Ron Nelson; Sonora, CA: I have a 2,000-pound T-bucket with a 350ci small-block Chevy. I installed a solid lifter cam that has 256 degrees of intake and 264 degrees of exhaust duration with 0.506 lift and a 105-degree lobe-separation angle. The camshaft to lifter clearance is intake 0.026 and exhaust 0.028.
Is there a way to set the lifter clearance with a cold engine? I have the degree tape on the harmonic balancer, so I can set each cylinder to TDC. Would the cold setting valve gap be less at a higher engine temp? Would the valve gap on both the intake and exhaust be set at a single spot on the degree tape? Adjusting the valves on a running, warm/hot engine requires parking in the center of a Walmart parking lot at 1 a.m. and wearing a wet suit because everything gets covered with oil. Any light you could shine on this will help greatly.
Jeff Smith: You're right, Ron, that setting lash on a running engine with the valve covers off is a messy affair—but there's a much better way. A long time ago, I learned how to set lash on a static engine that doesn't require memorizing the firing order or using a timing tape. It's a really simple process, and all you have to remember is "Exhaust Opening and Intake Closing" or E-O-I-C.
The process goes like this: Warm the engine up, pull all the spark plugs (so it's easier to turn the engine), and remove the valve covers. Let's start with No. 1 cylinder. You can start anywhere, but this is convenient. No. 1 on a small-block Chevy is the front cylinder on the driver side. Slowly turn the engine clockwise until the exhaust rocker has opened the valve roughly a quarter of the way. At this point, the intake lobe on this cylinder is on its base circle, which allows you to set the intake lash. In your case, the intake lash figure is 0.026 inch for a warm engine, so set that clearance between the valve tip and the rocker arm. Once that's completed, turn the engine until the intake valve is roughly halfway closed. Now the exhaust lifter is on the base circle of its lobe, which will allow you to set the lash at the 0.028-inch clearance. You've now completed both valves for that cylinder, so you can move to the adjacent cylinder. I do it this way because of the simplicity, since I can just run right down the line of valves doing each pair of valves per cylinder. For the rookies who have not tried this before, you can set the intake first and then the exhaust; the order isn't important as long as you follow the order of lashing the intake when the exhaust is opening and lashing the exhaust when the intake is closing. The key is making sure the valve you are setting is actually on the base circle of the lobe.
The one drawback to this procedure is that you have to turn the engine over a couple of more times than you would if you set the lash according to the engine's firing order. Once you become adept at setting lash this way, you will discover you can do it on any four-stroke engine of any design—a V2, flat-four, inline-four, V6, V8, or V12, it doesn't matter. All you need to remember is Exhaust Opening and Intake Closing (EOIC). If you get the letters confused, just turn the engine over and watch the valves operate. You will quickly realize that trying to set intake lash with exhaust closing won't work because the intake valve is also opening and because the cam is in its overlap phase. The beauty of this procedure is that even if you forget the sequence of the letters, the engine will remind you. This procedure is also the same for preloading hydraulic lifters. The only difference is you set hydraulic lifters with a specified amount of preload instead of clearance. For most performance situations, I like to use a quarter turn of preload rather than a full turn or more, but there is evidence ("8,500 RPM!" Feb. '14) that preloading a high-quality hydraulic lifter to about a turn and a quarter will improve performance.
You also asked about setting lash on a cold engine, and you are correct in assuming the lash changes between a hot and cold engine because of something called linear thermal expansion. This simply means that as an engine comes up to operating temperature, the metals expand. We won't get into the metallurgy, except to say that aluminum expands roughly twice as much as cast iron, so changing the lash specs from the published hot specs to a cold engine will depend upon whether the engine has aluminum or cast-iron parts. Crane has published a handy little chart that we've reproduced that gives you a starting point. To use your engine as an example, we'll assume for our first example that the engine is a cast-iron block with iron heads. With a hot intake lash of 0.026 inch, to set the lash on a cold engine you would add 0.002 inch for a total of 0.028 inch. As the engine warms up, the lash will tighten up, but you should still recheck it to ensure that the clearance is what you desire.
For an engine with an iron block and aluminum heads, Crane's spec changes to subtracting 0.006 of lash from the hot setting for a cold engine. If the engine is all aluminum, then you would subtract 0.012 inch from the hot lash for a cold setting. Again, these are merely recommendations to start a cold engine, and you should recheck the lash once the engine is at operating temperature.
I will also take this opportunity to dive into one of my pet peeves around setting lash. It seems that a wives' tale still persists that you must constantly reset lash on any mechanical lifter street engine. I've heard guys say they have to reset lash as much as once a week on a daily driven street engine with a mechanical lifter camshaft. If the engine's lash is in fact changing, my contention is that it's likely due to those stock-type locking rocker stud nuts that are allowing the clearance to loosen. Those stock pinch nuts are only good for perhaps one setting. After that, they begin to lose their built-in tension. After several settings, they are probably no better than a regular fine-thread nut. In that case, pitch those things and buy a set of poly locks. Now that the adjusting nut is truly locked in place with an Allen set screw, the lash should not change. Think about it: If while using poly locks the lash changes within a short number of miles of driving, the only reasonable explanation is that something is either bending or wearing very rapidly. As an example, the 420ci small-block Chevy in my '65 Chevelle uses a mechanical roller camshaft that's been in the engine since 1991. In that time, it has been raced unmercifully at multiple drag races, hillclimbs, road-course events, and even two 90-mile WOT Pony Express Open Road Races. Within that time, I have checked the lash dozens of times, and it has never appreciably changed. The valvetrain is very stable; the springs probably should be replaced because they are so old, but nothing is wearing—so the lash has not changed.
Automotive Racing Products; 800/826-3045; www.ARP-Bolts.com
Comp Cams; 800/999-0853; www.CompCams.com
Crane Cams; 866/388-5120; www.CraneCams.com
The color for our '71 Demon project car is called '69 Chrysler Blue Fire. Look for it next month.
Richie Green; via CarCraft@CarCraft.com: Great article on the HEI conversion (Junkyard Builder, Nov. '13). I thought those modules were no good above 5,500 rpm because they couldn't keep up. Is this true?
Jeff Smith: I think this may be a new record for the shortest tech question to date! As usual, in the best tradition of Ask Anything, your short question requires a more detailed answer. I will attempt to be brief. You are mostly correct that the HEI has trouble above 5,500 or 6,000 rpm, but not because of the module. The answer has less to do with the module and more to do with single-coil inductive ignition systems, in general. Let's start, as always, with some electrifying basics. The HEI (and all factory ignition systems) are designed as inductive ignitions where system voltage (14 volts) is fed to the primary side of the coil. An inductive ignition coil uses a primary side with a given number of windings wrapped around a metal core. When the distributor module completes the circuit (or the points close, if you remember ancient automotive history), this feeds voltage and current to the primary windings. When the module disconnects (opens) the circuit, the magnetic field energy created around the primary windings collapses across the secondary (high tension) side of the coil that is wrapped with 100 times the number of windings. These windings are connected to the high-tension lead for the coil wire. As the primary field collapses, the greater number of secondary windings increases, or steps up the voltage. This is how a basic step-up transformer works. This increases the voltage from 14 volts to between 20,000- and 40,000-plus volts. This has also been referred to as a Kettering ignition system, developed by Charles Kettering and first used in Cadillacs in the very early 1900s.
This system works the best when there is sufficient time to allow the primary coil windings to fully saturate, which occurs with no problem at 3,000 rpm. But at 6,000 rpm, there is only half the time and primary coil winding saturation degrades. This consequently reduces both the voltage and spark energy available at the spark plug. In the '60s, the idea behind dual points was to increase the dwell time (the amount of time the points were closed) to increase coil saturation. But that was a Band-Aid applied to the real problem. One solution was the capacitive discharge (CD) ignition. A CD uses a charged capacitor to hit the primary side of the coil with around 500 volts, which radically increases the secondary voltage—and it does all of this very quickly. This is why MSD is able to fire the spark plug three times (below 3,000 rpm) because the capacitor can recharge the coil so quickly. It was this feature that created the brand name Multiple Spark Discharge, MSD. The disadvantage to a CD ignition is extremely short spark duration. But it is also capable of delivering high voltage and good spark energy at extremely high engine speeds of 8,000 to 10,000 rpm. The advantage for an inductive ignition and why it is used in all production engines is that it creates a very long duration spark, which helps ensure the fire is lit in the chamber at low speeds.
So this leads us back to the HEI and any single-coil inductive ignition system's weak point, the single coil. Unless we hit the coil with higher voltage, it requires lots of time to recharge the primary windings, even with a full 14 volts. The old points systems were even worse because they could only deliver barely 6 volts to the coil. Any more would quickly burn the points to dust. The HEI delivers better spark energy than points, but it still suffers from the same coil saturation dilemma, which results in reduced ignition power above 6,000 to efficiently help make more power. When GM created the HEI, they weren't concerned with high-rpm power. Remember that the HEI was created during the '70s when emissions requirements demanded high voltage to ignite lean air/fuel ratios. When we say power, we don't just mean voltage. Lots of coils are capable to 40,000 volts, but if the spark plug only requires 25,000 volts to ionize the spark-plug gap and push the electrons across that gap, then that's all the voltage the coil will deliver. Many feel that the spark energy delivered across the spark-plug gap is more important to helping complete combustion. Here is where the inductive ignition system has a slight advantage with its longer spark duration compared to a CD. The OEMs have solved the coil saturation problem by using a dedicated coil for each cylinder. On a V8 engine, each coil now has eight-fold more time to saturate before it fires again versus a single-coil ignition system. I suspect that the main reason that the new car companies went with distributor-less ignition system (DIS) is because the coil-near-plug design reduces emissions because of higher spark-plug energy and improved timing accuracy. This improved ignition performance results in fewer trace misfires, so power improves and emissions—especially unburned hydrocarbons (HC)—are reduced. So now we have an inductive ignition system that is capable of running as high as 8,000 rpm or perhaps higher with very little appreciative loss in spark energy.
Other problems with the HEI can be traced to misfires that often occur due to faulty modules and grounding spark through the rotor. We've outlined several simple HEI improvements in previous Car Craft stories that can be found online, so we won't go into them here, but starting with a high-quality cap and rotor are essential steps. Always choose a cap with real brass contacts instead of the cheaper aluminum spark plug wire contacts. Aluminum is a poor conductor of electricity because it is subject to oxidation, which increases resistance. Copper has a 55-percent-higher electrical conductivity than aluminum, making it a far better choice for connections on the high-tension side of the ignition system. Then invest in a really high-quality set of spark-plug wires like MSD or Moroso, and you're most of the way to optimizing an HEI distributor.
Converting Hot to Cold Lash Clearance
(Chart courtesy of Crane Cams)
||Add 0.002 inch
||Subtract 0.006 inch
||Subtract 0.012 inch
Autotronic Controls Corp. (MSD); 915/857-5200; www.MSDPerformance.com
Moroso Performance Products; 800/544-8894; www.Moroso.com
We saw these 6.4L Hemi heads (aka Apache) at Superior Performance in Placentia, CA. Superior owner Joe Jill claimed that they will flow more than 400 cfm at 0.650 lift with the right valve job.
Rick Allemandi; Watsonville, CA: I have an '81 Corvette. I bought it really cheap from a woman I work with. It seems her husband was arrested with a another woman in the car, and she hasn't let him drive it in several years. Anyway, I picked it up really cheap. I've put on some wider tires, upgraded to KYB shocks, lowered it a couple of inches, installed new brakes, braided brake lines, and new calipers. I've also added some Flowmaster mufflers, a performance catalytic converter, and poly bushings all around.
I love the fastback body style, and I love the way it handles. The problem is the car can barely get out of its own way. It has the stock 350 and 4V carb. The car has an onboard computer that controls the carb and the timing. It is a California car, so I'm stuck with the emissions equipment. I can't find any smog-legal headers, and I don't think a cam swap would allow me to pass the smog test. I thought about installing headers and welding in the smog tubes, but I've been told that is illegal. What can I do to make this car move like it should?
Jeff Smith: Unfortunately, 1981 was second to the worst year for street small-block engines in the Corvette. That L-81 350 made a measly 190 hp. Imagine, a Corvette with only 190 hp. Sadly, back in 1975, the base 350 made only 165 hp—the weakest of the late-model Corvette engines and a low point in the Corvette history. The biggest problem with the L-81 engine, besides the low-rise intake, lame camshaft, and restrictive catalytic converters, is the compression—or more accurately, the lack of compression. When brand-new, the L-81 squeezed with what Chevy claimed was an 8.2:1 compression ratio. My guess is that if you measured all the variables, it's likely to be closer to 8.0:1 compression. Let's just call this lamentable. My first suggestion would be to replace the iron 76cc chamber heads with a set of aluminum 64cc chamber heads. This would immediately pump the compression up exactly one point—so if your current compression ratio is 8.0:1, a 64cc chamber will take it to 9.0:1. Theory states that this is worth roughly 4 percent power, which if the engine was making 190 hp, the compression only bumps that to roughly 198—call it 200. But the added flow improvement of, say, an Edelbrock Performer RPM emissions-legal head would also pump the power up perhaps another 20 hp at least. I would suggest adding a Performer EGR manifold that would also help power, but then the cork in the system is, as you have recognized, a lack of a decent header. The other restrictive part of your exhaust is the catalytic converter. I'm not 100 percent certain, but it's likely that your car may retain the original catalytic converter, which in 1981 could be a pellet-type converter—which is highly restrictive. The first thing I would change before any of the inlet modifications would be to a California-legal monolithic-style catalytic converter. This will at least help minimize the exhaust restriction and improve performance. The problem of headers is indeed significant because, as you pointed out, California severely limits modifications to the exhaust upstream of the catalytic converter to parts with a Bureau of Automotive Repair (BAR) executive order (EO) number. This means that the component has been tested and proven not to increase emissions. This precludes you from legally adding headers. At the very worst, you could install them and then every two years install the stock exhaust on the engine to pass the smog test. The major gain in performance from headers would certainly be worth the hassle.
Other changes you could make would be to add an emissions-compatible camshaft to accompany the heads and intake change. For example, Crane makes a hydraulic flat tappet, emissions-legal camshaft with an EO for your engine with 204/214 degrees of duration and 0.423/0.446-inch lift that would certainly contribute to an increase in power. Add a good set of rocker arms, and you have a package that could easily make 300 to 320 hp at the flywheel, which is nearly a 70 percent increase in power. All these changes could be accomplished with the stock short-block in the car. The biggest hassle would be swapping the cam, but the rest would be relatively easy. This isn't the only way to go, but it's probably the easiest. The Edelbrock heads (PN 60909, $1,369 a pair, Summit Racing) aren't cheap but are sold as direct-replacement heads and are therefore legal. The intake will be an Edelbrock Performer EGR (PN 3701, $189.97, Summit Racing) that will accommodate the EGR valve necessary to make your package emissions legal. The Crane cam and lifter package is another affordable swap (Crane PN 114122, $190, Summit Racing), but you will also need gaskets, and you should also purchase the proper break-in oil to ensure that the cam doesn't go flat. Lucas sells a high-quality break-in oil, as does Joe Gibbs Driven. You're looking at investing around $2,000 with all these parts plus gaskets, oil, RTV, new coolant, and perhaps a set of good head bolts from ARP (PN 134-3601, $80.24, Summit Racing). That's assuming you do the work yourself. You should also include a new timing gear and chain set (Crane PN 11975-1, $118.60, Summit Racing). One advantage is that you can install these parts a little at a time, but the best way to do it is to install everything at once so that you only have to invest in one set of gaskets. Otherwise, if you install the intake first and later the cam, you will end up buying two or three intake gasket sets, not to mention the additional effort.
We also didn't recommend changing the carburetor because that original Q-jet is a decent fuel mixer. But you should also consider having it rebuilt because those early Q-jets used a plastic material called nitrophyl for the float that will absorb fuel and become heavy as it ages. This raises the float level and makes the engine run poorly. These carbs also suffered leaks that would drain fuel into the intake manifold. All of these things can be repaired (and they may likely already have been performed). If so, then merely tuning the air/fuel ratio with secondary metering rods and adjusting the air valve door on the carburetor can also make a world of difference even on the stock engine. If you need a good place to take your Q-jet, Sean Murphy Induction can easily handle this for you in the Los Angeles area. If you live in northern California, Ole's Auto Parts in San Bruno has an excellent reputation for tuning these older cars to run on today's reformulated gasoline. In fact, tuning the carburetor and ignition curve should be up at the top of the list (but after the catalytic converter change) of things you could try before diving inside the engine with major upgrades. Along with the carb tune would be a good set of plugs, wires, and an HEI cap, and rotor replacement is another wise idea. Pay attention to the mechanical advance mechanism on the HEI distributor. Those early HEI's were notorious for seizing up the mechanical advance mechanism because of corrosion. If the area underneath the rotor has a brown, rusty color, that's a good indication the mechanical advance mechanism is frozen. Free it up with lube and making sure the weights move freely will also really help the engine run better.
Crane Cams; 866/388-5120; www.CraneCams.com
Edelbrock; 310/781-2222; www.Edelbrock.com
Joe Gibbs Driven; 866/611-1820; www.JoeGibbsDriven.com
Lucas Oil Products; 800/342-2512; www.LucasOil.com
Ole's Auto Parts; 650/589-7377; www.OlesCarb.com
Sean Murphy Induction; 714/843-9169; www.SMICarburetor.com
This guy wanted $39,000 for this '69 Firebird. We don't know why, either.
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