As you probably know, there are a whole bunch of GM LS, LQ, and LM variants. Some of them are more popular than others, but they all share one thing in common: they’re all naturally aspirated.
Well, all but two engines. The only engines in the GM LS engine family which aren’t naturally aspirated are the LSA and the LS9. These two engines are nearly identical and if you didn’t know any better you’d probably think that they’re the same, but there are some key differences between the two.
Based on GM LS3
The reason that these engines are so similar is that they’re both based on the LS3. The share the same bore, stroke, compression ratio, block, heads, displacement, and more. The biggest and arguably most important difference between the LS9 and LSA are the different superchargers.
On the LSA you’ll find 1.9L roots style six-generation supercharger with single charge cooler on top of the supercharger. Meanwhile, on the LS9 you’ll find a 2.3L roots style sixth-gen supercharger with a dual charge cooler system. Both supercharger utilize a 160-degree rotor twist. The stock boost pressure on the LSA is 9psi, compared to the LS9 where the stock pressure 10.5psi.
To simply all that, the LS9 has a larger supercharger which outputs more boost in stock form and it uses a better charge cooler. That being said, both superchargers aren’t all that great compared to many aftermarket superchargers. This is especially true if you were to switch from a Roots style supercharger to a more thermally efficient centrifugal style supercharger.
The heads are very, very similar, but they have different casting numbers and a few different small features. The important changes in the heads are the LS9’s titanium intake valves and sodium-filled exhaust valves. This is different than the LSA which just has standard stainless steel intake and exhaust valves.
Both engines have the same intake and exhaust valve diameter, although interestingly enough the valve angle on the LS9 is 3 degrees steeper than the LSA at 15 degrees compared to 12 degrees. Both LS9 and LSA heads are constructed from 356-T6 Rotocast Aluminum which is different than all other LS engines.
With the Roto-cast method, the mold rotates to more evenly distribute the molten alloy, creating a denser head casting that virtually eliminates porosity. And compared to the similar LS3 head, the LS9 features reinforced webbing and a thicker deck for greater rigidity and minimal distortion.
The last important difference in the cylinder heads is that the LS9 uses marginally stronger head bolts compared to the LSA. Both LS9 and LS9 heads are based on LS3 heads. However, they have a flow vain in the intake port. This helps emissions and idle stability but reduces flow. CNC porting the heads is common. This removes the vain and improves airflow by about 70 CFM.
The camshafts are another area where you’ll see pretty significant differences between these engines. To put simply, the LS9 cam is quite a bit more aggressive than the LSA cam. It has more lift and more duration on both the intake and exhaust side.
- LS9 Cam – lift 0.558/0.562 – duration 211/230 degrees – LSA 122.5 degrees
- LSA Cam – lift 0.480/0.480 – duration 198/216 degrees – LSA 122.5 degrees
As a matter of fact, the LS9 cam is a popular upgrade for LSA owners, since it’s an easy way to pick up as much as 30hp without any other major changes.
Cylinder Blocks & Internals
The cylinder blocks are the same and they’re both based on the LS3 block and they’re both beefed up compared to a normal LS3 block. LS9 and LSA blocks have the same casting numbers but different part numbers. As far as I can tell, the only reason for the different part numbers is because the LS9 head bolt holes are M12 and the LSA head bolt holes are M11.
Looking at the bottom end we’ll find that the LSA does not have the same titanium forged rods but forged powder metal rods. More specifically, the LS9 connecting rods are about 200 grams lighter than the LSA connecting rods and a bit stronger. The pistons in the LSA are hypereutectic aluminum alloy, where the LS9 pistons are forged.
Both crankshafts are forged steel and as far as I can tell they are equally as strong, although they have different part numbers because the crankshaft flanges have different bolt patterns. It’s also worth noting that the main bearing caps on the LS9 are forged steel but on the LSA they’re nodular iron.
To put it simply, GM gave the LS9 are really strong bottom end, which is a bit stronger than the LSA bottom end. That’s not to say that LSA has a weak bottom end, because in stock form the LSA bottom end is capable of up to 900whp.
Honestly, you could argue that the LS9 is “overbuilt” for the stock power output, but GM wanted to build something that could withstand years of abuse. What’s also interesting is that LS9 engines are handbuilt in Wixom, MI where the LSA are presumably assembled like any other engine at Silao, MX.
Which One is Better?
The last few differences I want to bring up are the LS9’s superior dry-sump oiling system which is way better for track use. The LS9’s 6600rpm rev limiter compared to the LSA’s 6200rpm rev limiter. and lastly that the LSA uses a standard cast-iron exhaust manifold and the LS9 uses a stainless steel exhaust manifold.
All of these differences amount to power output 638hp and 604lb-ft for the LS9 and 556 to 580hp for the LSA. To put this entire video simply, the LSA is a detuned and slighter weaker version of the LS9 with a smaller supercharged.
So, to answer the question of which one is better? I think it’s pretty clear that the LS9 is the better engine. It has a bigger supercharger, better heads, bigger camshaft, better internals, and a better oiling system.
If you were to swap a used engine into your project car, the LSA will be better because it’s going to be easier to find because it was used in the Camaro ZL1 and the CTS-V, where the LS9 was only used in the Corvette C6 ZR1.