LS3 vs LS7 : Detailed Comparison & Crucial F.A.Q’s

When I first moved to the US, I was ecstatic and wanted to build an American-built car with a V8 (obviously). As one would know that the American V8s have a totally different character than the German V8s. The American V8s are all about horsepower and straight-line brutal acceleration that is why people are crazy about them. I went into my friend’s garage and asked him what engine should I select to build my car. He almost instantly replied – an LS V8. I replied back, “But which LS?”. After a long discussion, we both were stuck between two choices- LS3 and LS7.

I decided to do thorough research about LS3 and LS7 engines so it could help all of us choose what’s best for us!

While the LS7 has a displacement (therefore horsepower and torque) advantage, LS3 is a better value proposition as it is cheaper than an LS7. Both are reliable products by GM, but many users have reported certain issues with LS7 whereas there have been fewer issues complained against LS3 engines.


Comparison Table between LS3 and LS7:-

 LS3LS7
Engine typeLS-Series Gen-IV Small-Block V-8LS-Series Gen-IV Small-Block V-8
Displacement6.2-liter7.0-liter
Block materialCast-aluminum with six-bolt, cross-bolted main capsCast-aluminum with six-bolt steel main bearing caps
ReliabilityHighMedium
Weight403 lbs454 lbs
Power430 HP505 HP
Torque425 LB-FT470 LB-FT
Maximum RPM66007000
Compression ratio10.7:111:01:00
Bore x Stroke4.065 x 3.622 inches4.125 x 4.000 inches
Cylinder headsAluminum L92-style port; “as cast” with 68-cc chambersCNC ported LS7-style ports; 70-cc CNC combustion chambers

 

 

Differences:

  • Reliability: Both LS3 and LS7 are engines manufactured by GM, hence the reliability factor is high. There is just a single issue that is very common and many users complain of the same thing in LS7, cylinder heads issue. If you buy an LS7 engine, make sure to get your cylinder heads inspected by a good mechanic. Apart from that, both engines are as reliable as one can get.

 

  • Performance: LS3 and LS7 are high-performance small block 4th generation V8 engines and both have a good reputation for power figures. LS3 has a power figure of 430 HP @5900 RPM and a torque figure of 425 LB-FT @4600 RPM as a stock engine whereas LS7 has a power figure of 505 HP @6300 RPM and a torque figure of 470 LB-FT @6300 RPM.

 

  • Engine Size: LS7 has a longer bore than LS3 which results in an increase in displacement (or volume) of an engine. Therefore, The LS3 engines have a displacement measuring 6162-cc or 376.0 cubic inches. LS7 engines have a 7008-cc or 427.6 cubic inch displacement.

 

  • Boost: A boost in an engine refers to a power bump by using either a turbocharger or a supercharger. Even with a turbocharger or a supercharger, the stock LS3 bottom end can handle quite a reasonable amount of boost. The stock motor can easily handle 5 to 6 pounds of boost from a supercharger which is actually not that much for a stock LS3. A stock LS3 can easily handle 12psi of boost from a turbocharger kit without ruining the engine.A stock LS7 block is basically an LS3 block, with a slightly longer bore. Doing this makes the cylinder walls thinner leaving them vulnerable to heat which can lead to the sleeves melting. More boost, more heat. You can run methanol, or nitrous to aid in heat, but a more positive way to approach it is by having the sleeves replaced with stronger ones, or by switching to another LS block.

 

 

  • Cylinder heads: The cylinder heads of LS3 are L-92 style ported with 68-cc of combustion chambers while the cylinder heads of LS7 are CNC ported LS7 style-ports with 70-cc combustion chambers. So, obviously, LS7 has the advantage in this regard.Also, LS7 has slightly larger valves as compared to LS3.Due to larger combustion chamber and valves, LS7 performs better than LS3, but the only downside is that LS7’s cylinder heads are almost double the price of LS3’s cylinder heads. When you take this into account, LS3’s ‘bang for the buck’ cylinder heads make more sense.

 

  • Intake: The intake valves are an integral part of the engine assembly, as it is the entry point of the air-fuel mixture (in gasoline engines) or air (in diesel engines). The more the amount of air-fuel mixture or air, the more is the power obtained from the power stroke.The intake valve diameter for the LS3 is 2.165” and 2.20” for the LS7. While the LS7 has an intake runner volume of 270-cc, the LS3 has an intake runner volume of 257-cc. Therefore, LS7 has an upper hand over LS3 in this regard.

 

  • Sound: In stock condition and from outside the car, LS7 has a throatier sound as compared to LS3. This is because the compression ratio of LS7 is more than that of LS3. While sitting inside the car, LS3 engines seem to be louder than LS7 engines.If you want a whining sound like that of a Dodge Challenger, install a supercharger in your engine. Superchargers have the most beautiful sound in our opinion.

 

 

 

Similarities:

  • Engine type: The LS-Series Gen-IV Small-Block V-8 type engines are very similar to the LS2 engines except for their bore length along with a few minor updates.

 

  • Block material: These engine blocks are made out of aluminum resulting in a lightweight engine. Also, these engines have a robust casting which results in a more durable build. On the downside, it cannot provide as much durability as the cast-iron engine.

 

  • Weight: The structure of the engines is made of lightweight aluminum, therefore they have almost similar weights. They only have a few pounds of the weight difference between them which is mostly due to different materials of connecting rods and a few other parts.

 

  • Fuel: Both the LS3 and LS7 engines are equipped with sequential fuel injection systems. The fuel is provided to the engine through injectors that fire individually. Because these aren’t multiport systems, it remains more efficient.Along with that, the fuel type used in both the engines is premium pump type. LS7 engines must use premium fuel featuring a minimum of 91 octanes. While this is also recommended for the LS3 engine, it is not mandatory to use this. If you do not have access to 91 octanes or higher, you can also choose to use regular or mid-grade options too.

 

  • Lifters: Lifters are cylindrical components that are placed between the camshaft and the inlet-outlet valves. They are responsible for the opening and closing of the valves. The lifters used in the LS3 and LS7 are exactly the same and one can be used in place of the other.

 

Advantages and Disadvantages:

 

Advantages:

  • LS3: The obvious advantage that the LS3 had was its immense power that too before any kind of a turbocharger or a supercharger. All that power comes with a stamp of reliability of GM. This package comes with a pretty cheap price tag and hence, LS3 offers a superb value for money deal.The engine is built with aluminum which is strong and light. All this makes for a robust build of the engine which enhances the durability factor of the engine. The maintenance of LS3 is pretty simple and cheap as every other GM-manufactured engine.
  • LS7: LS7 has a longer bore as compared to LS3 which results in even larger displacement and more potent power and torque figures as compared to LS3. That power can further be increased by boosting the engine using a turbocharger or a supercharger.The engine is made out of casting aluminum which is durable and lightweight. The maintenance of the engine is easy and affordable.LS7 comes with a dry-sump lubrication system which provides an edge over LS3. Dry-sump lubrication helps the engine to remain lubricated even in long corners and helps the engine to be positioned a bit lower so as to increase the center of gravity (CG) of the engine.

 

Disadvantages:

  • LS3: Like a few other LS engines, LS3 has been afflicted with bad piston ring seals. This should be inspected as soon as possible otherwise it could lead to high oil consumption or can also create a high amount of engine blow-by which can result in rattling sound in an engine or even can lead to an engine failure in the worst case.The small and compact size of the LS3 also means that the engine is a bit congested to work on sometimes.

 

  • LS7: The major problem that has been reported by many customers is the cylinder head issue. Every Corvette Z06 (which has an LS7 engine) user that I have ever come across has told me about this issue. GM has agreed to this issue and claims that it was only in Corvettes from 2008 – 2011 which were plagued with this issue. The problem was that one of the suppliers of cylinder heads was not machining the cylinder heads correctly which resulted in this issue. On these LS7s, the valve guides and valve seats were not concentric, which led to severe wear of the valve guides.

 

 

Some important FAQs:

 

How much horsepower can you get out of an LS3 and LS7?

The LS3 motor will pump out 426 to 436 horsepower at 5900 RPM, while the LS7 is rated at 505 horsepower at 6300 RPM in stock conditions. However, if you are planning to equip the motor with a turbocharger or a supercharger, a turbocharger can take the power figure to 900 HP and an advanced supercharger can take the power figure to 800 HP.

 

How much boost can an LS3 handle?

Even with a turbocharger or a supercharger, the stock LS3 bottom end can handle quite a reasonable amount of boost. The stock motor can easily handle 5 to 6 pounds of boost from a supercharger which is actually not that much for a stock LS3. A stock LS3 can easily handle 12 psi of boost from a turbocharger kit without ruining the engine.

 

How long will an LS3 engine last?

If the engine is left in stock form, the LS3 should go easily over 100,000 miles. We have even seen LS3s going to around 150,000-200,000 before something major would go bad. However, it starts burning a lot of oil after 150,000 miles. The reliability factor is high in LS3s so one need not worry about that.

 

Can you put LS1 heads on an LS3?

Basically, you need to pay attention to the block’s bore diameter. Running a cylinder head intended for a larger bore size can result in valves crashing into the block. LS3 and LS9 blocks can use LS1, LS6, LS2, LS3, or LS9 heads. Therefore, it is possible to put LS1 heads on an LS3 cylinder.

 

Conclusion:

If you are in need of a low-cost, high-performance engine for your build, the LS3 will probably provide everything you are looking for. With 430 horsepower, you will not be disappointed in the level of performance by any means.

If you are willing to spend more for even more power, we highly recommend the LS7 engine. It provides a healthy dose of 550 HP before any boost. You just have to get your cylinder heads inspected and you are good to go.

No matter which of these GM small block V8 engines you choose, you are sure to be exhilarated by the sweet performance and handy reliability. These engines do not break a sweat and can provide you with an exemplary driving experience for many years.