Did you know that the LQ4 and LQ9 are the most preferred Gen III LS blocks for junkyard builds? These two truck engines are very similar and can be hard to differentiate based on looks alone. Despite their interior differences, they are both durable and capable of handling over 1000 horsepower.
In this article, we are going to look at how they came about, their specifications, where they are applied, and how they hold up to date. We will pay attention to their key differences to help you choose the best one for your next build.
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LQ4 was designed and manufactured in 1999 to join the LS truck engine lineup of General Motors (GM). General Motors used it in its pickups, SUVs, and vans from 1999 to 20007. Referred to as the Vortec 6000, GM manufactured the LQ4 engines in Michigan, Romulus, and Silao, Mexico.
General Motors applied the Vortec 6000 in many specific models, which include Chevrolet Express, Chevrolet Silverado 2500 Pickup, Chevrolet Suburban, Hummer H2, GMC Yukon Denali, and GMC Sierra 2500 HD Pickup.
LQ9 was designed and manufactured in 2002 to be used in the Cadillac Escalade. Its application was limited to GM pickups and Escalade models until 2007. The VIN N applications ended in 2007 when the engine was built into the Classic Chevrolet Silverado and GMC Sierra performance edition. Like its predecessor, GM also produced the LQ9 in Romulus and Michigan.
LQ9 is considered a successor to the LQ4. Improvements were made to the engine to make a high-output version of the LQ4, which was later dubbed as the Vortec HO 6000. The LQ9 was also known as the VortecMax.
The LQ4 and LQ9 are part of General Motors’ 4.00-inch bore blocks that were built between 1999-2007. They are both larger versions of the LS motor meant to be a good balance between enormous blocks and new small blocks in truck applications.
LQ4 vs. LQ9
Difference in parts
The LQ4 and LQ9 share a lot of parts, which means their design, size, and functionality are more or less similar. The piston material (hyper eutectic cast aluminum alloy) is the same in both engines and the connecting rods are made of powdered metal. The crankshaft material is cast iron and the connecting rods have the same I-Beam style.
However, for the piston style, the LQ4 has dished pistons with +6.7 cc volume, while the LQ9 comes with flat top pistons. The flat-top design helped in increasing the compression ratio from 9.4:1 to 10:1, increasing the horsepower to 345 hp. For the 1999-2000 LQ4 models, the cylinder head came with an oval exhaust port shape while later models of the LQ4 and all LQ9s featured a D port exhaust port shape.
The 1999-2002 LQ4 models featured an all-cable operated throttle control while later models (most models) were equipped with a drive-by-wire (electronic) throttle control. The electronic throttle control was kept in the LQ9 truck engines to keep up with the advancements in the automobile industry.
The LQ9 is a better performer than the LQ4 because of the improvements in the piston style which facilitates the creation of higher output. The implication of this is that the LQ9 has a higher horsepower, and responds better to upgrades like high-flow cylinder heads, turbos, superchargers, nitrous oxide, and intake systems.
The increased compression in the LQ9 helps it output 30 more horsepower. However, a higher compression does not mean the LQ4 with lower compression is easily outdone. The LQ4 is better for boosted applications since the lower compression allows for a range of power adders. The horsepower difference is noticeable but may not make a lot of difference since they both function relatively the same under normal load.
Premium fuel or gasoline, which is higher in octane value and pricier than standard gasoline, is preferred in the LQ9 engines. However, the type of fuel won’t affect the performance and fuel economy. This is because the onboard computer will compensate for whatever octane level is present in the gasoline.
The electronic throttle control (ETC) system has been integral in creating a system-level solution to issues of fuel economy and vehicle safety. The electronic throttle control system is in later models of the LQ4 and all LQ9s.
The system helps in improving the fuel economy in these engines by optimizing the operations in connecting the engine to other systems. Additionally, you will get your vehicle up to the required speeds with less motor strain and less fuel using the ETC.
On average, the LQ9 gets you a fuel economy of 13-15 mpg on city roads and 18-20 on highways. LQ4 is rated at around 10-12 mpg on city roads and 13-15 mpg on highways. The implication of this is that the LQ9 has a better fuel economy than the LQ4. The ETC system on LQ9 engines is more efficient and reliable than the one in LQ4 engines.
The price of the LQ4 and LQ9 is largely determined by the scarcity of each model. LQ9 is considered a limited production engine when compared to LQ4. The high output V-8 6.0-liter engine is more desirable to those who want the most out of the Gen III engine, making it more expensive than the LQ4.
The price will also depend on the mileage/years of use since these affects the condition and lifespan of the engine. Later LQ4 models are also more expensive than the original ones because of the various modifications they underwent.
A good way to save on cost may be to get an LQ4 engine and perform some standard modifications that mimic the LQ9. You can change the camshaft specifications using various packages like the Z06 Cam package or the SS Cam package. Both modifications will help improve the horsepower to 375 hp and 425 hp, respectively.
A lower price of $700 can get you a 375 hp LQ4 engine block, whereas you will have to spend as much as $1000 to get 425 hp, the same cost of getting an LQ9 engine block. You can expect to spend between $1000 – $1800. For example, a junkyard LQ9 with 69,000 mileages from an SS can cost $1,800, while the same LQ9 with 50,000 mileages will go for $1,200.
How to tell the difference between the LQ4 and the LQ9
You can distinguish the LQ4 from the LQ9 by taking a look at the type of piston using a bore light and scope to see whether the engine has flat top pistons or dished pistons. The LQ4’s piston has a dished top whereas the LQ9’s is flat.
However, the best way to tell the difference between the LQ4 and LQ9 is through the VINs. These VIN numbers can be found on the driver-side door pillars, under the hood of a side engine bay, or on the front of the dashboard looking through the windshield. You can also check the VIN numbers with an OBD scanner.
The 8th digit VINs show the type of engine, with ‘U’ being the LQ4 engine and ‘N’ the LQ9 engine. VINs from the original vehicles will do a better job of identifying the engine than the model of the vehicle or year of manufacture.
The LQ9 is a higher-performance engine when compared to the LQ4. You will get the most out of the LQ9 since the high compression ratio allows for a higher output that increases the horsepower being produced.
However, the LQ4 isn’t so different from the LQ9 apart from the compression ratio and its lower compression can be a bigger advantage for boosted applications. Moreover, the LQ4 is cheaper than LQ9, which is definitely a point for consideration.