We all know the GM LS engine is a popular choice for engine swaps. You’ll LS engines swapped into everything from Jeeps, Miatas, Mustangs, planes, helicopters, boats, and more.
The thing is, there are a lot of engines in the LS family and they’re all very similar. Two of the most popular LS engines include LS2 and LS6. These two engines are different generation LS engines but they share a lot in common.
So, let’s dive in, cover the differences and figure out which one is better.
As you may or may not know, there are different generations of the LS engine family: Gen III and Gen IV. They share a lot in common, the Gen IV uses some newer technology and some redesigned parts which we’ll talk about in just a bit.
The main difference between all the LS engines is displacement, intake manifold, camshaft, heads, and head port shape and size. There are tons of other little changes, but these are arguably the most significant.
The immediately obvious difference between the LS2 and LS6 is the displacement. The LS6 has 5.7L of displacement which makes sense because it’s based on the LS1 which is also 5.7L and the LS2 has 6.0L of displacement.
- LS2 Bore x Stroke: 101.6mm x 92.075mm or 4in x 3.625in
- LS6 Bore x Stroke: 99mm x 92mm or 3.78in x 3.622in
In theory, more displacement means more torque and more power with less work. Of course, this isn’t always, but generally speaking, if you increase displacement, you increase the peak power potential.
Of course, the differences go past just having more bore and stroke. Part of the reason for the change in bore and stroke is because the LS2 is the first member in the Gen IV family, where the LS6 was a member of the Gen III family.
I think it goes without saying, displacement is only part of the puzzle. It doesn’t matter how much displacement you have if your cylinder heads can’t adequately keep up with the airflow demands.
As a whole the LS family is known for having superb head flow in pretty much every variant, the LS2 and LS6 included.
More specifically, on the LS6 you’ll find GM 243 heads, which are just an improved version of the LS1’s 241 heads. Those 243 heads in totally stock form flow around 210cfm on the intake side and 75cfm on the exhaust side, which is slightly better than the 241 heads they’re based on.
One of the nice features on the 243 heads are the hollow valve stems and sodium-filled valves, which are great if you plan on using the engine forced induction.
You would think that the LS2 would use different heads, considering it was supposed to be the new Gen IV with all the new features, but nope. The LS2 uses the same 243 casting heads, although with a few modifications.
From what I could dig up, the LS2 and LS6 243 heads are identical minus the exhaust valves, where the LS2 doesn’t have sodium-filled valves although it still uses the LS6 valve springs.
To put it simply, the heads on the LS2 and LS6 are pretty much identical, but technically speaking the LS2 are better because of the sodium-filled valves, but that’s a pretty minor improvement all things considered.
This is particularly interesting because you would think the heads wouldn’t be interchangeable with the different bore sizes, but they are.
I think it’s also worth noting that the 243 heads use cathedral style ports compared to the square ports found on later LS engines. Another thing worth noting is that GM 243 and 799 heads are nearly identical.
Moving on to the camshafts, we can see some more notable differences. Technically, there were different cams used in the LS2 and LS6 depending on the year and model, so for the sake of simplicity, we’re going to just compare the biggest OEM camshafts used in either engine.
- LS2 cam: 0.525/0.525 lift | 201/211 degree duration | 116 degree LSA
- LS6 cam: 0.551/0.547 lift | 204/218 degree duration | 117.5 degree LSA
Without too much detail, the LS6 camshaft offers more lift, more duration, and a wider lobe separation angle. With more lift and more duration, you’re going to get more air into the engine and the wider lob separation angle should theoretically give the LS6 a wider powerband.
The LS6 cam is the most aggressive cam GM put out for any cathedral port LS engine.
You can see the effects of the more aggressive camshaft in the power figures. The LS2 outputs 400hp and 400lb-ft of torque and the LS6 405hp and 400lb-ft of torque.
On paper, we’re talking about a mere 5hp increase, but with displacement accounted for, you can see the LS6 makes 5 more horsepower per liter of displacement, which can mostly be attributed to the camshaft as well as some other things.
If we were to take those two power per liter figures and make both engines 6.0L, the LS6 would make 426hp rather than 405.
- LS2: 66.6hp/liter and 66.6lb-ft/liter
- LS6: 71hp/lter and 70lb-ft/liter.
LS2’s pistons have a true flat-top design with all three rings having lower tension than LS1 and LS6 rings. Lower tension reduces friction to free up horsepower.
The pistons also have full floating wrist pins that help reduce the piston slap noise that’s common on Generation III engines (LS1, LS6). Gen IV engine blocks (LS2, LS3) have siamese cylinder bores, meaning that a water slot between bores is unnecessary for adequate cooling and that all bores have a solid, uninterrupted connection.
This resulted in a stronger block that is less prone to heat distortion in the cylinders. Less bore distortion means less friction and pumping losses.
Significant improvements were made with the intake when GM developed the LS2. Intake runner geometry was optimized for six-liter displacement, it used larger bell-mouth, throttle-body size increased from 76-mm to 90-mm, the entire induction system was redesigned for lower restriction.
Overall, the intake system on the LS2 flows upwards of 15% more air than the LS6 intake system.
That being said, the intake manifold by itself is a different story. When you remove the rest of the induction system and compare just the intake manifolds, the LS6 has a superior intake manifold in a stock form which is preferred by many enthusiasts who like to swap LS parts around.
Up this point, the LS6 has had better or equal components than the LS2. It has a bigger cam, marginally better cylinder heads, and a better intake manifold. The LS2 wins when it comes to displacement, but there is another thing that we need to look at which is pricing.
On paper, the LS6 is the better in most categories, but when you consider the cost of buying one of the engines, the LS2 is the better engine. To put it simply, the rarity of the LS6 simply makes it more expensive to buy used.
That being said, the LS2 is also expensive compared to cheaper LS engines like LQ or LM truck motors.
What makes the LS2 popular with engine builders is that the block is compatible with the high flowing and desirable L92 cylinder heads. The larger, 4.00-inch bore of the LS2 enables it to use LS1/LS6 heads, as well as L92-style heads. The LS6 on the other hand is pretty limited as far as head options because of the smaller bore.
Which One is Better?
So, to answer the question of “which one is better?”. The LS6 has a has bigger camshaft, better intake manifold, and marginally better cylinder heads.
The LS2 has more displacement and is cheaper to buy used. Stock vs stock, I’d say the LS6 is better, but in the real world, you’d probably be better off with an LS2 and some aftermarket parts like a bigger cam and some mild head work.