It's pretty funny how people's thoughts go on the whole LS vs big block argument. I posted up a pic on my Instagram over a year ago with that very question and I got a ton of response and a lot of flack from the LS fanboy crowd. Let us first point out I'm not saying the LS is a bad engine. Far from it. They are phenomenal engines for the design and have been getting even better until the ICE gets mandated out of existence (discussion for another time). They make crazy HP with small mods to full-on single and twin turbski's.
But let us look at that design in the context of what this forum is based around. Heavy, solid axle-equipped 4wd trucks. Now anybody that has driven a truck that came from the factory with an LS engine stock can vouch they do make better power than the Vortec 350 that they replaced but with one noticeable difference. Where the torque comes in. In all three original gen 3 truck engines 4.8, 5.3, and 6.0 the torque comes on later in the RPM than the 350 it replaced. Sure the 6.0 did better than the 5.3 and that did better than the 4.8. With similar cam profiles, it really came down to displacement. For the basis of the discussion let's also make an assumption that the engines are stock and not fitted with better heads or different profile camshaft.
Why does the torque come on later? One of the reasons is the valvetrain. Roller lifters and factory roller rockers help the LS engines rev. With even the stock teeny cam profiles they do. Geared right where you can keep them wound up they can get the job done. But get used to the tach needle swinging past 5,000 RPMs to get there. Getting that gearing right based on tire size is really critical to the enjoyment factor. Go too big on tire size with too little gearing and it's still a turd. No different than any other engine. You aren't getting enough leverage with the gearing to keep the engine in its happy sweet spot. With a 700r4 or 4L60e in OD at highway speed you'll have the engine too far below that the meat of the torque curve the transmission is going to be dropping to 3rd or 2nd of the load increases with a grade or even pushing a headwind. More gear will overcome that, but you'll be cruising at a higher RPM, essentially working the engine more. Granted that's not as big a deal in an LS-swapped Muscle car but in a massively heavy 4wd truck it really can be.
So with the insight on an LS and how gearing is important why make the comparison to the dinosaur Big Block? Specifically the L29 454 and by extension the L18 8.1, both with EFI. The reason is displacement and low-end torque. More cubes can mean more power down low. Getting into the torque sooner helps get our heavy 4wd trucks rolling from a stop and maintaining cruising speed without working nearly as hard. Because of the low-end grunt, you can get away with some less than ideal tire/gear combos because the big block is going to get the load rolling easier at a lower RPM. The engine with more torque is going to hold OD better without requiring the busy downshifts in order to keep the engine in the torque curve to maintain speed.
But what about the dyno curves? I'm a big fan of Richard Holdener's Youtube channel. He does a lot of real-world straight from the junkyard tests on engines. He has many videos on LS engines and many on the TBI and L29 454 big block. He's released a video that is making the direct comparison between the gen 3 LS truck engines 4.8/5.3/6.0 vs the L29 454 for the specific target of low-end torque. All four engines are stock short of removal of the accessory drive, Holley ECU, and long tube headers. The results are no surprise but seeing the curves layered out over each other gives a better visual than just talking about it.
I'm probably one of very few that have had both an LS and an EFI big block in the same truck. Mine has an 8.1, which adds a touch more displacement over the L29 but the effects work out the same. I ran the 5.3 for 5 years and a good chunk of that time had the added load (weight and aero) of the camper on the back. Prior to the camper installation, the 5.3 was great until the truck got loaded heavy. I could boil the tires pretty easily with 4.10 gears and the 35" tires. It got great fuel mileage for what it was (15-16mpg). Loaded for a week in the desert you could tell the 5.3 was getting worked harder. Fuel mileage dropped to 12-13mpg on the trip. Steep mountain highway passes sucked with the big camping load. 2nd gear at 45-55mph was the norm. The camper's added heft and even worse aerodynamics dropped the normal average fuel mileage to the same as the loaded for a week of camping all the time. Actual desert trip mileage dropped to 11-12 with a couple of tanks in the single digits. Mountain passes still sucked but I got used to anticipating the grade and held it to 3rd and manually downshifted to 2nd sooner to keep the engine wound up and maintaining higher speed. I had to turn up the tunes and not look at the tach to avoid my old school brain from freaking out over the stupid high revs to maintain speed. Off-road worked just fine, but I typically did more in 4lo to bump the power with more gear reduction.
Fast forward to the 8.1 swap. Fuel mileage was one of the points the LS fanboys were sure I'd be always in the single digits on. That's true if I drive it like a pissed-off teenager all the time. A year's worth of driving says otherwise. The overall average is still right in that same 12-13 mpg range the 5.3 had loaded. I had one tank on the way to Blazer Bash from just outside of Golden CO to Parachute CO (across nothing but the Rockies and two major passes) that got 16 mpg at 70mph most of the way. I was so shocked I did the math three times on top of what my mileage app showed. How can an engine that is 2.8 liters larger get the same mileage as the smaller engine? That comes right back to torque. The 8.1 torque curve is so much lower in the RPM scale vs the 5.3 it doesn't need to be revved out to keep the truck going at the same speed. Put really simply, spin the engine faster it's going to use more fuel. Even a smaller engine.
So here's the thing. If you are shopping for a junkyard or used late model engine to swap into your earlier truck you really want to take a look at what the use of your truck is going to be. Keep in mind with the white-hot status of LS engines, boneyards are wise to the demand and charge accordingly for the price. The 6.0 commands a high premium over its smaller brothers. The L29 however is often overlooked for the LS engines and isn't carrying the previous high price tag they used too. 8.1's aren't cheap due to the low numbers of production unless you buy a wrecked truck with one in it. But the L29 is an overlooked gem with a stock roller lifter cam and decent heads. You can get a standalone harness and computer to run them for the same price as the LS stuff. The bonus is the L29 is a bolt-in affair vs the adapter mounts needed with an LS. Stock squarebody big block manifolds fit along with headers for a BBC-equipped square.
Do your own homework but if you want awesome low end grunt in a stock package they are hard to beat.
But let us look at that design in the context of what this forum is based around. Heavy, solid axle-equipped 4wd trucks. Now anybody that has driven a truck that came from the factory with an LS engine stock can vouch they do make better power than the Vortec 350 that they replaced but with one noticeable difference. Where the torque comes in. In all three original gen 3 truck engines 4.8, 5.3, and 6.0 the torque comes on later in the RPM than the 350 it replaced. Sure the 6.0 did better than the 5.3 and that did better than the 4.8. With similar cam profiles, it really came down to displacement. For the basis of the discussion let's also make an assumption that the engines are stock and not fitted with better heads or different profile camshaft.
Why does the torque come on later? One of the reasons is the valvetrain. Roller lifters and factory roller rockers help the LS engines rev. With even the stock teeny cam profiles they do. Geared right where you can keep them wound up they can get the job done. But get used to the tach needle swinging past 5,000 RPMs to get there. Getting that gearing right based on tire size is really critical to the enjoyment factor. Go too big on tire size with too little gearing and it's still a turd. No different than any other engine. You aren't getting enough leverage with the gearing to keep the engine in its happy sweet spot. With a 700r4 or 4L60e in OD at highway speed you'll have the engine too far below that the meat of the torque curve the transmission is going to be dropping to 3rd or 2nd of the load increases with a grade or even pushing a headwind. More gear will overcome that, but you'll be cruising at a higher RPM, essentially working the engine more. Granted that's not as big a deal in an LS-swapped Muscle car but in a massively heavy 4wd truck it really can be.
So with the insight on an LS and how gearing is important why make the comparison to the dinosaur Big Block? Specifically the L29 454 and by extension the L18 8.1, both with EFI. The reason is displacement and low-end torque. More cubes can mean more power down low. Getting into the torque sooner helps get our heavy 4wd trucks rolling from a stop and maintaining cruising speed without working nearly as hard. Because of the low-end grunt, you can get away with some less than ideal tire/gear combos because the big block is going to get the load rolling easier at a lower RPM. The engine with more torque is going to hold OD better without requiring the busy downshifts in order to keep the engine in the torque curve to maintain speed.
But what about the dyno curves? I'm a big fan of Richard Holdener's Youtube channel. He does a lot of real-world straight from the junkyard tests on engines. He has many videos on LS engines and many on the TBI and L29 454 big block. He's released a video that is making the direct comparison between the gen 3 LS truck engines 4.8/5.3/6.0 vs the L29 454 for the specific target of low-end torque. All four engines are stock short of removal of the accessory drive, Holley ECU, and long tube headers. The results are no surprise but seeing the curves layered out over each other gives a better visual than just talking about it.
I'm probably one of very few that have had both an LS and an EFI big block in the same truck. Mine has an 8.1, which adds a touch more displacement over the L29 but the effects work out the same. I ran the 5.3 for 5 years and a good chunk of that time had the added load (weight and aero) of the camper on the back. Prior to the camper installation, the 5.3 was great until the truck got loaded heavy. I could boil the tires pretty easily with 4.10 gears and the 35" tires. It got great fuel mileage for what it was (15-16mpg). Loaded for a week in the desert you could tell the 5.3 was getting worked harder. Fuel mileage dropped to 12-13mpg on the trip. Steep mountain highway passes sucked with the big camping load. 2nd gear at 45-55mph was the norm. The camper's added heft and even worse aerodynamics dropped the normal average fuel mileage to the same as the loaded for a week of camping all the time. Actual desert trip mileage dropped to 11-12 with a couple of tanks in the single digits. Mountain passes still sucked but I got used to anticipating the grade and held it to 3rd and manually downshifted to 2nd sooner to keep the engine wound up and maintaining higher speed. I had to turn up the tunes and not look at the tach to avoid my old school brain from freaking out over the stupid high revs to maintain speed. Off-road worked just fine, but I typically did more in 4lo to bump the power with more gear reduction.
Fast forward to the 8.1 swap. Fuel mileage was one of the points the LS fanboys were sure I'd be always in the single digits on. That's true if I drive it like a pissed-off teenager all the time. A year's worth of driving says otherwise. The overall average is still right in that same 12-13 mpg range the 5.3 had loaded. I had one tank on the way to Blazer Bash from just outside of Golden CO to Parachute CO (across nothing but the Rockies and two major passes) that got 16 mpg at 70mph most of the way. I was so shocked I did the math three times on top of what my mileage app showed. How can an engine that is 2.8 liters larger get the same mileage as the smaller engine? That comes right back to torque. The 8.1 torque curve is so much lower in the RPM scale vs the 5.3 it doesn't need to be revved out to keep the truck going at the same speed. Put really simply, spin the engine faster it's going to use more fuel. Even a smaller engine.
So here's the thing. If you are shopping for a junkyard or used late model engine to swap into your earlier truck you really want to take a look at what the use of your truck is going to be. Keep in mind with the white-hot status of LS engines, boneyards are wise to the demand and charge accordingly for the price. The 6.0 commands a high premium over its smaller brothers. The L29 however is often overlooked for the LS engines and isn't carrying the previous high price tag they used too. 8.1's aren't cheap due to the low numbers of production unless you buy a wrecked truck with one in it. But the L29 is an overlooked gem with a stock roller lifter cam and decent heads. You can get a standalone harness and computer to run them for the same price as the LS stuff. The bonus is the L29 is a bolt-in affair vs the adapter mounts needed with an LS. Stock squarebody big block manifolds fit along with headers for a BBC-equipped square.
Do your own homework but if you want awesome low end grunt in a stock package they are hard to beat.
