’40 Chevy and I get more than 2x his mpg. The LH6 Aluminum block puts out more HP and is lighter than mine, so obviously would have higher expectations. 🙂

    • Robert Maletta says:

      Depending on gear and driving conditions 17 mpg with a well adjusted 600 carb 20 mpg with a good fuel injection I have a 1984 Monte Carlo ss with a LS2 with CNC ported LS3 heads 4:10 gears 700r4 trans 3000 stall 600 lift hydraulic roller cam 850 Holley DP carb if l keep rpms under 2400 rpm it gets 14 miles to the gallon but it’s hard to do with the loose converter but converter has a lockup which makes it possible

  15. Look into the Project Sledgehammer or Humble Pie Roller cam articles. Both made more than 400 hp and over 420 TQ from a 350 without reving higher than 6,500 rpm.

  16. I got my lm7 for $300 complete and running…180k miles and no ridge on the cylinders no scuffing on the bearings..In fact when I took the rods out I rotated the crank with my fingers and it sounds like it was on ball bearings. The ls with the central thrust bearing and 6 bolt main will shame any gen 1 smally in fatigue resistance and power handling capability…Sorry old timers all I can say is let’s line em up.

  17. I have built many of the Gen 1 Small Block Chevy engines over the years and they have proven to be well design engines. I have also built a 5.3L engine for my 2002 Chevy short bed Silverado truck with a Whipple Supercharger, 6.0L heads (8.5:1 compression ratio) that makes 400HP at the rear wheels. The LS engines are very well designed especially in the bottom end with the six main bolt design. They are both great engines, but they have their place in time. I prefer to keep the engines to the cars they came with. A 69 Camaro with an all aluminum original 427 Big Block Chevy is what I prefer…….

  18. Keep your LS. I’ll run off and leave it crying all the way down plus LS motor are super high and also parts are cheap and everywhere for a sbc.

    • Robert Maletta says:

      Can you buy cylinder CNC ported heads that flow 358 on intake side for a old small block for 1200 dollars complete with valves and springs no the more the heads flow the faster you will go good luck trying to get a old style 23 degree head to flow more than 280 on intake side and they cost 1600 dollars at air flow research l want to see you make 500+ hp with a old style stock chevy short block stock pistons rods and crank with just CNC ported stock heads cam aftermarket hardened pushrods and aftermarket SFI balancer it won’t last as long or make as much power or be as reliable as a LS motor how many old style small blocks are still running well with 200,000 + miles without a rebuild seen 5.3 LS chevy truck motors with over 100,000 miles take 75 times of 150 hp hit of nitrous and still run without any problems driven everyday to and from work try that with a stock 350 small block with 100,000 miles on it you’d be lucky to make 2 passes before it gernades there is no comparison I’m 54 years old have been racing chevys since 1980 LS engines are the best thing to happen to chevy since the introduction of the first V-8 engine in 1955 really

  19. Barry McCollum says:

    Have 05 Colorado with 3.5 and auto like some input for swaps 4.8 5.3 6.0 if possible has ls z71 package, 8″ rear end with 342 of 373

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