Will a 5.3 fit a Buick Enclave
With enough money ANY engine will fit in ANY car!
The short answer is NO.
Not without great effort and shocking expense. The relatively rare LS4 variant would be your best bet.
I doubt that you could get it registered in your state. If you need a new engine, I suggest you look for an exact replacement. You couldn’t get a rebuilt engine or, if you can’t afford that, get a used engine.
At the very least, the OP would also need to swap-in the ECM and the TCM for the 5.3 engine, and even then, things might not work properly without installing a trans that was designed to mate-up with that engine.
Back in the 1950s, I had s high school classmate that had a 1951 Mercury with a Cadillac OHV engine. I knew about a 1953 Studebaker with a 322 Buick engine under the hood. Our neighbors bought a 1951 Oldsmobile 98 with a 1955 Oldsmobile engine. All of these cars were troublesome. In the case of the Mercury and the Oldsmobile, the starter motors were designed for 12 volt systems but the cars had 6 volt systems. There always seemed to be electrical issues when these cars were converted to 12 volts.
Today’s engine swaps pose even greater problems.
Probably need to replace the sensors, too.
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The Enclave is FWD based, so it would be a HUGE project to do this.
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use the motor/trans from a grand prix gxp. i figure the OHV motor is narrower than the DOHC but it is longer since it is a v8 vs a v6. so my money is that it will fit in the engine bay. make it work? probably not
the 3.6 is 275hp. the 5.3 is 300hp? pretty much same torque so i dont see the bother
both cars are fwd so packaging is not an issue
The 3.6L makes 275 HP and 251 lb/ft of torque. The LS4 5.3L (FWD variant) makes a little over 300 HP but 323 lb/ft of torque. So significantly more more torque. However the 6 speed transmission with the 3.6L does help mitigate some of that discrepancy. I don’t think it would be would be worth the time, trouble, or expense either.
I’d pay (not much) to see a 5.3 in a “Smart Car” .
As I said, it can be done, but not on the cheap.
Watch here for free! Not a 5.3 but a 7.5 liter Big Block Chevy V8 in a Smart car;
i saw a caddy northstar and 4t80e trans in a vw golf. i know the 4t80 weighs 256lbs and the 4t60 is in the 180lb range so its not a huge weight savings. they even sell a 4bbl intake for the northstar. so swapping it into a non-computer car is feasible. though i expect an 08 enclave owner would want some late model tech
At a recemy car show I saw a 65 Corvair 2 door with an Olds Toranado front drive engine, transmission, suspension and subframe installed in the rear, making a mid engined V8 Corvair. The back seat and part of the rear seat floor and trunk floor had been removed and a firewall had been constructed from behind the front seats up to the bottom of the rear window. The radiator had been mounted horizontally just above where the rear floor had been.
You can do just about anything you want with old cars and engines in NY but once you get into the new stuff , it’s a whole different story.
Ha! That’s funny. Love the exhaust pipe poking out the wheel well.
To be fair, it’s not really IN a Smart car. The only part of the original Smart car appears to be the external body parts…
huh…learned something today!
Well, its kinda “in” the car.
Some stuff just needed to hang out a bit! Sort of like a fat guy in a Speedo swimsuit. 
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My eyes!
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At least I didn’t post a picture to go along with it… 
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Nah, my point is the entire undercarriage is a fabricated tubular frame. I’d say they simply bolted a Smart car body onto their drag chassis but even that isn’t accurate. It looks like only the outer sheet metal and some plastic panels affixed to a new chassis with integral tubular roll cage. Some fine fabrication work BTW! It was fun to watch, thanks for sharing!
fat guy in a Speedo swimsuit
However, you can keep that “you’re about to see something you can’t unsee” image stuff to yourself 
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