John DaLuz of JMC Motorsports in San Diego, California, shares this one. As with carburetors, cylinder-head port sizing, and header tube size, valve sizing is another one of those situations where bigger isn't always better. Rule of thumb is simple-no larger than 1.94/1.60 inches (intake/exhaust) for 221, 260, 289, and 302 engines for street use. Larger 2.02/1.60-inch valve sizes work for 289/302ci engines with closer examination of valve-to-piston clearances, and valve-to-cylinder wall clearances. Larger 2.02-inch intake valves make sense when the chamber and cylinder wall don't shroud the valve. To make the right decision, look at all cylinder-head designs and options available.
If you are considering larger valves, ask yourself if they will yield any benefit. Is the larger valve size shrouded? If so, how can you expect improved airflow? Flow-bench testing shows time and again that larger valve sizing doesn't always improve air flow because a shrouded valve can suffer from airflow shortcomings throughout its travel. Bigger valves don't always net bigger power.
When a customer comes to MCE Engines with an engine project, Marvin McAfee asks what he wants the engine to do most of the time. McAfee subscribes to a strict regiment of proper parts selection and compatibility in every engine he does. He says customers come to him with collections of parts seeking an estimate, but he won't do an engine unless he is certain all of the parts will work well together. As a rule, he prefers to select and acquire the parts, clearing all phases with the customer as he goes.
Expect disappointment when you top an intake manifold with a carburetor ill-suited to the displacement, manifold, heads, and driving conditions expected. Anticipate trouble when you fit an aggressive cam to a block topped with incompatible heads with soft valvesprings. Figure on lackluster performance when you opt for a mechanical distributor for the daily commute that doesn't have a vacuum advance. Plan your engine build like you would your career or a dream home. It all has to work well together or you're wasting both time and money.
Before buying anything or even choosing an engine, know exactly how you're going to use it most of the time-then plan each phase of your engine build with liberal doses of common sense and patience. It's easier to wait on buying parts than it is to be sorry later when you've made a bad decision.
MCE Engines takes a methodical approach to every engine it builds. This means inspecting and measuring at least three times during mock-up and assembly phases. Measuring once is courting trouble, according to McAfee. It's too easy to misread a micrometer or dial-bore gauge. Go back and measure again later to ascertain precise measurements. Write them down on the first pass, then write them down again on the second and third passes. And remember, you should be able to turn a crankshaft using two fingers with all eight pistons and rods installed. The weight of a 11/42-inch breaker bar alone should turn the crank before pistons are installed. If it just hangs there, clearances are too tight.
Too Much, Too Little Endplay
Crankshaft endplay doesn't get checked enough during engine builds, in our estimation. We've seen enough of them where we had to remind the builder to check. Trust your parts, but verify dimensions always, even with new components. Too much crankshaft endplay can bite you in the butt just as badly as too little endplay. Much of it depends on how you intend to use the engine.
If you're going with a manual transmission, clutch engagement and disengagement causes the crankshaft to ride the thrust bearing-on the clutch, off the clutch. The result is wear every time you step on the clutch. The more endplay you have, the harder shifting is on the thrust. Step on the clutch and the crank rides the thrust bearing hard. Minimum crank endplay is 0.004 inch. Maximum is 0.008 inch regardless of whether you are running an automatic or stick.
Another important item that is rarely checked is camshaft endplay-again 0.004-0.008 inch maximum. Excessive camshaft endplay leads to timing-set failure, lifter damage, and other unthinkables.
Here's one we see all the time. Did you know improper ignition tuning not only adversely affects performance, but it also can do permanent engine damage? Here's why: Ignition timing isn't just about aiming a timing light and getting 6 or 12 degrees BTDC timing at idle. What really counts is total timing and how it synchs with engine rpm. Total timing, meaning total spark advance in degrees of crankshaft rotation/position, should be completely in by 3,000 rpm.
As a rule, total timing should never exceed 36 degrees BTDC at 3,000 rpm and higher. Some people push the envelope and crank a few extra degrees in there thinking it will net us more power. But, when you dial in too much timing, you run a high risk of serious engine damage from detonation/spark knock. This happens when fuel ignition occurs too early on compression/ignition stroke.
The objective is to light the mixture at exactly the right time as the piston rises in the cylinder to where combustion is fully underway when the piston reaches top dead center. This hinges on fuel octane rating, ambient temperature, humidity, cam profile, chamber size and shape, air/fuel mixture, and atmospheric pressure (or pressure altitude). Every situation is different, which means no two engines will respond the same way to ignition curve. What works on your buddy's 302 likely will not work on yours.
And remember something else: Total timing when the engine isn't under a load is different than total timing with a load. With a load, you often need less timing because detonation typically occurs heavy load at wide-open throttle at low rpm. This calls for retarding total timing one degree at a time.
|MCE Quick Tip: |
|Power begins to fall off with small-block Fords at 32 degrees BTDC. McAfee advises 34-36 degrees BTDC total timing.|
Carburetor tuning can make or break an engine as much as ignition timing. A lean mixture can fold an engine over as quickly as early spark timing. This is why carburetor tuning is crucial to not only performance, but also to engine life because air/fuel mixture affects combustion temperature. A lean mixture raises temperatures. A rich mixture lowers temperatures. Lean mixtures and high temperatures place undue stress on piston crowns and ring lands.
This is why a spark-plug reading is important to carb tuning. The whiter the porcelain firing tip, the leaner the mixture. You want a porcelain tip that's tan in color. Sooty black is too rich. Jet size up for a richer mixture, and down for lean one step (jet size) at a time. It's a good idea to keep a jet kit handy for carb tuning. This allows you to swap jets anywhere you go. Hard acceleration at wide-open throttle with a clean shut-off is the best way to do a plug reading. Take it out for a blast, listen for pinging (spark knock), and do a plug reading afterward. This not only determines fuel mixture, it also determines spark-plug heat range. Examine the spark-plug cross electrode to determine heat range. If the cross electrode has particles, is blue, or appears burned, it's too hot. Normal color means proper heat range.
|MCE Quick Tip: |
|If you're going racing (repetitive wide-open throttle), consider the next lowest spark-plug heat range. Also consider richer jetting in steps. Holley jetting, for example, increases fuel flow by 4 percent per the next largest jet size.|
Cleanliness Is Next To . . .
We are always shocked at how many engines we see in shops that are not properly protected against dust. Those of you in desert regions understand dust because it's a part of daily life. We're always dusting furniture in the West. However, those of you in humid, rainy regions also have to consider dust because it exists everywhere in one form or another. Flaking human skin and hair generates dust particles, as does the simple decay of just about everything from free radicals in the atmosphere.
Keep your engine bagged, plugged, and covered whenever you're not working. You don't have to spend a lot of money on engine plug kits. Use paper towels, duct tape, whatever it takes to keep dust and moisture out. Paper towels, for example, will absorb moisture, which makes them a good idea. And during assembly, clean all parts thoroughly. Dust particles will eat the life out of new bearings, pistons and rings, cylinder walls, oil pump cavities, and more.
|MCE Quick Tip: |
|Never operate an engine without an air filter-ever.|
Another shocker is engine builders who use assembly lube between bearings and blocks, and bearings and rods. Surfaces between bearings and saddles must be completely dry because it is the saddle's job to secure the bearing. Simply put, you don't want the bearing to turn in the saddle or connecting rod journal. You want a soft crush on the bearing, coupled with the security only dry surfaces will yield.
|MCE Quick Tip: |
|Assembly lube goes on bearings only after installation and the bearing is fully seated.|
How many times have you turned an engine over in vain attempts to get it to light off? Check your ignition coil to ascertain proper connection of the positive and negative terminals. Positive from the car's wiring harness-negative to the ignition points or module inside the distributor. Another item that nails us from time to time is the two terminals on the starter solenoid. When we get those backwards, the starter will turn over immediately when we turn the ignition switch to "on." Brown wire to "I" and blue with a red stripe to "S." "I" provides 12 volts to the ignition during cranking (instead of passing through the resistor wire). "S" latches the starter solenoid (electromagnet) to get battery power to the starter. One more thing, did you connect the ground strap between the engine and firewall?
|MCE Quick Tip: |
|Did you put fuel in the tank?|
Exhaust valveguide to stem clearances
Valve stems cease when clearances are too tight and engines get hot. By the same token, oil gets past the stems and guides when tolerances are too loose. Valve-stem-to-guide clearance should be no tighter than 0.002 inch on the exhaust side and 0.0015 inch on the intake side.
|JGM Quick Tip: |
|Check stem-to-guide clearances with great care. Exhaust-valve stem-to-guide clearancing is especially critical due to extreme heat.|
Oil Pump PickUp To Pan Clearance
JGM reminded us of this one, and we see it time and again-oil-pump pickups that touch oil pans. Most of us never check this one. Just because there's oil in there doesn't mean the pickup won't chafe. Pickups need to be close to the sump bottom, but no closer than 31/48-inch minimum.
Using Synthetic Engine Oil For Break-In
Synthetic engine oils are terrific forms of engine lubrication because they offer unequalled protection for moving parts. But when breaking in a new engine, plain, old-fashioned, mineral-based petroleum SAE 30-weight is what you want. Regular SAE 30-weight engine oil allows piston rings to properly seat during run-up because it offers a different kind of lubricity than synthetic oil. Synthetic engine oil has a different molecular structure than regular engine oil. During break-in, piston rings need better cylinder wall contact only regular engine oil can give them for proper seating. Once the rings have seated (around 500-1,000 miles), switch over to synthetic and enjoy long engine life.
|MCE Tip: |
|Always hand-fill the oil filter before installation to keep a solid oil wedge during start. Empty filters on start-up ultimately damage bearings.|