LS3 Vs LS7 Engines – Differences, Similarities & Common Issues

We all know the GM LS is a very popular engine for engine swaps. You’ll find it in everything from jeeps, miatas, trains, boats, planes, helicopters, etc. Some of the more popular LS engines include the LS3 and LS7.

The LS3 engine is a small block engine that was used in the Corvette C6, GTO, and Camaro while the LS7 is a small block engine that was used in the Z06 and ZR1 Corvettes. Both of these engines are very similar, but they have some differences.

There’s been some debate about the LS3 or LS7. Both engines are great to have, but they have their strengths and weaknesses. The key to getting the most out of either engine is knowing the differences and similarities.

The main difference between the two engines is that one is more powerful than the other. The LS7 was built for performance and will provide you with more horsepower than its counterpart, but it’s also a bit more expensive and less efficient on gas.

In this post, we’ll be looking at these two to see what significant differences they have, and hopefully help you make an easy decision on which one to go for based on your needs.

LS3 vs LS7

The LS3 Engine

The LS3 is a gen 4, 6.2-liter aluminum small block engine. One of its significant features is its increased displacement. The LS3 cylinder heads which are identical to those found on the L76 and L92 use 2.165-inch intake valves and 1.59-inch exhaust valves. This is a notable increase from the LS2.

It’s also worth noting that the LS3 heads are some of the best OEM heads that you can buy. GM also improved how they manufactured the LS2 head so they’re cheaper to manufacture and sell. This makes them even more desirable because the price point is actually pretty low for what you’re getting.

The LS7 Engine

The LS7 was the c606 engine that was manufactured from 2006 through 2013. The engine started out as the 5.5 liter v8 used in the c5r and c6r race cars. The manufacturing company – General Motors then did a bunch of machine work and changes to get 7 liters of capacity. Hence, the LS7’s 427 cubic inches which produces 505 horsepower. This was a beast of an engine.

However, if you’re looking at buying one of those cars and you do any kind of research online, you’d probably come across comments about their heads going bad, huge engine problems, or flawed design.

The LS7 revs to 7,000 RPMs which is pretty high. This was because, GM wanted it to rev faster than the average Corvette LS2, LS3, and so on.

So they added things into this engine that weren’t found on any other GM-manufactured engine – the exhaust and intake valves are very specific to the LS7.

The intake valves are made of titanium in order to save weight because they’re very hard. The exhaust valves are made of stainless steel, and the stems of those valves are sodium-filled to help in dissipating heat.

LS7 Engine Problems

Some of the common LS7 problems reported on the internet are that the valves go bad, the engine will swallow a valve, or that the engine will burn a hole in a piston because of a flawed design.

While some of these things have happened, and in 2006, GM did openly admit that there were some problems they had with a certain group of heads that were machined incorrectly, that didn’t get carried over into subsequent years.

The verified LS7 engine problems were in 2006, right at the beginning. But there have been some cases of severe problems happening all the time with these cars.

In order to understand why some of these failures are happening, you’d need to understand that for an engine that is as specifically engineered as the LS7, the tolerances are very tight and the airflow is tightly regulated.

So, anytime that airflow is interrupted or changed, that engine is no longer running as designed. Therefore, when you do things like adding a cold air intake or long tube headers, or you do a performance chip, and so on, you’re changing the internal functions and the airflow of that engine and this stresses things.

There are almost zero failures on an LS7 engine that was stock. In fact, the failures on stock LS7 engines tend to be camshafts and they’re very few.

Other Differences Between LS3 vs LS7 Engines

1. Displacement/Size

The LS3 engine has a displacement measuring 6162cc or 376.0 cubic inches, while the LS7 engines contain a 7008 cc or 427.6 cubic inch displacement.

It’s meant to fit the Corvette Z06 and Camaro Z28. The LS3 contains a 103.25 mm cylinder bore size, while the LS7 is measured at 104.8 mm.

The LS3 engine has an 8-cylinder design with a 90-degree crankshaft angle and 4 valves per cylinder, with two valves per cylinder on each camshaft (via pushrods) and four camshafts that are timed together by gears in the front of each head/block assembly (via powertrain).

2. Power/Torque Output

The LS3 will pump out 426 to 436 horsepower at 5900 RPM, while the LS7 is rated at 505 horsepower at 6300 RPM. The LS3 also offers a wider torque curve with a peak of 415 lb-ft of torque in its 5500 to 6000 rpm range.

3. Compression Ratio

The compression ratio is the amount of air that can be squeezed into a cylinder during its compression stroke. A higher compression ratio means more potential power, but it also increases the likelihood of engine knock or detonation.

The LS3 has a 10.7:1 compression ratio (10.7:1), while the LS7 mill is capable of 11.0:1 (11/100ths). This means that you’ll get better performance from your LS3 motor if you want to keep your car running at high rpm levels without knocking or detonating on you.

4. Fuel System

The LS7 engine requires premium fuel, featuring a 91 or higher octane level. While this is also recommended for the LS3 engine, you don’t have to use premium fuel for your car to run perfectly well.

As long as your car’s manufacturer recommends a certain type of gas and you follow those guidelines (i.e., don’t mix different grades or types), then everything should be fine.

5. Reliability

Reliability is a huge factor when it comes to determining the best engine. The LS7 offers a slight advantage because of its performance level, but you may end up paying more in terms of maintenance costs if your car is equipped with this engine.

The LS3 seems to come with more issues than other engines, so if you’re looking for something reliable and affordable, this might not be the right choice for you.

6. Cost

Like many other things in this world, the cost of an LS engine depends on what you’re willing to pay. The LS3 is relatively affordable and can be purchased for under $2,000. The LS7 costs about twice as much, but it’s still not a tremendously expensive engine.

For those who are looking for the best bang for their buck, we recommend going with the LS3. It has all the power of a high-performance engine without breaking your bank account—and it’ll still leave you with enough cash left over to buy some nice performance parts.

Similarities Between LS3 and LS7 Engines

Both the LS3 and LS7 are V8 engines that were designed to be used in a Corvette. Both engines have similar displacement, making them great for racing.

Also, the LS3 and LS7 have similar specs. They both produce about 435 horsepower at 6000 RPM and 400 lb-ft of torque at 4600 RPM.

Here are other similarities:

1. Block Material

The LS3 and LS7 blocks are both made out of aluminum, which is the lightest material commonly used in car engines. Aluminum is also much cheaper to work with compared to iron and steel.

While you could use a block made from either material for your next engine build, we would recommend sticking with an aluminum block for its lighter weight and lower cost.

2. Engine Type

The LS7 engines are very similar to the LS3 engines except for their bore length along with a few minor updates. These include a change in piston design, adding a water pump, and other small changes.

3. Weight

LS3 and LS7 both have similar weights. Both are made of lightweight aluminum which is a material that does not add much weight to the engine, so they are almost identical to each other. Their only difference in weight is due to different materials of connecting rods and a few other parts that can be made from steel or aluminum.

4. Lifters

Lifters are cylindrical components that are placed between the camshaft and the inlet-outlet valves. They serve two main purposes: to apply pressure on the valve and to act as a “floating” pivot point for the push/pull mechanism of each valve lifter.

The lifters used in the LS3 and LS7 are the same, so one can be used in place of another (though it’s recommended not to swap them during an engine swap).

LS3 vs. LS7 Engines – Which Is Better?

Buying an LS3 engine is a great way to get into the Corvette world, but it’s not going to give you the most horsepower. If you want more power, there are two options: upgrading to an LS7 or buying a brand-new Corvette with the latest LT1 engine.

The LC9S offers up to 514 horsepower and 460 lb-ft of torque from its supercharged 6.2-liter V8. The car can hit 60 mph in 3 seconds flat and has a top speed of 190 mph (or higher if you choose the Z06). With supercar performance at fractional supercar prices, it’s easy to understand why so many people love this car.

What are the Common Problems of the LS7 and LS3 Engines?

1. Burning Oil

Sometimes, the oil pumps in both engines fail to deliver enough pressure to lift the oil up and into the rocker arm assembly. This would result in an overflow. The reason for this is most likely due to an issue with your filter or pump itself, which can be solved by replacing either one. If you’re still experiencing this problem after replacing both components, then it may be time for another new engine altogether.

2. Knocking Noise

This happens when the pistons are not sealing properly with the cylinder walls. This is usually because the piston rings have developed a groove in them, and a lot of different things can cause this. They can develop grooves if they aren’t manufactured properly or if they get stuck to the cylinder wall during compression due to bad valve seals and/or gaskets.

3. Oil Pressure Issues

Oil pressure issues are also a common problem associated with these engines. If you’re experiencing oil pressure issues, this is likely due to the camshafts wearing down.

In order to fix this, you’d need to replace your camshafts with LS1 or LS6 camshafts. You can also purchase an aftermarket kit that includes all of the needed components and parts to repair your car’s engine.

Read: Car Shakes in Reverse

LS7 vs LS3 Heads

LS7 HeadsLS3 Heads
Delivers 505 horsepowerDelivers 495 horsepower
470 Ib-ft of torque473 Ib-ft of torque
Costs around $300 – $400Costs around $1,200

FAQs on LS3 and LS7 Engines

What Cars Have the LS3 Engine?

The following cars use the LS3 engine: Corvette C6, Pontiac GTO, Camaro, 1994 to 1996 Chevrolet Impala SS, and the 1994 to 1996 Buick Roadmaster.

What is the Max Speed of the LS7 and LS3 Engines?

Both engines are capable of reaching a maximum speed of about 6,000 rpm. However, there are some differences between the two engines that determine their maximum speed. One is a naturally aspirated engine while the other is supercharged, which means it has forced induction.

Supercharging helps raise an engine’s power output by forcing more air into its cylinders. This allows for higher revving speeds because all those extra air molecules can help keep things burning longer in each combustion cycle.

Conclusion

The LS3 and LS7 are two of the most popular engines in the world. They both have their pros and cons, but they’re both equally good at what they do. It comes down to personal preference when it comes to deciding which engine has more value for you.

The main difference can be seen in their performance capabilities. Other differences also include; Displacement/Size, fuel system, reliability, cost, power output, and compression ratio.

Although these two engines’ differences are glaring, there are still some similarities between them. For instance, the two engines are made from the same block material which is aluminum.

Also, the weight, engine type, and lifter are similar. This means that your preference will decide the best one for you.