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April 2011 Chevy High Performance Q&A

Fuelish Pleasures

Kevin McClelland Mar 8, 2011
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Have you ever noticed that we tend to cause most of our own car problems? Well, this weekend I caught myself, and I was just about to make a problem that could have been hard to find.

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We all like to build nice packages for our street/race cars, and, over time, we generally end up stepping up the combinations, right? Let’s say you have a Chevelle or Camaro that runs in the high- to mid-12-second range and has run perfectly for the past several years. And more recently, you’ve got the itch to transform your street car into more of a weekend warrior than a cruiser. Let’s also say that mid 11s is your goal and you’re going to use most of the hardware on your current combination, like your single-plane performance intake and the 750 double-pumper Holley.

This carburetor worked perfect when it was running 60-foots in the 1.80 range, but all of a sudden it dropped to the mid 1.50s, causing the engine to bog off the line and roaring back to life just as quickly as it left. Have you ever run into this? These parts worked fine on the mildly warmed-over 350, and quite frankly, the new 383 setup isn’t that far off with your current carb and manifold. Well, sometimes we can overlook the simple things, like being a quarter of a second faster in the first 60-foot; what you may have not noticed is that with standard Holley center-hung float, the fuel is running away from the main jets on the secondary side on the launch.

So that’s where I almost was. This weekend we were swapping out the stocker 305 and trans, dropping in the 350-bracket engine with a transbrake Powerglide into the wagon. We usually use a modified 750 Holley on the 350 engine, but since the engine had been out for six months, I grabbed it and put it on Daniel’s 406 in his Caprice. It worked like a dream, but it left me without a carb for the wagon. Since the plan is to drop an L92 in the wagon within the next year, I decided to dial in a race 850 that I’ve used on the engine dyno for the past 20 years. I knew this carb would work well with our combination, but I almost forgot to install the secondary jet extensions and attending float to clear them. Holley sells a notched float kit with jet extensions for center-hung floats that includes two extensions and a new float relieved for the extensions (PN 116-10).

If I wouldn’t have remembered that this thing needed extensions, there’s a good chance I would have been scratching my head during the first outing. Remember, you can’t always catch everything the first time around, so try to be patient when you run into problems and think of what you’ve changed; listen to what the car is telling you.

LQ4/LQ9 I.D.

Q: I’ve heard many times that the LQ4/LQ9 truck engines are simply great, inexpensive iron LS1 blocks. Which trucks do they come in, and how can they be identified? I want to be absolutely certain I have one before I pull it. Thanks!
Jack Stackewich
Via email

A: The LQ4/LQ9 6.0L engines are outstanding low-cost building blocks for any project. The LQ4 was introduced in 1999 and was a two-year release with cast-iron cylinder heads. They also had an odd to the LS engine family rear crankshaft flange location that was only on the ’99-00 model years. These two things would steer us away from those engines. The LQ4s from ’01 and up were equipped with aluminum heads and came in with 9.5:1 compression. The power came in at 300 hp and 360 lb-ft of torque. This engine design was found in many Chevrolet and GMC trucks and vans. In the pickups they were installed in the Silverado/Sierra 2500, 3500, Crew Cab, cab and chassis, Denali, and 1500HD Crew Cab. They were also in the Suburban, Yukon XL, and the Hummer H2 SUT, as well as the Chevy Express and the GMC Savana vans.

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.

Sluggish 355

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!
Barry Robinson
Kane, PA

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.

If this is the case and you’re still running the stock distributor, you need to swap out to an ’81-and-earlier HEI distributor or pick up an MSD HEI billet distributor (PN 8365). This fully adjustable distributor gives you features of all MSD’s racing distributors. Both the mechanical and vacuum advance is adjustable, allowing you to tailor the advance curve to your specific engine package. You will want to give your engine an initial advance of 16-18 degrees of timing with the mechanical advance coming in around 1,300 rpm and achieving a total advance of approximately 32 degrees of spark at 3,200-3,400 rpm. On top of this mechanical curve, add around 12 degrees of vacuum advance to squeeze the maximum fuel economy out of your engine package.

With the above advance curve, your 355 should be around 400 hp and 410 lb-ft of torque. If you had around 10:1 compression we’d push these numbers closer to the 420 range for horsepower. You are correct in expecting your engine to have great low-end torque with those cylinder heads, camshaft, and torque converter selection. Good luck finding the wheelspin within your little small-block!


Too Slow Monte

Q: First off, love the mag, especially Performance Q&A. I’ve got an ’85 SS Monte Carlo, completely street-legal, with a lift-off Harwood hood and a 10-gallon fuel cell. The engine is a 406ci small-block; an Eagle 4340 forged crank; ESP H-beam rods, 5.7 inches; Wiseco forged pistons; ARP main, rod, and head studs; Brodix Track-1 heads, 221cc inlets with 2.08/1.60-inch valves; a Lunati solid-roller cam (0.600/0.618-inch max lift, 258/268 degrees duration at 0.050-inch tappet lift, ground on 106 centers); Crane roller rockers; a Pro Comp single-plane intake; an MSD Digital 6 Plus and Pro Billet dist; and a Pro Form race series 750-cfm carb. It has a TH400 trans, a B&M Holeshot 3,600 converter, and an 8.5-inch 10-bolt with 3.73:1 gears, on 28x9 MT ET drag slicks.

Am I expecting too much from this car? The best e.t. so far is 7.80 at 89.6 mph, with a 1.76 60-foot. Buddies and fellow gearheads all estimate 6.90s-7.00s. Does this sound doable? Is this an OK cam for the engine? And how much more miles per hour can be expected with 0.2-quicker 60-foot? Any info would surely be appreciated. Thanks, and keep up the awesome job you do!
Chris Chace
Huntingdon, TN

A: We’re going to have to side with your gearhead buddies. With the engine you have built, your Monte should be close to the performance they’re calling out. Let’s dig a little deeper into your build to see why you’re not seeing this type of performance.

First of all, the 406 that you’ve put together is one nice little small-block. This engine should make an easy 600 hp and a good deal of Monte-moving torque. However, with your build this engine is going to be a higher-rpm 406. We’d say the real powerband of this engine is between 4,500 and 7,500 rpm. That said, the car needs to be geared and convertered accordingly if you expect the e.t.’s you’ve listed. Also, if your suspension, gearing, and converter were working together you should easily be in the high 1.50 range for 60-foot times. Our ’80 Malibu wagon in bracket trim with our 460hp 350-cid small-block has an average 60-foot of 1.56, and has had an absolute best of 1.51! This is with an eighth-mile time in the 7.40 range, and a quarter-mile time in the 11.60s-11.70s. We are currently running 4.88:1 gears with a 28x9 Hoosier tire in the rear. To make the suspension work, we’re running Moroso Super Trick coil springs front and rear, and Competition Engineering adjustable shocks front and rear. We’ve also raised the upper pickup points on the upper rear control arms at the rear axle to move the instant center of the rear suspension back and down to plant the tire. If you are experiencing wheelspin after the launch, you’re not getting the weight transferred to the rear tires. This all comes from the car not rotating because of its steep gearing and stock suspension.

Finally, we’re assuming you have an exhaust and fuel system to support the power level of your mighty Mouse. If you have any deficiencies in these areas, you’re not going to achieve your performance goals. Good luck, and send us a photo of your Monte with the wheels hanging when you get it worked out.


Search Help

Q: I have tried all my available resources and need help. My truck is an ’81 Chevy C20 two-wheel drive with 454, a TH400 trans, and 4.10:1 gears at the rear that I use to pull trailers around a lot. It is all factory, with only 46,000 miles on it, with factory cruise and A/C. The cruise doesn’t work right all the time and the A/C has an idle compensator that is vacuum controlled by an electrical solenoid. This has a relay connected into this circuit that seems to not be working right. I need to trace this out and find the problem but just need the drawings. The local Chevy dealer told me it’s too old for that technical of a drawing, and the Chilton’s manual I have doesn’t help either. I need complete electrical drawing and vacuum drawings for cruise control and A/C.
Brent Pew
Via email

A: Finding the information you need can be really tough at times. Helm’s Incorporated is the source for the GM factory repair and service manuals. They are the bomb! We’ve got a pretty good library of these manuals from years of working in dealerships and ordering when buying used GM products. They are invaluable when running into issues like yours. Now the bad news: Helm’s has discontinued printing of the manuals for your truck! However, a quick search of eBay Motors came up with at least 10 sets of used and N.O.S. (new old stock) of the factory service, unit repair, and wiring diagram manuals for your ’81 C20. Go to eBay Motors and search under manuals and literature and use 1981 Chevy truck as your search. Over 50 listings came up, and there were at least 10 hits of the books you need. Also, they were very affordable.

As soon as you pick up a new or used GM vehicle, order the factory manuals to support your new ride. Helm’s can help you out with that, and if they are out of circulation, use the power of the web. Good luck tracing wires!


Technical questions for Kevin McClelland can be sent to him at



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