These are typical self-aligning rockers identified by the two guide tracks that straddle t
Gary Hoerner; Saratoga Springs, NY: I have a question regarding self-aligning rockers on Chevy TBI motors. I have a ’91 350 TBI motor that is using full roller rockers instead of the self-aligning stamped rockers. Will this hurt anything? The heads are 191 and the pushrod reliefs are slotted, not round, so there is not much side-to-side movement.
Jeff Smith: If we go way back to the early days of the small-block Chevy, the designers came up with what was back then a radical departure from shaft rockers with an inexpensive stamped rocker arm that pivoted on a simple stud and a half-sphere ball. Lateral movement of the rocker arm was limited by the slot cut in the cylinder head for the pushrod. As performance engine builders cranked more lift and duration into the camshaft and added roller rockers, it made controlling lateral movement more difficult. That’s when pushrod guideplates became the standard, also requiring hardened pushrods. Then in the late ’80s, GM came up with a guided rocker arm that featured two small rails stamped into the rocker arm valve tip used to retain the rocker over the valve tip. This required a slightly taller valve-stem tip to protrude slightly beyond the valvespring retainer to locate the rocker. Along with guided rockers, the small pushrod slots in the head were opened up, and in some cases the entire pushrod area between the intake ports was windowed completely to save weight.
The only real warning with a system like this is to avoid combining guide systems. This means you should not use pushrod guideplates with guided rocker arms, as this could create a bind situation. In your case, Gary, using the pushrod slots in the heads to locate the rocker arms will work, but it may allow the rocker to migrate sideways across the top of the valve tip. The ideal situation would be to modify the heads for screw-in studs and guideplates that would ensure the rocker arm is properly located over the valve.
LS Truck Engine Power
Mike Ptacek; Brookville, KS: Some time ago you did a story on an LQ4 short-block that made 480 hp. I was impressed with the numbers the carburetor with the Hot cam pulled. I have an LQ4 that had an engine fire when my wife was involved in an accident with our crew cab. She is almost completely healed. The truck was an ’02 with only 50K on it, and the factory intake and wiring was damaged. I am planning to build the motor for a kit car I have. The only problem in using your setup in the article is I believe it is going to be too tall for my application. Cutting a hole through the back window is not an option on this car. I like the price of the carburetor setup, but I think I will have to go with an LS6 intake. Does anybody have any numbers for the same setup except with an LS6 intake? Do you recommend GM’s stand-alone engine controller, although it is expensive?
A low-profile LS1 or LS6 intake manifold is much shorter than either the truck manifold or
Jeff Smith: First of all, it’s good to know your wife is OK. Cars and parts can be replaced. Since the carbureted manifold appears to be too tall for your application, the simplest and easiest conversion would probably be to retain electronic fuel injection by using the low-profile intake manifold used on the early Corvette/Camaro LS1/LS6 engines. Before we get into the specifics of the swap, keep in mind that using this manifold will also require changing the front accessory drive to accommodate the lower position of the throttle-body. The truck accessory drive will crash into any induction piping that leads to the throttle-body, so you have two choices. First, you could use an early, factory F-body–style accessory drive. This will require replacing all the brackets and using a different power steering pump and an F-car harmonic balancer. This could get expensive, and this system is hard to find used because they are in such demand. I’d suggest using Kwik Performance’s conversion kit that allows you to retain the truck balancer and use Kwik’s brackets to reuse the truck alternator as well. You will have to purchase a new power steering pump, but they are not expensive, especially if you get them through Rock Auto. The Kwik Performance bracket kit that mounts just the power steering and alternator is PN K10168, which sells for $287.00. If you want to relocate the factory A/C compressor, Kwik makes a separate mount for that as well.
When using the LS1/LS6 intake, which should be easy to find used, the real question becomes how to control the fuel injection. Since this is an ’02 engine, it uses the older-style 24x crankshaft shutter wheel with a cam sensor at the back of the engine. You could use a factory computer and aftermarket wiring harness. It appears you might get lucky here because both the LS1 and truck injectors are rated at around 25 lb/hr. The computer can generally compensate for this flow difference, but it will still require an aftermarket wiring harness. For example, Painless sells a wire harness for late-model LQ4 engines using an electronic throttle and 4L80E trans that sells through Summit Racing for just a touch more than $1,000. While that seems a little pricey, the beauty of this system is that you have a factory computer with control over the system, including the use of a mass airflow sensor (MAF). Plus, purchasing this harness from Painless qualifies you for a powertrain control module reflash service from Painless based on what you need. This makes the price a bit more palatable and worthy of consideration. Along these lines, there are also other aftermarket companies that offer factory-compatible wiring harnesses that may come in a little less expensive.
FAST makes an EZ-EFI system to control your engine, and you get to choose the air/fuel rat
Our pals at Tuned Port Induction Specialties (TPIS) have been working on LS engines since they first came out. TPIS’ Jim Hall reports that on a recent LQ4 dyno test, he fitted an engine with a TPIS ZL11 cam (215/220 degrees of duration at 0.050-inch tappet lift, and 0.560 inch of lift on both the intake and exhaust) and an LS1 intake manifold and the engine made 441 lb-ft of torque at 4,700 rpm and a solid 443 hp at 5,900. He said with an LQ9’s higher compression, you could expect those numbers to jump another 15 lb-ft and 10 hp. This is at the limit of what the stock injectors can deliver for fuel flow.
Another approach is one that few car crafters are aware of. If you have an engine like an LQ4 or LS2 that does not have a computer or wiring harness, FAST has created a very affordable EZ-EFI system designed for EFI engines. You are probably familiar with the self-learning EZ-EFI system, but in summary, it uses a wide-band oxygen sensor that reads the existing air/fuel (A/F) ratio and then the computer matches that to the target A/F you load into the computer. As you drive, the computer reprograms itself and establishes the injector pulse widths needed to establish those target ratios. For example, at part-throttle cruise, you tell the EZ-EFI you want a 14.7:1 air/fuel ratio, but at wide-open throttle the engine should run at 12.9:1. After a few runs, the computer has established these parameters, and all you have to do is drive around. The best part about this technology is that the FAST system configured for your engine (PN 30200) is priced at $873.95 from Summit Racing. One advantage to EZ-EFI is that while proper injector sizing will still be necessary to make the desired horsepower, the computer really doesn’t care what size the injector is, as it tunes for your specific combination. Be aware that EZ-EFI is a fuel-only system, so you will need an ignition controller. The best one on the market is the MSD 6LS (PN 6010) that will plug right into your LQ4 engine. This adds another $319.95 (through Summit Racing) to the cost of your system, but it is virtually a plug-and-play type of system.
But since injector sizing is an important criterion, let’s quickly go over what it will take to make 450 hp with your combination. Right away, it will be difficult to make that much power with stock injectors. There are several online calculators that will do this work for you, but it’s also important to know the variables involved with injector sizing. For example, these Gen III engines run at higher fuel pressures, as much as 58 psi line pressure, or four bar (one bar is sea level pressure of 14.7 psi). Fuel injector flow rates are often expressed in three bar standards, or 43.5 psi. Just a change in fuel pressure from three bar (43.5) to four bar (58.8 psi) will increase the flow rate of the injector by more than 12 percent. The simplest way to calculate the injector size you need is to use a brake-specific fuel consumption number of 0.50 with a standard 43.5-psi line pressure and an injector duty cycle of no more than 85 percent. Duty cycle refers to the amount of time the injectors are open relative to the amount of time they are closed. At 85 percent duty cycle, the injector is open for 85 percent of the time and closed the other 15 percent. You must size your injectors to deliver enough fuel at or below 85 percent duty cycle at wide-open throttle. This is important because holding the injectors open 100 percent of the time will burn them up. We won’t go through the math formula, but trust us that 450 hp will require a minimum of a 33 lb/hr injector at 43.5-psi line pressure. If you jack the line pressure up to 55 psi, a smaller injector will deliver this horsepower, or this same 33-lb/hr injector will be capable of nearly 500 hp.
Fuel Air Spark Technology (FAST); Memphis, TN; 901/260-3278; FuelAirSpark.com
Kwik Performance; Springfield, MO; 417/955-1467; KwikPerf.com
Painless Wiring; Fort Worth, TX; 817/560-8324; PainlessPerformance.com
Tuned Port Induction Specialties (TPIS); Chaska, MN; 952/448-6021;
Random ’69 Camaro. I don’t think we met our quota for the month yet.
Spotted at the Summer Nationals: massive turbocharger in a third-gen Firebird.