The LQ9 was released in the Cadillac Escalades in 2002 and ran through the ’06 model year. The LQ9s had a half point more compression and a different computer calibration that bumped the horsepower up to 345 hp and 380 lb-ft of torque. In 2003 the LQ9 found its way into the Silverado SS trucks and was used through the ’07 model year. In 2004 and 2005 you could find the LQ9 dropped into the Silverado and Sierra Vortec H.O. editions only. Then in 2006 and 2007 it was also used in the Silverado and Sierra as the Vortec MAX option.
The best way to know you’ve found the goods is by the casting numbers. The block casting numbers you’re looking for are 12573581 and 12577184. There was the early casting number (’99-00), but as we said, you will want to stay away from it. The block casting number is located on the driver side rear of the block, right above the bellhousing flange and right below the driver side cylinder head. It’s rather difficult to read in the car and probably only done with a mirror. Also, another telltale marking is on the left-hand side of the cylinder head, right below the valve cover; find the last three digits of the cylinder head casting number. All the LQ4s and LQ9s used the same aluminum cylinder head with a casting number of 12562317. On the left-hand corner, as you look down at the valve cover, you’ll find 317 cast right into the head. Between the block and cylinder head casting number you should be confident you’ve found the goods.
If we were you, we would only get the LQ9. That half point of compression will give you a good starting point to build up a nice hot rod. In the later years, those flat-tops are the same pistons and rods used in the LS2s with full floating piston pins. Get on the search and find your building block. Enjoy.
Q: The 355 on my ’87 Monte Carlo SS just doesn’t run like it should. The engine is very sluggish out of the hole, such as not to spin the tires much, if at all. The engine has good power at around 4,500-6,500 rpm, but below that something is not right. I have the timing set at 8 degrees at idle and have changed the secondary spring in the carb. I have the lightest spring in the carb now, but they all seem the same in performance. I think this engine should be a lot stronger, but it seems to be running half of what it should be.
Any help you could provide would be greatly appreciated, and a horsepower estimate, if you could. The engine is built as follows: a stock crank with Stage
1 rods (shot-peened), 9.3:1 flat-top pistons, an LT4 Hot cam with LT4 roller rockers 1.6:1, Vortec heads machined for 0.550-inch max lift and 30 degrees back-cut valves, an Edelbrock RPM Air-Gap intake, a Holley 650 vacuum-secondary dual-feed, an ACCEL HEI Super Coil, Edelbrock headers, a four-core aluminum radiator with electric fans, a beefed-up 700-R4 trans, 4:10 Richmond gears with an Eaton Locker, and a 2,500-stall convertor. I’m guessing around 440 hp. Thanks!
A: Thanks for the photo with your question; that and the parts list gave us your answer. You stated that you are running an ACCEL HEI Super Coil. What distributor are you using? The car was originally equipped with an ECM to control the air/fuel ratio of your original Q-jet carb and the spark timing of the distributor. If you’re still running the stock distributor, you do not have any mechanical or vacuum advance to increase the spark timing as the engine speed increases. The electronic ignition module in the computer-controlled distributors had a limp home mode if the computer wasn’t working. It basically took whatever base timing you had and advanced the spark around 10 degrees once the rpm increased over approximately 1,500.